Regeneration of Pinus halepensis stands after partial cutting in southern France: Impacts of different ground vegetation, soil and logging slash treatments
Introduction
Considerable attention has been given in past studies to Aleppo pine seedling recruitment after fire (e.g. Daskalakou and Thanos, 1996, Daskalakou and Thanos, 2004, Martínez-Sánchez et al., 1999, Pausas et al., 2003). Early and massive cone production, presence of a high percentage of serotinous cones in the canopy and absence of competitive ground vegetation confer on this species its ability to easily reproduce in post fire conditions (Nathan and Ne’eman, 2004, Ne’eman et al., 2004). By contrast, fire-free recruitment relies on different processes and has received, relatively, much less attention. In the absence of fire, seed release is induced by air drying (Nathan et al., 1999). Soil composition, predation and competition by the ground vegetation induce completely different patterns of seedling recruitment. In this context, previous studies have emphasized the difficulty of regeneration in pine stands. Obstacles to regeneration beneath Aleppo pine canopy have been described as being related to insufficient light availability (Thanos, 2000), seed predation (Acherar and Lepart, 1984), thick needle layer (Arianoustou and Ne’eman, 2000). These results tend to support the theory that Aleppo pine seedling establishment matches the escape hypothesis (Nathan et al., 2000) as survival probabilities are lower close to or beneath the parent tree. Absence or insufficient natural regeneration in Aleppo pine stands is thus a problem the forest manager has to deal with in areas where wild fires seldom occur. Presently in Southern France where Aleppo pine covers about 250,000 ha, the renewal of some mature pine stands is problematic and there is a need of sylvicultural techniques favouring pine recruitment. With this aim, usual recommendations in the case of pine stands consist in combining partial cutting (or regeneration cutting) with soil and ground vegetation treatments in order to increase seedbed quality and to control vegetation development (e.g. Nilsson et al., 2002, Boucher et al., 2007). These techniques are widely applied in temperate Europe (Nilsson et al., 2002, Nilsson et al., 2006) but are much less frequently used in the Mediterranean area and have not been tested, to our knowledge, on Aleppo pine.
In this context, our study aims at testing the impacts of different ground vegetation and soil treatments, including prescribed burning, on natural seedling establishment in a partially cut treated mature Aleppo pine stand. Our goal is to determine which treatment of soil and ground vegetation can favor Aleppo pine regeneration and whether logging slash management has an influence on seedling recruitment.
Section snippets
Site description
The study site was located in a 90-year-old Aleppo pine stand of approximately 10 ha within the communal forest of Barbentane (43°54′01″–4°44′55″) near Avignon city in southern France (Fig. 1). The area did not experience major forest fires during the last century. The vegetation was composed of a monospecific dominant Aleppo pine tree layer, a weakly developed subcanopy layer of Quercus ilex, a shrub layer mainly dominated by Buxus sempervirens and Quercus coccifera and a ground layer where
Treatments effects on seedling density
Mean density of living seedlings for all treatments increased from 1.04 m2 at the end of 2005 to 2.09 m2 at the end of 2006 but dropped to 1.25 m2 at the end of 2007.
Results of the ANOVA following the Scheirer–Ray–Hare procedure indicate that soil and ground vegetation treatments were always highly significant, slash treatment was significant in 2007 and 2005 and no block effect was detected in any of the years (Table 2). Analysis of interactions indicates that interaction between slash and soil
Seedling dynamics
Aleppo pine seedling emergence after a wild fire was reported to take place almost exclusively after the onset of the postfire rainy season (Daskalakou and Thanos, 2004). In fire-free conditions seedling emergence usually starts in the rainy season (November–December) of the Mediterranean climate (Nathan and Ne’eman, 2004). This pattern was confirmed by our study in 2005 and 2006: most of the seedling emergence occurred in autumn while emergence was weaker in spring. In autumn emergence was
Conclusion
This study shows that soil and ground vegetation treatments influence pine recruitment. The positive effect of scarification found in this study is in line with many other studies conducted in temperate pine forests (e.g. Karlsson and Nilsson, 2005, Nilsson et al., 2002, Karlsson, 2000) but had not been tested on Aleppo pine in the Mediterranean area. The success or failure of the regeneration in Mediterranean pine stands is also largely dependant on the timing of scarification in a good seed
Acknowledgements
This study was supported by the Region Provence-Alpes-Côte d’Azur.
The authors are especially grateful to Guillaume Favand and Jean-Michel Lopez for providing the first analyses of this study and to Roland Estève, Aminata N’Daye and Willy Martin for data collection. The authors also thank Mrs. Ripert for revising the English, Philip Roche and Anne Ganteaume for statistical advice and help.
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