Soil development along an altitudinal transect in a Bolivian tropical montane rainforest: Podzolization vs. hydromorphy

Knowledge about soil formation in tropical montane rainforests is scarce and patchy. We examined the altitudinal change of soils in a Bolivian tropical montane rainforest, aiming to illuminate the contribution of podzolization and hydromorphic processes to soil formation. In three transects from 1700 m to 3400 m a.s.l. we determined the pH, exchangeable cation exchange capacity, carbon and nitrogen stocks, and iron and aluminium fractions from 26 soil profiles. Three zones of different dominant soil forming processes were found: In the lower montane forest (LMF, 1700–2200 m a.s.l.), Dystropepts with high nutrient concentration and acidity were common. The pronounced change to the upper montane cloud forest (UMCF, 2200–2700 m a.s.l.) coincided with the appearance of Placorthods with more acidic conditions, deep ectorganic horizons and increasing translocation of sesquioxides. In the sub-alpine forest (SCF, 2700 m–3400 m a.s.l.), hydromorphic processes dominated over podzolization, resulting in Placaquods with low mineralization rate and nutrient concentration. This shows that due to increasing wetness and colder temperatures at high altitudes, dominant soil forming processes change from podzolization to hydromorphism soils with increasing altitude.