Epsilon Archive for Student Projects

Abstract

Soil organic carbon (SOC) stocks and the effect of thinning on SOC were simulated by using the Yasso07 model in Norway spruce stands at eight sites in southern Sweden. Five thinning treatments (A, B, C, D and I) with different intensity and frequency were under consideration. The model requires litter input to soil and climate data. Biomass of Norway spruce stands was estimated using tree height and tree diameter with Marklund biomass equations. Litter production was calculated by multiplying the compartment specific turnover rates with biomass. Climate data on temperature and precipitation were taken from closest weather points. The model was run for the total thinning period and at least six years later for each site with yearly litter input and climate data. The sensitivity of the model was checked by increasing and decreasing the temperature and precipitation by 20 %. Simulated mean values of SOC were used to assess the results. Total average and per year average difference in SOC between first and last year of simulations were calculated. General linear model was applied for statistical analysis. Simulated SOC stocks varied from 101 Mg ha-1 to 161 Mg ha-1 at eight sites. There was a tendency towards higher SOC at high site index locations. No clear trend was observed with respect to latitude of sites, stand age and basal area. Overall, thinning treatments had significant effect on SOC (p ≤ 0.000). All thinning treatments negatively affected the SOC, except no thinning treatment (control, I), which had positive affect. One very heavy thinning treatment (C, 70% basal area removal) had highest negative rate of change in SOC. This treatment was significantly different from all other treatments. Treatment A, B and D were normal to heavy in their intensity. These treatments also had negative rate of change in SOC, but were statistically similar. The model was sensitive to both climate parameters (temperature and precipitation) but largest deviation was observed with actual temperature and a 20 % decrease in precipitation.