Surival and growth of tropical tree seedlings to simulated changes in climate along an elevation-climate gradient

Background/Question/Methods

Tropical landscapes are critical for global climate as they are a significant carbon sink globally.  Tropical landscapes, especially secondary landscapes, also possess exceptional carbon sequestration potentials.  How tropical landscapes will respond to climate change, specifically how the carbon storage and sequestration capacities of these landscapes will change, will depend on how juvenile tropical tree seedlings will respond to changes in climatic variables such as precipitation, temperature and cloud cover, as these recruits will most likely form the “forests of the future.”.  Changes in climatic variables are critical for composition of plant communities, especially in montane and cloud forests.  To examine the effect of changes in climate on tropical tree species, we conducted a downslope common garden transplant experiment with species limited to higher-elevations and species with a wider elevation range along an elevation gradient (600-1400 m, 4-5^oC differential) in southwestern Costa Rica.  We examined the survival and growth of higher-elevation tree seedlings (Hyeronima oblonga (HO), Viburnum costaricanum (VC), Quercus insignis (QI)) in the warmer climate of lower elevation plots.  We also examined the survival and growth of tree species that are common along the elevation gradient (Heliocarpus apendiculata (HA), Croton draco (CD), Inga densiflora (ID)) transplanted in different elevations to see if individuals from different elevations respond differently to changes in climate.  

Results/Conclusions

During the experiment (2009-2011), two higher elevation species did not survive and grow in warmer climates as well as in the cooler climates of their native elevation (HO, P= 0.048, VC, P=0.023) while there was no difference in growth and survivorship of QI across climates/elevations (P=.25).  Two of the species common along the elevation/climate gradient showed no response to change in climate (HA, P=0.64, CD, P=0.4) while ID grew significantly more in the warmer climates of lower elevation (P=0.039).  The general trend in data follows predictions of topical high elevation tree species being less tolerant to climate change and highlights the potential of species with broader climate niche to proliferate in niches emptied by upward migration of climate sensitive tree species.