Comparison of teak and pine plantations in northern Thailand

A thesis. Soil factors (chemical and physical characteristics), ground flora, nutrient cycling and litter decomposition were compared for sample sites in natural teak (Tectona grandis) forest, teak plantations aged 6-, 32-and 50-years old, a degraded teak forest (deforested in 1994) in Ngao district, Lampang, and pine (Pinus kesiya) plantations aged 31-, 20- and 6-years old in Hot District, Chiang Mai, both sites in northern Thailand. Measurements were made of soil organic carbon, pH, cation exchange capacity and nutrients. In the teak area, the highest organic C content was recorded in the natural T. grandis forest and the lowest level was in the 50-year-old T. grandis plantation (3.65 and 1.96%, respectively). In the pine area, soil organic C increased with increasing plantation age, from 1.17% in the 6-year-old plantation to 2.72% in the 31-year-old stand. The net primary production of the ground flora was highest in the degraded teak forest area (2264 kg/ha year-1) and lowest in the P. kesiya plantation (140 kg/ha year-1). In the T. grandis plantations and natural T. grandis forest, the net primary production was not significantly different (500-700 kg/ha year-1). Species diversity index (Hill's number) of ground flora was highest in the natural teak forest (rainy and dry season values were 36.45 and 26.97, respectively), whereas the highest value in pine plantations was 25.72 during the rainy season. In terms of ground flora and soil properties, the teak plantations represented a greater ecological benefit to the area than the pine plantations, and with increasing age, plantation ground flora communities become more similar to that of the natural forest. However, the presence of Imperata cylindrica in the 50-yr-old teak plantation suggests that the community is developing into a more fire-resistant one, due to annual disturbances caused by burning. Ground flora in pine plantations is significantly different from that of teak plantations, and it is recommended that additional species are introduced for soil improvement and conservation.