Changes in quantitative patterns of dead wood in maritime pine plantations over time

Abstract

Although the volume of dead wood is commonly acknowledged as an indicator of biodiversity in sustainable forest management schemes, only few data are available for plantation forests. To evaluate the volume and qualify the diversity of woody debris along a chronosequence of maritime pine plantations, we sampled downed woody debris, snags and stumps in 143 stands of different ages. To test the hypothesis that the pattern of dead wood accumulation mainly results from silvicultural operations, we developed a predictive model. It combined an empirical growth model evaluating the amount of dead wood produced by successive thinnings with a decay function that estimated the loss of dead wood with time. The volume of dead wood averaged 15 m 3/ha. Downed woody debris, stumps and snags represented 81%, 11% and 8% of this volume, respectively. Pieces of downed woody debris were equally distributed between fine and coarse woody debris however large pieces (diameter ≥20 cm) were scarce. The dead wood was mainly from anthropogenic origin (77%) and its volume significantly increased with stand productivity. The pattern of dead wood accumulation along the forestry cycle showed a convex shape with a peak in stands of ca. 30-year-old, after the third thinning. The dynamics was successfully predicted for downed woody debris ( r = 0.47, P < 0.001) and for stumps ( r = 0.45, P < 0.001) by the model combining inputs from thinnings and loss with time. This model may help to predict the effect of alternative forestry practices on dead wood accumulation by forest managers or nature conservationists in similar pine forest plantations.