LETTER LETTER

Downward shift of montane grasslands exemplifies the dual threat of human disturbances to cloud forest biodiversity

The study by Morueta-Holme et al. (1) provides global warming [at rates similar to those provide, we must find ways to slow or reverse unique and invaluable insight into how tropical observed by Morueta-Holme et al. (1) for the downslope expansion of human-dominated montane ecosystems have responded to climate alpine plant species] (3, 4). In order for grasslands, and thereby allow forest species to change and other anthropogenic disturbances these cloud forest species to continue mi- respond to climate change through upward over the past two-plus centuries. Clearly, one of grating upslope, they will eventually need to migrations. the most important findings of their study is expand their ranges past the current treeline a,b,1 c that many species and ecosystems have shifted into the areas occupied by the Pajonal or Kenneth J. Feeley and Evan M. Rehm their distributions upslope to higher elevations, other montane grasslands. If the lower dis- aDepartment of Biological Sciences, in accord with rising global mean temperatures tributional limit of the grasslands is stable, or International Center for Tropical Botany, (1). Another extremely important finding of the even worse if the grasslands are expanding Florida International University, Miami, FL study that is deserving of extra attention is that into lower elevations as was observed at 33199; bFairchild Tropical Botanic Garden, the high-elevation grasslands of Chimborazo Chimborazo, then cloud forest species will Coral Gables, FL 33156; and cDepartment of Fish, (i.e., the Pajonal) have expanded their distribu- be prevented from shifting the leading edges Wildlife, and Conservation Biology, Colorado tions not only upslope but also downslope by of their ranges upslope (2). This will result in several hundreds of meters. The upslope ex- reduced population sizes and increased risks State University, Fort Collins, CO 80523 pansion of the Pajanol fits with the predictions of extinction for many species, as the lower of species migrations driven by rising temper- elevation portions of their ranges become in- 1 Morueta-Holme N, et al. (2015) Strong upslope shifts in atures; on the other hand, the downslope ex- tolerably hot but the species are prevented Chimborazo’s vegetation over two centuries since Humboldt. Proc pansion of the Pajanol is likely driven by the from migrating into higher cooler elevations Natl Acad Sci USA 112(41):12741–12745. increasing impacts of human activities, such as (5). This process is analogous to the “moun- 2 Rehm EM, Feeley KJ (April 1, 2015) The inability of tropical cloud ” forest species to invade grasslands above treeline during climate forest clearing for agricultural expansion, cattle taintop extinctions predicted for many spe- change: Potential explanations and consequences. Ecography, 10.1111/ grazing, and the setting of fires to improve cies of various alpine systems, but in this case ecog.01050. fodder (1). The downslope expansion of the extinctions will be driven not by the 3 Rehm EM (2014) Rates of upslope shifts for tropical species depend on life history and dispersal mode. Proc Natl Acad Sci USA Pajonals is not limited to Chimborazo; pre- physical absence of land at higher elevations 111(17):E1676. vious studies have similarly observed that the but instead by the fact that any lands at 4 Duque A, Stevenson PR, Feeley KJ (2015) Thermophilization of “ ” adult and juvenile tree communities in the northern tropical Andes. treeline (the ecotone transition between high- higher elevations are made unavailable to Proc Natl Acad Sci USA 112(34):10744–10749. elevation montane grasslands and the un- forest species by human activities that favor 5 Feeley KJ, Silman MR (2010) Land-use and climate change effects derlying cloud forest) is stable or moving grasses over trees. In other words, our activ- on population size and extinction risk of Andean plants. Glob – downslope throughout many parts of the ities are simultaneously forcing many cloud Change Biol 16(12):3215 3222. tropics (2). At the same time, a growing forest species to migrate upslope but at the number of studies show that many of the same time we are preventing them from do- Author contributions: K.J.F. and E.M.R. wrote the paper. tropical montane plant and animal species ing so. Given the incredibly high biodiversity The authors declare no conflict of interest. that occur below the current treeline are shift- of tropical montane cloud forests and the 1To whom correspondence should be addressed. Email: kjfeeley@ ing their distributions upslope in response to many important ecosystem services that they gmail.com.

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