Abstract:

Characteristics of tree growth and soil properties in the mixed and pure Pinus luchuensis stands were investigated in northern Okinawa, southwest Japan. The results showed that the production of the pine-broadleaf mixed stands were much higher than that of the pure pine stand. The total basal area and stocking volume for the mixed stands were, respectively, 55.2～72.1m²·hm^-2 and 406～638 m³ ·hm^-2 ; which were 63.3%～113.3% and 94.2%～205.3% greater than those of the pure pine stand, respectively. Result from the analysis of height-DBH relation of individual tree indicated that the growth of tree height for luchu pine in the mixed stands was significantly promoted. The mean height of pine trees in the mixed stands reached 18.4 m which was 46.0% higher than the pure stand. Litter accumulation on the ground surface in the mixed stands averaged 9.8 Mg·hm^-2 , and its decomposition constant was 0.20 However, for the pure pine stand, they were 17.5 Mg·hm^-2 and 0.46, respectively. Amounts of nutrient accumulation in A₀ horizon under the mixed stands were evidently lower than that under the pure pine stand except for Zn. Soils under the mixed stands had higher porosity, greater water-holding capacity, and better water regime in comparison with the pure pine stand. The contents of soil organic C, total N and available P were much greater in the mixed stands than in the pure pine stand. It is evident that the mixture of P. luchuensis and Schima wallichii kort. Ssp. liukiuensis Bloenb could increase the turnover rate of forest floor organic matter and accelerate nutrient cycling. The results from this study demonstrate that the mixture is suitable for maintaining soil fertility and site productivity in long_term, promoting its growth and establishing a stable, man_made forest ecosystem.

Key words: Soil physico-chemical properties, Organic matter turnover, Pine-broadleaf mixture, Schima wallichii kort. Ssp. Liukiuensis Bloenb, Pinus luchuensis