Modeling Survival and Destruction of Teak Plantations in Java, Indonesia

Abstract

Tbak plantations in Java show severely declining productivity due to various disturbances. The risk of stand destructjon, however, is still ignored in determining annual allowable cuts, partly due to the lack of reliable methods to estimate the rate of stand destruction. This study therefore proposed an alternative method, based on the theory of survival analysis coupled with forest register data, 'for estimating survival probability and destruction rate ot teak plantations. We used the forest regist,er data of teak plantations in Kebonhar.ie, Central Java, for the period 1977-2007, Survival and destruction of plantations were modeled using probability distribution modiels. To estimate model parameters, we usecl the rnaximum likelihood estimation method clesigned for lefetruncated and right-censored data, Results showed that survival probability and destructlon rate varied ever stand age and planning period. Rates of stand destruetion were relatively low (< 2% per yeari in the period 1977-1987, but increased up to 3% ancl 14% per year in the period 1987-1997 and 1997-2007, respectively Tlie highest rate oi destruction mostly occurred in young stands (s 30 years old), indicating an alarming condition for the sustainability ef teak plantations. The survival and destruction medels are usefu1 for forest rnanagers to quantify the i'ange of historical variability in forest disturbances and to support the deve]opment of alternative harvest scheduling methods that incorporate the risk of stand destruction for teak plantations in Java. The proposed method can also be applied to other r'egions, especially when only forest register data are available.