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Permanent landscape attributes such as topography (elevation [m]) and microtopography (local variation in elevation [cm]) can increase the risk of cold air drainage down-slopes and in microtopographic depressions, causing important temperature gradients that generate localized growing-season frosts. Since most studies on growing-season frosts are restricted to the northern parts of the boreal forest or to mountainous areas, their negative consequences on tree productivity at the boreal-temperate forest ecotone is often ignored. We quantified the intensity and probability of growing-season frosts at the boreal-temperate forest ecotone in regard to topographic and microtopographic landscape attributes, which were extracted from airborne LiDAR surveys. In situ air temperature was measured for two summers (2016–2017) with 252 temperature loggers installed in two 18-years-old spruce plantations established in both temperate and boreal mixedwood forests. Growing-season frosts were more intense and probable at the boreal mixedwood forest site compared to the temperate forest site. Still, at both sites, when growing-season frost occurred, air temperature could vary by 4 °C along the elevation gradient of 15 m, often reaching sub-zero values at low elevation while reaching above-freezing values at high elevation. The importance of microtopography on the risk of sub-zero temperatures increased where frost events were less likely to occur such as at the temperate forest and at high elevation. Considering that growing-season frosts can considerably reduce tree productivity, the effects of both topography and planting microsite should be considered when determining where to establish plantations in the landscape and to determine suitable frost-free planting microsites within a plantation.

RESUMEN: El monitoreo a largo plazo es fundamental para comprender las respuestas a acciones de restauración en especies de lento crecimiento como la conífera nativa Pilgerodendron uviferum. Luego de incendios catastróficos, la mayoría de los árboles y semillas de esta especie fueron eliminados, restringiendo su recuperación natural. El objetivo de este estudio fue analizar las implicancias del monitoreo a corto y largo plazo en la interpretación de resultados en ensayos de restauración pasiva y activa de Pilgerodendron uviferum, posterior a incendios en la Isla de Chiloé. Durante 10 años se evaluó la producción de semillas, el reclutamiento natural, y la regeneración asistida mediante plantaciones de P. uviferum bajo diferentes condiciones de micrositio en bosque turbosos y luminosidad en bosque de mejor drenaje. La producción de semillas de P. uviferum fue irregular y abundante cada siete años (⁓200 semillas m-2). La regeneración natural luego de ocho años aumentó en un 80 %, principalmente en sustratos cubiertos con musgos y en asociación con Donatia fascicularis y Astelia pumilia. La abundancia de regeneración natural estuvo positivamente asociada a árboles semilleros de mayor edad, la altura y diámetro de las plantas fue favorecida por la protección arbustiva. En sitios turbosos, la plantación en camellones alcanzó mayores tasas de sobrevivencia (78 %) y en sitios con mejor drenaje, fue mayor bajo protección de dosel superior (100 %). Los resultados sugieren que especies de lento crecimiento como P. uviferum requieren de periodos prologados de monitoreo para interpretar adecuadamente los resultados de ensayos de restauración en bosques quemados.

Background Over the last century, fire exclusion has caused dramatic structural and compositional changes to southern New England forests, highlighting the need to reintroduce fires into the historically pyrogenic landscape to study the response. We investigated the effects of a single overstory thinning and midstory removal to create an open oak-hickory woodland structure, followed by repeated prescribed burns. We hypothesized that burning would create greater floristic diversity comprising fire-tolerant woody regeneration and shade-intolerant herbaceous flora. We followed shifts in plant structure, composition, and diversity over a 23-year period, using a before-after-control-impact design with data collected once prior to burning and twice after burn treatments had begun and with soil samples collected after nearly 20 years of burning. Results We observed a dense ingrowth of saplings on unburned plots that were largely absent from burned plots and a shift in midstory composition to favor mesic sweet birch (Betula lenta L.) in the unburned treatment, as opposed to the hickories (Carya Nutt. spp.) and oaks (Quercus L. spp.) that dominated the burned treatment. Burning resulted in a significantly greater density, richness, Shannon diversity, and evenness of understory vegetation (forbs, shrubs, tree seedlings). These four measures remained high on burned plots, despite a decrease in both floristic diversity and evenness on unburned plots and a reduction in unburned site-level richness. Understory composition varied significantly by year and burn treatment, with unburned plots largely characterized by shade-tolerant species while burned plots showed an enhanced abundance of heliophilic plants. Conclusions Our results suggest that periodic burning increases nutrient microsite heterogeneity and periodically maintains greater understory light, both of which in turn increase understory plant density and diversity and cause a shift in understory composition. This study shows that repeated prescribed burns in an open New England woodland have lasting structural and compositional effects capable of restoring pre-settlement, pyrogenic vegetation patterns.

La vegetación no vascular está formada por líquenes, musgos, algas y cianobacterias tanto epífitas, como creciendo sobre el suelo. El objetivo de este trabajo fue estimar los cambios producidos por el fuego en la cobertura de briófitos y líquenes del suelo en parcelas de bosques de Polylepis australis (tabaquillo) en el Parque Nacional Quebrada del Condorito (PNQC) en el centro de Argentina. En un sector del Área Protegida incendiado en setiembre de 2015 se seleccionaron 40 parcelas de 30 x 30 m, 20 en bosques no quemados y 20 en bosques quemados. Quince meses después del siniestro, en cada parcela se seleccionaron al azar cinco cuadrados de 2 x 2 m para estimar cobertura en suelo diferenciando líquenes y briófitos. Además, se registraron la cobertura de plantas vasculares, suelo desnudo y mantillo. Como variables explicativas se midió la orientación y pendiente en cada cuadrado y en cada parcela. Además, se estimó la cobertura de bosque previo al incendio y la severidad del fuego. Los resultados muestran una muy baja superficie ocupada por líquenes y briófitos en el suelo afectado por el fuego a pesar de la recuperación de la vegetación vascular. La cobertura de líquenes y briófitos varían en función de características del micrositio tanto en parcelas quemadas como no quemadas. Se discute el posible impacto de la pérdida de esta cobertura en el ecosistema de bosque de Polylepis. The non vascular vegetation is formed by lichens, mosses, algae and cyanobacteria, both epiphytic and growing on soil. The aim of this work was to estimate the impact of fire on the coverage of bryophytes and soil lichens in forest plots of Polylepis australis (Tabaquillo) in Quebrada del Condorito National Park (PNQC), in central Argentina. In a sector of the Protected Area in Setember 2015, 40 plots of 30 x 30 m were selected, 20 in unburned and 20 in burned forests. Fifteen months after the incident, five quadrates of 2 x 2 m were randomly selected in each plot to estimate ground cover, differentiating lichens and bryophytes. In addition, the coverage of vascular plants, bare soil and mulch were recorded. As explanatory variables, orientation and slope of each square and plot measured. Furthermore, we estimated the forest cover before fire and fire severity. The results show a very low surface of the burned soli covered by lichens and bryophytes, despite the recovery of the vascular vegetation. Lichens and bryophytes coverage vary depending on the microsite characteristics, both in burned and unburned plots. Here, we discuss the possible impact of the loss of this coverage on forest ecosystem of Polylepis. Fil: Perazzo, Agostina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Centro de Ecología y Recursos Naturales Renovables; Argentina Fil: Rodriguez, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Centro de Ecología y Recursos Naturales Renovables; Argentina

Canopy openings due to harvesting practices constitute a disturbance that changes the environmental conditions of microsites. Its impact on the relative performance of the regeneration of different tree species could also be affected by site conditions and forest structure. The objective of this study was to determine how regeneration establishment of Nothofagus mixed forests is influenced by shelterwood silvicultural system. We focused on Lanin National Reserve (Neuquen, Argentina) where this silvicultural system has been applied since the late 1980s. The microsite scale analysis (one managed forest) showed that canopy cover was a key factor conditioning Nothofagus regeneration establishment, with older and larger individuals growing in less exposed microsites. Low understory dominance and leaf litter thickness were also associated with microsites with regeneration, while successful establishment (saplings taller than 2 m) showed positive correlation with soil moisture. Variations of these patterns were observed among species reflecting their specific eco-physiological requirements. On a stand scale (two managed forests along Lacar watershed) regeneration of N. dombeyi and N. alpina showed significant correlation with site and specific basal area, while N. obliqua was correlated with total basal area. Regeneration taller than 2 m was mainly correlated with site and altitude. At both, microsite and stand scale, the relative abundance of species changed between mature trees and regeneration. In particular, for N. alpina, an abundance decrease was observed on regeneration. Our results suggest that forest management systems should diversify silvicultural practices throughout the forest landscape, to provide at each site the micro-environmental conditions required by each species in order to maintain biodiversity and forest functions.

Chinese pine (Pinus tabulaeformis Carr.) is a widely distributed moderately shade-tolerant tree species with important economic and ecological value in northern China. The productivity of the plantations established by the government in the 1970s has apparently begun to decline. Therefore, the identification of silviculture measures that can feasibly and reasonably balance timber production and sustainable forest management is of interest to many operators and researchers. The main purpose of our study was to understand whether the height growth of trees regenerating under the canopy would positively respond to thinning and provide sufficient high-quality regenerating trees for the successful transformation to uneven-aged forests. Four different thinning intensity treatments were implemented in a 40-year-old plantation based on the number of trees that were cut down using the thinning-from-below approach: 0.0% (unmanaged), 20.0–21.0% (weak thinning), 30.0–31.0% (moderate thinning), and 40.0–41.0% (strong thinning). After five years of thinning, the differences in growth among the different thinning intensities were compared using nonparametric statistical methods. Additionally, the height growth rates of regenerating trees over the past five years were predicted using a linear mixed-effects model that included variables related to stand characteristics, soil physiochemical properties and measurements of individual regenerating trees. The results showed that thinning could significantly promote the height growth of regenerating trees in comparison to the growth in unmanaged plots. Significant differences were found among thinning intensities in terms of growth, excluding ground diameter, with the maximum and minimum values in the strong thinning and unmanaged plots, respectively. However, the models never explained more than 50% of the variation regardless of whether the plot level or the individual level was considered, although they included the majority of the evaluated variables. In conclusion, strong thinning is a potentially feasible silvicultural method for uneven-aged Chinese pine plantations in northern China. Some factors that are important in terms of the growth of regenerating trees but were not tested in our study, such as competition, light intensity and distribution, and microsite environment, are recommended to be considered in future research to improve the explanatory power of the model. Moreover, based on our results and to supplement thinning, the gap expansion harvesting system should be carried out in gaps opened by thinning to not only maintain stand stability but also facilitate the growth of regenerating trees into the canopy for canopy recruitment.

Teak (Tectona grandis Linn. f.), one of the most-valued tree species in the world, is slow-growing with a long period until it can be harvested; therefore, ensuring that only high-quality seedlings or clones are selected for planting is critical. The main objective was to determine performance and repeatability of selected clones in terms of growth and survival rates in different micro-environments. A 2-year clonal trial using 41 clones and a local seedling of teak as a control were grown at 4 microsites differing in spacing, soil fertility and alley crops to assess tree height, diameter and survival rate that was evaluated in Purwakarta, West Java, Indonesia using a randomized complete block design with four replicates of each clone at each microsite. Teak growth was influenced by clone (p

Two comparable sites with uneven-aged mixed forest stands with more than 20% Douglas-fir in the growing stock at an altitude of 650 m a.s.l. were selected. The physiological response of young trees to different light intensities was measured during the main growing season in three consecutive years, and four different light categories, which were determined from hemispherical photographs. The four light intensity categories were defined according to Indirect Site Factor (ISF%): in the open (A-ISF &gt, 35%), at the outer forest edge (B-25% &lt, ISF &lt, 35%), at the inner forest edge (C-15% &lt, 25%), and under complete canopy under mature forest stand (D-ISF &lt, 15%). Climate data were obtained from the Royal Netherlands Meteorological Institute ‘Climate Explorer’ website. For the intensive micrometeorological observations, four monitoring sites were established along the elevation gradient at each site during summer and late fall to record relative humidity (RH%) and temperature (°C) with a 30 min recording interval sequence. Measured assimilation responses (A) and light use efficiency (Φ) at one site followed the expected pattern, while humidity combined with microsite conditions proved significant in explaining the specific response of young Douglas-fir to the different light intensity at the other site. For higher survival and optimal future development of Douglas-fir in the changing environment, microsites with higher capacity for storage moisture and favorable microclimate should generally be preferred to exposed and dry sites.

Environmental conditions and seedling quality interact to produce complex patterns of seedling survival and growth. Root growth potential (RGP) is one metric of seedling quality that can be rapidly measured prior to planting, but the correlation of RGP and seedling performance is not consistent across studies. Site factors including microsite objects that cast shade and competing vegetation can also influence seedling performance. We examined the effects of RGP, presence/absence of a microsite object, and competition cover on the survival and growth of three native conifers to the Inland Northwest, USA, over 5 years. We found that RGP had no effect on the survival or growth of western larch (Larix occidentalis), Douglas fir (Pseudotsuga menziesii var. glauca), and grand fir (Abies grandis) at a mesic north aspect site and a xeric south aspect site. Comparatively, the presence of a microsite increased the odds of survival by 37% for western larch and 158% for grand fir, while the absence of forb cover increased the odds of survival of western larch by 72% and of grand fir by 26%. Douglas fir was less sensitive to microsites and competition. The strong effects of neighborhood conditions around seedlings help inform silvicultural practices to enhance the establishment of western larch and grand fir, including planting seedlings near shading objects and competition control, while these practices may not be as important for Douglas fir.

PTDC/AGR‐FOR/2471/2012 Fire regimes are changing in several regions of the world. In those regions, some exotic species may be better adapted to new regimes than the native species. This study focused on identifying the microsite characteristics associated with the occurrence of post-fire Eucalyptus globulus regeneration from seeds, outside the species native-range. This information is important in helping to assess the naturalization status of the species, to understand its invasion risk, and to manage wildlings in plantations. To characterize the establishment niche, pairs of microsites (sapling presence/absence) were sampled in four salvage-logged plantations of E. globulus two years after fire (20 pairs/plantation). Microsites of wildlings from three size classes and control microsites were established in one of these plantations (20 quartets) in order to characterize the recruitment niche and to assess ontogenic niche shifts. Two post-fire wildling cohorts were identified. The first emerged just after fire and was abundant. The second emerged after logging and was scarce, probably due to seed limitation. First-cohort wildlings were observed in microsites characterized by a high incidence of fire-related variables (charcoal, ash, increased soil pH and K). The aggregated distribution of these wildlings and their association with other species may indicate the existence of facilitative relationships and/or the exploitation of resource-rich patches. All these factors were relevant for first-cohort persistence and likely also for its establishment and recruitment. Second-cohort wildlings occurred in microsites where salvage-logging disturbance was evident, showing the importance of this disturbance for its emergence. Wildling size diversity was explained by the two recruitment events and by the asymmetrical competition between wildlings and adults. No niche shifts were detected. The high densities of E. globulus wildlings found established in burnt plantations indicated naturalization was in progress. The timing of major recruitment events and the phenology of the species should be considered for monitoring this regeneration and scheduling control interventions, if required. publishersversion published

As labour for manual tree planting becomes scarcer, regeneration costs are steadily increasing in Nordic forestry. Today’s intermittently advancing tree planting machines provide excellent silvicultural results, but are expensive to operate because of poor productivity. In contrast, continuously advancing planting machines, thanks to high productivities, are increasingly being regarded as a solution to these runaway regeneration costs. The Silva Nova was a historical, continuously advancing tree planting machine with high productivity. However, Silva Nova’s weaknesses included high labour costs (it required two operators) and the random nature of how it chose planting spots. In contrast, SuperSilva, a purely conceptual modernisation of Silva Nova, involves both automation and microsite identification to make the machine more efficient. We used discrete-event simulation to analyse the stocking rate and spatial distribution of tree planting with SuperSilva. The simulation results showed that introducing sensors for identifying suitable microsites will allow continuously advancing planting machines (like SuperSilva) to plant seedlings in a numerically and spatially adequate manner on moraine soils. Hence, these sensors will increase the competitiveness and versatility of tree planting machines. Unfortunately, such reliable and robust sensor technology (unaffected by a wide variety of operating conditions) is not yet commercially available.

Tree size diversity is an indicator of biodiversity values of a forest. Microsite conditions of a forest determine the survival and growth of trees. However, the contribution of variable habitats to tree size hierarchy and segregation is poorly understood. Tree size variation in a population is caused by different competition mechanisms. Therefore, the size distribution and spatial pattern of trees can identify the process governing resource utilisation in the forest. The objective of the study was to investigate the tree stem structural diversity in the Elephant Camp natural forest in the Omo Forest Reserve. Three and four 0.09 ha sample plots were established in Riparian (RF) and Old-growth forests (OF) in the Elephant Camp natural forest, respectively. The tree stems (Dbh ≥ 5cm) were identified to the species level and enumerated within each plot, and the stem density was computed. The diameter at breast height (Dbh) was measured with diameter tape. Species diversity was assessed using Shannon–Weiner (H’) and Simpson indices (1-D’), while size inequality was assessed using the Gini coefficient (GC), coefficient of variation (CV), H’ and I-D’. The performance of single two- and three-parameter Weibull models was evaluated using Kolmogorov–Smirnov (K-S) chi-square (χ2), root-mean-square error (RMSE), bias and the coefficient of determination (R2). Data were analysed using descriptive statistics. A total of 27 and 24 tree species were identified in RF and OF, respectively. The stem density of RF was significantly higher than that of OF. The values of species diversity (H’, 1-D’) and evenness (E’) were higher in OF than in RF, while richness (Margalef and number of species) was higher in RF than in OF. The Dbh was 38.30 ± 21.4 and 42.87 ± 19.2 cm in Riparian and Old-growth forests, respectively. Size-density distributions of both forests were positively skewed and expressed exponential pattern. The forest types of the Elephant Camp natural forest comprise the same size-density frequency shape but a different proportion of tree sizes and structural diversities.

The results of study of the population ontogenetic structure of the main forest-forming species (Pinus sylvestris, Quercus robur, Acer platanoides, Betula pendula, Populus tremula) of the Left Bank Polissia of Ukraine are presented. The study covered plant communities, which are the most common and typical in the region. They are represented by four formations of forest vegetation, viz. Pineta sylvestris, Querceta roboris, Betuleta pendulae, Populeta tremulae, and belonged to 24 syntaxes in the rank of association groups and up to 42 syn-taxons in the rank of associations. The study was based on the use of geobotanical and population-ontogenetic approaches and methods. It was established that in the forests of the region, the most part of main forest-forming species populations have left-sided ontogenetic spectrum. Invasive populations are the predominant category. Only in the populations of the species involved in the formation of the second and especially the first tier of stands reveals the centred and bimodal spectra. In these species, the frequency of normal population occurrence increased, but their proportion was within 6.7–13.6%. No regressive populations were found in the main forest-forming species of the region. It was fixed that the ontogenetic spectra of the most of populations of the studied species were incomplete due to the absence of plants of some ontogenetic states. It was noted that the individual extinction of the young generation before they reached the generative ontogenetic state, was the clear evidence of significant disturbance in the region forests of the generation variability in forest-forming species. The limited representation of windfall microsite complexes in the composition of the forest plant communities of the Left-Bank Polissia of Ukraine as well as gaps enough in size to ensure successful undergrowth development and formation of a continuous flow of generations is one of the consequences of long-term man-made impact on these forests. Keywords: forest phytocoenosis, forest-forming tree species, population analysis, population structure, ontogenetic spectrum, Polissia of Ukraine

Information and material biological legacies that persist after catastrophic forest disturbance collectively constitute the ecological memory of the system and may strongly influence future stand development. Catastrophic disturbances often result in an influx of coarse woody debris (CWD), and this material legacy may provide beneficial microsites that affect successional and structural developmental pathways. We examined how microenvironmental characteristics influence the regeneration of woody plants in a subtropical woodland that experienced a large influx of CWD from a catastrophic wind disturbance. Specifically, we asked (1) what microenvironmental factors best explain woody plant density, richness, and height in the regeneration layer and (2) does woody plant density, richness, and height benefit from the large influx of CWD to a degree that competition dynamics and succession may be modified? Data were collected in a Pinus palustris woodland that had experienced an EF3 tornado and was subjected to a four-year prescribed fire rotation. We documented live woody plants &lt, 5 cm diameter at breast height, soil, and site characteristics and tested for differences in seedling and sapling density, species richness, and height in relation to CWD proximity. We used a random forest machine learning algorithm to examine the influence of microenvironmental conditions on the characteristics of woody plants in the regeneration layer. Woody plant density and species richness were not significantly different by proximity to CWD, but plants near CWD were slightly taller than plants away from CWD. The best predictors of woody plant density, richness, and height were abiotic site characteristics including slope gradient and azimuth, organic matter depth and weight, and soil water content. Results indicated that the regeneration of woody plants in this P. palustris woodland was not strongly influenced by the influx of CWD, but by other biological legacies such as existing root networks and soil characteristics. Our study highlights the need to consider ecological memory in forest management decision-making after catastrophic disturbance. Information and material legacies shape recovery patterns, but, depending on the system, some legacies will be more influential on successional and developmental pathways than others.

Among four species of Clusiaceae (sensu lato) occurring in a mosaic of different types of tropical vegetation, Kielmeyera coriacea Mart. & Zucc. and Calophyllum brasiliense Camb. were C3-species with similar performance at micro-sites of contrasting water supply, Clusia criuva Cambess—although potentially a C3/CAM intermediate species—performed C3-photosynthesis, while Clusia arrudea Planchon & Triana ex Engl. performed C3-photosynthesis or CAM-cycling depending on site characteristics and dry or wet season. Depending on individual species, C3-photosynthesis proves to be a suitable option at a variety of environmental conditions, while CAM-cycling appears to be an escape under more severe stress. In this ecophysiological field work, we investigated possible microhabitat-dependent expression of modes of photosynthesis among species of Clusiaceae (sensu lato) in a mosaic of tropical vegetation. The study site was in the Serra de Sao Jose (21°08’S, 44°17′W; in the municipality of Tiradentes, state of Minas Gerais, SE-Brazil). The mosaic of tropical vegetation types was made up of rupestrian grasslands, cerrado, small rock outcrops, and riverine and gallery forest alongside a small river. Four species were measured, namely C. criuva Camb., C. arrudea Planchon & Triana ex Engl., K. coriacea Mart. & Zucc., and C. brasiliense Camb. K. coriacea and C. brasiliense performed C3-photosynthesis with midday depressions and reversible acute photoinhibition in response to varying environmental conditions related to habitat types and wet and dry seasons, respectively. The C3/CAM intermediate C. criuva also performed C3-photosynthesis with midday depression and acute photoinhibition. It appeared not to be stressed enough to switch to its intrinsic CAM option. In contrast, while C. arrudea under favourable conditions in the gallery forest and the wet season also performed C3-photosynthesis, under drier conditions, it used CAM-cycling. For particular species, realization of CAM-options is a possibility of acclimation. Other species contemporarily may rely on different alternatives such as plastic performance of C3-photoynthesis. At the microsite level, overlapping functional diversity of species and diversity of habitats contributes to the complexity of this vegetation type.

Reforestation in the tropics mitigates the negative effects of climate change by sequestering carbon in biomass. However, tree growth is limited by nutrient availability in many tropical regions. A clear understanding of nutrient constraints and topography on growth of native timber species is thus essential to improve both the economic return on reforestation and the ecosystem services in tropical degraded lands. To address this, we use 7-year growth data from a 75-ha reforestation experiment in central Panama to test a modeling approach to predict growth of these species. The experiment includes five valuable timber species in 21 treatments, including monocultures and mixtures. We first fit a non-linear growth model as a function of tree age, then expand the former model parameters as a function of variables related to species mixture and micro-site soil conditions. Finally, we built a final model for each species to predict growth along three axes: nutrient availability, slope and species mixture. The models successfully identified how variation in growth was related to micro-site conditions and the species mixture. Although all species were long-lived pioneers, most were overall more sensitive to nutrient availability and between-trees interactions than to slope. However, the fastest growing species on average was more sensitive to slope than the other species and less sensitive to nutrient availability, showing better performance than the other species even under adverse conditions. Our models aid identification of species with the best growth potential to use in reforestation on infertile soils, leading to a better species selection according to site conditions.

The increasing frequency and severity of fire and drought events have negatively impacted the capacity and success of reforestation efforts in many dry, western U.S. forests. Challenges to reforestation include the cost and safety concerns of replanting large areas of standing dead trees, and high seedling and sapling mortality rates due to water stress, competing vegetation, and repeat fires that burn young plantations. Standard reforestation practices have emphasized establishing dense conifer cover with gridded planting, sometimes called ‘pines in lines’ followed by shrub control and pre-commercial thinning. Resources for such intensive management are increasingly limited, reducing the capacity for young plantations to develop early resilience to fire and drought. This paper summarizes recent research on the conditions under which current standard reforestation practices in the western U.S. may need adjustment, and suggests how these practices might be modified to improve their success. In particular we examine where and when plantations with regular tree spacing elevate the risk of future mortality, and how planting density, spatial arrangement, and species composition might be modified to increase seedling and sapling survival through recurring drought and fire events. Within large areas of contiguous mortality, we suggest a “three zone” approach to reforestation following a major disturbance that includes; (a) working with natural recruitment within a peripheral zone near live tree seed sources; (b) in a second zone, beyond effective seed dispersal range but in accessible areas, planting a combination of clustered and regularly spaced seedlings that varies with microsite water availability and potential fire behavior; and (c) a final zone defined by remote, steep terrain that in practice limits reforestation efforts to the establishment of founder stands. We also emphasize the early use of prescribed fire to build resilience in developing stands subject to increasingly common wildfires and drought events. Finally, we highlight limits to our current understanding of how young stands may respond and develop under these proposed planting and silvicultural practices, and identify areas where new research could help refine them.

Phytophthora root rot is considered one of the main factors associated with holm oak (Quercus ilex L.) mortality. The effectiveness and accuracy of soilborne pathogen and management could be influenced by soil spatial heterogeneity. This factor is of special relevance in many afforestation of southwestern Spain, which were carried out without phytosanitary control of the nursery seedlings. We selected a study area located in a 15 year-old afforestation of Q. ilex, known to be infested by Phytophthora cinnamomi Rands. Soil samples (ntotal = 132) were taken systematically from a grid under 4 trees, and analysed to quantify 12 variables, the colony forming units (cfu) of P. cinnamomi plus 11 physical and chemical soil properties. The combined analysis of all variables was performed with linear mixed models (GLMM), and the spatial patterns of cfu were characterised using an aggregation index (Ia) and a clustering index (&nu, ) by SADIE. Cfu values ranged from 0 to 211 cfu g&minus, 1, and the GLMM built with the variables silt, P, K and soil moisture explained the cfu distribution to the greatest extent. The spatial analysis showed that 9 of the 12 variables presented spatial aggregation (Ia &gt, 1), and the clustering of local patches (&nu, i&ge, 1.5) for organic matter, silt, and Ca. The spatial patterns of the P. cinnamomi cfu under planted holm oak trees are related to edaphic variables and canopy cover. Small-scale spatial analysis of microsite variability can predict which areas surrounding trees can influence lower oomycetes cfu availability.

Tree growth of Nothofagus betuloides forests south of 50°S is affected by local temperature and precipitation together with large-scale high-latitude climate patterns, but also significant influences from the Tropical Pacific were found. The characterization of past climate dynamics in southern South America is difficult due to the shortness of instrumental data. However, abundant forests in the southernmost part of the continent makes it an ideal place to assess the dendroclimatological potential for developing high-resolution climate proxy time series to extend the observations back in time. Whereas the majority of dendroclimatological studies have focused on latitudes north of 50°S, we present six new Magellan’s beech (Nothofagus betuloides (Mirb.) Oerst.) tree-ring width (TRW) chronologies, spanning between 202 and 500 years, developed from southernmost Patagonia (> 50°S), Chile. The climate signal in the trees was analyzed using local station data, regional sea surface temperature (SST) and large-scale atmospheric indices: the Southern Oscillation Index (SOI) and the southern annual mode (SAM). The correlations between individual site chronologies and observed summer temperatures and precipitation varied, reflecting diverse microsite conditions and local scale geographic patterns. An influence of southern Pacific SST was evident at two of the northern sites. Although the associations with SOI and SAM were weak, the influence of regional sea level pressure on tree growth in the region was evident.

The effective sustainable management of introduced woody species requires understanding of the mechanisms which affect successful colonization in different forest habitats. We studied the spontaneous spread of the alien species – Northern red oak (Quercus rubra) in the Scots pine (Pinus sylvestris) forest located in Poland. We analysed the impacts of seed source distance, presence of and distance from linear structures (public and forest roads) in the landscape, as well as microhabitat diversity, on the distribution of juvenile red oaks. We also studied the effects of types of acorn deposition sites (under shrubs, within clumps of Vaccinium myrtillus, in the open), and ways of seed burial (in moss wefts, in rodent corridors) by animal seed hoarders on seed germination and seedling growth. Field data were collected in six transect lines divided into 3300 plots (1 m2 each). We found that Q. rubra efficiently colonizes Scots pine monoculture. Results of spatially explicit hierarchical generalized linear models showed that distance from acorn sources and occurrence of sparse shrub layers are the most important predictors of Q. rubra ecological success, defined as establishment of juvenile specimens. The presence of roads – potential migration corridors for avian and mammalian acorn consumers/dispersers – favoured non-random red oak spread. The “nurse effect” of native understory components on red oak seed germination and seedling growth was indicated by higher numbers of juvenile specimens as well as by higher proportions of germinated seeds noted under shrubs than in open areas (without shrubs) or within clumps of V. myrtillus. All red oaks developed from seeds buried in compact moss wefts or in spacious caches and corridors created by rodents in the moss layer, which indicated a positive “burial effect”. We conclude that microhabitats make the Scots pine forests very suitable for Q. rubra invasion. Because of the wide distribution of numerous red oak stands in European temperate forests and the presence of numerous oak seed dispersers, the continuous colonization of widespread Scots pine monocultures by Q. rubra must be expected.

Timber harvests may facilitate ant invasions of forested landscapes, fostering interactions between non-native and native ants. Harvests that include removal of low-value woody biomass as forest bioenergy feedstock may reduce residual coarse woody debris, thereby altering food and cover resources for ant species. We manipulated: (1) volume and distribution of coarse woody debris in stand-scale treatments ranging from intensive coarse woody debris removal to no coarse woody debris removal; and (2) coarse woody debris availability at microsite locations within stand-scale treatments, including piles of hardwood stems, piles of conifer stems, and no pile locations in North Carolina, USA and windrows (i.e., long, linear piles of harvest residues) and no windrows in Georgia, USA, in recently clearcut pine plantations (n = 4 per state). We captured ants in regenerating stands and tested treatment- and location-level effects on non-native and native ant relative abundances. Invasive ants represented 19% of ant taxa richness, but comprised 94% of total ant captures. Red imported fire ant (Solenopsis invicta Buren, hereafter “RIFA”) dominated the ant community in young plantations. RIFA avoided windrows, but its relative abundance did not differ among stand-scale treatments. Coarse woody debris retention in stand-scale treatments and at microsite locations favored non-RIFA ants, including Asian needle ant (Brachyponera chinensis Emery) and several native ant species. Dual invasions of RIFA and Asian needle ant in young plantations of the eastern United States may commonly occur because the two species may not compete for resources on the forest floor. Reduction of coarse woody debris via intensified woody biomass harvesting may negatively affect non-RIFA ant species and promote RIFA colonization, thereby indirectly increasing deleterious effects of RIFA on other wildlife.

Prescribed burnings have been generally used for fuel reduction in Mediterranean forest ecosystems and in fire-prone areas. It is usually held that prescribed fire may alter microsite conditions, but very little is known about the impact of prescribed burning on Mediterranean pine species’ natural regeneration. In this study, we aim to know the effect of prescribed burning, soil preparation (scalping) and seed protection on the initial recruitment of Spanish black pine (Pinus nigra Arn. ssp salzmannii), maritime pine (Pinus pinaster Ait.) and Aleppo pine (Pinus halepensis M.) in the Cuenca Mountains (central-eastern Spain) after a 1 year of experiments. Our results indicated that the seed emergence rate was higher in the scalped plots for Maritime pine and Aleppo pine. In the case of Spanish black pine, differences comparing treatments for the emergence rate were weaker. Scalped and protected plots showed the highest seedling survival rate for Aleppo pine and Spanish black pine whereas protected and control plots perform better in the case of Maritime pine. Thus, seed protection is a crucial factor for ensuring seedling survival after the first growing season. By considering our results about early pine species recruitment, prescribed burning must be carefully planned when the natural regeneration of Spanish black pine, maritime pine and Aleppo pine is the aim.

Wind disturbance generates heterogeneous microsite structures, including downed logs, windthrow mounds, and pits. While these structures can provide opportunities for regeneration of certain tree species, the long-term influence of microsites and microsite heterogeneity on forest development has not been quantified. We used long-term measurements of a formerly old-growth Tsuga canadensis – Pinus strobus forest severely damaged by a category 3 hurricane in 1938 to quantify the impact of microsite conditions on overstory composition and structure. We asked (i) “What are the patterns in live-tree size, growth, and mortality five and seven decades after disturbance?” and (ii) “What roles do microsite heterogeneity and the presence of disturbance-generated microsites play in long-term forest development following disturbance?” We compared live-tree (>2 cm DBH) development and survival to microsite heterogeneity at the 100 m2 scale. Microsite diversity was positively related to overstory species diversity and stem density and negatively related to average tree size. We propose that plots with higher microsite diversity may have experienced more severe local disturbance, which allowed more species and individuals to establish and created varied niches that allowed these individuals to coexist and generate greater stand-level diversity. These persistent relationships highlight how microsite conditions affect forest development after severe disturbances.

Stand structural complexity enhancement is an increasingly popular management objective, especially on public lands. Complex stand structures are hypothesized to support a relatively high degree of native forest diversity and be more resistant and resilient to disturbances. Complex structures are characterized by the presence of deadwood and heterogeneity of tree-size classes and tree architecture. Relatively little is known about how discrete disturbance events affect structural complexity and compositional diversity in Quercus-dominated stands at fine spatial scales (i.e. neighborhoods). We established 20 0.05 ha fixed-radius plots on the Sipsey Wilderness of William B. Bankhead National Forest in northern Alabama to quantify woody plant species composition and structure. Trees were mapped on each plot to quantify overstory structural complexity and compositional diversity. We extracted two cores from all canopy Quercus spp. ≥ 5 cm diameter at breast height to quantify age, recruitment pulses, and reconstruct canopy disturbance history. Shannon species diversity in the sampled area was 1.75 for trees, 2.08 for saplings, and 1.69 for seedlings. Quercus alba had the greatest basal area, and Ostrya virginiana had the highest density. The stand exhibited a reverse J-shaped distribution with a q-factor of 1.72. The oldest Quercus dated to 1795, and the largest recruitment pulse occurred in the 1870s. The mean return interval for intermediate-severity disturbance was 38 years. Although we documented no relationships between disturbance frequency and compositional diversity at the neighborhood scale (0.05 ha), less frequent disturbance was associated with higher structural complexity (r2 = 0.258, p = 0.026) at the neighborhood scale. We suggest that localized disturbance increases species diversity and structural complexity, but these processes are manifest at the stand level and not at the neighborhood scale. We conclude that the spatial variability (i.e. size, shape, orientation, microsite conditions) is likely more influential on diversity and complexity than the temporal variation (frequency) of these processes at the neighborhood scale.

On deforested or degraded land, planting mixtures of native forest tree species facilitates establishment of incoming tree seedling species (species recruitment) by rapidly re-establishing canopy cover. However, delayed colonization of plantations by large-seeded, zoochorous (LSZ) tree species can affect the species composition, structure, and function of the developing forest. The objective of this study was to investigate whether microsites limit establishment (germination and early seedling survival) of LSZ tree species in three 13-year-old, seasonally dry, tropical forest restoration plantations in northern Thailand. We conducted a seed sowing experiment that combined five LSZ tree species with four microsite treatments in a split-plot design. All five tree species were previously absent from the understory of the plantations, despite seed sources being present in nearby natural forest. The four treatments simulated potential microsites that naturally-dispersed seeds may encounter. They included seed deposition on the surface of soil and on leaf litter, as well as seed burial beneath soil and beneath leaf litter. We fenced the experimental areas to prevent seed predation and focus on the environmental effects of microsites on the different stages of seedling establishment. Following seed sowing, we measured germination and seedling survival, mean height, and stem diameter over 26 months. The microsites treatments did not significantly affect germination and seedling survival, providing strong evidence that establishment of the tested species was not limited by the applied microsite environments. Furthermore, although there were significant differences in germination and survival among species, relatively high overall germination (37%) and 26-month seedling survival (58.5%), irrespective of microsite treatment, suggested that environmental conditions in the 13-year-old plantations generally met the requirements for germination and early seedling establishment. Microsite treatments also did not correlate with seedling height or stem diameter at 20 months, suggesting that initial germination microsites have no effect on seedling growth and robustness. Taken together, the results of this investigation support the hypothesis that seedlings of LSZ tree species are slow to colonize tropical forest restoration plantations because of seed limitations resulting from inadequate seed dispersal or low seed availability. The successful establishment of LSZ seedlings from sown seeds in this experiment suggests that direct seeding beneath the canopy of restoration plantations may be an effective way to offset seed dispersal limitations in restoration plantations. Furthermore, the absence of microsite treatment effects suggests broadcast sowing of seeds may be a simple way to recolonize closed-canopy restoration plantations with LSZ tree species.

We analysed the impact of forest gap characteristics and understory vegetation on the natural regeneration patterns of Norway spruce (Picea abies (L.) Karst.) and birch (Betula spp.). The gaps were...

Pinus sylvestris tree-ring delta C-13 and delta O-18 records from locally moist sites in central and northern Sweden contain consistently stronger climate signals than their dry site counterparts. ...

Among recovery strategies for secondary and degraded tropical forests, the introduction of tree species is one of the most commonly used. This is achieved particularly through the planting of nursery-grown seedlings (i.e. seedling introduction). Another less common technique, but one that could prove efficient, is sowing seeds (i.e. direct seeding) in the forest floor. However, very few comparisons have been made in the literature in terms of the ecological and economic costs and benefits between these two techniques. This study presents a cost-efficiency analysis of the introduction of seedlings and seeds of Oreomunnea mexicana (a threatened species in Mexico) in a secondary Tropical Montane Cloud Forest in central Veracruz, evaluating (1) the performance of the seedlings derived from each of the two practices, (2) the relationship of their performance with the environmental variables at the microsite level, and (3) the ecological and economic cost-efficiency of each practice. At the end of the experiment, survival was higher in the nursery-grown than in the direct-seeded seedlings (97% vs. 22%, respectively); however, the relative growth rate in height was lower for the planted than the emerged seedlings (0.02 ± 0.002 vs. 0.03 ± 0.002 cm cm−1 month−1). Relative growth rate in diameter was similar in seedlings introduced by either technique. No predation of seeds or seedlings was registered. The cost-efficiency analysis revealed that, considering the costs of production and plantation, introducing seedlings was almost two times more expensive compared to direct seeding. Results suggest that recovery of this species is feasible with combined practices depending upon the life stage of the plant and the conditions of the microsite. Improvements to these techniques, such as protection of the seed plumules, could confer even greater ecological and economic advantages for the introduction of O. mexicana in tropical secondary forests.

Natural regeneration of European beech (Fagus sylvatica) and Norway spruce (Picea abies) plays a crucial role in the future of many European mountain forests. It is affected by various soil and stand-related factors whose relative importance, especially in mixed stands, is still not known. In this study, we assessed the importance of stand composition, soil wetness, disturbances and different microsites and seedbeds for regeneration of beech and spruce in a mixed old-growth mountain forest. We also focused on how the effects of these factors change as regeneration gets older. We sampled all regeneration in 563 plots from different microsite types (deadwood, intact soil, treethrow pits and mounds), distinguishing three seedbeds (mosses, beech litter, bare substrate) for seedlings. We used soil survey and tree census data with generalized linear mixed models and variance partitioning to identify the main factors driving tree regeneration and their relative importance. Although beech was slightly less abundant in the canopy than spruce, it strongly outnumbered spruce in regeneration. Beech regeneration showed an affinity for beech litter-rich microsites and drier soils, while spruce was more common on deadwood and moister soils and its response to the seedbed was microsite-specific. The regeneration of both species was positively related to the proportion of their own species in the canopy, but more so in seedlings than in older regeneration cohorts, where soil wetness was more important. The overall pattern of tree regeneration thus resulted from a complex interplay between site conditions and their alterations by current and former generations of canopy trees through the creation of new microsites (deadwood, uprooting mounds) or litter production. Where beech regeneration is not suppressed by excess soil wetness, it is much more successful than spruce due to its shade tolerance and ability to be established in the beech litter that dominates the forest floor. On the other hand, spruce regeneration is mostly restricted to elevated microsites with lower litter accumulation, such as deadwood and treethrow mounds. Our results indicate that both species exhibit an ability to modify their environment in favor of their own regeneration, but under current conditions, beech is more successful than spruce and can be expected to increase its dominance in the future.

It has been firmly established that oak regeneration benefits from prescribed burning and reduced competition with fire-intolerant tree species. Despite recommendations for research on the role of the microsite environment for oak regeneration, very little is known about the interacting effects of fire, soil, and surrounding plant community on oak establishment. We collected undisturbed and burned soil in the aftermath of a wildfire in Great Smoky Mountains National Park and used amplicon sequencing to identify differences in composition of bacterial and fungal communities between unburned and burned soils. To assess the effects of plant community, fire-induced shifts in soil microbial communities, and their interaction we conducted a glasshouse experiment and grew Quercus velutina seedlings in factorial treatments of plant neighbor (oak vs. pine seedling) and soil burn status (unburned vs. burned soil). Fire reduced the diversity of plant pathogenic and saprotrophic fungi and reduced the relative abundance of plant pathogenic fungi. Fire did not affect soil bacterial communities. Shifts in soil fungal community composition enhanced oak seedling root growth, but the effect of the soil microbiome was mediated by plant neighbor interactions. Seedling root growth was negatively correlated with diversity of pathogenic fungi. Root growth was enhanced in burned soil relative to unburned soil, but only when growing with a pine seedling neighbor as opposed to an oak seedling neighbor. Results from this study show that interactions between soil microbes and nearby plants can in part mediate oak seedling growth. As such, nuanced decisions that consider the ecological interactions of the microsite environment are needed to achieve desired outcomes for oak regeneration.

Throughout much of its range, northern white-cedar (Thuja occidentalis L., hereafter cedar) has experienced a bottleneck in recruitment: cedar seedlings are often abundant in these stands, particularly in lowland settings, yet cedar sapling densities are quite low, leading to concerns that cedar canopy trees are not being replaced. Several barriers to cedar recruitment have been suggested; however, findings from previous studies have been inconsistent with regard to limiting factors. Our objective was to characterize the microsite conditions associated with the establishment of cedar seedlings and saplings. We achieved this objective by mapping the location of seedlings, saplings, and overstory trees in 15 lowland cedar stands at five sites in Maine, USA, and examining the fine-scale site conditions (microtopographic features, canopy openness) in which cedar seedlings and saplings occurred. In particular, we recorded the occurrence of seedlings and saplings on microtopographic mounds, pits (small depressions), and flats (transitional features between mounds and pits). Substrate moisture content in these features decreased in the order pits > flats > mounds. Contingency-table results demonstrated that live cedar seedlings, and to a slightly lesser extent saplings, were found more often than expected by chance on mounds, and less often on flats and pits. Logistic regressions using status (live vs. dead) as the response variable generally supported these findings: dead seedlings were strongly associated with pits; however, the occurrence of live seedlings and saplings did not differ between flats and mounds. A companion planted-seedling experiment strongly supported these results, showing that after two growing seasons, survival was significantly lower in pits (12%) when compared to flats and mounds, which had similarly high levels of survival (62 and 80% respectively). Logistic regressions also showed live seedlings and saplings to be prevalent under more open canopy conditions (mean 19%, range 6 to 42% openness); though results from a planted-seedling experiment suggested that greater canopy openness (mean 32%, range 13 to 57%) was detrimental to survival. Regressions also showed that browsed seedlings were more likely to be found dead. These findings point to management prescriptions that maintain microtopographic diversity, create moderately open canopy conditions, and protect stands from browsing to promote viable cedar populations in these ecologically and economically important forests.

The subalpine ecotone is experiencing significant changes in habitat availability and connectivity as a result of climate change. The conversion of meadow habitats to forests has been observed in many mountainous regions. Rates of conifer encroachment into meadows appears to have increased in the 20th century, but the patterns of conifer establishment seem highly variable over both space and time. To understand how and why these changes vary temporally and spatially in the Pacific Northwest, we collected cross-sections and whorl counts from conifers along four transects in subalpine meadows around Mt. Baker, Washington. We quantified the relationships between temporal patterns of conifer establishment and a suite of climate variables, and between spatial patterns of conifer density and microsite characteristics. Our results show that establishment occurred in pulses throughout the 20th century, with greater establishment on drier sites during periods of greater precipitation, and greater establishment on wetter sites during periods of higher temperatures. We found that April precipitation and September temperature are particularly strongly correlated with establishment rates, suggesting that the best conditions for conifer seedling establishment occur in years with the warmth and soil moisture needed for the growing season to start earlier or last longer. Within individual meadows, conifer seedling establishment was greater on convex surfaces and in areas with a higher percentage of Vaccinium cover. Our findings at Mt. Baker show that periods of conifer establishment occurred somewhat synchronously across multiple mountains in the region, but we also identified distinct spatial and temporal differences linked to local site conditions.

The coastal tailed frog (Ascaphus truei) has a biphasic life-history that includes the use of montane streams adjacent to mature old growth forests. This species is at risk from a variety of land-use activities, including forest harvesting, that results in younger and more fragmented terrestrial habitats. Post-metamorphic tailed frogs are cryptic and difficult to capture, making for few studies of the terrestrial life stage of the species. At the northern extent of the species’ range, we investigated the spatial ecology of tailed frogs across riparian and adjacent upland forest in three forest types: mature to old unharvested, streamside forest retention, and clearcut. Post-metamorphic frogs were fitted with Very High Frequency radio transmitters and monitored for an average of 10.75 days (SE 0.89). Females moved further from their origin of capture during the monitoring period ( x ¯ = 68.89 m, SE 16.3) when compared to males ( x ¯ = 36.85 m, SE 7.9). We used Resource Selection Functions to quantify habitat selection of female and male tailed frogs. Monitored frogs were positively associated with habitats containing well-decayed coarse woody debris (≥ 7.5 cm diameter), less ambient light, adjacency to the larval stream, hygric and subhygric microsites, and cool temperatures (11–12 °C). Females were more selective in their choice of habitat than males. Overall, the relationship between distribution and activity of tailed frogs was reflective of the sex of the frog in combination with microsite or broader climatic conditions ameliorated by stand-level habitat conditions. Our data suggest that habitat management for post-metamorphic tailed frogs focus on the retention of both streamside (within 40 m) and upland forest (> 50 m from larval stream), as well as stand-level attributes such as hygric and subhygric microsites, and coarse woody debris with advanced decay.

Regeneration of coniferous tree species depends on forest structures related to tree death: canopy gaps, decaying wood, and windthrow mounds and pits. This also applies to Norway spruce (Picea abies), which abundantly regenerates from seeds on dead wood and windthrow mounds, and which benefits from gaps in the forest canopy. Accumulated evidence shows much lower mortality of seedlings on elevated structures than on soil, but for saplings the long-term mortality pattern is poorly known. We studied Norway spruce sapling mortality in a natural old-growth subalpine forest in the Western Carpathians (S Poland), tracking the fate of 1304 saplings growing in different conditions. We found that the 25-year sapling mortality rate significantly differed between three types of microsites, being highest on dead wood (49%), intermediate on undisturbed soil (41%) and lowest on mounds (30%). Sapling mortality decreased with increasing canopy openness. Mortality was highest for medium-sized saplings (2–3 m high), regardless of microsite type and mortality cause. For saplings growing on dead wood, mortality increased with increasing decay class of the wood. For those growing on soil, mortality was higher in patches of Athyrium distentifolium than when surrounded by Vaccinium myrtillus and Dryopteris dilatata. We did not detect differences in mortality between saplings growing next to tree trunks and those growing away from them. The pattern of sapling mortality differed from that of seedlings, but it did not change the regeneration pattern over microsites, which is established at the seedling stage. In particular, we believe that the considerable differences in mortality rates between dead wood and the other microsites at the sapling stage cannot counterbalance increased seedling recruitment and survival on dead wood.

Early regeneration, involving the transition from a seed into a successfully recruited seedling, is a complex process characterized by high mortality rates and the strong association with environmental filters. However, we have limited understanding of the factors and transitional regeneration stages that lead to these broad mortality events, even in species that are key for ecosystem function and comprise the bulk of species in diversity assessments, such as Ficus species. Using eight, 1-ha long term monitoring plots, established along an elevation gradient in tropical to subtropical forests in southern China, and partitioning the early plant regeneration process into four stages (seed germination, seedling emergence, establishment and recruitment), we conducted a seed addition experiment to assess the factors driving the early regeneration process. We used four hemi-epiphytic and four non-hemiepiphytic Ficus species, specifically asking whether elevation, microsite conditions and growth form affect the success of regeneration outcomes. We observed that Ficus early regeneration was highly limited throughout the subtropical landscape with similar seed germination probabilities along all elevations, but greater seedling emergence at higher elevations. Growth form and elevation interacted significantly during seed germination and seedling emergence stages. The strongest filtering effect was observed during seedling emergence, with greater canopy openness facilitating, but drier and cooler soils being less conducive to seedling emergence, especially for hemiepiphytic species. Once emerged, Ficus seedlings were released from the environmental filters assessed here, yet, continued to face successively greater mortality during establishment and recruitment. Greater seed germination and seedling emergence on the ground observed in hemiepiphytes indicate that they may benefit from evolutionary traits associated with canopy regeneration under water and temperature stress, but only at the early regeneration stages, as seedling establishment and recruitment were similar in both groups. In general, our results demonstrate that even when seeds are available, successful recruitment is strongly limited by microsite conditions and growth form, through filtering mechanisms associated with the transition from seedling emergence to seedling establishment. The identification of environmental filters that operate during the complex and vulnerable early regeneration stages provides a baseline to develop management strategies for ex situ conservation, as well as in situ population reestablishment for restoration.

Although there are ample data on growth trends and climate growth relationships of trees from the leading edge of their distribution at treeline, information from the neighbouring trailing edge of the vegetation belt dominated by alpine shrubs is missing. We expected trees at their upper limit to exhibit unambiguous temperature limitation with a clearly positive growth response to recent warming. On the other hand, shrubs at the lower limits of their distribution and because of their low-stature are assumed to be less constrained by temperature, with ambiguous growth trends as compared to trees. We collected tree-ring series from sites with co-occurring Norway spruce (Picea abies) and Mountain pine (Pinus mugo) in four mountain ranges of Central Europe (the High Tatras, the Hrubý Jesenik Mts, the Krkonose Mts and the Bavarian Alps), assembled a suite of tree-ring chronologies containing either long-term trends or high-frequency variability, and compared climate-growth relationships and growth trends between spruce and pine. Our results show that in all areas under study, growth patterns of spruce statistically differ from those of pine. The growth of spruce is characterized by a tight relationship with June–July temperatures, maximum correlations ranging between 0.5 and 0.6. The climatic signal in tree-rings of pine is also characterized by a significant influence of summer temperature, albeit weaker than that observed in spruce (mostly between 0.3 and 0.4). All sites exhibited increasing growth trends for spruce since the 1980s; trend slopes for pine were either less positive (Hrubý Jesenik and Krkonose Mts) or negative (High Tatras). To conclude, the growth of spruce at its leading edge clearly resembled temperature-limited growth with corresponding recent growth acceleration, while the response of low-stature mountain pine to warming was weaker because of its tight coupling with microsite conditions and the location at the trailing edge of its distribution.

The poor natural regeneration of Korean pine represents a substantial hurdle limiting the restoration of secondary forests to mixed broad-leaved Korean pine forests (MBKPFs). Active restoration based on direct seeding or planting seedlings is accordingly considered to be a prerequisite for promoting Korean pine recruitment in secondary forests. To evaluate the most effective practices for restoring Korean pine in secondary forests, we studied the effects of microsites associated with gaps of different sizes and within-gap locations on direct seeding (rodent access/exclusion and soil/litter cover) and seedling planting (1-, 2-, and 3-year-old seedlings). We found that an average of 82.4% of sown seeds were eaten by rodents, with only 9.9% germinating and surviving after two growing seasons. Among the germinated seedlings, 37.6% were subsequently excised by rodents, whereas 6% died due to other natural causes. Furthermore, compared with the control sites (forest understorey), we detected no significant differences among the different microsites with respect to an effective reduction in rodent damage or promotion of seed germination, whereas rodent exclusion was more effective in protecting seeds from predation than the effect of microsite. With regards to planted seedlings, we found that the proportion of survival and relative root collar diameter growth were highest in the center (64.1%) and edge (60.0%) sites of large gaps, and that the survival of planted seedlings (43.7%) was considerably higher than that of seedlings derived from directly sown seeds (9.9%). Collectively, our findings indicate that, owing to seed predation and seedling excision by rodents, direct seeding with either mesh or soil cover would not represent an effective strategy for promoting Korean pine recruitment in secondary forests. Accordingly, for the purposes of restoring secondary forests to MBKPFs, we recommend planting 3-year-old Korean pine seedlings in large gaps within secondary forests.

Quaking aspen (Populus tremuloides) is an important component of western U.S. forests, however knowledge concerning processes of aspen seedling establishment, survival, and growth is limited and frequently anecdotal. Following a widespread post-fire establishment event in southern Utah, we explored spatial establishment patterns of >1000 aspen seedlings and tracked their survival and growth for two growing seasons. Specifically, we assessed the influence of landscape-level variables, microsite factors, and competition with suckers on aspen seedling establishment, survival, and growth. Aspen seedlings occurred across large areas of the 29,000 ha fire footprint, with an average plot density of 23,033 seedlings ha−1, and establishment more likely at higher elevations and closer to seed sources. Aspen seedlings preferentially established in concave microsites and were tightly associated with burned soil. A total of 33% of tagged seedlings remained alive after two growing seasons. Seedling persistence was strongly impacted by competition with co-occurring aspen suckers, with survival lower for aspen seedlings closer to nearby suckers and seedling growth reduced in plots with high sucker density. Given the long dispersal distances of aspen seeds and the ability of seeds to take advantage of initial post-disturbance conditions, sexual regeneration in aspen may represent an important pathway for maintaining forest resilience and associated ecosystem services, especially following fires with large patches of high burn severity.

Human-shaped treelines are a common feature in mountain landscapes across Europe, and particularly in secularly managed Mediterranean high-elevation areas. The abandonment of traditional land use, and especially the reduction in grazing pressure at high elevations, triggered secondary succession in treeless grassland areas, and favored the upward shift of anthropogenic treelines in some cases. We investigated this process in four anthropogenic treeline ecotone sites in the Central Apennines, Italy, populated by European black pine (Pinus nigra Arn.). The upward treeline shift was controlled by microsite topography and the proximity to plantations acting as seed source. We found a 50% probability of producing cones in trees with basal diameters of 15–25 cm, heights of 2–5 m and ages of 20–25 years. The role played by climate on growth and the recruitment processes seems to be secondary, or could be masked by human-shaped processes. The presence of reproductive age trees at the treeline, mainly growing on debris-rich and steep slope sites, could indicate that the recruitment process will increase in future, leading to patchy tree patterns at different elevations. The high growth and encroachment rates observed at these human-shaped treelines would indicate that general growth dynamics are speeding up, including the tree colonization of treeless areas. These succession processes could cause a significant long-term decline in plant diversity in species-rich grasslands. Nonetheless, tree encroachment could increase forest protection against landslides and avalanches in the context of global change.

Surface mining extensively alters the physical, chemical and biological characteristics of the soil, and therefore, the revegetation of mine spoil through natural process takes a very long time and poses a major problem because nutritionally it is a recalcitrant medium for plant growth. We review important studies on the restoration of mine spoils in the tropical dry region of India. Through this communication, we suggest that the microbial biomass of soil is a critical factor in the recovery of mine spoils because it plays a major role in the re-establishment of nutrient cycling. The levels of microbial biomass C, N and P can be treated as functional indexes for soil re-development. Tree plantations have been reported to significantly accelerate the re-development process. Ground seeding of the mine spoils with suitable tree and grass species together with NPK fertilization has been reported to promote growth, and consequently leads to increase in biomass production. Species-specific variations are reported to occur in the response to fertilization. Relatively, greater variation has been reported for non-leguminous, rather than for leguminous species. Furthermore, leguminous species exhibit higher growth rates as compared to non-leguminous species. Our review also suggests that the microsite conditions on the mine spoils exhibit differences and should be given more consideration for accelerating the process of re-vegetation and fulfilling the post-mining land use objectives.

The direct seeding method of artificial regeneration has a long tradition in silvicultural management. The main application of the direct seeding of silver fir (Abies alba Mill.) today occurs in the context of the conversion of Norway spruce stands in central Europe. Although direct seeding is often considered to closely resemble natural regeneration in many respects, tree planting is currently more commonly employed in forestry. Presented in this paper is an extensive historical review showing the variety of facets associated with and experiences of direct seeding gleaned through scientific experiments or based on forestry practice. This review also illustrates the fluctuating practical relevance of the direct seeding of silver fir depending on the prevailing objectives of forest owners, harvesting methods, forest structures and the possibilities for technical implementation. An overview of the available ecological knowledge of the development stages and processes within the natural regeneration cycle of silver fir is provided, highlighting the most relevant environmental factors and the resources determining the success of natural regeneration. Having identified these factors, the individual technical steps involved in direct seeding can be analysed. The means by which the individual steps in the direct seeding approach can be used to manipulate environmental factors and microsite conditions such as the density of overstorey shelter, soil and seedbed preparation, and to reduce competition pressure to optimise the direct seeding of silver fir are outlined. Finally, on the basis of the analyses presented, these complex relationships are integrated in a step by step decision pathway to provide an individual forest stand decision-making process. This ecologically based approach can improve the success of direct seeding and may allow for the adaptation of the direct seeding process to suit individual forest stand conditions. Consequently, the growing efforts to convert and enrich homogenous Norway spruce stands by means of the direct seeding of silver fir can be promoted in a close-to-nature way, while employing controlled silvicultural measures.

Understanding tree recruitment is crucial to assess species turnover in mixed forests and woodlands, particularly in light of current anthropogenic impact. Here, we investigate whether oak recruitment (density of young oaks) in co-existing deciduous and evergreen oaks is disproportional to the abundance of their corresponding reproductive trees, favoring regeneration of some species over others, which may anticipate a future species turnover. We also examined whether browsing damage and microsite location play a differential role in such recruitment process. We uncovered an overall underrepresentation of young oaks ( Q. lobata and Q. douglasii ), compared to the evergreen oak ( Q. agrifolia ), even in areas where deciduous species were the locally predominant mature trees. Such differential recruitment was accentuated in areas where Q. lobata was predominant, with young evergreen oaks reaching densities 3-times higher than those of the deciduous oak. Recruitment of all three species was significantly associated with shrub cover, suggesting a facilitative effect, via reduction of both occurrence and intensity of herbivory. However, evergreen oaks were much less vulnerable to herbivory (lower occurrence and intensity) than deciduous oaks and, thus, evergreen recruits were able to thrive even in uncovered areas. Overall, our results provide evidence of differential recruitment at the juvenile stage in co-occurring oak species, which may lead to a replacement of deciduous species with evergreen oaks. The disproportionate effect of shrubs as safe microsites for regeneration of both deciduous and evergreen species suggests that herbivory pressure is an important factor reducing the abundance and heterogeneity of favorable regeneration niches, particularly for the most herbivore-sensitive tree species. Further studies should address to what extent the recruitment patterns described here translate into future differences in adult stages, and whether the actual biased regeneration is mostly due to differential herbivory on deciduous vs. evergreen species. We posit that, for the management and conservation of multi-specific oak savannas, regeneration of deciduous oaks should be prioritized over that of live oaks in order to maintain greater levels of biodiversity and reduce biotic homogenization.

Background Bush clearing of encroached rangelands is crucial for restoration of herbaceous cover and diversity. Regeneration after bush clearing depends largely on the soil seed bank (SSB) size and composition. To assess the potential of the SSB to facilitate post-clearing herbaceous restoration, we examined the SSB density, composition and diversity and similarity between SSB and aboveground vegetation (AGV). Methods The study was conducted in semi-arid rangelands of Maseding and Kgomokgomo in North-West Province of South Africa. In each rangeland, all woody plants in three 1250 m2 plots were cut using saws and loppers, with the stumps treated with picloram. Paired observations were conducted in cleared and uncleared microsites. Soil samples were collected at three depths (0–10, 10–20 and 20–30 cm) in each microsite in April (pre-treatment), August, October and December 2016 and in April and August 2017. SSB was assessed using seedling emergence method, whereas pre- and post-clearing surveys of AGV were conducted in February 2016 and 2017, respectively. Results Cleared microsites had significantly (p < 0.01) higher seed bank densities (1872 and 693 seeds m-2 at Maseding and Kgomokgomo, respectively) relative to uncleared microsites in August 2017, with grasses accounting for higher densities than other plant functional groups in the upper 0–10 cm. Pioneer grasses (Aristida congesta subsp. barbicollis, Brachiaria eruciformis and Tragus berteronianus) and invasive forbs (Bidens pilosa and Schkuhria pinnata) dominated the SSB in cleared microsites at Maseding, whereas succulents (Portulaca spp.) and pioneer grasses (T. berteronianus and Urochloa mosambicensis) were abundant at Kgomokgomo in August 2017. SSB and AGV were dissimilar until December 2016; thereafter, similarity increased significantly (p < 0.05) in cleared microsites (Sørensen’s coefficient = 0.60 to 0.66 at Maseding and 0.43 to 0.52 at Kgomokgomo) compared to uncleared microsites. Species diversity was highest in August 2016 and April 2017 at Maseding, but it did not differ between two microsites (p > 0.05). At Kgomokgomo, SSB was more diverse in cleared than uncleared microsites in April and August 2017. Conclusion High seed bank densities in the upper soil layer in cleared microsites would promote passive restoration, but regeneration is likely to be initiated by early successional species. However, close monitoring and eradication of invasive forbs and succulents is necessary following bush clearing. The tendency of SSB resembling AGV over time in cleared microsites signifies that seed production from AGV is important for passive restoration following bush clearing.

Coastal sand dunes near the Baltic Sea are a dynamic environment marking the boundary between land and sea and oftentimes covered by Scots pine (Pinus sylvestris L.) forests. Complex climate-environmental interactions characterize these ecosystems and largely determine the productivity and state of these coastal forests. In the face of future climate change, understanding interactions between coastal tree growth and climate variability is important to promote sustainable coastal forests. In this study, we assessed the effect of microsite conditions on tree growth and the temporal and spatial variability of the relationship between climate and Scots pine growth at nine coastal sand dune sites located around the south Baltic Sea. At each site, we studied the growth of Scots pine growing at microsites located at the ridge and bottom of a dune and built a network of 18 ring-width and 18 latewood blue intensity chronologies. Across this network, we found that microsite has a minor influence on ring-width variability, basal area increment, latewood blue intensity, and climate sensitivity. However, at the local scale, microsite effects turned out to be important for growth and climate sensitivity at some sites. Correlation analysis indicated that the strength and direction of climate-growth responses for the ring-width and blue intensity chronologies were similar for climate variables over the 1903–2016 period. A strong and positive relationship between ring-width and latewood blue intensity chronologies with winter-spring temperature was detected at local and regional scales. We identified a relatively strong, positive influence of winter-spring/summer moisture availability on both tree-ring proxies. When climate-growth responses between two intervals (1903–1959, 1960–2016) were compared, the strength of growth responses to temperature and moisture availability for both proxies varied. More specifically, for the ring-width network, we identified decreasing temperature-growth responses, which is in contrast to the latewood blue intensity network, where we documented decreasing and increasing temperature-growth relationships in the north and south respectively. We conclude that coastal Scots pine forests are primarily limited by winter-spring temperature and winter-spring/summer drought despite differing microsite conditions. We detected some spatial and temporal variability in climate-growth relationships that warrant further investigation.

In eastern Canada, spruces (Picea spp.) and pines (Pinus spp.) are among the main commercial species being logged for their lumber or wood fiber. Annually, about 175 million seedlings are planted in areas totaling ~100,000 ha. Appropriate microsite selection is essential during reforestation operations, given that it can improve the chances of survival and initial growth of the seedlings. In fir (Abies spp.) and spruce forests of eastern Canada, the optimal characteristics of establishment microsites have yet to be identified, these would be determined by different physical and climatic variables operating at several scales. Our study determined the influence of climatic (regional-scale), edaphic (stand-scale), local (microsite-scale) and planting conditions on the establishment substrate and initial growth of black spruce (Picea mariana Britton, Sterns and Poggenb.) and jack pine (Pinus banksiana Lamb.). Substrate characterization and growth monitoring (three growing seasons) for the two species were conducted on 29 planted cutblocks that were distributed over an east&ndash, west climatic gradient (precipitation and temperature) in the balsam fir and black spruce&ndash, feather moss forests of Quebec (Canada). Linear mixed models and multivariate analyses (PCAs) determined the effects of climatic, edaphic and micro-environmental variables and their interactions on the establishment substrate and seedling initial growth. The predictive models explained, respectively, 61% and 75% of the growth variability of black spruce and jack pine. Successful establishment of black spruce and jack pine depended upon regional conditions of precipitations and temperature, as well as on their interactions with stand-scale edaphic variables (surface deposit, drainage and slope) and local variables (micro-environmental) at the microsite-scale (establishment substrate types and substrate temperature). Mineral, organo-mineral and organic establishment substrates exerted mixed effects on seedling growth according to regional precipitation and temperature conditions, as well as their interactions with edaphic and local variables at the stand and microsite-scales, respectively.