Uriarte, M., C. D. Canham, J. Thompson, J. K. Zimmerman,
L. Murphy, A. M. Sabat, N. Fetcher, and B. L.
Haines. 2009. Natural disturbance and human land
use as determinants of tropical forest dynamics:
results from a forest simulator. Ecological Monographs
79:423–443.
Abstract:
Forests are often subject to multiple, compounded disturbances, representing
both natural and human-induced processes. Predicting forest dynamics requires that we
consider how these disturbances interact to affect species demography. Here we present results
of an individual-based, spatially explicit forest simulator that we developed to analyze the
compounded effects of hurricane disturbance and land use legacies on the dynamics of a
subtropical forest. We used data from the 16-ha Luquillo Forest Dynamics Plot in Puerto
Rico, together with a reconstruction of historical wind damage, to parameterize the simulator.
We used the model to ask two questions. (1) What are the implications of variation in
hurricane frequency and severity for the long-term dynamics of forest composition, diversity,
and structure? Both storm severity and frequency had striking effects on forest dynamics,
composition, and structure. The periodicity of disturbance also played an important role, with
periods of high hurricane activity fostering the establishment of species that may become rare
in the absence of severe storms and quiescent periods allowing these species to reach
reproductive size. Species responses to hurricane disturbance could not be predicted from their
life history attributes. However, species perceived to be primary forest species exhibited low
temporal variation in abundance through the simulations. (2) How do hurricanes and legacies
from human land use interact to determine community structure and composition? Our results
suggest that, over time, regardless of the storm regime, land use legacies will become less
apparent but will lead to a forest community that contains a mixture of secondary and
primary forest species formerly dominant in areas of different land use. In the long term,
hurricane disturbance generated two communities with slightly greater similarity than those
not subject to storms. Thus, the inclusion of hurricane disturbance does not alter the
prediction that land use legacies in this tropical forest will diminish over time. Our simulations
also highlight the contingent effects of human legacies on subsequent community dynamics,
including the response to hurricane disturbance, therefore supporting the notion that
compounded disturbances can interact in ways that cannot be predicted by the study of single
disturbances. The widespread importance of land use as a large-scale disturbance makes it
imperative that it be addressed as a fundamental ecological process.