Does the recruitment pattern of Spanish black pine (Pinus nigra Arn ssp salzmannii) change the regeneration niche over the early life cycle of individuals?

The abundance and distribution of Mediterranean tree species are determined mainly during early regeneration stages, when seedlings and saplings are most vulnerable to their immediate environment. Initial recruitment of Spanish black pine (Pinus nigra Am ssp. salzmannii) was studied under field conditions in a central population (1200 m a.s.l.) and at the upper elevation limits (1500 m a.s.l.) in the Cuenca Mountains (central-eastern Spain). The goal was to assess the effects of (1) overstory density (low density: 15-20 m(2) ha(-1), medium density: 25-30 m(2) ha(-1) and high density: 35-40 m(2) ha(-1)), (2) soil preparation (scalping and control), and (3) sowing date (51: February; S2: March; S3: April; S4: May) on seedling survival and initial seedling development (height, basal diameter and crown volume). Results from this study showed that initial recruitment of Spanish black pine depends on the habitat altitude, on the soil preparation and varies with the density of the stand. Site preparation showed a significant negative influence on initial seedling growth, with greater seedling height and basal diameter in the absence of soil preparation. Sowing date had no significant effect on seedling survival or initial seedling growth. The results from this study are discussed within the framework of ontogenetic niche shifts for plant-regeneration dynamics and in the context of the development of management guidelines to improve the natural regeneration of black pine. (C) 2012 Elsevier B.V. All rights reserved.