Abiotic alterations caused by forest fragmentation affect tree regeneration: a shade and drought tolerance gradient in the remnants of Coastal Maulino Forest
Plant regeneration is strongly determined by light and soil moisture differences between habitáis; both variables are modified by large-scale forest fragmentation. Several studies have indicated this alteration as the mechanism involved in tropical forest community change. The effects of fragmentation may be much more severe in Mediterranean and deciduous forests, because plant species in these forests show a stress tolerance tradeoff between shade and drought. Our study was performed in the deciduous fragmented Coastal Maulino Forest: Reserva Nacional Los Queules (RNLQ) and surrounding small fragments. We hypothesised that Aristotelia chilensis (shade intolerant but drought tolerant) should increase its regeneration in small patches as a consequence of the change in habitat suitability (i.e. luminous and drier), while Cryptocarya alba (shade tolerant but drought intolerant) should have less regeneration in small fragments. We also expected that Nothofagus glauca and N. obliqua, which have shade and drought tolerances intermedíate between A. chilensis and C. alba, should respond less to forest fragmentation. We used two estimations of plant regeneration: (i) seedling and sapling densities via field observations and (ii) seed germination and seedling establishment via a field-based experiment. Natural regeneration patterns of C. alba indicated a depressed regeneration within small forest fragments compared to RNLQ, although experimental germination, establishment and recruitment proportions did not vary between habitáis. In contrast, A. chilensis regeneration was favored by forest fragmentation, with increased seedling and sapling densities and germination in small forest fragments. Both N. glauca and N. obliqua were less affected by forest fragmentation in their natural and experimental regeneration. This study highlights the relevance of studying changes in abiotic factors as a consequence of human activities, and considering safe sites (defined by regeneration niche attributes) for implementing conservation actions and ecological restoration.