| Summary: | 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. Meginmarkmið rannsóknarinnar var að kanna skammtímaáhrif skógræktaraðgerða, nánar tiltekið grisjunar og áburðargjafar, á jarðvegsöndun í íslenskum asparskógi. Einnig var fylgst með trjávexti, laufflatarmáli og breytingum á loft- og jarðvegshita. Hefðbundin snemmgrisjun (50%) hafði lítil áhrif á jarðvegshita. Mikil grisjun (80%) jók jarðvegshita að vori og sumarlagi en hafði lítil áhrif yfir veturinn. Grisjun hafði engin áhrif á magn næringarefna í laufi eða trjávöxt fyrsta árið. Áhrif grisjunar á jarðvegsöndun voru nokkuð óvænt: hún minnkaði marktækt í kjölfar grisjunar, þrátt fyrir að hitastig hafi hækkað og allt lífrænt efni sem féll til við grisjun hafi verið skilið eftir á skógarbotni. Einu áhrif áburðargjafar á trjávöxt fyrsta árið komu fram í auknu magni næringarefna í laufi. Jarðvegsöndun jókst hins vegar marktækt í ...
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