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Sediment deposition at the bottom of artificial reservoirs has become a worldwide problem. This comprises a dual issue that is, in the first place, associated with the reduction in storage capacity and lifetime of large reservoirs. The second aspect comprises the threat that the sediment represents for the dam structure. This research is mainly aimed at identifying and inferring the main sediments' triggering processes through a rigorous analysis of deposition shapes in a large reservoir. For identifying the main deposition shapes, a sequential methodology was designed and developed comprising the following stages. First, an analysis of XYZ cartography from bathymetric development was conducted. Then, a shapes categorization was developed that comprises the identification of six types of shapes based on four parameters: slope continuity, slope break, absolute and relative slope, and arc configuration. The third stage comprised a visualization and spatial calculation of shapes through GIS-based cartography. The fourth stage comprised an interpretation of deposition shapes processes: for that, a dual analysis was developed. First, an analysis based on fluvial sediments transport processes was realized. The second stage implied an analysis of the dam influence on fluvial hydrodynamics and sediments transport. Results comprised a quantitative assessment of each shape as well as physical processes identification and interpretation, generating a robust equivalence between shapes and triggering processes. This research proved successful for the identification and characterization of the main deposition and transport processes that may help to prevent, palliate, and/or correct phenomenon of silting in large reservoirs. This detailed knowledge of deposition forms opens new strategies to release sediments from storage water more effectively. [ABSTRACT FROM AUTHOR]

The 'mass ratio' hypothesis states that ecosystem functioning is driven by the functional traits of the most dominant species in communities. Thus, we aimed to evaluate (i) How topographical conditions and stand age determine changes in tree community composition, richness, abundance and carbon dominant (CD) species, and (ii) Assess whether community-weighted mean of functional trait values of CD species explain aboveground carbon (AGC) stock. We used community-weighted mean of wood density and maximum stem diameter to evaluate the effect of functional dominance in AGC stock. We found that different topographic conditions and stand age change community composition, richness, abundance and CD species along the late-secondary stage. Our results showed that functional trait values of CD species determine AGC stock. Thus, the proportion of CD species was shaped by topography and stand age, whereas carbon stock by the dominant species' functional traits (wood density and diameter). This study advances our understanding of the mechanisms that drive carbon stock in tropical forests and supports the 'mass ratio' hypothesis. We emphasize the relevance of the trait-based approach to understand forest functioning and trait functional composition and taxonomic identity for carbon storage, recovery and increase in secondary Atlantic Forests. [ABSTRACT FROM AUTHOR]

Aims: Unravelling the most prevalent causal direction between diversity and function in naturally recovered plant assemblages can greatly improve our understanding of the functional significance of diversity and its applications under the ongoing environmental changes. In this study, we apply a structural equation model framework to unravel the most plausible causal direction in the diversity–productivity relationship in subseral Mediterranean shrub‐dominated communities. Methods: Total shrub cover (as a proxy of productivity when controlled by the time since land use cessation or the last wildfire), the number of species, and the number of functional types based on the dominant life forms (phanerophytes vs. chamaephytes), and the dominant foliar syndromes (deciduous vs. evergreen, needled vs. broad‐leaved), were sampled in 195 circular plots distributed along an elevation gradient ranging from 400 to 1400 m a.s.l. in the Central Iberian Peninsula. We first explored the distribution of functional types along the elevation gradient using a non‐metric multidimensional scaling (NMDS). Secondly, a structural equation model (SEM) framework using mixed‐effects models was defined to unveil the prevalent causal direction between diversity (species and functional types) and productivity at the landscape scale. Results: Model selection using the Fisher's C information criterion supported a causal direction from total shrub cover to diversity in this landscape. Interestingly, the best supported model also supported a positive relationship between species richness and the number of functional types, which in turn is driven by the total shrub cover along the elevation gradient. Conclusions: Our results suggest that more species might not necessarily boost productivity. On the contrary, ongoing warming temperatures and aridity, which are characteristic of low elevations compared to highlands, might significantly reduce the number of species (victim rather than rescuer) through deleterious effects on productivity. [ABSTRACT FROM AUTHOR]

Tree‐ring data has been widely used to inform about tree growth responses to drought at the individual scale, but less is known about how tree growth sensitivity to drought scales up driving changes in forest dynamics. Here, we related tree‐ring growth chronologies and stand‐level forest changes in basal area from two independent data sets to test if tree‐ring responses to drought match stand forest dynamics (stand basal area growth, ingrowth, and mortality). We assessed if tree growth and changes in forest basal area covary as a function of spatial scale and tree taxa (gymnosperm or angiosperm). To this end, we compared a tree‐ring network with stand data from the Spanish National Forest Inventory. We focused on the cumulative impact of drought on tree growth and demography in the period 1981–2005. Drought years were identified by the Standardized Precipitation Evapotranspiration Index, and their impacts on tree growth by quantifying tree‐ring width reductions. We hypothesized that forests with greater drought impacts on tree growth will also show reduced stand basal area growth and ingrowth and enhanced mortality. This is expected to occur in forests dominated by gymnosperms on drought‐prone regions. Cumulative growth reductions during dry years were higher in forests dominated by gymnosperms and presented a greater magnitude and spatial autocorrelation than for angiosperms. Cumulative drought‐induced tree growth reductions and changes in forest basal area were related, but initial stand density and basal area were the main factors driving changes in basal area. In drought‐prone gymnosperm forests, we observed that sites with greater growth reductions had lower stand basal area growth and greater mortality. Consequently, stand basal area, forest growth, and ingrowth in regions with large drought impacts was significantly lower than in regions less impacted by drought. Tree growth sensitivity to drought can be used as a predictor of gymnosperm demographic rates in terms of stand basal area growth and ingrowth at regional scales, but further studies may try to disentangle how initial stand density modulates such relationships. Drought‐induced growth reductions and their cumulative impacts have strong potential to be used as early‐warning indicators of regional forest vulnerability. [ABSTRACT FROM AUTHOR]

Global change is shifting disturbance regimes that may rapidly change ecosystems, sometimes causing ecosystems to shift between states. Interactions between disturbances such as fire and disease could have especially severe effects, but experimental tests of multi‐decadal changes in disturbance regimes are rare. Here, we surveyed vegetation for 35 years in a 54‐year fire frequency experiment in a temperate oak savanna–forest ecotone that experienced a recent outbreak of oak wilt. Different fire regimes determined whether plots were savanna or forest by regulating tree abundance (r2 = 0.70), but disease rapidly reversed the effect of fire exclusion, increasing mortality by 765% in unburned forests, but causing relatively minor changes in frequently burned savannas. Model simulations demonstrated that disease caused unburned forests to transition towards a unique woodland that was prone to transition to savanna if fire was reintroduced. Consequently, disease–fire interactions could shift ecosystem resilience and biome boundaries as pathogen distributions change. [ABSTRACT FROM AUTHOR]

The negative impacts of drought on forest growth and productivity last for several years generating legacies, although the factors that determine why such legacies vary across sites and tree species remain unclear.We used an extensive network of tree‐ring width (RWI, ring‐width index) records of 16 tree species from 567 forests, and high‐resolution climate and normalized difference vegetation index (NDVI) datasets across Spain during the common period 1982‒2008 to test the hypothesis that climate conditions and growth features modulate legacy effects of drought on forests. Legacy effects of drought were calculated as the differences between detrended‐only RWI and NDVI series (i.e. after removing long‐term growth trends) and pre‐whitened RWI and NDVI series predicted by a model including drought intensity. Superposed Epoch Analysis (SEA) was used to estimate whether legacy effects differed from random. Finally, legacy effects were related to water balance, growth persistence and variability, and tree species identity.We found a widespread occurrence of drought legacy effects on both RWI and NDVI, but they were seldom significant. According to SEA, first‐year drought legacies were negative and different from random in 9% and 5% of the RWI and NDVI series respectively. The number of significant second‐ and third‐year legacies was substantially lower. Differences between RWI and NDVI legacies indicate that canopy greenness and radial growth responses to drought are decoupled. We found variations in legacies between tree species with gymnosperms presenting larger first‐year drought legacies than angiosperms, which were exposed to less severe droughts. Greater growth variability can explain the presence of first‐year RWI legacies in gymnosperms from dry sites despite that the relationship between growth variability and legacies was complex.Synthesis. Accounting for species and site responses to drought provides a better understanding of the magnitude and duration of drought legacies on forest growth and productivity. Despite the widespread occurrence of growth reductions in the years during and after drought occurrence, significant legacies were not very common, mostly lasted one year, and were more widespread in gymnosperms. These are relevant factors to be considered in the future when studying the consequences of drought on forest productivity and tree growth. [ABSTRACT FROM AUTHOR]

Copyright of Biotropica is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Drought is one of the key natural hazards impacting net primary production and tree growth in forest ecosystems. Nonetheless, tree species show different responses to drought events, which make it difficult to adopt fixed tools for monitoring drought impacts under contrasting environmental and climatic conditions. In this study, we assess the response of forest growth and a satellite proxy of the net primary production (NPP) to drought in peninsular Spain and the Balearic Islands, a region characterized by complex climatological, topographical, and environmental characteristics. Herein, we employed three different indicators based on in situ measurements and satellite image-derived vegetation information (i.e., tree-ring width, maximum annual greenness, and an indicator of NPP). We used seven different climate drought indices to assess drought impacts on the tree variables analyzed. The selected drought indices include four versions of the Palmer Drought Severity Index (PDSI, Palmer Hydrological Drought Index (PHDI), Z-index, and Palmer Modified Drought Index (PMDI)) and three multi-scalar indices (Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Precipitation Index (SPI), and Standardized Precipitation Drought Index (SPDI)). Our results suggest that--irrespective of drought index and tree species--tree-ring width shows a stronger response to interannual variability of drought, compared to the greenness and the NPP. In comparison to other drought indices (e.g., PDSI), and our results demonstrate that multi-scalar drought indices (e.g., SPI, SPEI) are more advantageous in monitoring drought impacts on tree-ring growth, maximum greenness, and NPP. This finding suggests that multi-scalar indices are more appropriate for monitoring and modelling forest drought in peninsular Spain and the Balearic Islands. [ABSTRACT FROM AUTHOR]

Abstract: Forecasted increase drought frequency and severity may drive worldwide declines in forest productivity. Species‐level responses to a drier world are likely to be influenced by their functional traits. Here, we analyse forest resilience to drought using an extensive network of tree‐ring width data and satellite imagery. We compiled proxies of forest growth and productivity (TRWi, absolutely dated ring‐width indices; NDVI, Normalized Difference Vegetation Index) for 11 tree species and 502 forests in Spain corresponding to Mediterranean, temperate, and continental biomes. Four different components of forest resilience to drought were calculated based on TRWi and NDVI data before, during, and after four major droughts (1986, 1994–1995, 1999, and 2005), and pointed out that TRWi data were more sensitive metrics of forest resilience to drought than NDVI data. Resilience was related to both drought severity and forest composition. Evergreen gymnosperms dominating semi‐arid Mediterranean forests showed the lowest resistance to drought, but higher recovery than deciduous angiosperms dominating humid temperate forests. Moreover, semi‐arid gymnosperm forests presented a negative temporal trend in the resistance to drought, but this pattern was absent in continental and temperate forests. Although gymnosperms in dry Mediterranean forests showed a faster recovery after drought, their recovery potential could be constrained if droughts become more frequent. Conversely, angiosperms and gymnosperms inhabiting temperate and continental sites might have problems to recover after more intense droughts since they resist drought but are less able to recover afterwards. [ABSTRACT FROM AUTHOR]

In the Mediterranean region, over the past few centuries human activity has modeled the landscape, leading to forest degradation. However, as in many parts of the European continent since the second half of the twentieth century, the Iberian Peninsula has been subject to a substantial degree of land abandonment that has led to the expansion of important secondary forests. One of the dominant tree species in the transitional forests of mountain areas between the Mediterranean and Euro-Siberian regions of the Iberian Peninsula is the deciduous oak, Quercus pyrenaica Willd. The main objectives of the present work were to study the mode of regeneration and forest dynamics of Q. pyrenaica in several types of stands: young forests, mature and previously perturbed forests, and abandoned Pinus reforestations. With this in mind we established eight plots in the mountain range of the Sierra de Francia–Quilamas, in the west subdivision of the Spanish Central System. We analyzed the age and dbh distributions, regeneration density, and the spatial structure of trees and saplings. Young Q. pyrenaica stands were seen to show episodic recruitment after land abandonment consistent with a ‘catastrophic’ mode of regeneration. These stands were characterized by unimodal age-cohorts, with tree recruitment dropping drastically as the canopy developed and closed in, except at some study sites where the more shade-tolerant Castanea sativa was found. Older and previously disturbed Q. pyrenaica stands showed bimodal age cohorts, the young ones exhibiting a clumped pattern associated with canopy gaps and/or a lower tree density of the older cohort. In abandoned Pinus reforestations, the recruitment of Q. pyrenaica was also associated with canopy openings. These findings show that Q. pyrenica also undergoes a gap-phase mode of regeneration. An abundant regeneration of Q. pyrenaica could be found at all the stands, guaranteeing the persistence of seedling banks (but a scarcity or lack of saplings) under closed forests, until canopy gaps may allow some Q. pyrenaica individuals to grow and reach the main canopy. [ABSTRACT FROM AUTHOR]

Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tree plantations have been proposed as suitable carbon sinks to mitigate climate change. Drought may reduce their carbon uptake, increasing their vulnerability to stress and affecting their growth recovery and resilience. We investigated the recent growth rates and responses to the climate and drought in eight Atlas cedar (Cedrus atlantica) plantations located along a wide climate gradient from wetter sites in south-eastern France and north Spain to dry sites in south-eastern Spain. The cedar growth increased in response to the elevated precipitation from the prior winter to the current summer, but the influence of winter precipitation on growth gained importance in the driest sites. The growth responsiveness to climate and drought peaked in those dry sites, but the growth resilience did not show a similar gradient. The Atlas cedar growth was driven by the total precipitation during the hydrological year and this association strengthened from the 1980s onwards, a pattern related to the winter North Atlantic Oscillation (NAO). High winter NAO indices and drier conditions were associated with lower growth. At the individual level, growth resilience was related to tree age, while growth recovery and year-to-year growth variability covaried. Plantations' resilience to drought depends on both climate and tree-level features. [ABSTRACT FROM AUTHOR]

Abstract  We examined the effects of simulated folivory by caterpillars on photosynthetic parameters and nitrogen (N) resorption efficiency in Quercus pyrenaica saplings. We analyzed the differences between intact leaves in control plants, punched leaves in damaged plants, and intact leaves in damaged plants. We then established two levels of simulated folivory: low (≈13% of the leaf area of one main branch removed per plant) and high (≈26% of the leaf area of one main branch removed per plant) treatments. No differences were found in net assimilation rate and conductance between either leaf type or treatment during the most favourable period for photosynthesis. However, the N content was lower in punched than in intact leaves, and as a result PNUE was higher in damaged leaves from treated trees. In leaf-litter samples, N mass was significantly higher in punched than in intact leaves in treated plants, and LMA was significantly higher in damaged than in intact leaves of both the treated and control plants. Consequently, N resorption efficiency was around 15% lower in damaged leaves as compared with intact leaves from treated and control plants. Mechanical injury to leaves not only triggered no compensatory photosynthetic response to compensate a lower carbon uptake due to leaf area loss, but also affected the resorption process that characterizes leaf senescence. [ABSTRACT FROM AUTHOR]

Several populations of Fitzroya cupressoides (Mol.) Johnst. (Cupressaceae, common name “alerce”), a threatened, long-lived conifer endemic to southern Chile and parts of Argentina, have recently been found in Chile’s Central Depression, where the species was thought to have been extirpated. The objective of this study was to determine, on eight sites in the Depression, Fitzroya’s regeneration behavior in relation to disturbance, its substrate and cover requirements for establishment, and whether regeneration is by seed or vegetative means. This objective required inspection of tree age-class distributions, analyses of microsite conditions and spatial distributions of Fitzroya individuals, and genetic analysis of Fitzroya trees using random amplified polymorphic DNA (RAPD) analysis. Age-class distributions indicated a “catastrophic” regeneration mode, in which seedling establishment follows stand-devastating disturbance, such as fire. Regeneration was both by seed and vegetative means (root sucker sprouting and layering), although overall, vegetative reproduction was more prevalent (63% of all regeneration). Regeneration from seed occurred primarily under open canopies (<40% cover) and on substrates of humus, moss beds, and coarse woody debris. Spatial analyses revealed clumping at various scales for Fitzroya seedlings, saplings, and trees. Several obvious clumps of trees were assumed to be sucker sprouts from cut stumps; however, RAPD analyses indicated they were of seed origin. Such clumping is likely due to the patchy co-occurrence of appropriate substrates and canopy covers. Despite substantial environmental differences between the Central Depression and the portions of the Coastal and Andean Cordilleras where Fitzroya is found, populations in all three regions show striking similarities in their regeneration and stand dynamics. Fitzroya’s longevity and at times abundant regeneration provide the biological basis for its persistence in Chile’s Central Depression. [Copyright &y& Elsevier]

• Only EA and NAO climatic patterns control temperature and rainfall variability. • Warmer and wetter conditions concur during EA+NAO- phases. • EA influence on radial tree growth is higher than NAO in the three pine species. • There are clear species-specific responses to climatic patterns. • Trees respond to climatic patterns according to their biogeographical character. Large-scale climate indices, such as the Atlantic Multidecadal Oscillation (AMO), the East-Atlantic pattern (EA), the North-Atlantic Oscillation (NAO) and the Western Mediterranean Oscillation (WeMO), are recognized as important drivers of tree growth and forest productivity in south-western Europe. However, it is still poorly understood whether species respond to these climatic influences differently. Do different pine tree species respond similarly to the main climatic patterns in south-western Europe? If not, will the species respond according to what should be expected from their biogeographical character? Here we analyse the paper of climatic patterns on tree growth in a mountainous Mediterranean environment where three contrasting pine species cohabit (Pinus nigra , P. pinaster and P. sylvestris). We first identified the climatic patterns that most influence temperature and precipitation variability during the coldest months of the year. Secondly, we evaluated the role of these climatic patterns as drivers of Basal Area Increments (BAI) using mixed-effect models separately for each of the three pines considered. A backward model selection was applied using AICc. Only two out of the four climatic patterns analysed were supported as potential drivers of temperature and precipitation variability in our study site. Specifically, EA correlated positively with temperatures and precipitation, whereas NAO correlated negatively with precipitation. Model selection supported both EA and NAO as important drivers of BAI in P. nigra and P. sylvestris , while P. pinaster was sensitive to EA. Our results highlight EA as the most influential climatic driver of tree growth in this area. Furthermore, and according to the biogeographical characters of the species studied, the models show how high temperatures influence P. pinaster the most, while P. sylvestris is the most sensitive species to precipitation variability. Our findings show the existence of clear species-specific differences in tree growth responses to climatic variability patterns. [ABSTRACT FROM AUTHOR]

Key message: Quercussecondary forests show a gradual transition toward mixed forests, with sweet chestnut (Castanea sativa) becoming increasingly abundant in the western Spanish Central System. Additionally, in chestnut-dominated stands, it shows a certain resistance to competitive displacement byQuercus pyrenaica. Our results partially refute the traditional view thatC. sativais unable to recruit in the absence of cultural inputs.Context: Sweet chestnut, Castanea sativa, is a component of European broadleaf forests and is one of the most managed trees. Due to a reduction in cultural inputs, chestnut-dominated stands tend to be invaded by other species, and it is unclear how chestnut is able to persist in natural mixed forests.Aims: Our work aimed to identity the main factors that limit the establishment of C. sativa and to analyze the recruitment and mortality processes of C. sativa trees.Methods: The age, growth ring patterns, regeneration density, and the spatial structure of trees and saplings in 11 plots in the Spanish Central System were analyzed.Results: Chestnut seedling density increased with C. sativa basal area, but transition toward the sapling stage appeared limited owing to light availability. In Quercus pyrenaica secondary forests, sparse canopies did not constrain chestnut regeneration, and in old chestnut stands, C. sativa showed a certain resistance to competitive displacement. By contrast, mixed young coppices showed a high mortality, most likely due to competition with other vigorous resprouters.Conclusion: Quercus secondary forests showed a gradual transition toward mixed forests with sweet chestnut becoming increasingly more abundant. In old stands, C. sativa is likely to persist under a gap-phase mode of regeneration. Our results partially refute the traditional view that C. sativa is unable to recruit in the absence of cultural inputs. [ABSTRACT FROM AUTHOR]

• Positive and significant relationship between the interannual variability and the secondary growth. • Similar average correlations among all different forest types. • Maximum correlations found between NDVI and tree-ring growth are recorded considering cumulative NDVI values. • Temporal lags may be expected due to particular physiological processes. This study links tree-ring growth and gross primary production for a variety of forest types under different environmental conditions across Spain. NOAA-AVHRR satellite imagery data were combined with dendrochronological records and climate data at a fine spatial resolution (1.21 km2) to analyze the interannual variability of tree-ring growth and vegetation activity for different forest biomes from 1981 to 2015. Specifically, we assessed the links between tree-ring width indices (TRWi), the Normalized Difference Vegetation Index (NDVI) and a variety of environmental conditions, represented by climatic variables (air temperature, precipitation, evapotranspiration and water balance) and elevation. The impact of these variables on tree growth was assessed by means of the Predictive Discriminant Analysis (PDA). Results reveal a general positive and significant relationship between inter-annual variability of the NDVI at a high spatial resolution (1.21 km2) and tree-ring growth. Maximum correlations between NDVI and tree-ring growth were recorded when cumulative NDVI values were considered, in some cases covering long time periods (6–10 months), suggesting that tree growth is mainly related to Gross Primary Production (GPP) at annual scale. The relationship between tree-ring growth and inter-annual variability of the NDVI, however, strongly varies between forest types and environmental conditions. [ABSTRACT FROM AUTHOR]