Identifier les rôles de l'émergence, la survie et la croissance dans une pinède en phase de régénération et soumise à des travaux du sol et de la végétation de différentes intensités

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVINInternational audienceThe regeneration phase is often a critical step in population dynamics but it is still incompletely understood due to the intricacy and complexity of the factors concerned. We investigated the role played by emergence, survival and growth in the recruitment process of a mature Aleppo pine forest (Age: 90, basal area =12 m2/ha) located in SE France and submitted to disturbances of various intensities. Disturbances were produced by site treatments replicated 4 times and including mechanical chopping, mechanical chopping followed by soil scarification in one or two directions, controlled fire of low or high intensity, and control. Seedling emergence, survival, dimensions were monitored over 6 years (2005-2010) on 580 one-square-meter plots in which the individual fate of each seedling was surveyed. Covers in bare soil, grass and shrub were also recorded. Seedlings did not emerge continuously and regularly with time but mostly during peaks particularly marked in the rainy autumnal seasons of the two first years. This specific pattern defined a ‘window’ of emergence characterised by the duration during which seedlings emerged, the number of emerged seedlings and the shape of the seedlings distribution with time. Survival and growth decreased from the earliest cohort to the latest cohort as soil conditions became less favourable mainly due to grass development. Emergence, survival and growth did not respond in the same way to treatments and soil surface conditions. The most intense treatments (scarification, high-intensity fire) were also the most efficient for creating sites free of ground vegetation favourable to seedling emergence. In contrast, less intense treatments (chopping, low-intensity fire) with lower impacts on soil and ground vegetation were also less efficient in promoting emergence. The high-intensity controlled fire treatment was the most beneficial to survival whereas the highest growth was recorded in the scarification treatments. From these results, it appeared that environmental factors controlling survival, emergence and growth processes differed and that their importance was likely to fluctuate with time. A clear illustration was given by the contrasting role played by shrubs that exerted a negative influence on emergence but a positive one on survival and growth We concluded that environmental factors controlling survival, emergence and growth processes could differ and their importance could fluctuate with time. Adapting silvicultural treatments to foster regeneration could thus benefit from a more detailed understanding of the processes involved in seedling recruitment