PS 15-15 - Consequences of the seed production timing on germination rates and seedling survival in highly seasonal environments: A case study of an evergreen live oak species (Quercus oleoides) in tropical dry forests of Northwest Costa Rica

Tuesday, August 9, 2011
Exhibit Hall 3, Austin Convention Center
Alyson E. Center, Plant Biological Sciences, University of Minnesota, St Paul, MN and Jeannine Cavender-Bares, Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN

Germination is a complex physiological process that is largely influenced by temperature and water potential making seed production timing a large determinant in germination and subsequent seedling survival, especially in species that lack seed dormancy like the live oak species (Quercus oleoides) found in neotropical dry forests. Quercus oleoides commonly forms monodominant stands that provide shade during the dry season. Given this species’ important role in tropical dry forests, the objective this research is to understand how the timing of acorn production, in relation to seasonal water availability, influences germination rates, and seedling growth and survival within a geographically and genetically distinct population of Q. oleoides in Northwestern Costa Rica.

A previous study by Deacon (2010) showed that in Northwest Costa Rica, flowering time of Quercus oleoides follows a unique pattern, appearing to be more temporally spread out and in some sub-populations is characterized by two distinct flowering episodes resulting in the production of two cohorts of acorns. Both cohorts are produced in the wet season (WS) but the first is produced in June, corresponding to the beginning of the WS and the second is produced in September, corresponding to the later stages of the WS. A reciprocal transplant experiment in common gardens at Santa Rosa (SR) and Rincon de la Vieja (RI) national parks in NW Costa Rica is being conducted to examine the effects of both timing of acorn production and seed population source influences germination rates and seedling survival in relation to water availability.  


Results from the first year indicate that at both sites, acorns produced at the end of the September cohort germinated quicker (p<0.0001) than acorns produced in June.  There seems to be no population level effect on germination rates but interestingly, acorns from RI are larger in both length and diameter (p>0.001) than SR but size does not affect germination rates between seasonal cohorts. 

Climate change is predicted to have significant impacts on phenological processes in plants in the tropics. As stewards of the Earth, research into how species and ecosystems will respond to climate change is critical now more than ever. In the last two centuries, there has been unprecedented pressure put on tropical ecosystems because of the rapid increase in human populations and globalization. Understanding the consequences of the seasonal timing of seed production on germination rates and seedling survival can provide insight into plant responses to an altered climate.

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