Soil respiration in a Mediterranean oak forest at different developmental stages after coppicing

To assess the variation of soil respiration at different forest stages we measured it in a coppiced oak (Quercus cerris L.) chronosequence in central Italy during two campaigns, spanning 2 successive years, in four stands at different stages of the rotation: 1 year (S1), 5 years (S5), 10 years (S10) and 17 years (S17) after coppicing. The contribution of the different components of soil respiration flux (aboveground litter, belowground decomposition soil organic matter and root respiration) was estimated by a paired comparison of manipulative experiments between the recently coppiced stand (S1) and mature stand (S17). Ninety percent of soil respiration values were between 1.7 and 7.8 mu mol m(-2) s(-1), with an overall mean (+/- SD) of 4.0 +/- 2.7 mu mol m(-2) s(-1). Spatial variation of soil respiration was high (CV=44.9%), with a mean range (i.e. patch size) of 4.8 +/- 2.7 m, as estimated from a semivariance analysis. In the absence of limitation by soil moisture, soil respiration was related to soil temperature with the exponential Q(10) model (average Q(10)=2.25). During summer, soil moisture constrained soil respiration and masked its dependence on soil temperature. Soil respiration declined over the years after coppicing. Assuming a linear decline with stand age, we estimated a reduction of 24% over a 20-year-rotation cycle. The response of soil respiration to temperature also changed with age of the stands: the Q(10) was estimated to decrease from 2.90 in S1 to 2.42 in S17, suggesting that different components or processes may be involved at different developmental stages. The contribution of heterotrophic respiration to total soil respiration flux was relatively larger in the young S1 stand than in the mature S17 stand.