The identification of patterns in life-history strategies across the tree of life is essential to our prediction of population persistence, extinction, and diversification. Plants exhibit a wide ...range of patterns of longevity, growth, and reproduction, but the general determinants of this enormous variation in life history are poorly understood. We use demographic data from 418 plant species in the wild, from annual herbs to supercentennial trees, to examine how growth form, habitat, and phylogenetic relationships structure plant life histories and to develop a framework to predict population performance. We show that 55% of the variation in plant life-history strategies is adequately characterized using two independent axes: the fast–slow continuum, including fast-growing, short-lived plant species at one end and slow-growing, long-lived species at the other, and a reproductive strategy axis, with highly reproductive, iteroparous species at one extreme and poorly reproductive, semelparous plants with frequent shrinkage at the other. Our findings remain consistent across major habitats and are minimally affected by plant growth form and phylogenetic ancestry, suggesting that the relative independence of the fast–slow and reproduction strategy axes is general in the plant kingdom. Our findings have similarities with how life-history strategies are structured in mammals, birds, and reptiles. The position of plant species populations in the 2D space produced by both axes predicts their rate of recovery from disturbances and population growth rate. This life-history framework may complement trait-based frameworks on leaf and wood economics; together these frameworks may allow prediction of responses of plants to anthropogenic disturbances and changing environments.
Tree‐ring analysis is often used to assess long‐term trends in tree growth. A variety of growth‐trend detection methods (GDMs) exist to disentangle age/size trends in growth from long‐term growth ...changes. However, these detrending methods strongly differ in approach, with possible implications for their output. Here, we critically evaluate the consistency, sensitivity, reliability and accuracy of four most widely used GDMs: conservative detrending (CD) applies mathematical functions to correct for decreasing ring widths with age; basal area correction (BAC) transforms diameter into basal area growth; regional curve standardization (RCS) detrends individual tree‐ring series using average age/size trends; and size class isolation (SCI) calculates growth trends within separate size classes. First, we evaluated whether these GDMs produce consistent results applied to an empirical tree‐ring data set of Melia azedarach, a tropical tree species from Thailand. Three GDMs yielded similar results – a growth decline over time – but the widely used CD method did not detect any change. Second, we assessed the sensitivity (probability of correct growth‐trend detection), reliability (100% minus probability of detecting false trends) and accuracy (whether the strength of imposed trends is correctly detected) of these GDMs, by applying them to simulated growth trajectories with different imposed trends: no trend, strong trends (−6% and +6% change per decade) and weak trends (−2%, +2%). All methods except CD, showed high sensitivity, reliability and accuracy to detect strong imposed trends. However, these were considerably lower in the weak or no‐trend scenarios. BAC showed good sensitivity and accuracy, but low reliability, indicating uncertainty of trend detection using this method. Our study reveals that the choice of GDM influences results of growth‐trend studies. We recommend applying multiple methods when analysing trends and encourage performing sensitivity and reliability analysis. Finally, we recommend SCI and RCS, as these methods showed highest reliability to detect long‐term growth trends.
Climate change effects on growth rates of tropical trees may lead to alterations in carbon cycling of carbon-rich tropical forests. However, climate sensitivity of broad-leaved lowland tropical trees ...is poorly understood. Dendrochronology (tree-ring analysis) provides a powerful tool to study the relationship between tropical tree growth and annual climate variability. We aimed to establish climate–growth relationships for five annual-ring forming tree species, using ring-width data from 459 canopy and understory trees from a seasonal tropical forest in western Thailand. Based on 183/459 trees, chronologies with total lengths between 29 and 62 years were produced for four out of five species. Bootstrapped correlation analysis revealed that climate–growth responses were similar among these four species. Growth was significantly negatively correlated with current-year maximum and minimum temperatures, and positively correlated with dry-season precipitation levels. Negative correlations between growth and temperature may be attributed to a positive relationship between temperature and autotrophic respiration rates. The positive relationship between growth and dry-season precipitation levels likely reflects the strong water demand during leaf flush. Mixed-effect models yielded results that were consistent across species: a negative effect of current wet-season maximum temperatures on growth, but also additive positive effects of, for example, prior dry-season maximum temperatures. Our analyses showed that annual growth variability in tropical trees is determined by a combination of both temperature and precipitation variability. With rising temperature, the predominantly negative relationship between temperature and growth may imply decreasing growth rates of tropical trees as a result of global warming.
Stable isotopes in tropical tree rings van der Sleen, Peter; Zuidema, Pieter A.; Pons, Thijs L.
Functional ecology,
September 2017, Letnik:
31, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Summary
The notion that many tropical tree species form annual growth rings has triggered research on their growth and its environmental drivers over long periods of time. Even more recently, a large ...number of studies have also analysed the natural abundance of stable isotopes in tropical tree rings. The rapid developments in this young field call for a review. Here, we focus on stable isotopes of carbon (13C), oxygen (18O) and nitrogen (15N).
We start by explaining how environmental and physiological effects define the isotopic composition of wood in tropical trees. Abundance of 13C is mainly driven by water, light and nutrient availability. Here 18O values are chiefly determined by those of rainwater and additionally by rooting depth and factors determining leaf water evaporation. The 15N levels are determined by the 15N signature of nitrogen uptake, which in turn depends in complex ways on various processes in the nitrogen cycle.
We then discuss methodological aspects of isotopes studies in tropical tree rings. An important requirement is that rings are reliably dated. Furthermore, a key methodological concern is that temporal changes in isotopic values can be confounded by tree‐size driven changes, which can be avoided by sampling from a fixed diameter range or accounted for statistically.
Next, 50 studies are reviewed that measured stable isotopes of C, O, and/or N in tree rings of a total of 85 tropical tree species. Temporal variation in both δ13C and δ18O was correlated with precipitation and El Niño Southern Oscillation variability. Seasonality in δ13C and δ18O was successfully used for delimiting visually non‐distinct annual rings. Tropical tree responses to increasing atmospheric CO2 were effectively quantified, using δ13C as a measure of intrinsic water use efficiency. And finally, anthropogenic changes in the nitrogen cycle in tropical forests have been inferred from δ15N.
We conclude with methodological and ecophysiological recommendations for isotope studies in tropical tree rings. Future perspectives include the analysis of intramolecular isotopic distributions of isotopes in glucose that can advance our understanding of environmental effects on tropical tree physiology. Finally, we recommend that tropical tree ring isotope data are deposited in open access databases.
A lay summary is available for this article.
Lay Summary
Realistic forecasting of forest responses to climate change critically depends on key advancements in global vegetation modelling. Compared with traditional ‘big-leaf’ models that simulate forest ...stands, ‘next-generation’ vegetation models aim to track carbon-, light-, water-, and nutrient-limited growth of individual trees. Wood biology can play an important role in delivering the required knowledge at tissue-to-individual levels, at minute-to-century scales and for model parameterization and benchmarking. We propose a wood biology research agenda that contributes to filling six knowledge gaps: sink versus source limitation, drivers of intra-annual growth, drought impacts, functional wood traits, dynamic biomass allocation, and nutrient cycling. Executing this agenda will expedite model development and increase the ability of models to forecast global change impact on forest dynamics.
‘Next-generation’ global vegetation models track the performance of individual trees as a function of light, carbon, water, and nutrient availability, explicitly include forest demography, and simulate disturbances. This model development involves a major increase in complexity and in the amount of simulated processes.
The development and quality of next-generation models critically depends on the availability of insights to simulate these additional processes. Yet, knowledge on key processes such as sub-annual tree growth, source- versus sink-limited growth, dynamic biomass allocation, drought effects, and nutrient cycling is currently poorly available.
Wood biology can importantly contribute to filling this knowledge gap by providing knowledge on crucial processes for tree functioning. This field of science is well positioned due to recent progress in concepts, measuring tools, and analyses.
Tropical forests will experience major changes in environmental conditions this century. Understanding their responses to such changes is crucial to predicting global carbon cycling. Important ...knowledge gaps exist: the causes of recent changes in tropical forest dynamics remain unclear and the responses of entire tropical trees to environmental changes are poorly understood. In this Opinion article, we argue that filling these knowledge gaps requires a new research strategy, one that focuses on trees instead of leaves or communities, on long-term instead of short-term changes, and on understanding mechanisms instead of documenting changes. We propose the use of tree-ring analyses, stable-isotope analyses, manipulative field experiments, and well-validated simulation models to improve predictions of forest responses to global change.
Overhunting in tropical forests reduces populations of vertebrate seed dispersers. If reduced seed dispersal has a negative impact on tree population viability, overhunting could lead to altered ...forest structure and dynamics, including decreased biodiversity. However, empirical data showing decreased animal-dispersed tree abundance in overhunted forests contradict demographic models which predict minimal sensitivity of tree population growth rate to early life stages. One resolution to this discrepancy is that seed dispersal determines spatial aggregation, which could have demographic consequences for all life stages. We tested the impact of dispersal loss on population viability of a tropical tree species, Miliusa horsfieldii, currently dispersed by an intact community of large mammals in a Thai forest. We evaluated the effect of spatial aggregation for all tree life stages, from seeds to adult trees, and constructed simulation models to compare population viability with and without animal-mediated seed dispersal. In simulated populations, disperser loss increased spatial aggregation by fourfold, leading to increased negative density dependence across the life cycle and a 10-fold increase in the probability of extinction. Given that the majority of tree species in tropical forests are animal-dispersed, overhunting will potentially result in forests that are fundamentally different from those existing now.
High‐elevation forests are experiencing high rates of warming, in combination with CO2 rise and (sometimes) drying trends. In these montane systems, the effects of environmental changes on tree ...growth are also modified by elevation itself, thus complicating our ability to predict effects of future climate change. Tree‐ring analysis along an elevation gradient allows quantifying effects of gradual and annual environmental changes. Here, we study long‐term physiological (ratio of internal to ambient CO2, i.e., Ci/Ca and intrinsic water‐use efficiency, iWUE) and growth responses (tree‐ring width) of Himalayan fir (Abies spectabilis) trees in response to warming, drying, and CO2 rise. Our study was conducted along elevational gradients in a dry and a wet region in the central Himalaya. We combined dendrochronology and stable carbon isotopes (δ13C) to quantify long‐term trends in Ci/Ca ratio and iWUE (δ13C‐derived), growth (mixed‐effects models), and evaluate climate sensitivity (correlations). We found that iWUE increased over time at all elevations, with stronger increase in the dry region. Climate–growth relations showed growth‐limiting effects of spring moisture (dry region) and summer temperature (wet region), and negative effects of temperature (dry region). We found negative growth trends at lower elevations (dry and wet regions), suggesting that continental‐scale warming and regional drying reduced tree growth. This interpretation is supported by δ13C‐derived long‐term physiological responses, which are consistent with responses to reduced moisture and increased vapor pressure deficit. At high elevations (wet region), we found positive growth trends, suggesting that warming has favored tree growth in regions where temperature most strongly limits growth. At lower elevations (dry and wet regions), the positive effects of CO2 rise did not mitigate the negative effects of warming and drying on tree growth. Our results raise concerns on the productivity of Himalayan fir forests at low and middle (<3,300 m) elevations as climate change progresses.
Himalayan forests are experiencing exceptionally rapid warming during the last decades, yet knowledge on their physiological and growth responses to climate change is limited. Using dendrochronology and tree‐ring stable carbon‐isotope data of Himalayan fir, we found intrinsic water‐use efficiency has increased consistently at all elevations in both dry and wet regions during the past century. Warming has favored tree growth at higher elevations in wet regions, but growth reductions at low/middle elevations in both regions suggest that negative effects of warming and drying overruled positive CO2‐fertilization effects, thus raising concerns on the productivity of Himalayan fir forests under future climate change.
Ecology What are the ecological consequences of logging in a tropical forest? A detailed assessment of vegetation growth, bird and mammal numbers, and energy flows in logged and unlogged forests ...offers some surprising findings. ...the surrounding vegetation has a role, too. Comparative research will be needed to evaluate how these and other factors might modify the shifts in ecosystem energetics that are driven by logging. ...the study by Malhi and colleagues could mark the start of a new field - investigations of ecosystem energetics in human-modified forests.
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