Identification of windows of emergence and seedling establishment in a pine Mediterranean forest under controlled disturbances

The regeneration phase is a critical step in plant population dynamics, but is still incompletely understood owing to the intricacy and complexity of the factors concerned. We investigated the role played by pine emergence, survival and growth in the recruitment process of a Mediterranean pine forest under disturbances of various intensities. Disturbances were produced by site treatments including mechanical chopping, soil scarification, and controlled fire of low or high intensity. Pine seedling emergence, survival, dimensions and the relative cover of bare soil, grasses and shrub were monitored on 5801-m2 plots over 6 years in a mature Aleppo pine forest (Pinus halepensis Mill.).Seedlings did not emerge continuously and regularly with time, but mostly in bursts, which were particularly marked in the rainy autumnal seasons. This specific pattern defined a ‘window’ of emergence characterised by the length of time during which seedlings emerged, the number of emerged seedlings and the shape of the window. Survival and growth decreased from the youngest cohort to the oldest cohort. Emergence, survival and growth did not respond in the same way to treatments and soil surface conditions. In particular, scarification treatments were most favourable to emergence, whereas the high-intensity controlled fire treatment was most beneficial to survival. Shrub cover was detrimental to emergence, but positively influenced survival and growth.We conclude that environmental factors controlling survival, emergence and growth processes differ, and that their importance varies over time. A detailed understanding of the processes involved in seedling recruitment can be helpful for selecting the types and intensities of the controlled disturbances to be applied to successfully regenerate forest stands.