The impact of forest fires on the long-term sustainability of taungya teak reforestation in Bago Yoma, Myanmar

Abstract

Taungya teak reforestation in Myanmar has a long history and is considered an exceptionally successful example of tropical plantations. However, after one cycle of taungya teak reforestation, soil quality would deteriorate as large volumes of biomass are removed from the forest ecosystem through the harvesting of teak. Therefore, the recovery of soil productivity during the period of teak growth is crucial to the successive rotation of the system. In this study, the dynamics of soil organic matter (SOM) and litter were investigated during the teak growth period to evaluate the long-term sustainability of taungya teak reforestation from the viewpoint of SOM conservation. Especially, the effect of forest fires on SOM dynamics and litter was investigated. In Kabaung Reserved Forest and Bondaung Reserved Forest, where teak reforestation has been practiced since 1884, surface soil samples were collected from teak plantations of different ages (0-96 years) for total carbon and nitrogen content analyses. In mature teak plantations, litter production and decomposition rates of leaf litter were also measured. Accretion of SOM was not observed in any of the teak plantations, even 96 years after reforestation. This absence of SOM accretion was attributed to the combustion of forest floor litter - a main source of SOM - by forest fires. Given that the occurrence of forest fires overlapped the defoliation period of teak, most of the teak litter that had accumulated on the forest floor was easily burnt. The strong positive correlation between total carbon content and the C/N ratio of surface soil in teak plantations suggested that the effect of forest fires on the long-term dynamics of soil carbon was marked. We conclude that forest fires have a detrimental effect on the long-term sustainability of taungya teak reforestation.