Models as tools for understanding the effects of hurricanes on tropical forests.
Uriarte, Maria*,1, 2, Canham, Charles2, Thompson, Jill3, Zimmerman, Jess3, Brokaw, Nick3, 1 Dept of Ecology, Evolution and Ennvironmental Biology, New York, NY2 Institute of Ecosystem Studies, Millbrook, NY3 Institute for Tropical Ecosystem Studies, Rio Piedras
ABSTRACT- Hurricanes are the dominant natural disturbance in the tropical forests of Caribbean islands. We propose that the role of hurricanes in the long-term dynamics of tropical forests will only be clarified through the use of predictive, empirically-based models of forest dynamics, designed to incorporate the effects of hurricanes on the basic demographic processes that regulate forest community dynamics. Here we present details on the development and parameterization of a spatially-explicit model, SORTIE/PR. We used data from impacts of two hurricanes and three repeated tree censuses in the 16-ha Luquillo Forest Dynamics Plot in Puerto Rico, to parameterize submodels that reflect the effects of disturbance on demographic processes of 12 dominant tree species with different life history characteristics: (a) Disturbance submodel. We use a likelihood-based, ordinal logistic regression procedure to quantify species-specific relationships between local variation in storm severity and the degree of damage to individual trees; (b) Growth and mortality submodel: We predict both growth and mortality directly as a function of the configuration of neighboring saplings and adult trees around an individual; (c) Recruitment submodel: We use inverse modeling and incorporate a number of processes that reflect recruitment immediately following a hurricane; and (d) Light submodel: Spatial variation of understory light level is characterized as a function of the degree of hurricane damage to trees in a given neighborhood. The model is a powerful tool for addressing a diverse set of questions on the long-term effects of hurricane disturbance in tropical forests. Specifically, we ask: 1) What are the implications of variation in hurricane frequency and severity for the long-term dynamics of forest structure, composition and diversity? and 2) What life history traits play a key role in forest recovery from disturbance? The results demonstrate the range of species-specific responses to hurricane damage, the impact of neighbors, and the effect of density and light on seedling establishment. The relative importance of the species in the community and their responses to hurricanes will determine the fate of this forest.
Key words: tropical forest dynamics, hurricane disturbance, spatially-explicit models, successional niche
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