The forest canopy plays an important role in determining the nutritional status of forest floors and soils. Litterfall and throughfall are the main sources of soil nutrients in ombrogenous peatland forests. This article describes the results of monitoring ion budgets in the selectively logged peat swamp forest of Central Kalimantan, Indonesia; with emphasis on the role of the forest canopy in filtering rainfall, which subsequently affects the proton budget. In order to highlight the role of the forest canopy, the proton budget of the selectively logged forest is compared with that of burnt peat swamp forest. Mean annual rainfall was 2,800 mm and the total proton inputs from rainfall and throughfall were 0.54 and 0.45 kmolc ha-1 year-1, respectively. During the period December 2002 to March 2003 the canopy of the selectively logged peat swamp forest acted as a proton sink or buffer of 20 molc ha-1. The proton buffer of the forest canopy obtained in this study is much less than obtained elsewhere. Retention of HCO3 - ions by the forest canopy is one of the important mechanisms in buffering protons. It implies that the forest canopy is of importance for balances of HCO3 -|CO2 in the atmosphere-plant-soil system.