Pollination biology of a high-altitude wind-pollinated tree species

Background/Question/Methods

Successful sexual reproduction in wind-pollinated tree species depends on multiple demographic and reproductive traits. Reproductive success can also be negatively affected by anthropogenic disturbance, which can alter pollen movement and pollination efficiency. In this study, we examined several aspects of the pollination biology of a wind-pollinated tree species, Polylepis tomentella (Rosaceae), inhabiting the semidry Andean treeline and threaten by low recruitment rates, land-use practices, and global climate change. As in other species of the genus Polylepis, long-term human activities (e.g., logging, farming, and burning) have reduced the distributional range of the species and remaining populations exhibit low rates of seedling establishment mostly associated with changes on population structure and seed germination. For two consequtive years, we conducted a experimental study in natural populations under different degrees of disturbance by human activities. Several aspects of the reproductive biology of P. tomentella were examined. We specifically examined the extended in which fruit/seed production is pollen-limited, assessed whether the species is self-incompatible, and quantified variability in the pollination efficiency system.

Results/Conclusions

Results from field experiments showed that P. tomentella is self-compatible as it produces fruits/seeds from selfing and crossing. These results were supported by the pollination efficiency experiment, which showed a higher proportion of germinated pollen grains and pollen tubes in self-pollinated flowers. However, fruits from self-pollinated flowers were smaller suggesting partial inbreeding depression after selfing. Pollen addition did not increase fruit set, probably because open-pollinated flowers recieved a mix of pollen from the same plant and conspecifics. Results suggest that other factors than the pollination biology of the species are associated with the low production of viable seeds. Plants from strongly disturbed populations produce fruits but long-term population viability is threatened by unsustainable firewood extraction rates and land use intensification.