Uriarte M.

Effects of forest re-growth, urban expansion, and climate variability on water quality in a tropical landscape

PowerPoint: Watershed protection as an ecosystem service? “Forests are assumed to be economically important for preventing soil erosion and flooding, protecting the water supply, and maintaining rainfall patterns. These assertion are often made with little supporting evidence.…First, benefits must be computed relative to an alternative land use. Second, benefit levels are highly location-specific and scale dependent”.

Land Transitions in the Tropics: Going Beyond the Case Studies

Uriarte, M., Schneider, L. and Rudel, T. K. (2010), Land Transitions in the Tropics: Going Beyond the Case Studies. Biotropica, 42: 1–2. doi: 10.1111/j.1744-7429.2009.00580.x

Estimates of the percent of Earth’s land surface that has either been transformed or degraded by human activity range between 39 and 50 percent, with agriculture accounting for the vast majority of these changes. Although much of the focus of research on land use and cover change in the tropics has been on deforestation, ongoing socioeconomic changes both locally and globally have made land transitions in the tropics extremely fluid. In addition, feedbacks between land cover change and human behavior constrain the extent and trajectories of land transitions. The sustainability of land use systems in the tropics depends on an understanding of coupled human–natural systems that can lead to general frameworks for management and prediction. The unprecedented availability of land use/cover data together with ecological data collected at large spatial scales offer exciting opportunities for advancing our understanding of socioecological systems. We rely on six studies of land transitions in the tropics to illustrate some promising approaches and pose critical questions to guide this body of research.

Variation in Susceptibility to Hurricane Damage as a Function of Storm Intensity in Puerto Rican Tree Species

Canham, Charles D.; Thompson, Jill; Zimmerman, Jess K.; Uriarte, Maria. 2010 Variation in Susceptibility to Hurricane Damage as a Function of Storm Intensity in Puerto Rican Tree Species. Biotropica, 42 (1). 87-94. 10.1111/j.1744-7429.2009.00545.x

One of the most significant challenges in developing a predictive understanding of the long-term effects of hurricanes on tropical forests is the development of quantitative models of the relationships between variation in storm intensity and the resulting severity of tree damage and mortality. There have been many comparative studies of interspecific variation in resistance of trees to wind damage based on aggregate responses to individual storms. We use a new approach, based on ordinal logistic regression, to fit quantitative models of the susceptibility of a tree species to different levels of damage across an explicit range of hurricane intensity. Our approach simultaneously estimates both the local intensity of the storm within a plot and the susceptibility to storm damage of different tree species within plots. Using the spatial variation of storm intensity embedded in two hurricanes (Hugo in 1989 and Georges in 1998) that struck the 16 ha Luquillo Forest Dynamics Plot in eastern Puerto Rico, we show that variation in susceptibility to storm damage is an important aspect of life history differentiation. Pioneers such as Cecropia schreberiana are highly susceptible to stem damage, while the late successional species Dacryodes excelsa suffered very little stem damage but significant crown damage. There was a surprisingly weak relationship between tree diameter and the susceptibility to damage for most of the 12 species examined. This may be due to the effects of repeated storms and trade winds on the architecture of trees and forest stands in this Puerto Rican subtropical wet forest.

Synthesis: Land Transitions in the Tropics

Uriarte, M., L. Schneider, and T. K. Rudel. 2010b. Synthesis:
land use transitions in the tropics. Biotropica 42:59–62.

Land cover transformations in the tropics are not limited to deforestation; they include other complex transitions such as agricultural and urban expansion, pasture development, and secondary vegetation regrowth. Understanding the causes and extent of these highly variable and complex transitions requires close collaboration between biological, physical, and social scientists. Here we address three critical issues in the study of land transitions: (1) What methodological and socioecological criteria should be used for characterizing land cover categories and transformations? Results from case studies presented here call for the creation of continuous land cover classes that allow for detection of disturbance and human use dynamics and consideration of socioeconomic and biophysical criteria in characterizing and monitoring land transitions. (2) What are the most promising theoretical frameworks? Successful theoretical frameworks must bridge disciplinary boundaries, and encompass multiple spatial, temporal, and political scales. (3) Are regime shifts, constraints, and resilience of land transformations in the tropics predictable? Resilience of land use systems requires a feedback loop between ecological constraints and management decisions. This loop may be broken by policies, migration, and flow of capital from global commodity markets. In addition, land transformations may lead to novel interactions between land-use and natural disturbance leading to unpredictable regime shifts in ecosystems. Planning for sustainable patterns of land use requires some understanding of these regime transformations.

Natural disturbance and human land use as determinants of tropical forest dynamics: results from a forest simulator

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

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.

Hurricane Disturbance Alters Secondary Forest Recovery in Puerto Rico

Flynn DFB, Uriarte M, Crk T et al (2009) Hurricane disturbance
alters secondary forest recovery in Puerto Rico.
Biotropica 42:149–157

Land-use history and large-scale disturbances interact to shape secondary forest structure and composition. How introduced species respond to disturbances such as hurricanes in post-agriculture forest recovery is of particular interest. To examine the effects of hurricane disturbance and previous land use on forest dynamics and composition, we revisited 37 secondary forest stands in former cattle pastures across Puerto Rico representing a range of exposure to the winds of Hurricane Georges in 1998. Stands ranged from 21 to480 yr since agricultural abandonment and were measured 9 yr posthurricane. Stem density decreased as stands aged, while basal area and species richness tended to increase. Hurricane disturbance exerted contrasting effects on stand structure, contingent on stand age. In older stands, the basal area of large trees fell, shifting to a stand structure characteristic of younger stands, while the basal area of large trees tended to rise in younger stands with increasing hurricane disturbance. These results demonstrate that large-scale natural disturbances can alter the successional trajectory of secondary forest stands recovering from human land use, but stand age, precipitation and soil series were better predictors of changes in stand structure across all study sites. Species composition changed substantially between census intervals, but neither age nor hurricane disturbance consistently predicted species composition change. However, exposure to hurricane winds tended to decrease the abundance of the introduced tree Spathodea campanulata, particularly in smaller size classes. In all sites the abundance of the introduced tree Syzygium jambos showed a declining trend, again most strongly in smaller size classes, suggesting natural thinning through succession.
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