DOI: 10.6084/m9.figshare.24476461
title: <b>Changes to plant traits of two functional types across a soil water content gradient in a tropical dry forest impact tree growth rates</b> (Data sheet and R-code)

description: Specific differences in plant water-use strategies may critically shift the structure and productivity of plant communities in semi-arid and monsoonal climates. However, uncertainty still exists regarding the contribution of species’ trait plasticity in determining plant community responses to environmental changes. Our study aimed to understand shifts in trait means and variabilities, species composition, and structure and productivity of a tropical dry forest assemblage, across a soil water content (SWC) gradient using 45 dry forest fragments. We show that the trait variation (across site variation and within-site variation) of two major plant strategies, drought avoiders and drought tolerators, are strikingly different across the soil water content gradient in our study sites, and that those differences are further expressed in how plant-level and site-level productivity changes across the gradient. Consequently, we believe that the study provides novel insights into how global climate change (specifically aridity) will induce shifts in species composition and plant productivity, in monsoonal ecosystems generally, and in the Asian tropical dry forests more specifically.Scientific question addressed in this manuscript(1) How do functional traits of drought avoiding and drought tolerant species change across a soil water content (SWC) gradient in a tropical dry forest in terms of changes to mean values (plasticity) and pointwise variability?(2) How does the structure and productivity of the tropical dry forest ecosystem change across the SWC gradient, and what is the contribution from species of different water-use strategies? and(3) What contribution do shifts in mean trait values versus trait plasticity make in explaining these shifts in structure and productivity across SWC gradients?The key finding(s) that answer this question(1) Trait means often changed in opposite directions with increasing soil water content (SWC) for the two functional types, especially for water safety traits and leaf carbon capture traits. Trait variabilities often changed in opposite direction to trait means, and were generally greater at dry sites for drought avoiders and at wet sites for drought tolerators.(2) Drought avoiders were more common both in stem number and aboveground biomass in drier sites whereas drought tolerators were more common at the wettest sites. That drought avoiders showed greater trait variability towards dry SWC sites, which shows that individual leaf functional traits vary more widely under dry conditions in that group. The generally low variability of leaf carbon capture traits of drought tolerators, which decreases further towards drier SWCs, indicates that their carbon production is severely constrained by water limitation during the dry season.(3) The shorter leaf lifespan of drought avoiders at lower SWC may reflect plastic responses to greater water stress rather than a shift to species with shorter leaf lifespans, as its clear that the most abundant species in this functional group are dominant across the full SWC gradient measured. Both functional types had lower canopy extents at drier sites than wetter sites, indicating a response to prevailing water conditions. Our analysis shows that the trade-off between productivity and conservatism in seasonally dry systems differs between drought tolerators, which maintain canopies through the stressful period (dry season), and drought avoiders, which avoid the seasonal stress period through leaf shedding, causing different sets of traits to be important for their performance. The projected increases in soil water content will likely shift the vegetation to greater representation of drought tolerating species and will be accompanied by non-linear increases in standing biomass.