Data from: Coordination of bark and wood traits underlies forest-to-savanna evolutionary transitions

Aim: To test the hypothesis that adaptive shifts leading to the assembly
of tropical savannas involved coordination between bark and wood traits,
and to understand the underlying mechanisms. Location: Tropical South
America. Taxon: Angiosperms (woody). Methods: We compiled data on three
bark traits (total, inner, and outer relative bark thickness), wood
density, maximum height, five secondary xylem traits, and on species’
habitat information (light environment, climate, soil, and fire history)
for Neotropical savanna, forest, and generalist species (biome groups). We
tested for pairwise and multivariate associations among traits across
species, and if biome group and habitat conditions explained species
positions along the resulting strategy axes. Results: Traits covaried
along four different axes. The first axis was consistent with a trade-off
between fire (thick barks) and shade tolerance (low bark to diameter
ratio, high vessel density) and contributed to differentiate the three
biome groups according to preference for shaded environments. Forest
species also differed from savanna and generalist species in a separate
axis by being more resource acquisitive. Maximum height and wood density
did not strongly trade-off with bark thickness, although maximum height
negatively covaried with relative outer bark thickness. Preference for
shaded conditions was the main driver of variation in the two principal
strategy axes, but temperature, fire and soil sand content also explained
differences in plant stature between savanna and generalist species. Main
conclusions: Allocation to bark is constrained by trade-offs with wood,
opposing shade-tolerant and acquisitive forest species to fire-resistant
and conservative savanna species. Rather than a single strategy axis,
three axes are necessary to understand the functional differences among
savanna, forest, and generalist species. Because two of these axes are
controlled by light availability, the associated traits tend to covary in
space and time, but not across species.