Effect of burnt wood removal on the natural regeneration of Pinus halepensis after fire in a pine forest in Tus valley (SE Spain)

摘要

In order to determine the effect of burnt tree removal on post-fire natural regeneration of Pinus halepensis, two 2500 m2 areas were selected 6 months after the fire (February 1995) in a totally destroyed mature (>70 yr old) pine forest in Spain. Inone area, all the trees were cut down and removed 10 months after the fire (in June 1995), and in the other, all the trees were left standing (control). Tree removal is a traditional management practice, carried out both for commercial wood harvesting and for site preparation and sanitation purposes. In each area, 20 permanent plots of 20 m2 each were randomly placed, and all seedlings emerging within them labelled by individual numbered plastic tags. Emergence, mortality, density and growth (height) of 6649 P. halepensis seedlings were monitored during the first 4 post-fire years (to June 1998). Seedling emergence was concentrated in the first post-fire autumn-winter period. No positive effect on seedling emergence was detected as a consequence of burnt stem dragging and subsequent turning over of soil. Wood removal produced an immediate average seedling mortality of 33%, and notably increased seedling mortality during the subsequent summer, probably due to increased exposure of seedlings to sunlight and the possible debilitation of many individuals by mechanical contact during burnt wood removal. A negative correlation of pine seedling mortality with height was detected, which increased significantly on wood removal in the third post-fire year. That is, short seedlings (<10 cm) in treated plots were the most likely to die during this period. In spite of the detrimental effect of wood removal on sapling survival, seedling density 4 yr after fire in the cleared area was large (3.35 seedlings/m2 vs.3.89 in the control plots). Wood removal treatment reduced seedling growth: seedling height was significantly higher in the control stand, and differences in seedling height growth rate became particularly noticeable in the fourth post-fire year. The results indicate that traditional wood removal practices do not threaten natural post-fire P. halepensis re-establishment if initial seedling density is large enough. However, further studies focusing on wood removal effects on the final tree development level and other ecological aspects are necessary to choose adequate post-fire forest management.