ARE FUNCTIONAL TRAITS GOOD PREDICTORS OF DEMOGRAPHIC RATES? EVIDENCE FROM FIVE NEOTROPICAL FORESTS

Plant growth rates drive ecosystem productivity and are a central element of plant ecological strategies. For seedlings grown under controlled conditions, a large literature has firmly identified the functional traits that drive interspecific variation in growth rate. For adult plants, the corresponding knowledge is surprisingly poorly understood. Until recently it was widely assumed that the key trait drivers would be the same (e.g. specific leaf area, or SLA), but an increasing number of papers has demonstrated this not to be the case, or not generally so. New theory has provided a prospective basis for understanding these discrepancies. Here we quantified relationships between stem diameter growth rates and functional traits of adult woody plants for 41 species in an Australian tropical rainforest. From various cost-benefit considerations, core predictions included that: (i) photosynthetic rate would be positively related to growth rate; (ii) SLA would be unrelated to growth rate (unlike in seedlings where it is positively related to growth); (iii) wood density would be negatively related to growth rate; and (iv) leaf mass:sapwood mass ratio (LM:SM) in branches (analogous to a benefit:cost ratio) would be positively related to growth rate. All our predictions found support, particularly those for LM:SM and wood density; photosynthetic rate was more weakly related to stem diameter growth rates. Specific leaf area was convincingly correlated to growth rate, in fact negatively. Together, SLA, wood density and LM:SM accounted for 52 % of variation in growth rate among these 41 species, with each trait contributing roughly similar explanatory power. That low SLA species can achieve faster growth rates than high SLA species was an unexpected result but, as it turns out, not without precedent, and easily understood via cost-benefit theory that considers whole-plant allocation to different tissue types. Branch-scale leaf:sapwood ratio holds promise as an easily measurable variable that may help to understand growth rate variation. Using cost-benefit approaches teamed with combinations of leaf, wood and allometric variables may provide a path towards a more complete understanding of growth rates under field conditions.

A trade-off between growth and mortality rates characterizes tree species in closed canopy forests. This trade-off is maintained by inherent differences among species and spatial variation in light availability caused by canopy-opening disturbances. We evaluated conditions under which the trade-off is expressed and relationships with four key functional traits for 103 tree species from Barro Colorado Island, Panama. The trade-off is strongest for saplings for growth rates of the fastest growing individuals and mortality rates of the slowest growing individuals (r2 = 0.69), intermediate for saplings for average growth rates and overall mortality rates (r2 = 0.46), and much weaker for large trees (r2 < or = 0.10). This parallels likely levels of spatial variation in light availability, which is greatest for fast- vs. slow-growing saplings and least for large trees with foliage in the forest canopy. Inherent attributes of species contributing to the trade-off include abilities to disperse, acquire resources, grow rapidly, and tolerate shade and other stresses. There is growing interest in the possibility that functional traits might provide insight into such ecological differences and a growing consensus that seed mass (SM), leaf mass per area (LMA), wood density (WD), and maximum height (H(max)) are key traits among forest trees. Seed mass, LMA, WD, and H(max) are predicted to be small for light-demanding species with rapid growth and mortality and large for shade-tolerant species with slow growth and mortality. Six of these trait-demographic rate predictions were realized for saplings; however, with the exception of WD, the relationships were weak (r2 < 0.1 for three and r2 < 0.2 for five of the six remaining relationships). The four traits together explained 43-44% of interspecific variation in species positions on the growth-mortality trade-off; however, WD alone accounted for > 80% of the explained variation and, after WD was included, LMA and H(max) made insignificant contributions. Virtually the full range of values of SM, LMA, and H(max) occurred at all positions on the growth-mortality trade-off. Although WD provides a promising start, a successful trait-based ecology of tropical forest trees will require consideration of additional traits.

Plant growth rates strongly determine ecosystem productivity and are a central element of plant ecological strategies. For laboratory and glasshouse‐grown seedlings, specific leaf area (SLA; ratio of leaf area to mass) is a key driver of interspecific variation in growth rate (GR). Consequently, SLA is often assumed to drive GR variation in field‐grown adult plants. However, there is an increasing evidence that this is not the general case. This suggests that GR – SLA relationships (and perhaps those for other traits) may vary depending on the age or size of the plants being studied. Here we investigated GR – trait relationships and their size dependence among 17 woody species from an open‐canopy, fire‐prone savanna in northern Australia. We tested the predictions that SLA and stem diameter growth rate would be positively correlated in saplings but unrelated in adults while, in both age classes, faster‐GR species would have higher light‐saturated photosynthetic rate (Asat), higher leaf nutrient concentrations, higher branch‐scale biomass allocation to leaf versus stem tissues and lower wood density (WD). SLA showed no relationship to stem diameter GR, even in saplings, and the same was true of leaf N and P concentrations, and WD. However, branch‐scale leaf:stem allocation was strongly related to GR in both age groups, as was Asat. Together, these two traits accounted for up to 80% of interspecific variation in adult GR, and 41% of sapling GR. Asat is rarely measured in field‐based GR studies, and this is the first report of branch‐scale leaf:stem allocation (analogous to a benefit:cost ratio) in relation to plant growth rate. Our results suggest that we may yet find general trait‐drivers of field growth rates, but SLA will not be one.

Summary1. Functional traits are posited to explain interspecific differences in performance, but these relationships are difficult to describe for long‐lived organisms such as trees, which exhibit strong ontogenetic changes in demographic rates. Here, we use a size‐dependent model of tree growth to test the extent to which of 17 functional traits related to leaf and stem economics, adult stature and seed size predict the ontogenetic trajectory of tree growth.2. We used a Bayesian modelling framework to parameterize and contrast three size‐dependent diameter growth models using 16 years of census data from 5524 individuals of 50 rain forest tree species: a size‐dependent model, a size‐dependent model with species‐specific parameters and a size‐dependent model based on functional traits.3. Most species showed clear hump‐shaped ontogenetic growth trajectories and, across species, maximum growth rate varied nearly tenfold, from 0.58 to 5.51 mm year−1. Most species attained their maximum growth at 60% of their maximum size, whereas the magnitude of ontogenetic changes in growth rate varied widely among species.4. The Trait‐Model provided the best compromise between explained variance and model parsimony and needed considerably fewer parameters than the model with species terms.5. Stem economics and adult stature largely explained interspecific differences in growth strategy. Maximum absolute diameter growth rates increased with increasing adult stature and leaf δ13C and decreased with increasing wood density. Species with light wood had the greatest potential to modulate their growth, resulting in hump‐shaped ontogenetic growth curves. Seed size and leaf economics, generally thought to be of paramount importance for plant performance, had no significant relationships with the growth parameters.6. Synthesis. Our modelling approach offers a promising way to link demographic parameters to their functional determinants and hence to predict growth trajectories in species‐rich communities with little parameter inflation, bridging the gap between functional ecology and population demography.

Understanding the relationships between species' demography and functional traits is crucial for gaining a mechanistic understanding of community dynamics. While leaf morphology represents a key functional dimension for plants worldwide (i.e., the leaf economics spectrum), its ability to explain variation in trees' life history strategies remains limited. Plant growth is influenced by both leaf morphology and allocation; hence, incorporating both dimensions is essential but rarely done. Additionally, trait–performance relationships have mainly been studied in tropical communities, leaving gaps in our understanding of temperate forests where different seasonality patterns may alter these relationships. We examined whether species' leaf area index (leaf area per crown size, LAI), a measure of leaf allocation, explains the variation of juvenile tree species' potential growth rates in a winter‐deciduous broadleaf forest. LAI has not been characterized as a species‐level trait, but its ability to predict plant productivity at the ecosystem scale highlights its potential for explaining plant growth. We evaluated species' maximum LAI both individually and in conjunction with wood density (WD) and leaf mass per area (LMA). We expected that models would improve when both leaf morphology (LMA) and leaf allocation (LAI) were included and that species with denser crowns would have higher potential growth rates. LAI and LMA were significant predictors of growth but only when both were incorporated, and together explained a high proportion of species' growth variations (R2adj = 0.59). We found evidence of a trade‐off between LAI and LMA, with a negative relationship between them and each having a positive influence on species' growth, suggesting that there are multiple allocation strategies to achieve fast growth. A surprisingly positive LMA–growth relationship contrasts with observations from tropical forests. We did not find significant relationships with WD in this forest. Our results highlight that incorporating leaf allocation improves models of trait–performance relationships. They also suggest, in agreement with the limited literature, that temperate forests may exhibit different trait–performance relationships from those of tropical forests, where LMA is negatively related to growth and WD is often important. Clarifying the details and contexts of trait–performance relationships is crucial for applying the functional trait framework to understanding community structure and dynamics of forests globally.

Summary Plant functional traits, in particular specific leaf area (SLA), wood density and seed mass, are often good predictors of individual tree growth rates within communities. Individuals and species with high SLA, low wood density and small seeds tend to have faster growth rates. If community‐level relationships between traits and growth have general predictive value, then similar relationships should also be observed in analyses that integrate across taxa, biogeographic regions and environments. Such global consistency would imply that traits could serve as valuable proxies for the complex suite of factors that determine growth rate, and, therefore, could underpin a new generation of robust dynamic vegetation models. Alternatively, growth rates may depend more strongly on the local environment or growth–trait relationships may vary along environmental gradients. We tested these alternative hypotheses using data on 27 352 juvenile trees, representing 278 species from 27 sites on all forested continents, and extensive functional trait data, 38% of which were obtained at the same sites at which growth was assessed. Data on potential evapotranspiration (PET), which summarizes the joint ecological effects of temperature and precipitation, were obtained from a global data base. We estimated size‐standardized relative height growth rates (SGR) for all species, then related them to functional traits and PET using mixed‐effect models for the fastest growing species and for all species together. Both the mean and 95th percentile SGR were more strongly associated with functional traits than with PET. PET was unrelated to SGR at the global scale. SGR increased with increasing SLA and decreased with increasing wood density and seed mass, but these traits explained only 3.1% of the variation in SGR. SGR–trait relationships were consistently weak across families and biogeographic zones, and over a range of tree statures. Thus, the most widely studied functional traits in plant ecology were poor predictors of tree growth over large scales. Synthesis. We conclude that these functional traits alone may be unsuitable for predicting growth of trees over broad scales. Determining the functional traits that predict vital rates under specific environmental conditions may generate more insight than a monolithic global relationship can offer.

Spatial and temporal variation in length‐at‐age and environmental factors affecting variation in growth rate of juvenile Atlantic salmonSalmo salarwere studied using data from a long‐term study in the River Stjørdalselva, central Norway. Mean annual instantaneous growth rate among 1+ and 2+year juvenile Atlantic salmon varied between 0·59 and 1·50 g g−1 year−1and mean instantaneous daily growth rate of young‐of‐the‐year (YOY) varied between 0·013 and 0·033 g g−1 day−1. Between year variation in growth was larger than the within year intra‐watercourse spatial variation. For YOY and 1+year Atlantic salmon, a major part of the observed between year variation in growth rates was explained by variation in mean daily water discharge and spring temperature. For 2+year juvenile Atlantic salmon, mean daily water discharge and cohort density were the only variables to significantly explain variation in growth rates. A large part of the within water‐course spatial variation could not be explained by temperature variations and juvenile Atlantic salmon in the uppermost areas of the river, experiencing the lowest ambient temperatures during the growth period, displayed the highest growth rates. Within the baselines set by temperature, biotic and abiotic factors connected to water flow regime and variation in food availability are suggested to be a major determinants of the temporal and spatial variation in juvenile Atlantic salmon growth rates.

How demographic factors lead to variation or change in growth rates can be investigated using life table response experiments (LTRE) based on structured population models. Traditionally, LTREs focused on decomposing the asymptotic growth rate, but more recently decompositions of annual 'realized' growth rates using 'transient' LTREs have gained in popularity. Transient LTREs have been used particularly to understand how variation in vital rates translate into variation in growth for populations under long-term study. For these, complete population models may be constructed to investigate how temporal variation in environmental drivers affect vital rates. Such investigations have usually come down to estimating covariate coefficients for the effects of environmental variables on vital rates, but formal ways of assessing how they lead to variation in growth rates have been lacking. We extend transient LTREs to further partition the contributions from vital rates into contributions from temporally varying factors that affect them. The decomposition allows one to compare the resultant effect on the growth rate of different environmental factors, as well as density dependence, which may each act via multiple vital rates. We also show how realized growth rates can be decomposed into separate components from environmental and demographic stochasticity. The latter is typically omitted in LTRE analyses. We illustrate these extensions with an integrated population model (IPM) for data from a 26 years study on northern wheatears (Oenanthe oenanthe), a migratory passerine bird breeding in an agricultural landscape. For this population, consisting of around 50-120 breeding pairs per year, we partition variation in realized growth rates into environmental contributions from temperature, rainfall, population density and unexplained random variation via multiple vital rates, and from demographic stochasticity. The case study suggests that variation in first year survival via the unexplained random component, and adult survival via temperature are two main factors behind environmental variation in growth rates. More than half of the variation in growth rates is suggested to come from demographic stochasticity, demonstrating the importance of this factor for populations of moderate size.

Previous articleNext article No AccessNotes and CommentsIs Interspecific Variation in Relative Growth Rate Positively Correlated with Biomass Allocation to the Leaves?Hendrik Poorter, and Hans LambersHendrik Poorter Search for more articles by this author , and Hans Lambers Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 138, Number 5Nov., 1991 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/285282 Views: 5Total views on this site Citations: 24Citations are reported from Crossref Copyright 1991 The University of ChicagoPDF download Crossref reports the following articles citing this article:Gabriela Woźniak, Damian Chmura, Marcin K. Dyderski, Agnieszka Błońska, Andrzej M. Jagodziński How different is the forest on post-coal mine heap regarded as novel ecosystem?, Forest Ecology and Management 515 (Jul 2022): 120205.https://doi.org/10.1016/j.foreco.2022.120205Maria Amélia Martins-Loução, Teresa Dias, Cristina Cruz Integrating Ecological Principles for Addressing Plant Production Security and Move beyond the Dichotomy ‘Good or Bad’ for Nitrogen Inputs Choice, Agronomy 12, no.77 (Jul 2022): 1632.https://doi.org/10.3390/agronomy12071632Maria Pepe, Loretta Gratani, Maria Fiore Crescente, Giacomo Puglielli, Laura Varone Daily Temperature Effect on Seedling Growth Dynamic of Three Invasive Alien Species, Frontiers in Plant Science 13 (Mar 2022).https://doi.org/10.3389/fpls.2022.837449Prakash Bhattarai, Zhoutao Zheng, Kuber Prasad Bhatta, Yagya Prasad Adhikari, Yangjian Zhang Climate-Driven Plant Response and Resilience on the Tibetan Plateau in Space and Time: A Review, Plants 10, no.33 (Mar 2021): 480.https://doi.org/10.3390/plants10030480Vanessa Buzzard, Sean T. Michaletz, Ye Deng, Zhili He, Daliang Ning, Lina Shen, Qichao Tu, Joy D. Van Nostrand, James W. Voordeckers, Jianjun Wang, Michael D. Weiser, Michael Kaspari, Robert B. Waide, Jizhong Zhou, Brian J. Enquist Continental scale structuring of forest and soil diversity via functional traits, Nature Ecology & Evolution 3, no.99 (Aug 2019): 1298–1308.https://doi.org/10.1038/s41559-019-0954-7Sarathi M. Weraduwage, Marcelo L. Campos, Yuki Yoshida, Ian T. Major, Yong-Sig Kim, Sang-Jin Kim, Luciana Renna, Fransisca C. Anozie, Federica Brandizzi, Michael F. Thomashow, Gregg A. Howe, Thomas D. Sharkey Molecular Mechanisms Affecting Cell Wall Properties and Leaf Architecture, (Oct 2018): 209–253.https://doi.org/10.1007/978-3-319-93594-2_8Jianshuang Wu, Susanne Wurst, Xianzhou Zhang Plant functional trait diversity regulates the nonlinear response of productivity to regional climate change in Tibetan alpine grasslands, Scientific Reports 6, no.11 (Oct 2016).https://doi.org/10.1038/srep35649Vanessa Buzzard, Catherine M. Hulshof, Trevor Birt, Cyrille Violle, Brian J. Enquist, Markku Larjavaara Re‐growing a tropical dry forest: functional plant trait composition and community assembly during succession, Functional Ecology 30, no.66 (Oct 2015): 1006–1013.https://doi.org/10.1111/1365-2435.12579R. Milla, J. Morente-López, T. Peeters Limited evolutionary divergence of seedlings after the domestication of plant species, Plant Biology 17, no.11 (Jun 2014): 169–176.https://doi.org/10.1111/plb.12220Dianne B. J. Taylor, Kunjithapatham Dhileepan Comparative growth and biomass allocation of two varieties of cat's claw creeper, Dolichandra unguis-cati (Bignoniaceae) in Australia, Australian Journal of Botany 60, no.77 (Jan 2012): 650.https://doi.org/10.1071/BT12117Javier G. Puntieri, Soledad Ghirardi Growth-unit structure in trees: effects of branch category and position on Nothofagus nervosa, N. obliqua and their hybrids (Nothofagaceae), Trees 24, no.44 (Apr 2010): 657–665.https://doi.org/10.1007/s00468-010-0435-8Mark Westoby Generalization in Functional Plant Ecology, (Dec 2009).https://doi.org/10.1201/9781420007626.ch23S. A. Greco, J. B. 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Enquist On the Vegetative Biomass Partitioning of Seed Plant Leaves, Stems, and Roots. K. J. Niklas and B. J. Enquist, The American Naturalist 159, no.55 (Jul 2015): 482–497.https://doi.org/10.1086/339459M. A. Zavala, J. M. Espelta, Javier Retana Constraints and trade-offs in Mediterranean plant communities: The case of holm oak-Aleppo pine forests, The Botanical Review 66, no.11 (Jan 2000): 119–149.https://doi.org/10.1007/BF02857785 Roderick Hunt and J. H. C. 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Trade-offs between life history traits are context dependent; they vary depending on environment and life stage. Negative associations between development and growth often characterize larval life stages. Both growth and development consume large parts of the energy budget of young animals. The metabolic rate of animals should reflect differences in growth and developmental rates. Growth and development can also have negative associations with immune function because of their costs. We investigated how intraspecific variation in growth and development affected the metabolism of larval amphibians and whether intraspecific variation in growth, development, and metabolic rate could predict mortality and viral load in larvae infected with ranavirus. We also compared the relationship between growth and development before and after infection with ranavirus. We hypothesized that growth and development would affect metabolism and predicted that each would have a positive correlation with metabolic rate. We further hypothesized that allocation toward growth and development would increase ranavirus susceptibility and therefore predicted that larvae with faster growth, faster development, and higher metabolic rates would be more likely to die from ranavirus and have higher viral loads. Finally, we predicted that growth rate and developmental rate would have a negative association. Intraspecific variation in growth rate and developmental rate did not affect metabolism. Growth rate, developmental rate, and metabolism did not predict mortality from ranavirus or viral load. Larvae infected with ranavirus exhibited a trade-off between developmental rate and growth rate that was absent in uninfected larvae. Our results indicate a cost of ranavirus infection that is potentially due to both the infection-induced anorexia and the cost of infection altering priority rules for resource allocation.

A life-history trade-off between low mortality in the dark and rapid growth in the light is one of the most widely accepted mechanisms underlying plant ecological strategies in tropical forests. Differences in plant functional traits are thought to underlie these distinct ecological strategies; however, very few studies have shown relationships between functional traits and demographic rates within a functional group. We present 8 years of growth and mortality data from saplings of 15 species of Dipterocarpaceae planted into logged-over forest in Malaysian Borneo, and the relationships between these demographic rates and four key functional traits: wood density, specific leaf area (SLA), seed mass, and leaf C:N ratio. Species-specific differences in growth rates were separated from seedling size effects by fitting nonlinear mixed-effects models, to repeated measurements taken on individuals at multiple time points. Mortality data were analyzed using binary logistic regressions in a mixed-effects models framework. Growth increased and mortality decreased with increasing light availability. Species differed in both their growth and mortality rates, yet there was little evidence for a statistical interaction between species and light for either response. There was a positive relationship between growth rate and the predicted probability of mortality regardless of light environment, suggesting that this relationship may be driven by a general trade-off between traits that maximize growth and traits that minimize mortality, rather than through differential species responses to light. Our results indicate that wood density is an important trait that indicates both the ability of species to grow and resistance to mortality, but no other trait was correlated with either growth or mortality. Therefore, the growth mortality trade-off among species of dipterocarp appears to be general in being independent of species crossovers in performance in different light environments.

Summary 1. Surprisingly little is known about the relationship between functional traits and demographic rates of tree species under field conditions, particularly for non‐tropical species. 2. We studied the interspecific relationship between key functional traits (wood density (WD), maximum tree height, specific leaf area, nitrogen (N) content of leaves, leaf size and seed mass), demographic rates (relative growth rate (RGR) and mortality rate (MR)) and climatic niche for the 44 most abundant tree species in Spain. 3. Demographic data were derived from the Spanish Forest Inventory, a repeated‐measures scheme including c. 90 000 permanent plots spread over a territory of c. 500 000 km2. Functional traits data came primarily from a more detailed forest inventory carried out in Catalonia, NE Spain. 4. Our study region covers a wide range of climatic conditions and, not surprisingly, the studied species differed markedly in their climatic niche. Despite that fact, our results showed that the variability in demographic rates across species was much more related to differences in functional traits than to differences in the average climate among species. 5. Maximum tree height and, particularly, WD, emerged as key functional traits, and were the best predictors of demographic rates in our study. These two variables also mediated the marginally significant relationship between RGR and MR, suggestive of a weak trade‐off between growth and survival. 6. The main aspects of our results were not altered by the explicit incorporation of phylogenetic effects, suggesting that the observed relationships are not due to divergences between a few major clades. 7. Synthesis. Our study gives support to the notion that variation in functional traits across species allows them to perform largely independently of climatic conditions along environmental gradients.

Sexual reproduction has been a central topic in evolutionary biology because of its many costs: why have organisms evolved sexual reproduction despite the many costs of sex? To answer the question, researchers have conducted laboratory experiments to measure population growth rates with and without sexual reproduction under a stressor. Here we show that a single episode of sexual reproduction can produce a large amount of variation in population growth rates under dual stressors by laboratory experiments of a green alga, Closterium peracerosum-strigosum-littorale complex. We observed the population dynamics of the alga under dual stressors and confirmed that high salinity and low pH decreased growth rates. By comparing parental and their hybrid F1 populations, we observed larger variations in growth rates of F1 populations (i.e., transgressive segregation) when pH was low. Interestingly, even when parental populations had negative growth rates, some F1 populations showed positive growth rates in severe environmental conditions due to the large variation in population growth. By utilizing the recently obtained genomic information of the alga, we conducted a gene ontology enrichment analysis and found that genes with copy number variations between parental strains were more frequently associated with pH stress-related terms than salt stress-related terms. Our results suggest that recombination and variation in the number of gene copies might produce large genetic variation in the F1 generation. This will be an important step toward a better understanding of evolution of sex and evolutionary rescue where rapid contemporary evolution prevents population extinction in changing environments.

The Evolution of Functional Traits in Plants: Is the Giant Still Sleeping?

Intra-annual radial growth variations of two Norway spruce trees (Picea abies (L.) Karst.) were monitored over 4 years, at four heights up the stem, by means of point-dendrometers. The trees were then felled and radial wood samples were cut from the radii that had been monitored by the dendrometers and analyzed for density. From the radial growth measurements recorded by the dendrometers, we related positions within the rings to dates, thus making possible investigation of the relationships between changes within the rings in wood density and fluctuations in climate or growth rate. Radial growth started in early April and ended, with large intra-annual differences, in August or September. Short-term variations in growth rate were related to fluctuations in climate parameters and soil water reserves. The sensitivity of radial growth to climate decreased with stem height. Wood density responded strongly to drought events, and a dry period in June 1996 induced false-ring formation. Wood density was relatively independent of growth rate and climatic conditions during the first part of the growing season, but increased with decreasing radial growth rate later in the growing season.