Establishment of Pinus halepensis Mill. saplings following fire:: effects of competition with shrub species

An early study analysing the effects of competition from Cistus monspeliensis-dominated shrub canopy on Pinus halepensis saplings, both colonising a recently burnt area, has been extended in order to test initial predictions. Inter-specific competition effects on P. halepensis were experimentally analysed by a shrub thinning-out treatment carried out 1 year after fire. The extension of the recorded period confirmed (i) a significant increase in height, and (ii) the lack of variation in density of P. halepensis saplings when the shrub layer was removed. In contrast, the increase in relative growth rate in height (RGRh) and the decrease in mortality recorded during early post-fire stages for treated units did not persist in subsequent years. These two treatment-induced effects disappeared 1 year after the shrub clearing (29 months after fire). It is hypothesised that this time should represent a culminating point in the inter-specific competition established between Cistus and Pinus saplings simultaneously colonising recently disturbed areas and be a critical period for pine sapling survival. After this time, a reduction in relatively short-lived Cistus populations and an increase in R halepensis abundance should be expected in the community. It is concluded that a shrub-clearing treatment could be recommendable if the initial post-fire pine sapling density is not high enough to successfully face the early critical competitive period. Consequences of early shrub competition on forest productivity during mature phases are also discussed. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.