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The area-wide estimation of aboveground biomass (AGB) and its changes as a proxy for the sequestration and emission of carbon are currently associated with high uncertainties. Here we combined interferometric synthetic aperture radar (InSAR) height models derived from TanDEM-X with repeated ground-based inventories from the years 2012 and 2019 to estimate InSAR height and AGB changes in a structurally diverse and dynamic landscape in Sumatra, Indonesia. The results suggested that the InSAR height models were highly accurate and the relationship between InSAR height and AGB change resulted in a coefficient of determination R 2 of 0.65 and a cross-validated root mean square error (RMSE) of 2.38 Mg ha−1 year−1, equivalent to 13.32% of the actual AGB difference range. The estimated AGB changes with TanDEM-X were further related to the initial canopy height and fire activities in the study area. Initial canopy heights and the occurrences of fires had a significant effect on the AGB change. In general, low canopy heights tend to be associated with increasing AGB over time, whereas high canopy heights tend to be associated with stable or decreasing AGB. As expected, fires had a negative impact on the AGB changes being more pronounced in forest areas compared to oil palm concessions. The results of this study are relevant for the utilization of spaceborne InSAR height models and its potential to estimate canopy height and AGB change on large spatial scales. It was demonstrated that these changes can be related to their sources and ecosystem processes. This AGB change estimation technique can be used to model the impacts of fires on AGB change and carbon emissions, which are important for sustainable forest management.

For the purpose of informing biodiversity conservation efforts in managed landscapes, we explored whether and how understory plant communities (abundance, diversity, composition) were related to a topographic moisture index, called depth-to-water, in the boreal mixedwood forests of northwestern Alberta. Depth-to-water is an index of relative site moisture derived from the Wet Areas Mapping tool using a fine-scale digital elevation model based upon remotely-sensed lidar (light detection and ranging) data. Sample plots were placed along the depth-to-water moisture gradient in three forest types: conifer-dominated, mixedwood, and broadleaf -(deciduous) dominated. Understory vascular plant diversity, abundance, and composition were measured for each plot. We found understory attributes were related to the depth-to-water index with the relationships varying among forest types. In coniferous stands, diversity and abundance (cover) were higher on drier sites. In broadleaf and mixedwood stands, understory abundance was higher on drier sites, but diversity was not related to the depth-to-water index. Lastly, composition was significantly, but weakly, related to the depth-to-water index in all three forest types. Our study shows that this moisture index, based on remotely-sensed data, can be used to characterize patterns in understory vascular plant communities; hence it can be useful for identifying areas of particular interest for conservation or management.

In several tropical forested areas in which biodiversity conservation and indigenous cultures are interwoven, current conservation policies do not consider how the indigenous communities understand the concept of conservation that is promoted and implemented by conservation programs led by external actors, nor do they consider local traditional practices of resource management. To move towards more inclusive conservation policies that take these two aspects into account, research is required in indigenous settings that can inform policy makers. The present study, carried out in the lowland Maya area of Mexico, aims to investigate local meanings of rainforest conservation and dynamics of land use in two Maya common property holdings or ‘ejidos’ (Noh cah and X-Maben). The study used a Social-Ecological Systems approach comprising: (i) the Maya communities and their local meanings of conservation as a Social Subsystem, assessed through social surveys, and (ii) the rainforest of each studied ejido - which was regarded as an Ecological Subsystem and assessed through satellite images (from 2000 to 2012). In the former, interviewees were asked: “when you hear the phrase ‘conservation of the rainforest’ what do you think is being said?” They were also asked if there were local words in Maya or Spanish that were similar in meaning to the aforementioned phrase. The results relating to the meanings of conservation demonstrate that Maya people, who rely on the rainforest for multiple livelihoods, understand two types of meanings for looking after the rainforest; one promoted by governmental conservation programs, and the other called Kanan K’aax, a Maya phrase that represents their customary or community-based rainforest conservation. Differences between these two models of conservation encompass differences with respect to scale, gender and the Maya people’s own cultural practices. The results of the local dynamics of land use demonstrate that the landscapes of both study sites are dominated by mature rainforest (ranging from 73.9–82.7%), and are therefore in a good state of conservation, and that their agricultural frontiers have not expanded. Our empirical results are valuable in terms of informing the scientific community about the state of rainforest conservation in the Maya Zone, and providing policy makers (from the Maya area and elsewhere) with information to devise new, more inclusive conservation policies that take full account of the indigenous cultural practices of rainforest management.

Mortality is an important process to include when modelling forest stand development. Previous attempts to model mortality after partial cutting mostly focused on overturning and stem breakage. However, in old irregular and unmanaged stands, many processes may be acting at the same time, portions of the stands being at different developmental stages. In order to better understand the mortality processes in such stands, mortality after 5 years was analyzed in old-growth black spruce ( Picea mariana ) and balsam fir ( Abies balsamea ) stands subjected to a wide range of harvesting intensities . The study comprises three sites where five treatments were applied at two scales. Mixed logistic regressions explaining total mortality and its distribution across mortality types were developed. Results show that the effects of partial cutting in these stands are complex. Mortality in uncut stands was rather high and many trees died standing. Stem breakage was of minor importance, regardless of treatment. Mortality increased with DBH and harvesting intensity and was higher for balsam fir in comparison with black spruce. Mortality was influenced not only by the locally applied treatment (2500 m 2 ) but also by the treatment applied over a larger area (10–20 ha). Critical wind speeds derived form an adaptation of the ForestGales model were not successful in explaining total mortality or mortality type, although critical wind speeds were generally lower for dead trees in comparison with living trees. The increased mortality was directly related to an increase in the relative importance of uprooting. The type of mortality was more difficult to predict than total mortality and was related to individual tree variables. Results show an influence of crown width, with overturning being more prevalent for trees with wider crowns. Our study indicates that, until there is a better understanding of the factors leading to trees that die standing, it will continue to be difficult to predict mortality in these types of stand.

In January 1998, eastern North America experienced the worst ice storm ever recorded, which resulted in major damage to forests throughout the region. However, we know little about the long-term effects of such a severe weather event, or how its potential interaction with other biotic factors impacted tree mortality. In this study, we investigated the long-term influence of the 1998 ice storm on tree mortality in Boise-des-Muir ecological reserve, an old-growth forest in southern Quebec (Canada). Mortality rates for four out of the five tree species studied showed a striking increase a few years after the ice storm, between 2000 and 2004. After this peak, tree mortality rates remained higher than before 1998. These results indicate a lagged and persistent effect of the ice storm on tree mortality and suggest that the tree community of Boise-des-Muir was more severely impacted than previously reported. Tree species were differentially damaged by the ice storm, and more than 25% of all tree species lost more than half their crown. Using a Cox proportional hazard model, we evaluated the impact of different levels of initial canopy damage from the ice storm on long-term tree mortality while taking into account other important biotic factors, such as tree size, tree density, indices of species-specific competition, and the presence of the beech scale insect. Species differed in their response to the storm, suggesting fundamental differences in sensitivity to extreme weather events. In particular, eastern hop-hornbeam (Ostrya virginiana) and American beech (Fagus grandifolia) were the species most vulnerable to the ice storm, and severe canopy loss led to a large increase in mortality risk. These findings suggest that the difference in tree survival following a natural disturbance likely depends not only on the severity of the damage itself, but also on species-specific ability to repair injuries and maintain physiological processes. We also found that tree size and species-specific competition influenced tree mortality significantly but did not interact with level of canopy loss. Consequently, multiple biotic factors remain important to explain mortality even after a major disturbance and should be considered when evaluating tree mortality. Our results show that the impact of the ice storm on tree mortality was species-specific, lagged and persisted for several years after the disturbance, potentially resulting in long-term compositional changes in the forest. This underscores the necessity of conducting long-term monitoring studies to understand the complete impacts of ice storms and other extreme climatic events on forests.

Norway spruce (Picea abies), European beech (Fagus sylvatica), silver fir (Abies alba) and Scots pine (Pinus sylvestris) typically co-occur in European forests, but show contrasting response to climate and environmental change. Sustainable forest management therefore depends on species- and regional-specific information. Here, we use tree-ring width measurements of 334 beech, 280 fir, 144 spruce and 63 pine trees from 75 inventory plots in Slovakia to assess the predominant factors that control radial stem growth of Europe’s economically most important forest species. All four species exhibit significant shifts in stem growth over the past 100 years. Ring width patterns were, however, not significantly affected by tree species diversity and site elevation. The resistance, resilience and recovery of all species to the extreme summer droughts between 1950 and 2003 suggest that spruce is the species most unsuitable for the predicted warmer and drier future. Silver fir may benefit from warmer conditions, although we cannot conclude that it will not suffer from predicted increased frequency of climate extremes. Forest management in this locality should aim to avoid significant loss of forest cover by replacing Norway spruce monocultures with mixed stands of silver fir and European beech.

Patterns of phylogenetic diversity and structure of flora in refugial areas may be very complex due to habitat heterogeneity and legacies of various historical processes. Revealing these patterns can help understand the nature of the refugia. Here we study phylogenetic patterns of the flora in one of the main putative Pleistocene refugia of temperate forest biota in Europe through a community-level analysis for the main types of forests. For this purpose, a database of vegetation plots from deciduous and mountain coniferous forests of northern and central Greece was created. The plots were classified into floristically and ecologically interpretable community types. Faith’s phylogenetic diversity, mean phylogenetic distance and mean nearest taxon distance, as well as their standardized equivalents, were used to characterize the mean phylogenetic diversity and structure of each community type. All analyses were applied both for all the vascular plant taxa and for angiosperm taxa only. We related the measures of phylogenetic diversity and structure to ecological factors and compared them among community types. The 25 identified community types differed in their phylogenetic diversity and structure. The observed patterns were significantly different when old evolutionary lineages, such as gymnosperms and ferns, were taken into account. A random or overdispersed phylogenetic structure was observed for most of the community types, while only two oak-dominated community types were clustered. The highest phylogenetic diversity and a notably high proportion of plots with an overdispersed phylogenetic structure were observed in two mesic ravine forest community types (one of these transitional to beech forests). Phylogenetic metrics correlated with ecological conditions, in particular, overdispersion was more common in shaded, cool and moist forests. The high phylogenetic diversity and overdispersed structure of the two ravine community types can be related to the putative refugial role of these forest habitats.

The presence of shade-tolerant trees in the understory of mixed-species stands could produce a state of reverse growth dominance, but the growth dynamics between species has been little studied. Here, an analytical framework that was based upon the concepts of growth dominance (GD) and competition mode was used to study the growth dynamics of mixed-species stands. Because shade tolerance is an important trait that influences stand growth dynamics, stands in this study were composed of balsam fir (Abies balsamea [L.] Mill.) and one of four broadleaved species that together form a shade-tolerance gradient. The relative contribution of trees to entire stand growth was determined and then analyzed as a function of their size, species and allometric expectations based upon size-symmetric competition. Balsam fir trees were generally smaller than companion broadleaved species in each type of mixed stands. The small sizes and vigorous growth rates of balsam fir trees were typical of mixed stands that were characterized by negative GD values, i.e., reverse growth dominance. The low number of stands that had positive GD values was generally characterized by higher growth of broadleaved species compared to balsam fir. The growth rates of balsam fir as a function of its allometric expectations play a key role in explaining GD values of mixed-species stands, whereas that of broadleaved species is apparently insensitive to GD values. The concept of stand growth dominance, together with the prevailing mode of competition between trees, identified tree groups that are poor contributors to stand growth. This information can be used in selecting trees for harvest during partial cutting operations, if the purpose of the treatment is to maximize growth of residual stands.

Mangrove forests provide important ecological and economic services including carbon sequestration and storage. The conservation and restoration of mangroves are expected to play an important role in mitigating climate change, and understanding the factors influencing mangrove stem growth and wood production are important in predicting and improving mangrove carbon sequestration and responses to environmental change. In this study, we collected data of individual diameter at breast height (DBH) growth rate and stand level aboveground wood production in both non-plantation (commonly termed as natural) mangroves and mangrove plantations across the world. Climatic factors, proxies of edaphic factors, as well as biological factors (e.g. mangrove species) were included as explanatory variables in the analyses to determine factors influencing the global patterns of tree growth rate and stand wood production of mangroves. Using hierarchical Classification and Regression Tree (CART) analysis we found interactions among environmental and biological factors in controlling mangrove tree growth rate and stand wood production. We also found different global patterns of tree growth rate and stand wood production between non-plantation mangroves and plantations. Climatic conditions (precipitation of driest season, precipitation seasonality) were the most important factors influencing the global pattern of tree DBH growth rate in non-plantation mangroves, with edaphic and biological characteristics also playing a role under specific climatic conditions. The global pattern of stand wood production in non-plantation mangroves was primarily determined by stand mean DBH growth rate of individual trees. However, in mangrove plantations management measures, specifically species selection and planting density, were the most important factors influencing the global patterns of tree growth rate and stand wood production. Our study provides parameters for a global estimation of long-term carbon sequestration in both non-plantation mangroves and mangrove plantations. In addition, our results help us better predict the dynamics of tree growth and carbon sequestration of non-plantation mangroves under changing climate.

International audience; Context: Douglas-fir, a fast growing conifer from western North America, recently suffered diebacks following drought in France. We investigated the link between native-source climate and provenance drought resistance in a common garden in France. We compared the adaptive potential of provenances from different parts of the natural area. Methods: We collected branches from a 25-year-old provenance trial replicated in two test sites in southern France. We estimated provenance variation of cavitation resistance traits, survival and circumference. We compared Washington-Oregon provenances to coastal and interior Californian provenances. Results: In the common gardens, the hydraulic traits were significantly variable between provenances, with a strong site x provenance interaction, and significantly related to the climate of the natural area and survival. The relationships were different between variables and test-sites. The two test-sites and their particular climatic selective pressure revealed different geographical adaptive structures in the natural area. Conclusions: Douglas-fir evolutionary adaptation to drought results from natural selection to summer climate and shapes populations for cavitation resistance. In the dryer site only, the Interior California provenances seem more drought resistant. The strong within-provenance variations suggest that there is also a certain withinprovenance adaptation potential to drought at the cost of variable mortality rates.

We studied the fine root system of Fagus sylvatica in six mature stands on different bedrock down to the rock surface (or to 2 m) to investigate whether (1) the stand total of fine root biomass (FRB) increases, while the fine root live:dead ratio decreases, with decreasing soil base richness, (2) specific root area (SRA) and root tip frequency increase with a decrease in base richness, and (3) FRB is related to profile depth. The three beech stands on deep soil (>2 m profile depth) had on average by 38% larger FRB totals than the stands on shallow soil (60–80 cm), suggesting that limited root space is an important determinant of fine root system size in F. sylvatica. Despite large variation among sites, soil chemistry influenced root morphology only little: fine root diameter depended on soil C/N ratio and root tip frequency on base saturation in a few soil horizons. Much larger morphological differences were found between topsoil and subsoil roots within a profile. We conclude that the fine root system of F. sylvatica varies under similar climatic conditions remarkably little between base-poor and base-rich sites, in contrast to the pronounced topsoil-subsoil differences in root morphology and fine root density.

Mangroves often allocate a relatively large proportion of their total biomass production to their roots, and the belowground biomass of these forests contributes towards globally significant carbon sinks. However, little information is available on root production in mangroves due to the difficulties in carrying out measurements of belowground processes, particularly if there is regular flooding. In this study, we examined fine and coarse root production in the east coast of the Malaysian Peninsula. Ingrowth cores were used over the course of 17 months. In September 2014, twenty cores were randomly placed in each of five plots. Three cores were collected from each plot (fifteen cores in total), once every three months. Each core was divided into five 10 cm layers and root dry mass was recorded. Standing root biomass was also measured at the time of final collection using an additional 15 cores. There was a seasonal pattern in root production, which peaked in March and December 2015, after and during the monsoon season. Root biomass in the cores peaked at 33.23 ± 6.3 t ha−1 and 21.46 ± 7.3 t ha−1 in March and December respectively. Standing root biomass in February 2016 in the forest was 20.81 ± 2.8 t ha−1. After 17 months, the final root biomass in the cores was 14% less than the standing root biomass. These data suggest surprisingly rapid growth rates and turnover for mangrove roots. Total root biomass significantly increased with root depth and 78% of the roots, in all soil layers, consisted of fine roots (

Wide-spread use of single-tree harvest methods has inhibited regeneration of yellow birch in shade-tolerant hardwood forests. Shelterwood harvesting can improve recruitment, but incurs higher costs, longer harvesting cycles, and produces an even-aged structure. Group selection (GS) harvesting provides an alternative method with the benefits of single-tree selection (STS; mixed-ages, shorter cycles), yet produces larger gaps that may favour recruitment of mid/intolerant tree species. Recent GS trial studies have shown promise, but results vary and differences in edaphic conditions and competition dynamics associated with climate, historical management, and season of harvesting may influence responses. We evaluated the yellow birch recruitment efficacy of GS in an Ontario shade-tolerant hardwood forest by comparing change in regeneration as percent ground cover (stems 50 cm) over ten years in STS harvested and unharvested forest relative to two types of GS gaps: “typical” gaps placed in suitable microsites, and indiscriminate “systematic” interval gaps harvested on a grid. Autumn-harvested gaps established 2–4× more yellow birch cover and recruited 7–10× more large stems by year ten than STS and winter harvested gaps; unharvested controls remained unchanged. Typical gaps recruited 3× more stems than systematic gaps in autumn-only. Soil disturbance and seed tree proximity were correlated to establishment of yellow birch cover in year 1, which predicted large stem recruitment by year 10. Winter-harvesting favoured sugar maple cover in year 1, which predicted lower yellow birch recruitment by year 10. These results indicate that autumn-harvested typical gaps optimised germination and growth conditions for yellow birch (light availability, soil disturbance, reduced competition, seed proximity/dispersal). Consequently, GS harvesting in autumn can be considered an effective alternative to shelterwood harvesting for yellow birch recruitment in poorly-represented shade-tolerant hardwood stands.

Despite improvements of dendrochronological techniques in many forest ecosystems, studies describing the growth responses of trees following disturbance events including comprehensive data on factors and processes behind tree-growth release are rare, especially for European temperate forests, limiting the interpretation and generalization of dendroecological studies. Here we examine the effect of key factors on the growth reaction of Fagus sylvatica L. to disturbances in 8 old-growth forests in the Czech Republic, independently dated using three different data sources – tree censuses, dendrochronology and historical aerial photographs. Using 117 increment cores, we studied four parameters of radial tree-growth surrounding canopy gaps: magnitude, duration, abruptness and response shift, in relation to factors of different spatial scales, i.e. tree-, gap- and stand-level variables. Our results indicate that the beech growth response to gap formation strongly differs across a complex of factors at diverse spatial levels, frequently occurring in noteworthy interactions. A positive trend for the gap size * radiation interaction in the analysis of magnitude was found, suggesting that the effect of gap area differs among topographical features. As for duration and abruptness, the interaction of distance and mortality mode was identified, indicating a longer and more gradual reaction along with increasing distance of the cored tree from the gap centre, varying by the type of the gap maker’s death. In addition, an altitudinal gradient was found to predict the magnitude of growth changes and the time interval between the disturbance and the reaction of nearby trees. Surprisingly, the diameter of the surviving trees was not a good predictor of radial growth, with a significant positive relationship to just abruptness. An effect of locality was not observed, facilitating the broad applicability of our findings across a wide range of beech-dominated temperate forests. Our results emphasize the general limits of dendrochronological data in disturbance spatial pattern studies, as indicated by the considerable variability in the responses of neighbouring trees to identical disturbance event. A detailed examination of the growth reaction, considering not only the response magnitude but also other important parameters, plays a key role in the precision of detecting growth releases as well as in reducing the sample size required for summary disturbance history evaluations. In focusing on this issue we believe we contribute to future dendroecological research by demonstrating the need for more precise disturbance history evaluations.

The distribution of vegetation zones in northeastern North America forms a gradual transition from closed to open forests, and to tundra. Closed forests near the open forest/tundra boundary generally correspond to residual patches of a once larger forest community. Whether these forest patches have survived as untouched, fire-free communities or as resilient communities during the Holocene remains unknown. To answer to this question, we reconstructed the successional history of two black spruce closed-crown forests and one jack pine forest near the northern limit of closed forest ecosystems. Stand-scale postfire succession was analysed based on charcoal macrofossils. Extensive 14C dating and botanical identification of charcoal fragments located at the organic soil surface and buried in the mineral podzolic solum were used to reconstruct the successional pathways of the sites. The forest sites developed in a context of continuous fire disturbance, except for a short interval of several centuries. The fire history of the three sites is similar with a fire frequency of 34–37 fires over the last 5000–5800 years, which corresponds to a mean fire interval of 150–180 years. Based on parametric and non-parametric estimators, the regional fire regime of the Laforge area (combined fire data of two sites located about 7 km from each other) was most likely characterized by 38 fires over the last 5000–5800 years, i.e., at an interval of about 150–160 years. Birch (Betula papyrifera) was present in the spruce sites between 5800 and 3000 cal. years BP. Jack pine arrived at the pine site about 3000 cal. years BP, at the time when birch was extirpated from the spruce forests. The closed-crown forests near the open forest/tundra boundary are resilient postfire ecosystems which regenerated successfully since mid-Holocene. Compositional change of these forests, which led to the decline of birch but maintained the dominance of conifers, appears related to cooler and wetter conditions of late Holocene. Climatic conditions also slowed the eastward migration of jack pine, which explains the late arrival of this species at its northeastern range. Our data suggest that fire disturbance in these sites of the boreal biome has been a continuous and positive regenerative process since mid-Holocene despite the influence of climatic change on the tree flora.

Despite the critical role of pulsed resources on the dynamics and conservation of several forest-dwelling species, the transition between the period when the effects of a thinning-induced resource pulse are maximal and the period when only residual effects remain has yet to be documented in forest habitats. In this study, we investigated the occurrence of a transition period after a woody necromass resource pulse produced by commercial thinning operations on flying coleopterans. In a large-scale manipulative study, spruce plantations were subjected to commercial thinning treatments and beetles collected using flight intercept traps during the four years that followed thinning operations. 82,062 beetles from 50 families and 242 species were recovered. For two years after thinning treatments, beetle communities differed in composition between thinned and unthinned plantations, species richness and abundance being higher in thinned areas. By the third and fourth year after thinning treatments, these differences started to fade, indicating that the transition period was occurring. This was associated with a decline in the quality of woody debris found close to or onto thinning trails. These results support our hypothesis that fine woody debris, such as those produced by commercial thinning operations, are attractive to beetles for a short period because they rapidly decay and are rarely colonized by wood-boring species, inhibiting further colonization by fungi and mycophagous beetles. Yet, despite a decline in abundance and species richness in thinned areas during the last two years of the study, thinned plantations still harboured richer and more abundant beetle communities than unthinned plantations, suggesting that thinning trails continue to improve beetle dispersal as the woody necromass resource pulse weakens.

Quantifying the compositional differences among communities is central to answering some of the most challenging questions in community ecology. Traditional species-based estimates of community dissimilarity convey little information regarding the biological heterogeneity of species. More refined phylogenetic- and functional-based measures can improve the understanding of ecological mechanisms that drive species composition. However, a generalized framework, which unifies taxonomic, phylogenetic, and functional information of communities is still lackling. We present a new general framework for assessing the biological dissimilarity among communities based on species frequencies and biological (including taxonomic, phylogenetic, and functional) distances between species. We used the observations collected in a 30-hectare forest plot in northeastern China to illustrate the application of the new approach and its ability to discriminate communities along spatial and environmental gradients. The results suggested that both spatial and environmental gradients play significant roles in driving the species composition of forest communities. Compared with spatial gradients, local environmental conditions had a greater influence. Conclusion: The ability to measure differences among communities, based on species frequency and biological distances is useful for estimating effects of habitat heterogeneity, for understanding the mechanism of community assembly, and for assessing disturbance effects or species invasions at local or global scales. The Avalanche approach presented in this study represents an effective framework for comparing different measures of biological dissimilarity in one compatible system.

Restoring nutrients lost in the mining process and re-establishing nutrient-cycling are often key goals of mine restoration. One common strategy to facilitate these goals is to seed fast-growing legumes combined with one application of P-fertiliser to maximise legume growth and increase soil-N. However, the longer term effects of this strategy have received little attention. Here we report the results of a 15-year-old experiment that was established to test the effects of fertiliser-P application and seeding large understorey legumes, both singly and in combination, on jarrah forest restoration after bauxite mining. Fifteen years after the establishment of this experiment, the majority of the seeded legumes had senesced, with total legume cover having declined significantly compared with results of the same experiment at 5-years-of-age. Yet, despite the legumes having senesced there were still negative effects of both large legumes and P-fertiliser on species richness and abundance of non-leguminous understorey species. These negative effects may be mediated by the persistent effects of legume competition that was evident at 5 years and the accumulation of significant quantities of leaf litter and fine woody debris in the large legume × P-addition treatments. Compared with the 0 kg P ha−1 treatment, application of 20 kg P ha−1 significantly increased jarrah tree growth, but there was no additional benefit of 80 kg P ha−1. These data suggest that moderation of P-fertiliser and large understorey legumes could maximise understorey cover, tree growth and understorey species richness, and therefore simultaneously address multiple key restoration goals.

The mechanisation of forestry operations is too recent in France to have enough perspective and scientific knowledge of the effects on extensively managed soils. Two experimental sites on soils sensitive to compaction (silty acidic soils laying on top of a clayey subsoil) were set in Lorraine (France). A gentle and controlled compaction of these physically very analogous soils was carried out during spring 2007 at the Azerailles site (AZ) and during spring 2008 at the Clermont-en-Argonne site (CA). Immediate changes were observed for all ecosystem physical, chemical and biological functioning indicators. Soil restoration dynamics were followed using continuous monitoring of numerous parameters, including soil moisture and occurrence of a perched water table (PWT) (monitored at a daily time step) and PWT chemistry (monthly time step). Mid-term monitoring (7–8 years) results showed that both soils shifted towards a hydromorphic soil type attested by the increase in PWT frequency and duration, which invaded the soil upper layers, leading to characteristic Fe, Mn and S mobility and a change in organic compounds stability. Though soil types were very similar, the PWT characteristics varied notably between both sites. The mean residence time of the PWT was shown to be a major driver of its geochemistry, but with strong interaction with soil characteristics. A previous study made on both sites suggested that soil clay content and clay mineralogy controls the PWT dynamics through effects on aggregation. From a PWT perspective, seven years of monitoring were insufficient to observe any soil compaction recovery in the richer soil of AZ but a partial recovery was observed for the chemically poorer soil (CA). Compaction durably impacted the two studied soils and the probability that a new compaction event may occur before the complete recovery from the first disturbance must be considered in forest management.

Spruce budworm (SBW – Choristoneura fumiferana Clem.) is one of the most damaging defoliating insects in the coniferous forests of eastern North America. In Canada, the widely distributed balsam fir (Abies balsamea L. (Mill)) and black spruce (Picea mariana B.S.P. (Mill)) are its most important hosts. Defoliation by SBW reduces growth in the host trees and can lead to host mortality. Although SBW impacts on growth are well documented, much less is known about changes in wood properties resulting from defoliation. To address this knowledge gap, we sampled 36 SBW-infested stands located in the boreal forest of Quebec (Canada) to determine whether defoliation modifies the wood quality of affected trees. The selected stands had been subjected to one to four years of SBW defoliation. For both species, we assessed ring growth, wood density, and the anatomical characteristics of stem wood formed during the outbreak years. We determined that rings formed during the SBW outbreak had a significant and progressive loss of biomass production with a longer duration of defoliation. SBW significantly reduced latewood density in the second and third year of defoliation for black spruce and the third and fourth year for balsam fir. Average ring density was reduced only in black spruce and only after four years of defoliation. The observed changes in growth and density were associated with changes in anatomical features. While the cellular characteristics of the earlywood remained fairly constant, significant reductions occurred in latewood cell-wall thickness after three years of defoliation. Our study shows that not only do SBW outbreaks reduce annual radial growth, but the cellular characteristics in latewood cells are also modified momentarily. Thus, SBW outbreaks affect wood density and quality in both black spruce and balsam fir.

We investigated the growth and mortality dynamics of 22 northern hardwood stands with well-known disturbance histories in southern Quebec, Canada. The main objective of this study was to evaluate the effect of short- and long-term growth trends on both the probability of mortality and the radial growth response of trees following partial cutting. This was first achieved by identifying growth release episodes and characterizing growth patterns prior to tree death from entire tree-ring series of 86 live and 26 dead sugar maple (Acer saccharum Marsh.) trees. Using mixed-effects logistic regression, we quantified the effects of short- and long-term growth trends, as well as external variables such as neighbourhood competition and tree vigour status on the probability of mortality and growth release events. Results showed that long periods of continuous growth decline or long periods of slow radial growth after a severe decrease occurred in 88% of dead trees. These growth patterns were associated with a progressive decline in tree vigour that was mostly initiated by drought and insect defoliations during the 1980s, thereby supporting the relevance of studying long-term tree-ring chronologies to deduce causes of post-harvest mortality. Our model showed that predictions of post-cut mortality events could be significantly improved by considering long-term radial growth trends (25 years before cutting) in individual trees. In terms of growth response, 24% of live trees had a release event occurring after the selection cut, which is slightly lower than the response induced by natural disturbance in previous decades. None of the tested long-term growth variables were significantly related to the occurrence of growth release events. Consequently, suppressed sugar maple trees appear to maintain their capacity to respond positively to gap creation, regardless of the length of the suppression period. We conclude that while decreasing trends in long-term radial growth increase mortality probabilities, the growth release potential of trees is negatively impacted by the presence of defects affecting tree vigour (e.g. fungal infections and cambial necroses) and positively related to the removal of neighbouring trees, rather than to prior growth trends.

International audience; Increasing deer and wild boar populations in North America and Western Europe are suspected of threatening low-nesting forest birds. Ungulates may directly affect these birds by predating eggs or chicks, or indirectly attract other mammalian or avian predators or reduce nesting site availability and habitat quality. To test some of these various mechanisms in two French forests, 528 artificial nests, 77 of which (14.6%) were monitored with camera traps, were set up in 44 plots which were either unfenced or fenced to respectively include or exclude ungulates. We used generalized linear mixed models to relate the nest failure rate to indices of plot frequentation by ungulates and other nest predators, to vegetation structure and to local bird community richness indices. Nest failure rate was significantly higher in the unfenced plots (39%) than in the fenced plots (32%) but this was related neither to red deer nor to wild boar frequentation of the plots. Furthermore, levels of frequentation for other mammalian and avian predators tended to be positively correlated to ungulate presence but not to nest failure rate. Nest failure rate depended on both nest height and shrub cover: nests on the ground (31% failure rate) were less predated or disturbed than nests in low shrubs (41% failure rate). Nests surrounded by low shrub cover experienced a slightly higher predation risk. We conclude that ungulates have a limited influence on nest failure for low-nesting forest birds; in particular, they seem to contribute very little to egg predation compared to other predators.

Forest harvesting reduces mean stand age and dead wood amount. Among species dependent upon older forests and dead wood, primary excavators such as woodpeckers play an important ecological role by providing cavities for many other species. Conservation of these species thus requires striking a balance between timber harvesting and dead wood supply, especially under moderate natural disturbance regimes. In this study, we quantified habitat use in two closely-related, sympatric species: Black-backed (Picoides arcticus) and American Three-toed (P. dorsalis) Woodpecker, in the highlands of northern New Brunswick, Canada. Natural fires are rare in this ecoregion and forest harvesting is the main agent of landscape change, along with infrequent outbreaks of spruce budworm (Choristoneura fumiferana). Based on its habitat use patterns in other ecoregions, we hypothesized that Black-backed Woodpecker would select nest sites in mature coniferous forest stands and we expected that it would achieve a higher nest survival rate in forest stands than within, or at the edge of, cutblocks. Owing to sample size limitations for American Three-toed Woodpecker, statistical analyses were restricted to its occurrence patterns. Both species co-occurred, and there was no difference in detectability following conspecific and heterospecific playbacks. Contrary to our prediction, Black-backed Woodpecker selected nest sites with higher proportions of recently cut areas within 50 m than at randomly selected sites. Black-backed Woodpecker selected cutblocks for nesting when suitable snags were available and mature forest stands were present nearby as foraging habitat. For the species to persist in this landscape, the supply of snags must be continuous and forest stands must be sufficiently mature to host saproxylic insects.

The recent range expansion of the mountain pine beetle, Dendroctonus ponderosae Hopk. (Coleoptera: Curculionidae), into evolutionarily naive lodgepole and jack pine forests of northwestern Canada has triggered concern that continued eastward expansion through the boreal forest will threaten other pine species native to eastern North America. This unprecedented breach of a historic geoclimatic barrier was precipitated by a “hyperepidemic” west of the Rocky Mountains comprising the largest mountain pine beetle eruption in recorded history. We assessed climate-related latitudinal shifts of pre-outbreak populations of mountain pine beetle in western Canada over a 26-year period preceding the hyperepidemic, as movements of pre-outbreak populations determine, in part, the extent of subsequent outbreaks. We used digitized records of annual aerial overview surveys (1965–1979, 1986–1996) of tree-killing activity, comprising > 122,000 individual infestation polygons, and temperature and aridity data to associate trends in deviations of weather variables from historical averages with latitudinal shifts by the insect. Overall, we found that seasonal and multiyear weather phenomena such as anomalous temperature increases in a stable aridity regime, or vice-versa, and warmer-than-normal winter temperatures explained small but significant variation in northward annual range shifts after factoring out spatial and temporal variation. The numbers of discrete, tree-killing infestations increased rapidly during 1965–1979, and northward range shifts of 300 km in the early 1970s coincided with abnormally dry conditions. Mountain pine beetle populations advanced northward by 391 km from 1965 to 1996. Consistently high infestation levels of the mountain pine beetle occurred simultaneously with above-average temperatures that extended for nearly a decade immediately preceding the hyperepidemic. Climate-associated range shifts can provide gateways to rapid range expansions, and evoke concern with regard to future impacts of other bark beetle species inhabiting regions likely to experience multiyear droughts and/or temperature increases under climate change.

Following a disturbance, extensive aspen (Populus tremuloides) suckering is crucial for ensuring the continued productivity of the future forest. The aim of this study was to assess the suitability of using winter harvesting in a provincial park as a way to mitigate severe soil compaction and ensure sufficient aspen regeneration to rejuvenate the mature forest. Six harvested blocks were selected for this study based on a skidder traffic intensity map, which was generated using GPS data collected throughout the duration of the harvesting event. Soil bulk density, aspen regeneration, and vegetation indices were measured across the different levels of skidder traffic intensity. Soil bulk density increased significantly following as little as 1–5 skidder passes (1.39 g cm−3) compared to the unharvested control (1.29 g cm−3); however, bulk density remained relatively constant as the level of skidder traffic intensity continued to increase. No relationship was found between soil bulk density and the level of aspen regeneration; however, the level of skidder traffic intensity significantly influenced the level of aspen regeneration. Aspen root collar diameter, leaf area index, dry leaf biomass, total N, and total P all decreased as the level of skidder traffic intensity increased; but, these decreases were not significant. Conversely, both aspen sucker density and height decreased significantly as the level of skidder traffic intensity increased, decreasing nearly 50% and 28%, respectively, in areas with 51–100 skidder passes. Multispectral remote sensing using UAV to assess the level of aspen regeneration across an entire harvested block proved ineffective. Although several vegetation indices showed significant relationships with aspen properties, none of these relationships had a coefficient of determination greater than approximately 0.2. Overall, winter harvesting appeared to have mitigated soil compaction concerns as expressed by soil bulk density and. although areas with higher levels of skidder traffic intensity (51–100 passes) experienced a decrease in aspen regeneration vigor, these areas with decreased aspen regeneration only accounted for approximately 1–2% of harvested blocks.

International audience; We explored the ecological impact of a nitrogen-fixing shrub (Ulex europaeus, common gorse) cultivated as an intercrop species in the interlines of a young stand of maritime pine (Pinus pinaster). Nitrogen fixing species are well-known for their advantage of increasing the soil fertility in agriculture. Nevertheless, in forest ecosystems, their use is uncommon except in some associations in the tropics. The Landes de Gascogne forest range (SW France) has soil fertility issues and Ulex europaeus is a vigorous plant, native to this region. Therefore, an investigation of the association of this N-fixing species with trees is worthwhile. To this end, we compared a standard pine plantation management (control) with a treatment where gorse seeds were sown in the interlines at tree plantation (gorse sowing). This factor was combined with a phosphorus supply (control versus P-fertilisation), resulting in four treatments. The forestry practices evaluated here distinguish two main periods: a first period of six years after tree plantation when gorse individuals grew as an intercrop and formed dense vegetation, and a second period of three years after crushing this vegetation in the interlines. In the first period, pine mortality in the gorse sowing treatment was higher during the dry season than in the control treatment, suggesting competition for water. Pine diameter growth was reduced, but not height growth, indicating avoidance of light competition with gorse. In the presence of gorse, pine foliar-N was appreciably enhanced relative to the control, and natural pine pruning occurred, while pine browsing by animals was limited due to the protection of the thorny gorse thickets surrounding the trees. In the second period, soon after crushing the gorse vegetation in the interlines, enrichment of nitrogen in needles continued, suggesting a fertilising effect of the gorse remnants. Crushing also freed the pines from shrub competition and a “catch-up growth” was identified regarding diameter and stem volume growth. Two years after the gorse crushing, tree size and biomass were similar in the experimental treatments regardless of gorse sowing or not. Overall, during the first nine years after tree plantation, gorse introduction in the pine tree forests had various effects. On the one hand, gorse induced competition for light and water. On the other hand, it resulted in high inputs of nitrogen and organic matter into the ecosystem which could lead to sustained soil fertility and this might improve tree nutritional status. We recommend continuing the assessment of such pine-gorse forestry associations for longer observation periods and in very nutrient-poor sites in this forest range.

Most investigations of human impacts on biodiversity have been conducted within 1–3 years post-disturbance, although many biological responses develop over a longer period of time and annual community variation cannot be fully controlled. We therefore conducted a follow-up of carabid beetles over ten years in Norway spruce (Picea abies) dominated forests in Southern Finland, harvested using replicated logging treatments of different intensities. We collected carabids using pitfall traps in 1995 (prior to logging) and during four post-harvest seasons, 1996–98 (three first post-harvest summers) and 2006 (ten years after harvesting). The treatments were clear-cutting (no retained trees), modified clear-cutting (retention of three groups of 20–30 trees within a one-hectare plot) and gap cutting (three 0.16-ha openings within a one-hectare plot), and control (mature unharvested forest). (1) Total species richness and open-habitat carabids increased in gaps and in the two clear-cutting treatments, whereas forest carabids were slightly less abundant in clear-cuts than in the other treatments in 1997. These patterns were most evident in the second and third post-harvest summers. (2) Open-habitat carabids were less abundant and less speciose in both cleared and retained patches of gap cuts than in clear-cuts, Pterostichus adstrictus was more abundant in clear-cuts than in retained patches of modified clear-cuts or gap cuts, and carabid assemblage was more altered in both types of clear-cut than in gap cuts. (3) Ten years after logging, open-habitat carabid numbers were still elevated, whereas Calathus micropterus was less abundant, in the two types of clear-cut than in gap cuts or control stands. (4) We also found remarkable annual variation in carabid assemblages, such that was independent of logging. We conclude that even modest retention provides long-term support for forest carabids, but also that their full assemblage recovery takes longer than 10 years.

We followed how forest thinning, repeated twice during a period of 93 years, altered understorey plant community composition, affected the succession of forest understorey vegetation and the accumulation of logs in the long-term. The study was carried out in northern Finland by resampling 20 permanent experimental plots, established after a wildfire in 1920. Understorey vegetation was inventoried in 1961, 1986 and 2013 with forest thinning treatments done in 1953 and 1987, using four and three different harvesting intensities, respectively. We found succession to override the effects of forest logging until the latest study period (2013). We observed negligible long-term effects of logging on understorey communities during the two mid-successional stages (1961, 1986), when the forest was 41 and 66 years old respectively. The impacts of logging on understorey vegetation were strongest in the latest successional stage (2013), the forest being at the age of 93 years. In the latest successional stage (2013) logged plots had less coarse woody debris than unlogged plots. Forest management thus influenced the key feature for forest biodiversity and potential habitats for endangered species. These findings are of major interest since the studies of long-term impacts of less intensive forest management practices are scarce. Our results suggest that in addition to possible immediate impacts, harvesting treatments have legacy effects (subtle or delayed inherited effects of forestry in the past) that influence the forest understorey vegetation community composition and the amount of coarse woody debris. This finding deserves special attention when planning of species conservation, multiple use of forests and sustainable forestry.

Sugar maple (Acer saccharum Marsh.) is a commercially important species throughout much of eastern North America and concerns have been raised regarding its successful regeneration owing to nutrient limitation, especially calcium (Ca) caused by acidic deposition. Timber harvesting can alter nutrient availability in soil, but the short-term effects of selection harvesting on sugar maple seedling chemistry have not been studied. In this study, sugar maple seedlings were collected for elemental analysis from unharvested areas, canopy gaps and skid trails one and two years post selection harvest in a mixed hardwood forest in central Ontario, Canada. Plant community composition and sugar maple seedling morphology were measured along with soil physical and chemical properties. While there were few measurable differences in soil physical or chemical characteristics amongst sites, understory vegetation was markedly different and Carex spp. were dominant in skid trails. In addition, sugar maple seedlings in the disturbed sites (gaps and skid trails) were morphologically different (decreased height:diameter ratio) and had lower foliar concentrations of essential plant nutrients including nitrogen (N), magnesium (Mg), potassium (K), and phosphorus (P) compared with unharvested sites. Calcium concentrations in seedlings were unaffected by harvesting, perhaps due to low soil Ca levels across all sites. In contrast to Ca, foliar concentrations of K and P in seedlings growing in gaps and skid trails were below or approached reported nutrient deficiency thresholds for mature trees, which may have potential consequences for forest regeneration that have not been previously considered.

Wind is an important driver of forest dynamics in eastern Canada, but knowledge of variables that predispose forest stands to windthrow remains unclear. This is of particular concern as climate change is expected to alter the frequency of strong wind events that affect eastern Canada. In this study, we used widescale forest survey data from Nova Scotia, Canada, of wind damage caused by Hurricane Juan, to investigate variables that influence stand vulnerability to windthrow. Juan made landfall as a category SS2 hurricane with sustained winds of 158 km/h and damaged over 600,000 ha of forest. The damage zone was surveyed using aerial photography and satellite imagery, delineated according to level of wind damage, and digitized as a 15 × 15 m resolution spatial raster layer. We selected a random sample of 50,000 cells classified as intact forest and 50,000 cells classified as stand-replacing windthrow from the raster layer and used boosted regression tree analysis to explore the influence of various meteorological, topographic, soil, and forest structural variables on the occurrence of windthrow. Wind speed and forest structure, specifically stand height and species composition, were most influential in determining windthrow. Sustained winds of at least 95 km/h or gusts of 130 km/h caused >50% probability of windthrow. Taller stands were most vulnerable, especially those dominated by spruce (Picea spp.) and balsam fir (Abies balsamea), whereas higher hardwood and pine abundance reduced windthrow. Interestingly, topographical exposure (Topex) ranked low in overall influence; however, a clear relationship between increased exposure and windthrow was observed.

Planting shock can last for several years during which seedling growth may significantly slow down. This duration depends upon the time that is required for the root system to acclimatize to its new environment. We hypothesized that characteristics of the root system are important factors for black spruce (Picea mariana [Mill.] BSP) seedling establishment. To test this hypothesis, we compared growth and physiology of three stock types: containerized seedlings, with a dense initial root system restricted to the volume of a root plug; deeply planted containerized seedlings, with the stem buried during production to develop dense adventitious and initial root systems; and bareroot seedlings, with a less developed but unrestricted initial root system. The three stock types were planted on three microsites that are typical of reforestation sites found in eastern Canadian boreal forest: (1) bare mineral soil; (2) in presence of ericaceous shrubs; or (3) in presence of Sphagnum spp. and ericaceous species. Labelled nitrogen fertilizer was added to half of the seedlings to compare nitrogen uptake. We measured seedling growth (height, diameter, above- and belowground biomass), nutrition (including 15N uptake) and 13C discrimination (as an indicator of water stress) at the end of the second growing season. Except at the root level, there were few interactions between stock types and microsites. For fertilized microsites, we speculate that ericaceous species captured most added nutrients since seedlings that were planted directly on mineral soil had greater height and diameter increments than seedlings with competing vegetation. In unfertilized microsites, Sphagnum spp. and ericaceous species had significant negative effects on seedling growth. For stock type, the presence of a root plug allowed containerized and deeply planted seedlings to have a lower δ13C, suggesting less water stress compared to bareroot seedlings. Strong initial root system development of containerized seedlings resulted in greater total biomass. We hypothesized that the presence of adventitious roots in deeply planted seedlings positively influenced nutrient uptake, particularly N. As nutrient availability is one of the most limiting factors in the boreal forest, we suggest using deeply planted containerized seedlings to reduce planting stress.

Mixed plantations of Eucalyptus and N2-fixing trees are ecologically beneficial because they stimulate organic matter cycling and increase carbon (C) and nitrogen (N) pools in the soil. However, the microbial mechanisms that contribute to the improvement of C and N dynamics remain poorly understood in managed forest ecosystems. Here, we evaluated interactions between the bacterial community and biological functions involved in C and N cycles in the soil and litter layers resulting from pure or mixed Eucalyptus grandis and Acacia mangium plantations. We hypothesized that the mixed plantations induce changes in the bacterial community that would drive increases in C and N pools in soil and litter layers. We established a field experiment with treatments including pure E. grandis without (E) and with nitrogen fertilization (E + N), pure A. mangium (A), and mixed E. grandis and A. mangium (E + A). Soil and litter from all treatments were sampled 27 and 39 months after planting. We evaluated the soil and litter bacterial community and biological functions involved in C and N cycles (i.e., microbial and enzyme activities, functional gene abundance, and soil-litter nutrient cycling). The treatments A and E + A showed an increase in C and N contents in the organic soil fractions. We found higher bacterial diversity and OTU richness in soil and litter, and higher nifH gene abundance in the soil under A and E + A, when compared to pure E. grandis (especially E + N) plantation. Our data suggest that the total N content influences the bacterial community structure of the litter, which undergoes alterations according to the treatment and forest age. Equally, Rhizobium, Bradyrhizobium and Sphingomonas showed a positive correlation with nifH and soil N. Our study provided evidence that changes in the microbial community in mixed A. mangium and E. grandis plantations is correlated with increased C and N cycling. These findings have implications for increased productivity and environmental sustainability, besides allowing for the optimization of mineral fertilization in forest plantations.

When public lands were surveyed in the U.S., “witness trees” were often recorded to facilitate the relocation of property boundaries, and these records provide a snapshot of forest conditions prior to Euro-American settlement and land clearing. This study utilizes witness trees and present-day plot data to explore long-term vegetation changes at a regional scale. Landscape classes for a 5000 km2 study area in Appalachian Ohio were defined by slope, aspect, topographic position, soil pH, and available water capacity. Cluster analysis and ordination revealed topo-edaphic patterns in the presettlement (c. 1800) and present-day forests, based on 5765 witness trees and 3249 contemporary trees occurring on 547 Forest Inventory and Analysis (FIA) subplots. Mesophication is evident, as the oak-hickory presettlement forest is now dominated by maple-poplar. Size-class analysis suggests the presettlement forest also experienced mesophication following xeric conditions of the preceding centuries. In both presettlement and contemporary forests, ridges form distinctive communities compared to slopes and valleys, although topographic distinctiveness is now more prevalent. Several taxa revealed changes in site affinities over the past two centuries; shifts in their realized niches suggest mesophication acts through diverse individualistic responses to a multiple set of interacting drivers. Specifically, regionally documented changes in land use, drought, N deposition, and fire at the time of the original surveys lead to altered competitive relationships.

The hypothesis was tested that the size and the degree of isolation of Larix sibirica forests in the forest-steppe ecotone of Mongolia affects aboveground and belowground carbon pool densities. The research question was based on the fact that both microclimate and the drought sensitivity of stemwood production were earlier shown to differ with stand size and isolation in this ecotone. Contrary to our hypothesis, we did not find significant differences in the organic carbon stock densities of the tree biomass and the mineral soil. The depth, carbon content and carbon stock density of the organic layer increased with stand size, but was not a major determinant of total ecosystem carbon stock density. Nevertheless, the increasing depth and the increasing humus content of the organic layer with stand size could be significant by improving moisture availability and, thus, promoting forest regeneration. Furthermore, reduced organic layer thickness and humus content and thus water storage capacity could be one out of several causes of the previously observed higher drought vulnerability of stemwood formation in small forest stands of the Mongolian forest-steppe. A mean carbon stock density of 237 Mg C ha−1 for total ecosystem organic carbon stock density matches with earlier estimates for Mongolia’s boreal forest corroborating the view that the ecosystem carbon pool density at the southern edge of the boreal forest is lower compared to forests at higher latitudes with even colder climate and deeper and more widespread permafrost.

International audience; Tropical forests harbor the greatest terrestrial biodiversity and provide various ecosystem services. The increase of human activities on these forests, among which logging, makes the conservation of biodiversity and associated services strongly dependent on the sustainability of these activities. However the indicators commonly used to assess the impact of forest exploitation, namely species richness and biomass, provide a limited understanding of their sustainability. Here, we assessed the sustainability of common forest exploitation in the Guiana Shield studying the recovery of two ecosystem services i.e. carbon storage and wood stock, and an ecosystem function i.e. seed dispersal by animals. Specifically, we compared total and commercial biomass, as well as functional composition in seed size of animal-dispersed species in replicated forest plots before and 27 years after exploitation. Species richness is also studied to allow comparison. While species richness was not affected by forest exploitation, total and commercial biomass as well as seed size of animal-dispersed species decreased 27 years after exploitation, similarly to forests affected by hunting. These results show that ecosystem services and function likely did not recover even at the lowest intensity of forest exploitation studied, questioning the sustainability of the most common rotation-cycle duration applied in the tropics.

In this study, we examined the associations between field-assessed floristic and structural habitat values for mature forest and GIS-derived variables to assess whether high conservation value forests could be predicted for strategic reservation at a landscape scale. We investigated the Eucalyptus regnans forests of the Victorian Central Highlands in south-eastern Australia, where several extensive wildfires in the last century have left little mature forest. We assessed the extent to which the floristic composition and a suite of habitat-related structural variables could be explained by two forest inventory GIS variables (percentage senescence and site productivity) and whether explanatory capacity improved from inclusion of additional environmental variables (climate, soils, topography, structure and spatial location). Results showed that the floristic composition was weakly related to productivity, but not to percentage senescence. Four habitat-related structural variables were positively related to percentage senescence (density of old-growth eucalypts, the quadratic mean diameter (QMD) of both live and dead eucalypts, and the maximum eucalypt form class (a proxy for tree hollows)) while the volume of CWD had a marginally significant positive relationship. Three structural variables were related to productivity (the maximum eucalypt form class, the QMD of dead understorey trees and of dead eucalypts). However, in all cases the explanatory power of percentage senescence and productivity was weak (proportion of deviance explained by the models

Human assisted movement of reforestation stock poleward or upward in elevation has been proposed as a tool to address climate change in regular reforestation programs. However, moving warm adapted seed sources to colder environments could carry the risk of frost damage if seed sources are moved too far. Here, we assess genetic differentiation in growth potential, survival and cold hardiness of a wide-ranging tree species, white spruce (Picea glauca [Moench] Voss). We use data from a 34-year-old common garden experiment planted in the approximate center of the species range. Cold hardiness was negatively related to growth and positively to survival. Generalized additive models identified mean coldest month temperature and latitude (as a proxy for the day length regime) as an exceptionally good predictor for the onset of cold hardiness (R2adj = 0.91). The results suggest that day length, an environmental factor that is not influenced by climate change, is an important factor controlling the timing of the onset of hardiness. Survival was only moderately well predicted, primarily by precipitation of the provenance origin (R2adj = 0.36) indicating that other adaptive traits besides cold hardiness should be considered in assisted migration prescriptions. Survival of seed sources appears primarily compromised when transplanting sources from wet origins to a dry location. Nevertheless, acceptable migration distances without significant tradeoffs were up to 500 km north and 1500 km west towards a central planting location.

Analysis and 14C dating of charcoal fragments ≥2 mm buried in mineral soils make it possible to obtain a stand-scale portrait of Holocene fires that occurred in well-drained, fire-prone environments, as well as changes in forest stand composition over time, based on botanical identification of charcoals. However, it is not always possible to reconstruct all fire events, due to disturbances that altered soil stratigraphy. In order to evaluate the efficacy of this approach, we conducted a comparative analysis with a proximal environment that presents an a priori continuous stratigraphy of charcoal fragments. For two sites in the coniferous boreal forest of eastern North America, the charcoal record of a forest soil was compared with that of an adjacent peatland margin situated at a distance of 20 m. For both types of sedimentary environments, a similar fire history was reconstructed for a large part of the Holocene. The greatest differences were for the early Holocene period, for which a smaller number of fires was detected in the forest soil compared to the peatland soil. Retracing the oldest fires using mineral soils in a fire prone environment is more difficult, due to charcoal decay that results from repeated fire events. However, forest soils reveal a relatively accurate fire history for subsequent millennia if the number of charcoals dated is sufficiently large. Any accurate reconstruction of the fire history of proximal peatland environments is strongly dependent on continuous stratigraphic units of peat and charcoal. Indeed, the age of charcoal fragments in peat may be different from that of the sedimentary layer in which they are buried due to allogenic disturbances like erosion events caused by deep burning of the organic horizon and other mass wasting events. Despite the large number of 14C dates it requires, analysis of soil macrocharcoal yields a realistic picture of the fire history at the stand scale. The concurrent analysis of macrocharcoal from adjacent peatland deposits may be used as a complement to more accurately record the oldest fire events.

The geographical patterns in the distribution of fine root biomass (FRB) and in the contribution of fine roots to below-ground nitrogen and carbon stocks are poorly documented. Here, we examined FRB and the ecological factors that govern it, along a 1000 km long latitudinal gradient in unmanaged mixed boreal forests in North-East Europe. We sampled fine roots (diameter ≤2 mm; trees and field layer vegetation combined) twice per growing season in 2015 and 2016 from ten sites spaced one degree of latitude between 60°N (near St. Petersburg) and 69°N (near Murmansk, Russia). We separated living fine roots. The roots were dried and weighed; tissue carbon and nitrogen concentrations were measured. The obtained values were correlated with climatic, plant community and soil characteristics. Among-site variation in the total FRB and carbon and nitrogen concentrations were not explained by latitude or by climatic, plant community or soil characteristics. However, fine root density in the organic layer increased towards the north. The more superficial root system in the north than in the south may indicate a poleward increase in the vulnerability of boreal forests to abiotic risks (forest fires, drought). Our results suggest that the future climate may shift fine roots as well as carbon and nitrogen cycling from the organic layer to mineral soils, thereby increasing the volume of soil utilized by fine roots for water and nutrient uptake.

Most diversity and productivity relationship (DPR) studies have focused on one component of ecosystem production at one stage of stand development, which may have contributed to divergent DPR relationships. We tested the effects of species mixture on biomass production and its partitioning between aboveground (trees, understorey vegetation, and litterfall) and belowground (coarse and fine roots) with stand development in a post-fire boreal forest. We found an overyielding, i.e., species mixtures produce more than the average of its constituent monocultures, of total ecosystem production in young stands, but not in older stands. Species mixture led to more production partitioning belowground in all stand ages due to increased fine root production. The magnitude of the mixture effect on production partitioning to belowground increased with total production in species mixtures. Both aboveground production and its partitioning to aboveground increased significantly with the availability of soil nutrients. Our results suggest that it would be biased to infer the effects of plant diversity on total ecosystem production based on the estimates from one component of production or during one stand development stage.

Large-scale aerial spray operations against the spruce budworm (Choristoneura fumiferana (Clemens)) (SBW) with the biological insecticide Bacillus thuringiensis ssp. kurstaki (Btk) aim at maintaining trees alive during outbreaks. This objective is thought to be achieved when ≥ 50% of current-year foliage is preserved until the end of the outbreak. This protection target is associated with low balsam fir (Abies balsamea [L.] Mill.) mortality. However, it is unknown whether this approach is always needed or whether less frequent interventions could provide similar results at a lower cost. Between 2010 and 2016, we conducted field experiments in Quebec’s Cote-Nord region to determine the efficacy of five different Btk spraying scenarios for protecting balsam fir, white spruce (Picea glauca [Moench] Voss) and black spruce (P. mariana [Mill.] BSP) in mixed stands. We used the residual photosynthetic capacity (RPC) to evaluate the efficacy of the five scenarios. RPC makes it possible to take into account the impact of SBW defoliation on foliage contribution to tree photosynthetic effort over several years, and can be used as a proxy of the risk of tree mortality. We hypothesized that less frequent Btk applications could maintain the required RPC level to keep trees alive. Our results show that areas not protected resulted in great losses of RPC in balsam fir and white spruce. Btk applications every 3 years kept RPC above 50% for 2 years in balsam fir and 4 years in white spruce. RPC losses were above 62% after 4 years in both species. The strategy currently employed in Quebec (spraying every year after a first year of moderate-severe defoliation) and the intensive protection scenario (Btk applications every year) meet the protection goals for these hosts. However, their cost prevents their application at a large scale. Btk applications every 2 years seems a relevant alternative to the current strategy to protect balsam fir and white spruce stands given the adequate level of protection provided (RPC above 39%) and the reduction in the number of Btk applications required (36% fewer applications over 7 years, resulting in 36% lower cost), particularly if the objective is to maintain trees alive. Black spruce maintained at least 54% of its RPC, even without protection. Btk applications every 3 years might be a valid alternative to reduce growth losses in black spruce-dominated stands. The use of different spraying scenarios may allow us to develop cost-efficient treatment strategies to protect Quebec’s forests.

1. Fine root turnover plays a critical role in carbon and nutrient cycling in forest ecosystems. In this study, we focused on the most abundant deciduous species in Nordic countries, silver birch (Betula pendula Roth) and its fine root dynamics, including the amount of litter produced by fine roots as well as by aboveground vegetation. 2. The minirhizotron method was used to quantify fine root longevity of silver birch and understory fine roots and rhizomes in northern Finland. Fine root biomass per basal area and ectomycorrhizal short root numbers per mg were also quantified. The fine root litter production was estimated by fine root biomass and longevity, and then compared with the aboveground litter collected with litter traps. 3. Birch fine root biomass was 1.4-fold higher than that of understory fine roots and rhizomes (234 ± 22, 171 ± 19 g m−2 respectively). Fine root longevity of birch (372 days) was significantly (P

Spatial heterogeneity in site conditions and differing disturbance types are common features of natural landscapes. We asked: does the relationship between species diversity and functional trait diversity (SD-FD relationship) of plant communities vary among habitats experiencing different types of disturbance and among microhabitats (i.e., landscape position) within a landscape? We quantified the relationship between species richness and functional richness (FRic) and between species evenness and functional evenness (FEve) of riparian plant communities along small headwater streams at five spatially adjacent microhabitats in two types of disturbed (wildfire and clearcut logging with buffer) and reference habitats (unlogged mature forest) in northwestern Ontario, Canada. We found significant dependence of species richness vs. FRic relationship on microhabitat, but not on disturbance type. Species evenness vs. FEve relationship varied slightly among reference and wildfire sites, but not among microhabitats. A significant variation in functional trait dispersion (FDis) among microhabitats offered a mechanistic explanation to the observed variation in the SD-FD relationship. A very weak effect of disturbance type on the SD-FD relationship indicates that clearcut with buffer retention may emulate riparian plant composition created by wildfire. However, the microhabitat dependent variation in the SD-FD relationship indicates that the same range of species diversity may refer to different ranges of functional trait diversity depending on microhabitat. We suggest that microhabitat plays a stronger role than disturbance type in trait dispersion and ultimately modifies the SD-FD relationship in our studied communities. This result highlights the role of spatial environmental heterogeneity of a landscape and different dimensions of species diversity and functional trait diversity, e.g. richness and evenness, in understanding the functioning of a natural landscape.

Degraded tropical peatlands in Southeast Asia are a major challenge for reforestation. Often treeless, drained and several times burnt, these peatland areas are nutrient-poor hostile environments prone to droughts, heavy flooding and extreme diurnal temperature changes. In order to succeed in establishment of a viable tree stand, careful selection of species and management techniques is needed. In this study we investigated the suitability of five native tree species for reforestation of tropical peatlands with three site preparation treatments for potentially enhancing seedling success: weeding, mounding and fertilizing. The study area was a clear-cut, drained and repeatedly burnt former tropical peat swamp forest in Central Kalimantan, Indonesia. Seedlings were grown in a field nursery, planted in the field and their growth and survival were monitored regularly for 1.5 years. Seedling growth in response to environmental variables and treatments was studied by linear mixed models and seedling survival with Cox regression models. In most cases, weeding and fertilizing proved beneficial for the growth and survival of the seedlings, whereas mounding only had a minor impact on seedling performance. The seedlings of Shorea balangeran performed the best and can be recommended for reforestation of heavily degraded areas. Alstonia pneumatophora and Dacryodes rostrata performed relatively well depending on the treatments, whereas Dyera polyphylla had mixed results with problems in seedling production, and Campnosperma squamatum performed rather poorly. The effects of wildfires which engulfed the study area two years after planting were also monitored and are discussed.

Litter decomposition is a fundamental process of biogeochemical cycles and plays a critical role in regulating carbon (C) and nutrient mineralization in terrestrial ecosystems. Examining responses of litter decomposition to altered precipitation is crucial to understand terrestrial C dynamics and its feedback to climate change. To understand the effects of reduced precipitation on litter decomposition, a two-year throughfall reduction experiment was carried out in a natural evergreen broad-leaved forest in western China. Five throughfall reduction levels were investigated: control without throughfall reduction (Ctr), 5% (W1), 10% (W2), 20% (W3) and 50% throughfall reduction (W4). Throughfall reduction significantly reduced soil moisture, which was most pronounced in W3 and W4 treatments, and this was associated by significantly reduced cumulative litter mass loss and lower decomposition constants. Also, throughfall reduction significantly altered litter C, N and P dynamics. In particular in W2, W3 and W4 treatments the release of C and N was significantly reduced, whereas in W2 and W3 the immobilization of P was increased. Overall, the results suggest that future decrease in precipitation will suppress litter decomposition, whereas microbial P limitation in litter may be aggravated in broad-leaved forest ecosystems.

Although advance regeneration abundance and vigor are critical factors determining future forest composition and productivity, very few studies have focused on how they are affected by spruce budworm (SBW) outbreaks even though they affect millions of hectares of boreal forest on a cyclical basis. Post-SBW salvage logging is often used to reduce economic losses but could interact with the outbreak to affect advance regeneration. This study aims to determine the impact of SBW outbreaks and post-outbreak salvage logging on the defoliation of advance regeneration in mixed coniferous stands of northeastern Canada. Specifically, we assessed the effect of regeneration height and species (balsam fir or black spruce), as well as canopy composition, on the defoliation of advance regeneration. We then evaluated the effect of salvage logging on defoliation sustained by advance regeneration and compared it to the one observed in stands only affected by the SBW. Regeneration height and species, canopy composition and salvage logging all significantly affected defoliation and showed multiple interactions. Taller balsam fir seedlings were three times as defoliated as smaller ones, whereas it was 2.3 times for black spruce. Balsam fir seedlings were 15% more defoliated than black spruce. Seedlings of both species located beneath a balsam fir canopy were also more defoliated (>50% defoliation) than seedlings found under black spruce trees (about 26% defoliation). Salvage logging in black spruce-dominated stands resulted in a ∼25% increase in defoliation of tall (2.5 m) black spruce regeneration when compared to non-harvested sites. We speculate that this could increase the fir component in spruce-dominated stands, leading to forests that are more susceptible to future SBW outbreaks. To protect spruce advance regeneration from increased defoliation, salvage harvesting of spruce-dominated stands may thus be delayed until the outbreak has subsided. Long-term studies are needed to determine whether a compositional change occurs or not, particularly in spruce-dominated stands. As a precautionary measure, changes in salvage logging practices may be implemented immediately to avoid potential problems such as decreased black spruce abundance and increased susceptibility to future SBW outbreaks.

The West Chilcotin is a remote region located in the Sub-Boreal Pine-Spruce biogeoclimatic zone of British Columbia, Canada where cold climate and low annual precipitation have resulted in relatively dry and weakly developed soils. Lodgepole pine is the most widely found tree species in this region followed by hybrid white spruce. Their ability to grow on such nutrient-poor soils raise questions regarding nitrogen (N) inputs to these forest stands. A rarely evaluated but possible source of N could be N-fixing bacteria living in the internal tissues of pine and spruce trees (known as ‘endophytic diazotrophic bacteria’). To examine this possibility, we selected two sites with different soil moisture contents in a predominantly spruce stand and collected soil and plant samples from each site. Similarly, soil and plant samples were also collected from two sites with different soil moisture contents in a predominantly pine stand. Analyses of soil samples revealed that overall nutrient content of soils of low-moisture (LM) sites was significantly lower than high-moisture (HM) sites in both stands, particularly, available and mineralizable N in soil. We isolated 55 (LM: 27 and HM: 28) and 48 (LM: 20 and HM: 28) bacteria from internal tissues of pine and spruce trees, respectively on N-free media. N-fixing ability of these isolates was evaluated using the acetylene reduction assay and 18 isolates from spruce (LM: 10 and HM: 8) and 23 isolates from pine (LM: 13 and HM: 10) were tested positive in this assay. These endophytic diazotrophic bacteria were identified as mainly belonging to genera: Bacillus, Caballeronia, Paenibacillus, and Pseudomonas. These results indicate that pine and spruce trees growing on different sites in this region harbour naturally occurring N-fixing bacteria in their tissues, possibly to gain fixed N.

Heartwood rot (a fungal disease) has the potential to significantly reduce the sandalwood oil production of Santalum album. With new plantations being established with sandalwood oil as the major product, it is imperative to know the consequences of routine form-pruning in tropical areas. Examining pruning wound responses in 1 and 5-year-old trees at the end of the dry and wet seasons, it was possible to ascertain the best pruning age and season in relation to occlusion. Pathogenic wood fungi were isolated from wounds and fungal spore monitoring was undertaken at the two trial sites at time of pruning. Younger trees had smaller wounds which were quicker to occlude and produced a lower decay rating which decreased over time. Wood inhabiting fungi were isolated from all pruning wounds and identified using the ITS gene region. There was a total of 531 fungal isolates, identified in 75 fungal taxa. Older trees had significantly more fungal species compared to younger trees. Pruning season did not significantly affect occlusion, the amount of resultant decay, nor the total number of fungal species isolated. Endophytes were isolated from every tree, comprising 52% of isolations. Younger trees had more endophytes, but less rot fungi than older trees. Canker fungi were isolated from almost all the older trees. In the older trees, rot fungi were predominant in trees pruned at end of the dry season. Metabarcoding of spores collected in spore traps resulted in 565 operational taxonomic units (OTU’s) which were placed in 211 genera and 114 families, with about 55% classified as unknown fungi. About 23% of all reads corresponded to potential pathogens, however, the proportion of spore groups present at time of pruning at each plantation was not indicative of the fungal niches isolated from wounds. This study has shown that it is better to prune S. album when they are young to decrease the amount of potential decay. To reduce the risk of heartwood rot fungal diseases entering via the pruning wound, it would be preferable to prune at the beginning of the dry season. This will be applicable to other tropical tree species.

Estimation of biomass carbon per unit area of forests or woodlands is of great concern to ecologists and forest managers considering global climate change scenarios. In the framework of this study, we intend to develop allometric models to predict stem volume and stand level carbon stocks in monoculture mahogany (Swietenia macrophylla King) plantations. It was also investigated that how stand density would influence stem volume allometric equations as well as carbon stocks per unit area. Results show that the two-variable model having less than 3% mean prediction errors (MPEs) is suitable for stem volume allometric equation, and two-variable or combined-variable models having less than 2% MPEs are equally suitable for allometric equations of stand level carbon stocks. It was also found that in S. macrophylla, stem volume allometric equations are not significantly influenced by stand density. We found that mean tree carbon (kg tree−1) in S. macrophylla decreases at a rate of −1.58 with increasing stand density and stand level carbon stocks (Mg ha−1) decreases at a rate of −0.58 with increasing stand density (trees ha−1). The biomass carbon stocks (aboveground + belowground) in S. macrophylla varried between 34.4 and 351.9 Mg ha−1 having a mean of 120.2 Mg ha−1. The allometric equations of stand level carbon stocks show influence of density, which is particularly prominent in the one-variable models, in contrast to the two- or combined-variable models. High precision estimate of stand level carbon stocks can be obtained using stand basal area multiplied by mean or maximum tree height. Our work also has implications on stand density management and the use of allometric equations in estimation of stem volume and carbon stocks.

International audience; Tree-related microhabitats (TreMs) are important features for the conservation of biodiversity in forest ecosystems. Although other structural indicators of forest biodiversity have been extensively studied in recent decades, TreMs have often been overlooked, either due to the absence of a consensual definition or a lack of knowledge. Despite the increased number of TreM studies in the last decade, the role of drivers of TreM profile in primary forests and across different geographical regions is still unknown. To evaluate the main drivers of TreM density and diversity, we conducted the first large-scale study of TreMs across European primary forests. We established 146 plots in eight primary forests dominated by European beech (Fagus sylvatica L.) in the Carpathian and Dinaric mountain ranges. Generalized linear mixed effect models were used to test the effect of local plot characteristics and spatial variability on the density and diversity (alpha, beta, and gamma) of TreMs. Total TreM density and diversity were significantly positively related with tree species richness and the proportion of snags. Root mean square tree diameters were significantly related to alpha and gamma diversity of TreMs. Both regions reached similarly high values of total TreM densities and total TreM densities and diversity were not significantly different between the two regions; however, we observed between the two regions significant differences in the densities of two TreM groups, conks of fungi and epiphytes. The density and diversity of TreMs were very high in beech-dominated mountain primary forests, but their occurrence and diversity was highly variable within the landscapes over relatively short spatial gradients (plot and stand levels). Understanding these profile provides a benchmark for further comparisons, such as with young forest reserves, or for improving forest management practices that promote biodiversity.