Influences of Stand Density on Soil Respiration for Pinus Densiflora

Soil respiration (Rs) and environmental conditions were investigated for 55 to 75-year-old naturally regenerated Pinus densiflora with three different density stands (high density stand- HD; 1,000 trees/ha, medium density stand- MD; 625 trees/ha, and low density stand- LD; 375 trees/ha) located in Gwangneung Experimental Forest near Seoul, Korea. Aboveground biomass (t C/ha) for P. densiflora was significantly different among stands; 80.4 for HD, 99.8 for MD, and 67.1 for LD, while belowground biomass (t C/ha) for P. densiflora was 7.7 for HD, 7.4 for MD, and 4.6 for LD, respectively. Mean Rs rate (mg CO2/m2/hr) and total annual Rs rate (t C/ha/yr) from October, 2006 through March, 2008 measured by IRGA (EGM-4, PP Systems, UK) were significantly higher in MD than those in two other stands; 276.5 and 6.5 for HD, 346.5 and 8.2 for MD, and 316.3 and 7.5 for LD. Also Rs during the growing season (June-August) showed the similar pattern. Mean soil water content (%) was highest in LD (11.1), followed by MD (10.4), and HD (8.3). However, there were no significant differences mean soil temperature, soil carbon and nitrogen contents among stands. Although stand density appeared to influence soil moisture and soil respiration, the relationships between stand density and soil respiration and soil moisture were not consistent.