Restoration of degraded tropical rainforests through gap and line planting : effects on soil and light conditions and seedling performance

Sammanfattning: Enrichment plantings are a common way to restore structures and diversity lost through degradation of tropical rainforests. Large areas are degraded every year, and although disturbance over large areas seldom are homogenous, few, if any studies have compared effects of enrichment planting treatments in forests with varying degradation. Therefore the aim of this study was to compare the effects on factors important for seedling performance (i.e. soil and light conditions) under two enrichment planting methods in forests with varying degree of degradation. Further, to compare seedling performance under the two treatments, within and between the levels of degradation. The study was conducted within the INIKEA project area, which is located in the state of Sabah, Malaysia. The experiment forest was classified into three types depending on degradation level and forest structure, 30 years after disturbance. Each forest type were treated with gap planting, line planting as well as liberation (which is not included in this study) and also contained an untreated control. The planting treatments were planted with nursery raised seedlings from 32 species, 24 of which belonged to the Dipterocarpaceae family. Inventory and sampling was conducted 22 months after planting; seedling survival and height were recorded on plot level, light measurements (hemispherical photographs) were taken adjacent to each seedling and soil samples was taken in the centre of each plot. The results showed that seedling performance improved with higher light quantity and that seedlings in the gap plantings received higher light levels compared to those in line planting. An interaction between degradation level and treatment were apparent; indicating that in intermediately and heavily degraded forests, gap planting yielded better seedling performance than line planting. However, in the least degraded forests, seedlings in line planting exhibited better performance than those in gap planting. The conclusion from this study was that the degree of degradation should be considered when designing the enrichment planting approach.