November 05, 2015

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Altered Climate Leads to Positive Density-Dependent Feedbacks in a Tropical Rainforest

Warming induces positive density dependence

The Science

Rainforests are going to experience warmer and drier climate than current conditions but little is known about how plants will respond. Using a warming field experiment in Puerto Rico, we showed that plant growth and survival are altered by warming and drought. These changes might threaten the future of these diverse forests.

The Impact

Tropical rainforests are key ecosystems which not only host an incredible biodiversity but also help regulate the global weather. Here, we have shown that future climate might alter one of the key controls of plant diversity (negative density dependence). This suggests that future climate could lead to a decrease in plant diversity in these forests.

Summary

Climate change is predicted to result in warmer and drier Neotropical forests relative to current conditions. Plant enemies inflict negative density-dependent feedbacks, where by plants growing at high density experience more negative effects from enemies than plants growing at low density. These negative feedbacks are key to maintaining the high diversity of tree species found in the tropics, yet we have little understanding of how projected changes in climate are likely to affect these critical controls. Over three years, we evaluated the effects of a natural drought and in situ experimental warming on density-dependent feedbacks on seedling demography in a wet tropical forest in Puerto Rico. In the +4oC warming treatment, we found that seedling survival increased with increasing density of the same species. If positive density-dependent feedbacks are not transient, the diversity of tropical wet forests, which may rely on negative density dependence to drive diversity, could decline in a future warmer, drier world.

Principal Investigator

Benedicte Bachelot
Michigan State University
bean.bach33@gmail.com

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This research was funded by U.S. Department of Energy award numbers DE-SC-0011806, 89243018S-SC-000014, and DE-SC-0018942 awarded to MAC, TEW, and SCR. SCR was additionally supported by the U.S. Geological Survey Ecosystems Mission Area. The USDA Forest Service’s International Institute of Tropical Forestry (IITF) and University of Puerto Rico-Río Piedras provided additional support. All research at IITF is done in collaboration with the University of Puerto Rico.

References

B. Bachelot, et al.. "Negative density-dependent mortality varies over time in a wet tropical forest, advantaging rare species, common species, or no species". Oecologia 179 853–861   (2015). https://link.springer.com/article/10.1007%2Fs00442-015-3402-7.