Due to climate change and increasing global temperatures, many species are predicted to shift their geographic distributions upward or poleward, which should be reflected in the composition of species occurring at specific locations. In accord with predictions, species migrations and corresponding compositional shifts have been observed in many temperate systems. However, data from the tropics is sparse. While a handful of studies from tropical montane forests, have shown evidence of species migrations and thermophilization, the generalizability of these patterns and the responses of tropical and subtropical plant species to climate change remain uncertain. We used a newly complied database of forest plot inventories from the subtropical and tropical Andes Mountains to ask whether Andean tree communities are experiencing compositional shifts as to include higher relative abundances of lowland thermophilic species as is predicted under upward species migrations due to global warming. We used composition data from a network of 186 plots spread across >3000 meters of elevation from Colombia to Argentina to first calculate the Community Thermal Index per plot census. We calculated the Thermophilization Rate per plot (TRplot) for all recensused plots (n=63); we then used data from all plots to calculate the average Thermophilization Rate per thermal band (1.5C ͦ) (TRband) for all plots.
Results/Conclusions
We show that the phenomenon of thermophilization is widespread throughout the Andes: 70% of the plots with recensuses had positive TRplot (i.e., CTI increased through time) and average Thermophilization Rate (TRband) was positive at most elevations. However, the thermal composition of the communities appears to be more stable at highest and mid elevations. The apparent stability at some elevations may be due to the influence of other abiotic or biotic factors on tree species distributions, and/or may reflect the presence of highly specialized plant communities around ecotones (e.g., cloudbase and treeline). Forest throughout the Andes are responding to global warming through compositional shifts that are likely driven by upward species migrations. These shifts in species ranges and community composition can have important impacts on the extinction risks as well as the valuable ecosystem services that these forests provide.