Editorial: Tropical Montane Forests in a Changing Environment

They are most widespread in South America and in (semi-)humid mountain areas. The area covered by tropical and subtropical montane forests is approximately 305 million hectares, about 13% of the area covered by tropical and subtropical forests. TMFs occur under highly variable topography, including steep slopes and landslide-prone terrain. The latitudinal gradient, orography, and vertical thermal gradients have a direct influence on the fauna and flora of TMFs. The latitudinal pattern is not the same in all TMFs, with temperature and precipitation conditions occurring due to seasonality in the climate and being unambiguously linked to species climatic affinity preferences. Annual precipitation generally exceeds 1,000-1,200 mm and can be associated with low-level cloud cover or mist, resulting in a lower incidence of sunlight and lower primary productivity. TMFs store significant amounts of carbon in their soils, with the soil organic layer depth sharply increasing with lower mean annual temperatures. Lower temperatures also result in low nutrient inputs through slow mineralization of organic matter. Declining temperature appears to be the principal rate-limiting factor for litter decay with increasing elevation on tropical mountains. The low temperatures have also been linked to biogeochemical limitations, by reducing nitrogen availability and N2 fixation. Current global climate models suggest enhanced warming of the tropical mid and upper troposphere, with rates of temperature rise expected to be larger at higher than at lower elevations. The effects of temperature and changing moisture conditions on the cloud belt formation in TMFs are still uncertain, but upper displacements of the condensation belt are expected. Mountain regions are more frequently suffering the impacts of oceanic warming, such as El Nino Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO)/Atlantic Multidecadal Oscillation (AMO), but the effect of their drought and flooding spells on TMFs' flora and fauna are yet under-researched. Tropical montane forest ecosystems are fragile but exceedingly valuable ecosystems, due to their important role in the provision of ecosystem services, including the regulation of water and the regional climate, the capture and storage of carbon, and the harboring of a vast store of biodiversity. These vital ecosystems services are under threat, as climate change is undoubtedly affecting their species composition and metabolic profiles in a myriad of ways. Along an elevation gradient, as global average temperatures rise, elevational shifts in the distribution of species toward regions of lower temperature are to be expected.