Neighboring tree effect on the survival and growth of Shorea johorensis under a line planting system in a Bornean dipterocarp forest

Abstract

In Indonesia, in recent years, line planting of valuable Shorea species has taken place on logged forest to maintain the timber yield. However, there exists scant information about the effectiveness of such a method. Neighboring trees along the planting lines affect the planted trees. We assessed the survival, growth, and crown exposure of the planted trees to evaluate the effect of neighboring trees in three 1 ha-monitoring plots, in which Shorea johorensis seedlings had been planted at a 5-m spacing along five parallel lines separated by 25 m, all running in a north-south direction within a 3 m-wide strip. The planted trees were monitored for 11 years after planting. The crown exposure was evaluated using a three-dimensional spatial structure model and SExI-FS software. Eleven years after planting, 77.6 % of the planted S. johorensis had survived. The average diameter at breast height (DBH) was 16.7 +/- 5.6 cm, ranging widely from 5.3 to 33.6 cm. The initial growth 1 year after planting predicted the variance in DBH 11 years later. Trees showing rapid initial growth exhibited higher survival and subsequent growth rates. The variation in light conditions in the planting lines affects the growth and survival. The spatial structure model illustrated how neighboring tree crowns suppress the growth of the planted tree by casting shade. In a line-planting system, the neighboring tree effect influences the survival and growth of the planted trees, and this can be reduced by treatment of the canopy to ensure exposure of planted trees to sunlight.