Aboveground biomass storage of fallow vegetation in the Kalahan Forest Reserve, Philippines

Abstract

There has been renewed interest in the intimate link between fallows of the shifting cultivation cycle and secondary forests as forest re-growth on fallow fields can be considered an important provider of environmental services, such as carbon sequestration for climate change mitigation. Aboveground biomass storage of fallow fields in the eastern portion of the Kalahan Forest Reserve, Philippines was investigated through household surveys, interviews and field measurements using a chronosequence approach. Considering the possible effects of variability in land use history and management and biophysical characteristics of individual fields, mean aboveground biomass (expressed as MgOM) of the tree and understory and its equivalent amount of carbon (in MgC) were estimated for fallows abandoned from 1–5 y (28.49 MgOM/ha, 14.25 MgC/ha throughout), 6–10 y (87.51, 43.76), 11–15 y (140.76, 70.38), 16–20 y (305.36, 152.68), and 21–25 y (252.79, 126.40). Estimates for fallow fields abandoned between 1–15 years were within the ranges reported in the literature for secondary forest fallows in the humid tropics, while those abandoned for over 15 years have values that were higher. Fallow fields in the Kalahan Forest Reserve appear to accumulate biomass at a rapid rate which could extend to 15 years or more from the time of abandonment.