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The effects of management on soil carbon efflux in different ecosystems are still largely unknown yet crucial to both our understanding and management of global carbon flux. To compare the effects of common forest management practices on soil carbon cycling, we measured soil respiration rate (SRR) in a mixed-conifer and hardwood forest that had undergone various treatments from June to August 2003. The mixed-conifer forest, located in the Sierra Nevada Mountains of California, had been treated with thinning and burning manipulations in 2001, and the hardwood forest, located in the southeastern Missouri Ozarks, had been treated with harvesting manipulations in 1996 and 1997. Litter depth, soil temperature, and soil moisture were also measured. We found that selective thinning produced a similar effect on both forests by elevating SRR, soil moisture, and soil temperature, although the magnitude of response was greater in the mixed-conifer forest. Selective harvest increased SRR by 43% (from 3.38 to 4.82 µmol·m -2 ·s -1 ) in the mixed-conifer forest and by 14% (from 4.25 to 4.84 µmol·m -2 ·s -1 ) in the hardwood forest. Burning at the conifer site and even-aged harvesting at the mixed-hardwood site did not produce significantly different SRR from controls. Mean SRR were 3.24, 3.42, and 4.52 µmol·m -2 ·s -1 , respectively. At both sites, manipulations did significantly alter SRR by changing litter depth, soil structure, and forest microclimate. SRR response varied by vegetation patch type, the scale at which treatments altered these biotic factors. Our findings provide forest managers first-hand information on the response of soil carbon efflux to various management strategies in different forests.Résumé : Bien que cruciaux pour comprendre et gérer le flux global de carbone, les effets de l'aménagement sur les émissions de carbone du sol dans différents écosystèmes sont encore largement inconnus. Afin de comparer les effets des pratiques courantes d'aménagement forestier sur le recyclage du carbone du sol, les auteurs ont mesuré le taux de respiration du sol (TRS) dans une forêt mélangée de conifères et une forêt feuillue qui avaient subi différents traitements de juin à août 2003. La forêt mélangée de conifères, située dans la Sierra Nevada en Californie, avait subi des traitements d'éclaircie et de brûlage en 2001. La forêt feuillue, située dans les monts Ozarks au sud-est du Missouri, avait subi différents traitements de récolte en 1996 et 1997. L'épaisseur de la litière, la température du sol et la teneur en eau du sol ont aussi été mesurées. Ils ont observé que l'éclaircie jardinatoire a produit un effet semblable dans les deux forêts en élevant le TRS, la teneur en eau du sol et la température du sol quoique l'ampleur de la réaction ait été plus forte dans la forêt mélangée de conifères. La coupe de jardinage a augmenté le TRS de 43 % (de 3,38 à 4,82 µmol·m -2 ·s -1 ) dans la forêt mélangée de conifères et de 14 % (de 4,25 à 4,84 µmol·m -2 ·s -1 ) dans la forêt feuillue. Le brûlage dans le cas des conifères et ...

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How variations in carbon supply affect wood formation remains poorly understood in particular in mature forest trees. To elucidate how carbon supply affects carbon allocation and wood formation, we attempted to manipulate carbon supply to the cambial region by phloem girdling and compression during the mid-and late-growing season and measured effects on structural development, CO 2 efflux and nonstructural carbon reserves in stems of mature white pines. Wood formation and stem CO 2 efflux varied with a location relative to treatment (i.e., above or below the restriction). We observed up to twice as many tracheids formed above versus below the treatment after the phloem transport manipulation, whereas the cell-wall area decreased only slightly below the treatments, and cell size did not change relative to the control. Nonstructural carbon reserves in the xylem, needles and roots were largely unaffected by the treatments. Our results suggest that low and high carbon supply affects wood formation, primarily through a strong effect on cell proliferation, and respiration, but local nonstructural carbon concentrations appear to be maintained homeostatically. This contrasts with reports of decoupling of source activity and wood formation at the whole-tree or ecosystem level, highlighting the need to better understand organ-specific responses, within-tree feedbacks, as well as phenological and ontogenetic effects on sink-source dynamics.

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