Effects of afforestation and forest management on soil carbon dynamics and trace gas emissions in a Sitka spruce (Picea sitchensis (Bong) Carr.) forest

摘要

The establishment and intensive management of forests for the production of timberudcan have significant effects on the soil carbon dynamics. The establishment of forestudon organic soils under grasslands may lead to substantial losses in soil carbon, due toudthe site preparation for the planting of trees and other disturbances. This is graduallyudcompensated by carbon accumulation in tree biomass as the forest grows untiludclearfelling at maturity may initiate another substantial carbon loss.udThis study had two main aims. The first was to investigate the long-term effects ofudforest establishment on natural grassland as well as clearfelling and re-growth of theudforest during second rotation, by looking at the changes in soil carbon stocks and soiludcarbon balance in a Sitka spruce (Picea sitchsensis) in Harwood (N. E. England).udSecondly, to investigate the short-term effects of forest clearfelling on the fluxes ofudsoil CO2, N2O and CH4 and on the environmental factors (soil temperature, waterudcontent and water table depth) affecting them. The fluxes were initially measured inudtwo mature stands (40-years old) during one growth season. One of the two standsudwas subsequently clearfelled while the other was kept intact and fluxes wereudmeasured for a further ten months after clearfelling. The relationships between theseudfluxes and the environmental factors were also examined.udThe study also investigated the spatial variability of soil CO2 emissions usingudgeostatistical approaches. The soil CO2 fluxes were measured with two methods, audclosed dynamic chamber and a closed static chamber, giving the opportunity toudcompare their relative performance. A performance further investigation on thisuddiscrepancy between the two methods took place in lab experiments and on a soiludmonolith, excavated from the 40-year old stand and kept under controlled conditionsudin the greenhouse.