COS 239-2 - Genetic variation and differentiation among six populations of Quercus costaricensis Liebm. (Fagaceae) in Costa Rica: A comparison between old-growth and naturally regenerated stands

Background/Question/Methods

Dispersed on the high mountains throughout the tropics, montane cloud forests (TMCF) account for only 2.5 percent of the total area of tropical forest worldwide. TMCFs provide multiple hydrological and biogeochemical services that benefit human and biological communities surrounding them. The Talamanca Mountain range in southern Central America holds the most extensive tracts of primary rainforest in Costa Rica. At elevations higher than 2000 m, different oak species dominate mature TMCFs of the Talamanca Range. The construction of the Interamerican Highway in Costa Rica accelerated the destruction of TMCF in the Talamancas between 1950 and 1970. During that time, farmers established many clearings along or near the Highway. Scattered clearings were common in the forest vegetation because large oak trees were fallen for conversion to charcoal or wine barrel staves. This trend reversed in the 1980s, triggered by economic factors. Subsequently, TMCFs started to recover due to the abandonment of pastures and agricultural fields, legislation requiring government approval to clear forest for other uses, reforestation and forest protection policies, and the expansion of protected areas. This study aimed to determine the genetic consequences of those anthropogenic changes on the genetic diversity of Quercus costaricensis in naturally regenerated secondary forests.

Results/Conclusions

We found significant levels of genetic diversity for the eight microsatellite loci examined in this study; we identified thirty-four alleles in the Q. costarricensis tree sampled in the two old-growth forest stands. Our results show that the mean number of alleles per locus varies between 4.2 and 3.6 among the 79 trees with DBH > 50 cm included. The mean observed heterozygosity ranged from 0.338 to 0.568, and the expected heterozygosity ranged from 0.514 to 0.586. Genetic diversity indicators changed as we had trees with less than 30 cm in DBH in the regeneration stands. Analysis of Molecular variance (AMOVA) revealed that only 4% of the genetic diversity is found between stands when only trees with > 50 cm DBH were considered. Genetic differences between stands increased when the regeneration plots were considered in the analysis of molecular variance. The genetic variance between sites appeared to increase as new saplings were recruited in the regeneration plots. Moreover, the highest level of genetic differentiation among populations was found when only trees with less than 30 cm in DBH were included in the analysis, suggesting that newly recruited trees augment the genetic differences among stands.