The data for this study was collected in a transect from mature upper lowland to montane forests in NE Ecuador, in the area of the Sumaco Biosphere Reserve. About 20 soil chemical parameters were measured in undisturbed natural forests on 20 plots at 500, 1000, 1500 and 2000 m a.s.l. each (80 plots in total), including in situ N net mineralization and nitrification rate, plant-available phosphorus and salt-exchangeable calcium, potassium and magnesium concentrations in the organic and mineral topsoils. Aboveground biomass (AGB) and wood productivity were quantified, and the impact of soil chemistry on these parameters was analysed. Also an attempt was made to identify the key factors controlling liana abundance.