Tropical montane cloud forests (TMCF) are among the most biodiverse ecosystems on Earth. Páramo, the alpine ecosystems above equatorial Neotropical TMCF, host ~4700 plant species and are the Amazon River headwaters. Unique species evolved in both. Persistent cloud immersion created strikingly wetter habitats isolated on mountaintops. A fundamental unknown is whether, and where, climate change will affect TMCF or páramo extent or cloud immersion. Site-level studies suggest it will reduce cloud immersion in some TMCF but increase it elsewhere. Increased land surface temperatures could make air travel further up mountains before it cools enough to form clouds. Alternatively, increased humidity over warming oceans might increase cloud immersion. Global climate models are too coarse to target cloud forests. Questions: Where and how will climate change affect Neotropical TMCF and páramo extent and cloud immersion? How do these changes compare with land use and protection? Methods: We developed a new empirical approach combining hourly relative humidity (RH), frost, and novel application of maximum watershed elevation, to project change in TMCF and páramo for Representative greenhouse gas emissions Concentration Pathways (RCPs). We used a new dataset of coordinates representing cloud forest minimum elevation (CFmin) from 56 ecological studies, some 50-60 years old.
Results/Conclusions
The model projected CFmin increases where site-level studies suggest rises in cloud lifting condensation levels or species elevation ranges. Model relationships were as expected. We believe it is a first to project across continents climate change effects on defining features of TMCF and páramo, like cloud immersion metrics. Climate change would increase cloud immersion for only about 1% of Neotropical TMCF and in only a few places. Declines in cloud immersion dominate. Most TMCF shrink (from clouds forming at higher elevations), and dry, with RH declines suggesting fewer or thinner clouds. In as few as 25 years, climate change could shrink and dry 60-80% of Neotropical TMCF. In half of ecoregions, with RCP 4.5, cloud immersion declines are comparable to where upward species migrations are linked to climate change. Under RCP 8.5, 90% of them are impacted as early as 2060. In that scenario, 90% of páramo would disappear. TMCF are ~85% forested overall, but some TMCF least affected by climate change are most deforested or least protected. Conclusions: Neotropics-wide, and for most páramo, climate change poses a risk to species over areas at least as extensive as those negatively affected by land use, regardless of future land cover.