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Abstract

Adapting for competitiveness versus climatic stress tolerance constitutes a primary trade-off differentiating tree life-history strategies. This tradeoff likely influences where species’ range-limits occur, but such links are data-demanding to study and key mechanisms lack empirical support. Using an exceptionally rich dendroecological network, we assessed spatial variation in climate and competition effects on Picea abies and Fagus sylvatica throughout the Carpathian Ecoregion. Ring width synchrony aided in diagnosing how the prevalence of resource-limited (competition) and sink-limited (climate) growth changes with altitude and community composition. Contrasting growth patterns towards respective upper and lower range limits of Fagus and Picea reflected tradeoffs between competitive vs. cold-tolerant strategies. Fagus performance declined with altitudinal increases in climate sensitivity, but improved under interspecific competition. Picea growth increased towards the species’ lower range limit, but declined under interspecific competition. Warmer temperatures likely benefit competitively stronger species at mid elevations and thus imply range reductions for alpine conifers.

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1.Demographic events such as the birth and death of organisms are ubiquitous in nature. Disentangling the processes that underlie the demographic dynamics of species is fundamental to understanding how biodiversity is organized and will be re‐organized at multiple scales. 2.To provide new insights on multispecies demographic dynamics, I designed the present study to focus on local and biogeographic influences on mortality and recruitment rates for tree populations in forest biomes throughout the Japanese archipelago. 3.Most populations exhibited mortality that fell within the 95% confidence intervals of a neutral model (i.e., the expectation of demographic stochasticity). However, there were also important determinants that make population dynamics to deviate from the neutral expectation. Interspecific niche differentiation was important to reduce the mortality rate, regardless of the local rarity or ubiquity of a species. Although intraspecific aggregation that caused density‐dependent mortality was only significant for locally abundant species, the degree of isolation from a species’ central or optimal range determined mortality only for locally rare species. These differences between rare and common species provide important empirical quantification of aspects of population dynamics that have been less accounted for in ecology and biogeography studies. 4.Synthesis:Unifying different theories such as those rooted in local‐scale community ecology and macro‐scale biogeography is important. At this juncture, this study emphasises that disentangling the interactive roles of demographic stochasticity and determinism that operate at different scales would be a clue to advance the field of ecology both in theory and practice. This article is protected by copyright. All rights reserved.
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The demand for large-scale and long-term information on tree growth is increasing rapidly as environmental change research strives to quantify and forecast the impacts of continued warming on forest ecosystems. This demand, combined with the now quasi-global availability of tree-ring observations, has inspired researchers to compile large tree-ring networks to address continental or even global-scale research questions. However, these emergent spatial objectives contrast with paleo-oriented research ideas that have guided the development of many existing records. A series of challenges related to how, where, and when samples have been collected is complicating the transition of tree rings from a local to a global resource on the question of tree growth. Herein, we review possibilities to scale tree-ring data (A) from the sample to the whole tree, (B) from the tree to the site, and (C) from the site to larger spatial domains. Representative tree-ring sampling supported by creative statistical approaches is thereby key to robustly capture the heterogeneity of climate-growth responses across forested landscapes. We highlight the benefits of combining the temporal information embedded in tree rings with the spatial information offered by forest inventories and earth observations to quantify tree growth and its drivers. In addition, we show how the continued development of mechanistic tree-ring models can help address some of the non-linearities and feedbacks that complicate making inference from tree-ring data. By embracing scaling issues, the discipline of dendrochronology will greatly increase its contributions to assessing climate impacts on forests and support the development of adaptation strategies. https://authors.elsevier.com/c/1XWsP-4PRq7xR (free access until Sep 27)
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Primary forests are characterized by high vertical and horizontal stand diversity, which provides habitat for a diverse range of species with complex habitat requirements. Detailed knowledge of related ecological processes and habitat development of primary forest species are essential to inform forest management and biodiversity conservation decisions, but relationships are not well documented. We collected dendrochronological data and inventoried numerous structural elements in permanent plots throughout the primary temperate forests within the Carpathian Mountains. We fit and compared multiple predictive models to quantify the importance of 200 years of natural disturbance dynamics on the occurrence probability of an umbrella species – the capercaillie (Tetrao urogallus). We showed that a mixed-severity disturbance regime ranging from low through moderate to high severity disturbances is required to generate diverse forest habitats suitable for capercaillie. The variation in natural disturbance severity and its timing promoted key structural habitat elements, such as low natural regeneration density, low mature tree density, high ground vegetation cover, availability of forest gaps, and abundance of standing deadwood. This study demonstrates the importance of natural disturbance in maintaining the variety of conditions necessary to support primary forest specialist species. Managers of protected areas should be mindful that natural disturbances generate habitat for the capercaillie in mountain Norway spruce forests. Further intervention is unnecessary. Conservation planning and forest reserve design should shift focus to the large-scale spatial requirements needed to ensure that a wide range of forest developmental phases are represented in protected areas.
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Knowledge of the functional consequences of biodiversity is increasing through studies of both experimental systems and natural systems. Community assembly theory has also helped to reveal the causes of biodiversity organization. However, the causes and consequences of biodiversity have been discussed in parallel and simultaneous consideration of both has been limited, even though they are both influenced by regional environmental conditions. To understand the relationship between biodiversity and productivity, I focused on the linkages between the number of tree species and biomass productivity across forest biomes under a range of bioclimatic conditions. I found that high tree diversity generally increased productivity. This was primarily due to a selection process that results from a high probability of having high-performance species and their dominance at high diversity, regardless of the biome. In less-productive biomes, the residual importance of diversity, which likely reflects other forms of biological interactions (including species complementarity), increased productivity. These findings of differential diversity effects under different environmental conditions are consistent with the existing theory of community assembly, which predicts a shift in the assembly process from stochasticity to determinism with increasing environmental harshness. Analyses based on functional trait diversity also supported this theory: stochastic assembly (resulting in the selection effect) and deterministic assembly (possibly resulting from interspecific niche differences) became more important in productive and less-productive biomes, respectively. Synthesis. Increasing our understanding of the causalities between diversity and other characteristics, such as productivity, is crucial, particularly for forest ecosystems, because of the increasing interest in productivity-related ecosystem services supported by diverse assemblages of trees. © 2017 The Author. Journal of Ecology
Article
Climate is widely assumed to influence physiological and demographic processes in trees, and hence forest composition, biomass and range limits. Growth in trees is an important barometer of climate change impacts on forests as growth is highly correlated with other demographic processes including tree mortality and fecundity. 2.We investigated the main drivers of diameter growth for five common tree species occurring in the Rocky Mountains of the western United States using non-linear regression methods. We quantified growth at the individual tree level from tree core samples collected across broad environmental gradients. We estimated the effects of both climate variation and biotic interactions on growth processes and tested for evidence that disjunct populations of a species respond differentially to climate. 3.Relationships between tree growth and climate varied by species and location. Growth in all species responded positively to increases in annual moisture up to a threshold level. Modest linear responses to temperature, both positive and negative, were observed at many sites. However, model results also revealed evidence for differentiated responses to local site conditions in all species. In severe environments in particular, growth responses varied non-linearly with temperature. For example, in northerly cold locations pronounced positive growth responses to increasing temperatures were observed. In warmer southerly climates, growth responses were unimodal, declining markedly above a threshold temperature level. 4.Net effects from biotic interactions on diameter growth were negative for all study species. Evidence for facilitative effects was not detected. For some species, competitive effects more strongly influenced growth performance than climate. Competitive interactions also modified growth responses to climate to some degree. 6.Synthesis. These analyses suggest that climate change will have complex, species specific effects on tree growth in the Rocky Mountains due to non-linear responses to climate, differentiated growth processes that vary by location and complex species interactions that impact growth and potentially modify responses to climate. Thus, robust model simulations of future growth responses to climate trends may need to integrate realistic scenarios of neighborhood effects as well as variability in tree performance attributed to differentiated populations. This article is protected by copyright. All rights reserved.
Article
Climate and competition are often presented from two opposing views of the dominant driver of individual tree growth and species distribution in temperate forests, such as those in the eastern United States. Previous studies have provided abundant evidence indicating that both factors influence tree growth, and we argue that these effects are not independent of one another and rather that interactions between climate, competition, and size best describe tree growth. To illustrate this point, we describe the growth responses of five common eastern tree species to interacting effects of temperature, precipitation, competition, and individual size using maximum likelihood estimation. Models that explicitly include interactions among these four factors explained over half of the variance in annual growth for four out of five species using annual climate. Expanding temperature and precipitation analyses to include seasonal interactions resulted in slightly improved models with a mean R-2 of 0.61 (SD 0.10). Growth responses to individual factors as well their interactions varied greatly among species. For example, growth sensitivity to temperature for Quercus rubra increased with maximum annual precipitation, but other species showed no change in sensitivity or slightly reduced annual growth. Our results also indicate that three-way interactions among individual stem size, competition, and temperature may determine which of the five co-occurring species in our study could have the highest growth rate in a given year. Continued consideration and quantification of interactions among climate, competition, and individual-based characteristics are likely to increase understanding of key biological processes such as tree growth. Greater parameterization of interactions between traditionally segregated factors such as climate and competition may also help build a framework to reconcile drivers of individual-based processes such as growth with larger-scale patterns of species distribution.
Article
A long-standing theory, originating with Darwin, suggests that abiotic forces set species range limits at high latitude, high elevation, and other abiotically 'stressful' areas, while species interactions set range limits in apparently more benign regions. This theory is of considerable importance for both basic and applied ecology, and while it is often assumed to be a ubiquitous pattern, it has not been clearly defined or broadly tested. We review tests of this idea and dissect how the strength of species interactions must vary across stress gradients to generate the predicted pattern. We conclude by suggesting approaches to better test this theory, which will deepen our understanding of the forces that determine species ranges and govern responses to climate change.
Article
Multiple hypotheses have been put forward to explain the rise of angiosperms to ecological dominance following the Cretaceous. A unified scheme incorporating all these theories appears to be an inextricable knot of relationships, processes and plant traits. Here, we revisit these hypotheses, categorising them within frameworks based on plant carbon economy, resistance to climatic stresses, nutrient economy, biotic interactions and diversification. We maintain that the enigma remains unresolved partly because our current state of knowledge is a result of the fragmentary nature of palaeodata. This lack of palaeodata limits our ability to draw firm conclusions. Nonetheless, based on consistent results, some inferences may be drawn. Our results indicate that a complex multidriver hypothesis may be more suitable than any single-driver theory. We contend that plant carbon economy and diversification may have played an important role during the early stages of gymnosperms replacement by angiosperms in fertile tropical sites. Plant tolerance to climatic stresses, plant nutrition, biotic interactions and diversification may have played a role in later stages of angiosperm expansion within temperate and harsh environments. The angiosperm knot remains partly tied, but to unravel it entirely will only be feasible if new discoveries are made by scientific communities.
Article
This review reports on the processes associated with carbon transfer and metabolism in leaves and growing organs and the role of long-distance transport and vascular links in the regulation of carbon partitioning in plants. Partitioning is clearly influenced by both the supply and demand for photosynthate and is moderated by vascular connections and the storage capacity of the leaves and pathway tissues. However there appears to be little more than circumstantial evidence either that short distance transfer of carbon within either the source or the sink, or that long-distance transport in the phloem, are limiting photosynthesis or growth directly. Although individual biochemical and physiological processes relating to photosynthesis and growth may be well understood, the factors primarily responsible for the control of carbon partitioning in plants have not been clearly identified. There is a need for a greater understanding of organ initiation and development (source and sink formation and potential size), the clear identification of whether growth is sink or source limited (including possible sink-controlled photosynthesis) and a detailed assessment of the role of storage in buffering developmental and environmental changes in sink and source activity. Also more information is needed on the role of hormonal and nutritional factors in regulating source and sink activity (organ interactions not directly associated with carbon transfer).
Article
There is a need for a consistent forest restoration strategy for the `Black Triangle', Central Europe. In the past 50 years, forests in this area have been heavily affected by industrial pollution. Recently, the amount of pollutants has decreased. This means that effective forest restoration programmes can be started. Forest decline must be seen as an ecological disturbance which cannot be solved by applying technical measures only. An ecosystem approach to forest restoration must be introduced into restoration policy and management. Basic principles and working methods of such an approach are briefly described and proposals are made for forest restoration policy, management and research in the area.
Article
The use of both linear and generalized linear mixed-effects models (LMMs and GLMMs) has become popular not only in social and medical sciences, but also in biological sciences, especially in the field of ecology and evolution. Information criteria, such as Akaike Information Criterion (AIC), are usually presented as model comparison tools for mixed-effects models. The presentation of variance explained' (R2) as a relevant summarizing statistic of mixed-effects models, however, is rare, even though R2 is routinely reported for linear models (LMs) and also generalized linear models (GLMs). R2 has the extremely useful property of providing an absolute value for the goodness-of-fit of a model, which cannot be given by the information criteria. As a summary statistic that describes the amount of variance explained, R2 can also be a quantity of biological interest. One reason for the under-appreciation of R2 for mixed-effects models lies in the fact that R2 can be defined in a number of ways. Furthermore, most definitions of R2 for mixed-effects have theoretical problems (e.g. decreased or negative R2 values in larger models) and/or their use is hindered by practical difficulties (e.g. implementation). Here, we make a case for the importance of reporting R2 for mixed-effects models. We first provide the common definitions of R2 for LMs and GLMs and discuss the key problems associated with calculating R2 for mixed-effects models. We then recommend a general and simple method for calculating two types of R2 (marginal and conditional R2) for both LMMs and GLMMs, which are less susceptible to common problems. This method is illustrated by examples and can be widely employed by researchers in any fields of research, regardless of software packages used for fitting mixed-effects models. The proposed method has the potential to facilitate the presentation of R2 for a wide range of circumstances.
Article
A number of parallels are shown between economic theory and plant resource usage. An outline of economic theory leads to 5 predictions concerning plant processes. Resource acquisition, storage, growth, resource loss and sexual reproduction are considered in the light of these predictions. Plants adjust phenology and life history patterns to acquire resources when they are cheap, store these internally and utilise them when conditions are favourable for growth. Plants continue to produce leaves (and perhaps roots) only until the marginal revenue from this increased production is equal to the marginal cost. Plants adjust allocation so that their limitation of growth is more nearly equal for all resources. Plants adjust physiologically to changes in resource availability to reduce extreme exchange ratios; the balance of internal reserves within the plant thereby approaches the proportions that are optimal for growth of most plants.-P.J.Jarvis
Article
Gymnosperms, and conifers in particular, are sometimes very productive trees yet angiosperms dominate most temperate and tropical vegetation. Current explanations for angiosperm success emphasize the advantages of insect pollination and seed dispersal by animals for the colonization of isolated habitats. Differences between gymnosperm and angiosperm reproductive and vegetative growth rates have been largely ignored. Gymnosperms are all woody, perennial and usually have long reproductive cycles. Their leaves are not as fully vascularized as those of angiosperms and are more stereotyped in shape and size. Gymnosperm tracheids are generally more resistant to solute flow than angiosperm vessels. A consequence of the less efficient transport system is that maximum growth rates of gymnosperms are lower than maximum growth rates of angiosperms in well lit, well watered habitats. Gymnosperm seedlings may be particularly uncompetitive since their growth depends on a single cohort of relatively inefficient leaves. Later, some gymnosperms attain a higher productivity than co-occurring angiosperm trees by accumulating several cohorts of leaves with a higher total leaf area.
Article
Summary • The ongoing enrichment of the atmosphere with CO2 raises the question of whether growth of forest trees, which represent close to 90% of the global biomass carbon, is still carbon limited at current concentrations of close to 370 p.p.m. As photosynthesis of C3 plants is not CO2-saturated at such concentrations, enhanced ‘source activity’ of leaves could stimulate ‘sink activity’ (i.e. growth) of plants, provided other resources and developmental controls permit. I explore current levels of non-structural carbon in trees in natural forests in order to estimate the potential for a carbon-driven stimulation of growth. • The concentration of non-structural carbohydrates (NSC) in tree tissues is considered a measure of carbon shortage or surplus for growth. A periodic reduction of NSC pools indicates either that carbon demand exceeds con-current supply, or that both source and sink activity are low. A steady, very high NSC concentration is likely to indicate that photosynthesis fully meets, or even exeeds, that needed for growth (surplus assimilates accumulate). • The analysis presented here considers data for mature trees in four climatic zones: the high elevation treeline (in Mexico, the Alps and Northern Sweden), a temperate lowland forest of central Europe, Mediterranean sclerophyllous woodland and a semideciduous tropical forest in Panama. • In all four climatic regions, periods of reduced or zero growth show maximum C-loading of trees (source activity exceeding demand), except for dry midsummer in the Mediterranean. NSC pools are generally high throughout the year, and are not significantly affected by mass fruiting episodes. • It is concluded that, irrespective of the reason for its periodic cessation, growth does not seem to be limited by carbon supply. Instead, in all the cases examined, sink activity and its direct control by the environment or developmental constraints, restricts biomass production of trees under current ambient CO2 concentrations. • The current carbohydrate charging of mature wild trees from the tropics to the cold limit of tree growth suggests that little (if any) leeway exists for further CO2-fertilization effects on growth.
Article
The expected upward shift of trees due to climate warming is supposed to be a major threat to range-restricted high-altitude species by shrinking the area of their suitable habitats. Our projections show that areas of endemism of five taxonomic groups (vascular plants, snails, spiders, butterflies, and beetles) in the Austrian Alps will, on average, experience a 77% habitat loss even under the weakest climate change scenario (+1.8 °C by 2100). The amount of habitat loss is positively related with the pooled endemic species richness (species from all five taxonomic groups) and with the richness of endemic vascular plants, snails, and beetles. Owing to limited postglacial migration, hotspots of high-altitude endemics are situated in rather low peripheral mountain chains of the Alps, which have not been glaciated during the Pleistocene. There, tree line expansion disproportionally reduces habitats of high-altitude species. Such legacies of climate history, which may aggravate extinction risks under future climate change have to be expected for many temperate mountain ranges.
Article
Forest responses to climate change will depend on demographic impacts in the context of competition. Current models used to predict species responses, termed climate envelope models (CEMs), are controversial, because (i) calibration and prediction are based on correlations in space (CIS) between species abundance and climate, rather than responses to climate change over time (COT), and (ii) they omit competition. To determine the relative importance of COT, CIS, and competition for light, we applied a longitudinal analysis of 27 000 individual trees over 6–18 years subjected to experimental and natural variation in risk factors. Sensitivities and climate and resource tracking identify which species are vulnerable to these risk factors and in what ways. Results show that responses to COT differ from those predicted based on CIS. The most important impact is the effect of spring temperature on fecundity, rather than any input variable on growth or survival. Of secondary importance is growing season moisture. Species in the genera Pinus, Ulmus, Magnolia, and Fagus are particularly vulnerable to climate variation. However, the effect of competition on growth and mortality risk exceeds the effects of climate variation in space or time for most species. Because sensitivities to COT and competition are larger than CIS, current models miss the most important effects. By directly comparing sensitivity to climate in time and space, together with competition, the approach identifies which species are sensitive to climate change and why, including the heretofore overlooked impact on fecundity.
Article
Studies on Fagus sylvatica show that growth in populations toward the southern limit of this species' distribution is limited strongly by drought. Warming temperatures in the Mediterranean region are expected to exacerbate drought where they are not accompanied by increases in precipitation. We studied levels of annual growth in mature F. sylvatica trees over the last half-century in the Montseny Mountains in Catalonia (northeast Spain). Our results show significantly lower growth of mature trees at the lower limit of this species' distribution when compared with trees at higher altitudes. Growth at the lower Fagus limit is characterized by a rapid recent decline starting in approximately 1975. By 2003, growth of mature trees had fallen by 49% when compared with predecline levels. This is not an age-related phenomenon, nor is it seen in comparable populations at higher altitudes. Analysis of climate-growth relationships suggests that the observed decline in growth is a result of warming temperatures and that, as precipitation in the region has not increased, precipitation is now insufficient to ameliorate the negative effects of increased temperatures on tree growth. As the climate-response of the studied forest is comparable with that of F. sylvatica forests in other southern European regions, it is possible that this growth decline is a more widespread phenomenon. Warming temperatures may lead to a rapid decline in the growth of range-edge populations and a consequent retreat of the species distribution in southern Europe. Assessment of long-term growth trends across the southern range edge of F. sylvatica therefore merits further attention.
Article
Summary 1. Understanding the factors influencing tree growth is central to forest ecology because of the significance of growth to forest structure and biomass. One of the simplest, yet most controversial growth models, proposed by Enquist and colleagues, predicts that stem-diameter growth scales as the one-third power of stem diameter. Recent analyses of large-scale data sets have challenged the generality of this theory and highlighted the influence of resource competition on the scaling of growth with size. 2. Here we explore the factors regulating the diameter growth of 3334 trees of mountain beech ( Nothofagus solandri var. cliffortioides ) growing in natural single-species forests in New Zealand. Maximum-likelihood modelling was used to quantify the influences of tree size, altitude, the basal area of taller neighbours ( B L ) and the basal area of all neighbours ( B T ) on growth. Our interpretation of the models assumed that taller neighbours compete for light whereas all neighbours compete for nutrients. 3. The regression analyses indicate that competition for light has a strong influence on the growth of small trees, whereas competition for nutrients affects trees of all sizes. These findings are consistent with experimental manipulation studies showing that competition for light and nutrients inhibits the growth of small mountain beech trees, and fertilizer application studies showing that nitrogen limits the growth of large trees. 4. Tree growth declined with altitude. The regression analyses suggest that the intensity of light competition also declines with altitude, when trees with similar B T and B L values were compared along the gradient. These results are consistent with observations that trees become stunted and have more open canopies at high altitudes. 5. Our study is the first to build the effects of competition and environment into Enquist's model of tree growth. We show that competitive interactions alter the scaling of mean growth rate with size, whereas altitude does not influence the scaling of potential growth rate with size.
Article
In this paper, we have reviewed how the hydraulic design of trees influences the movement of water from roots to leaves. The hydraulic architecture of trees can limit their water relations, gas exchange throughout the crown of trees, the distribution of trees over different habitats and, perhaps, even tbe maximum height that a particular species can achieve. Parameters of particular importance include: (1) tbe vulnerabihty of stems to drought induced cavitation events because cavitation reduces the hydraulic conductance of stems, (2) the leaf specific conductivity of stems because it determines the pressure gradients and most negative water potentials needed to sustain evaporation from leaves, (3) the water storage capacity of tissues because this might determine the ability of trees to survive long drought periods. All of these parameters are determined by the structure and function of anatomical components of trees. Some of the ecological and physiological trade-offs of specific structures are discussed.
Article
The wide size range of conifer tracheids and angiosperm vessels has important consequences for function. In both conduit types, bigger is better for conducting efficiency. The gain in efficiency with size is maximized by the control of conduit shape, which balances end-wall and lumen resistances. Although vessels are an order of magnitude longer than tracheids of the same diameter, they are not necessarily more efficient because they lack the low end-wall resistance of tracheids with torus-margo pits. Instead, vessels gain conducting efficiency over tracheids by achieving wider maximum diameters. End-walls contributed 56-64% to total xylem resistance in both conduit types, indicating that length limits conducting efficiency. Tracheid dimensions may be more limited by unicellularity and the need to supply strength to homoxylous wood than by the need to protect against cavitation. In contrast, the greater size of the multicellular vessel is facilitated by fibers that strengthen heteroxylous wood. Vessel dimensions may be most limited by the need to restrict intervessel pitting and cavitation by air-seeding. Stressful habitats that promote narrow vessels should favor coexistence of conifers and angiosperms. The evolution of vessels in angiosperm wood may have required early angiosperms to survive a phase of mechanic and hydraulic instability.
A variable span smoother (No. LCS-TR-5). Stanford Univ CA lab for computational statistics
  • J H Friedman
Friedman, J. H. (1984). A variable span smoother (No. LCS-TR-5). Stanford Univ CA lab for computational statistics.