Hydrologic connectivity in the high-elevation tropics: Heterogeneous responses to land change

In the high-elevation humid tropics, human- and climate-driven land transitions can alter hydrologic connections between the atmosphere and surface waters, with local and downstream effects. We conducted a data synthesis to examine the influence of forest-to-grassland conversion, agroforest-to-nonforest conversion, tree plantation establishment on nonforest land, and recent glacier retreat on throughfall, evapotranspiration, runoff, and nitrate fluxes in montane Latin America (including the Caribbean) and Hawaii. Our synthesis reveals heterogeneous - sometimes unexpected - responses to land change. For example, in contrast with temperate highlands, forest-to-grassland conversion in the high-elevation tropics often results in little runoff increase and lower streamwater nitrate loss. Tree plantation establishment leads to diminished runoff; the magnitude of this effect is tenfold greater than with forest-to-grassland transitions. We highlight cases in which land use, land cover, and water relationships derived from temperate ecosystems do not apply to and, therefore, should not underpin watershed management programs in the high-elevation tropics.