Parentage analysis of a regenerating canopy palm population in a tropical second-growth forest.

摘要

Tropical secondary forests cover an estimated 500 million ha globally encompassing more land area than old-growth forests in many countries. Secondary forests will form the genetic template of future forests, and therefore require scientific attention. I studied dispersal and parentage of three generations of the abundant, animal-dispersed Neotropical canopy palm Iriartea deltoidea in a 24-yr old second-growth forest in northeastern Costa Rica. The founding generation revealed an extreme case of reproductive dominance, where more than half were produced as a result of mating events between only two of the 66 potential parent trees located in the adjacent old-growth forest. Spatial genetic analysis of trees in both forests demonstrated significantly lower genetic diversity among second-growth trees compared to the adjacent old-growth forest population. Inbreeding among founding trees within 400 m of the border with old-growth forest produced a cascading effect in the first generation of seedlings, further depressing genetic diversity. In contrast, seedlings and saplings in the old-growth and the distant portion (400-800 m) of second-growth forest showed high genetic diversity among all size classes. Seed dispersal and pollination distances obtained from the parentage analysis indicate a very large genetic neighborhood in this palm. Detailed analysis of parentage in five seedling patches surrounding reproductive trees revealed that few to none of the seedlings were produced by respective focal trees. At first sight, what appear to be seedling shadows of individual reproductive trees are, in fact, clusters of recruited seedlings from mixed genetic sources. Targeted deposition of seeds by toucans renders inverse models inaccurate for prediction of seed dispersal, as these models assume that the nearest reproductive tree is the genetic parent. Further, seedlings were to a large extent full or half-siblings originating from dozens of parents spread over large areas. Long-term genetic recovery of this species is possible, provided that diverse forests with intact animal dispersers remain in the surrounding landscape. At least for vertebrate-dispersed tree species with high rates of long-distance dispersal, second-growth forests can mitigate biodiversity loss following deforestation.