Globally, functional traits are weak predictors of juvenile tree growth, and we do not know why

1. 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. 2. 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. 3. We tested these alternative hypotheses using data on 27352 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. 4. 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. 5. 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. 6. 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.Additional co-authors: Hervé Jactel, Xuefei Li, Kaoru Kitajima, Julia Koricheva, Cristina Martínez-Garza, Christian Messier, Alain Paquette, Christopher Philipson, Daniel Piotto, Lourens Poorter, Juan M. Posada, Catherine Potvin, Kalle Rainio, Sabrina E. Russo, Mariacarmen Ruiz-Jaen, Michael Scherer-Lorenzen, Campbell O. Webb, S. Joseph Wright, Rakan A. Zahawi, and Andy Hecto

Globally, functional traits are weak predictors of juvenile tree growth, and we do not know why

1. 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. 2. 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. 3. 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. 4. 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. 5. 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. 6. 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

Contributions of a global network of tree diversity experiments to sustainable forest plantations

status: publishe

Young widowhood: Reconstructing identity

This study examines the process of identity reconstruction in young widowhood. Participants were widows between the ages of 20-39 who had been widowed for at least six months. The qualitative research design includes an interview protocol using open-ended questions. The theoretical foundations of the study include three bodies of identity development and bereavement research, including: Erickson's (1964, et al.) lifespan development theory, Gilligan's (1982) theory of women's identity development, constructivist and narrative methodology articulated by Neimeyer (2002; 2005) and research on a new model of bereavement by Hagman (2001). Additionally, theories and research on young widowhood and identity tasks were also used. Research questions focused on the widow's identity before and after the death of her husband, her internal assumptions about the world before and after the death, strategies for meaning reconstruction, identity development challenges faced, and ideas about what else might have helped them adjust. The results of this study are expected to yield useful information for mental health professionals working with young widows

Linear Systems on Tropical Curves

A tropical curve $\Gamma$ is a metric graph with possibly unbounded edges, and tropical rational functions are continuous piecewise linear functions with integer slopes. We define the complete linear system $|D|$ of a divisor $D$ on a tropical curve $\Gamma$ analogously to the classical counterpart. We investigate the structure of $|D|$ as a cell complex and show that linear systems are quotients of tropical modules, finitely generated by vertices of the cell complex. Using a finite set of generators, $|D|$ defines a map from $\Gamma$ to a tropical projective space, and the image can be modified to a tropical curve of degree equal to $\mathrm{deg}(D)$. The tropical convex hull of the image realizes the linear system $|D|$ as a polyhedral complex.Une courbe tropicale $\Gamma$ est un graphe métrique pouvant contenir des arêtes infinies, et une fonction rationnelle tropicale est une fonction continue linéaire par morceaux à pentes entières. Le système linéaire complet $|D|$ d'un diviseur $D$ sur une courbe tropicale $\Gamma$ est défini de façon analogue au cas classique. Nous étudions la structure de $|D|$ en tant que complexe cellulaire et montrons que les systèmes linéaires sont des quotients de modules tropicaux engendrés par un nombre fini de sommets du complexe. Etant donné un ensemble fini de générateurs, $|D|$ définit une application de $\Gamma$ vers un espace projectif tropical, dont l'image peut être modifiée en une courbe tropicale de degré égal à $\mathrm{deg}(D)$. L'enveloppe convexe tropicale de l'image réalise le système linéaire $|D|$ en tant que complexe polyédral

Leaf area increases with species richness in young experimental stands of subtropical trees

Aims: Most biodiversity–ecosystem functioning research has been carried out in grassland ecosystems, and little is known about whether forest ecosystems, in particular outside the temperate zone, respond similarly. Here, we tested whether productivity, assessed as leaf area index (LAI), increases with species richness in young experimental stands of subtropical trees, whether this response is similar for early-season leaf area (which is dominated by evergreens) and seasonal leaf area increase (which is dominated by deciduous species), and whether responses saturate at high species richness. Methods: We used a planted tree biodiversity experiment in south-east China to test our hypotheses. LAI was determined three times by digital hemispheric photography in 144 plots that had been planted with 400 trees each, forming communities with 1, 2, 4, 8 or 16 tree species. Important Findings: LAI increased significantly with tree species richness in the fifth year of stand establishment. Similar, but weaker, statistically non-significant trends were observed 1 year before. We did not observe leaf area overyielding and the presence of particularly productive and unproductive species explained large amounts of variation in leaf area, suggesting that selection-type effects contributed substantially to the biodiversity effects we found in this early phase of stand establishment. Effects sizes were moderate to large and comparable in magnitude to the ones reported for grassland ecosystems. Subtropical (and tropical) forests harbor substantial parts of global net primary production and are critical for the Earth’s carbon and hydrological cycle, and our results suggest that tree diversity critically supports these ecosystem services