Effects of early thinning and fertilization on soil temperature and soil respiration in a poplar plantation

The main goal of this study was to determine the short-term effects of forest management practices (precommercial thinning and fertilization) on soil CO2 efflux of a young black cottonwood (Populus trichocarpa) plantation in southern Iceland. Changes in leaf area index, tree growth, soil and air temperatures were also monitored during the first year following the management period. Traditional precommercial thinning (50%) had little effect on soil temperature, but heavy thinning (80%) led to higher soil temperatures in spring and summer. Thinning did not change foliage nutrient content or tree growth in the first treatment year. Effects on soil CO2 efflux were surprising; even if soil temperature was slightly higher and all organic material was left at site after precommercial thinning, soil CO2 efflux in the thinned stands was significantly lowered. Fertilization increased foliage nutrient content but did not significantly change tree growth during the first growing season following spring application. It did however significantly increase soil CO2 efflux rate in the first treatment year. These results are important when the effects of early forest management on carbon fluxes are modelled.