Published online by Cambridge University Press: 05 July 2011
In this study we assessed the sustainability of leaf harvesting of the palm Chamaedorea radicalis by modeling the dynamics of harvested populations using stage-structured transition matrices. Within the study site, El Cielo Biosphere Reserve, palm demography and population growth is dependent on substrate type; a relationship that is due to the role of rock outcrops as a refuge from herbivory by free-ranging livestock. We accounted for this environmental heterogeneity by using a source–sink model in which non-browsed palms on rock outcrops act as a source population for browsed palms on the forest floor (sink). To evaluate the impact of leaf harvesting on these populations we incorporated the demographic effects of local harvesting practices into population models using data from leaf harvesting experiments. Results showed that when the demographic effects of leaf harvesting were combined with the effects of livestock browsing, population growth dropped significantly below the replacement rate, indicating that the combination of the two was not sustainable. This result is explicable in the context of the source–sink dynamic described above, where browsed palms on the forest floor are dependent on the migration of seeds from protected palms on rock outcrops. Incorporating leaf harvesting into the model reduces the survival and fecundity of all non-browsed palms, including important “source” palms on rock outcrops, with the result that non-browsed rock outcrops are no longer a sufficient source of recruitment for the entire population. The source–sink model was critical in projecting the consequences of this interaction between browsing and harvesting.
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