Assessing trait‐based scaling theory in tropical forests spanning a broad temperature gradient

Abstract

Aim Tropical elevation gradients are natural laboratories to assess how changing climate can influence tropical forests. However, there is a need for theory and integrated data collection to scale from traits to ecosystems. We assess predictions of a novel trait‐based scaling theory, including whether observed shifts in forest traits across a broad tropical temperature gradient are consistent with local phenotypic optima and adaptive compensation for temperature. Location An elevation gradient spanning 3,300 m and consisting of thousands of tropical tree trait measures taken from 16 1‐ha tropical forest plots in southern Perú, where gross and net primary productivity (GPP and NPP) were measured. Time period April to November 2013. Major taxa studied Plants; tropical trees. Methods We developed theory to scale from traits to communities and ecosystems and tested several predictions. We assessed the covariation between climate, traits, biomass and GPP and NPP. We measured multiple traits linked to variation in tree growth and assessed their frequency distributions within and across the elevation gradient. We paired these trait measures across individuals within 16 forests with simultaneous measures of ecosystem net and gross primary productivity. Results Consistent with theory, variation in forest NPP and GPP primarily scaled with forest biomass, but the secondary effect of temperature on productivity was much less than expected. This weak temperature dependence appears to reflect directional shifts in several mean community traits that underlie tree growth with decreases in site temperature. Main conclusions The observed shift in traits of trees that dominate in more cold environments is consistent with an ‘adaptive/acclimatory’ compensation for the kinetic effects of temperature on leaf photosynthesis and tree growth. Forest trait distributions across the gradient showed overly peaked and skewed distributions, consistent with the importance of local filtering of optimal growth traits and recent shifts in species composition and dominance attributable to warming from climate change. Trait‐based scaling theory provides a basis to predict how shifts in climate have and will influence the trait composition and ecosystem functioning of tropical forests.

Afrotropical Tree Communities May Have Distinct Responses to Forecasted Climate Change

“…For this reason, the increasing radiative forcing associated with RCP 8.5 resulted in greater species loss than the more conservative RCP 4.5 scenario. Temperature specific responses are consistent with the theory that a unique ecological history in the Afrotropics (Malhi and Wright 2004;Maslin et al 2005;Parmentier et al 2007;Malhi et al 2013;Mayaux et al 2013;Enquist et al 2017;Sullivan et al 2017) cultivated tree communities with few wet-affiliated species (Leal 2009) Several considerations are necessary to situate this study in the literature. First and foremost, this analysis considered only the 76 most common species across plots.…”

“…We demonstrate a 3 -8% decrease in Afrotropical forest species richness by the end of the century for the most abundant tree species. This prediction is substantially less severe than 30-50% predicted for the Neotropics (Colwell et al 2008;Feeley and Silman 2010), and lends support to the argument that the unique evolutionary past of Afrotropical forest communities (Malhi and Wright 2004;Maslin et al 2005;Parmentier et al 2007;Malhi et al 2013;Mayaux et al 2013;Enquist et al 2017;Sullivan et al 2017) could have made them more resilient to climate change than their Amazonian or Asian counterparts (Hansen and DeFries 2004;Gardner et al 2007). It also indicates that predictions of tree species responses to climate change are not generalizable across continents.…”

“…It is unclear whether the world's other tropical regions will respond similarly to climate change (Malhi and Wright 2004;Maslin et al 2005;Parmentier et al 2007;Malhi et al 2013;Enquist et al 2017;Sullivan et al 2017). Afrotropical forests are distinct in having comparatively few wet-affiliated species given their climate (Leal 2009), and a high proportion of large trees that grow and recolonize rapidly (Fayolle et al 2012;Gond et al 2013).…”

Microbes Follow Humboldt: Temperature Drives Plant and Soil Microbial Diversity Patterns from the Amazon to the Andes

“…The mid-elevation zone is also where there is a transition in soil nutrient availability from N to P (Nottingham et al 2015b), which may promote plant b-diversity according to different nutrient-use strategies (Condit et al 2013). Although the pattern of shifts in plant b-diversity along elevation gradients is well described, and there is intensive work on plant functional traits on this transect (Asner et al 2014, Enquist et al 2017, Fyllas et al 2017, van de Weg et al 2009, van de Weg et al 2012, van de Weg et al 2014, the mechanistic basis of the generation of this pattern is not yet well resolved (Silman 2014), but will ultimately inform observed on-going and past shifts in climate and plant species range shifts (Bush et al 2004, Feeley et al 2011.…”

Increase in light interception cost and metabolic mass component of leaves are coupled for efficient resource use in the high altitude vegetation

“…Studies have been conducted in the past to analyze variation in α for A-M scaling relationship, across species (Milla and Reich 2007), species groups (Niklas et al 2007) and abiotic gradients (Pan et al 2013, Sun et al 2017), but such analyses for high altitude vegetation are lacking. In the high altitude region, such as in Himalaya, several gradients (presence of opposite slope aspects and elevational gradients) are present in a relatively small spatial scale making them as one of the most powerful 'natural laboratories' for studying ecological responses of plants (Körner 2007, Jump et al 2009, Dvorský et al 2016, Heggie 2016, Enquist et al 2017. Along these gradients, changes in temperature, solar radiation, partial pressure of gases, atmospheric humidity and wind velocity are the major factors that affect plant functioning.…”