Effects of Highland Swidden Farm Burning on Carbon Storage and Loss to Atmosphere

Abstract

This research aimed to study carbon storage during the fallow period, loss during slash-and-burn, and recovery after burning in long fallow period swidden farming, short fallow period swidden farming in a forest rehabilitation area at Doi Phu Kha National Park, Nan province. Each site consisted of 3 replication plots, and hence there were 9 plots in the study. Prior to slashing, fuel loading was estimated using a harvesting method. Moreover, 4 soil samples per plot at depths of 30 cm were also collected to determine the soil and root carbon contents and their pools. All residues and soil samples were collected immediately after burning. The transfer of carbon to the atmosphere during burning was calculated as the differences between the quantities of pre-burning carbon pool (plant and soil and fine root) and post-burning residues (ash, charred material, unburned material, post-burning soil and fine roots). In addition, carbon recovery was monitored for 6 months after burning.

The results showed that the carbon pool was highest in the rehabilitation area (79.22 ton/ha), followed by long swidden farming (73.01 ton/ha), and short swidden farm (45.56 ton/ha), respectively. However, the carbon pool from tree parts in the rehabilitation area was not included. A great portion of carbon was stored in the belowground part in both the long and short swidden farming. The relative carbon loss was lowest on the rehabilitation site (21%), compared to the swidden farms (ca. 35%). The overall carbon recovery in the long fallow period swidden farming and in the rehabilitation area was gradual at a rate of ca. 0.5 ton/ha/month, although the recovery for the short fallow period swidden farming was not clear. This finding may suggest that slash-and-burn agriculture by allowing long fallow period swidden farming may be sufficient to restore carbon to a similar level to pre-burning until the next slash-and-burn begins.

Keywords: carbon loss, rehabilitation area, slash-and-burn, swidden farming