One of the primary ways that tropical plant species are expected to respond to climate change is through shifts in their geographic distributions (i.e., “species migrations”) leading to altered patterns of diversity and community composition. Specifically, forests are predicted to undergo “thermophilization” in which the relative abundance of low-elevation heat-tolerant species increases through time. In order to test this prediction in Neotropical forests, we used recensus data from 43 forest dynamic plots located along three elevational gradients (Volcan Barva, Costa Rica; Antioquia, Colombia; and Kosniptata, Peru) and analyzed changes in their composition through time relative to species’ thermal optima estimated on the basis of their modelled geographic distributions.
Results/Conclusions
The results of our analyses indicate that within all three transects tree species composition is strongly linked to temperature and that composition is changing directionally through time, potentially in response to climate change and increasing temperatures. Mean rates of thermophilization [thermal migration rate (TMR), °C y−1]. The majority of study plots (33 of 43 plots = 80%, binomial probability < 0.0005) did in fact undergo thermophilization. The overall rate of thermophlization averaged 0.80 °C per century (95% CI = 0.4 – 1.3 °C per century) and did not vary significantly between the different transects. Importantly, results indicate that within all transects thermophilization is occurring primarily via range retractions and increased mortality of species within the lower hotter portions of their ranges (as opposed to range shifts or expansions into higher colder elevations). Range retractions will results in reduced population sizes and increased risks of extinction for many species. Additional research from other systems is desperately needed to understand if there is a temporally and spatially coherent response of tropical species and systems to climate change.