Mixed forests of Nothofagus pumilio and N. betuloides: Are they stable? Approximation based on the study of the first stages of natural regeneration cycle

Abstract

Flowering, seeding, seedling are a paramount process for tree regeneration, forest conservation and management. In mixed forests, the impact of limiting (biotic and abiotic) factors on tree reproductive success regulate the maintenance of species in balanced proportions or the conversion towards monospecific forests. Tree reproductive phenology were studied in three forest type (pure deciduous Nothofagus pumilio, pure evergreen Nothofagus betuloides and mixed forests) considering two location (coast and mountain), during three years in Tierra del Fuego, Argentina. The incidence of different loss factors (e.g., premature abortion, fruit, seed predation) was evaluated. Flowering and seeding varied interannually for both species for forest type. Both species showed advantages in pure forests than in mixed forests. A strong effect of location on seeding and in losses factors were detected. The main limiting factor in flowering results in empty seeds due to the pollen self-incompatibility. Premature abortion was associated with extreme climatic events (e.g., late frosts). N. pumilio presented in general higher losses associated with seed foraging and stratification losses in N. betuloides. Finish for each cycle, the seedling proportion was higher for N. pumilio in the mountains and coast than for N. betuloides. N. pumilio presents a better probability of transition than N. betuloides in the mixed forest. Therefore, in mixed forests the tendency would be to be non-stable forests. This study contributes to an understanding of the possible roles of reproductive phenology for detecting shifts in forest communities between pure and mixed forests under natural dynamics and the current climate change.