Document: TIM-3-87-22

Modeling restoration processes in a bottomland forest-agricultural landscape.

NUTTLE, T.* and J.W.HAEFNER

Utah State University, Logan, UT 84322-5305 USA ¹

Abstract:
Our model investigates tree invasion processes in wetland forest restoration sites of the Mississippi Alluvial Valley. Restoration sites occupy 78,000 ha within a landscape mosaic of active agricultural lands and forest patches. Existing forest simulation models are inadequate to address tree invasion processes in unforested sites because of restrictive assumptions of spatial scale and environmental homogeneity, and because they ignore survival and growth of seeds and seedlings, where the vast majority of mortality occurs. Because seed dispersal from forest to adjoining restoration sites is necessarily spatially patterned, as are environmental conditions that affect its establishment and growth, a model must address processes at relevant spatial and temporal scales to investigate the observed patterns of tree invasion. Thus, we developed a spatially explicit, individual-based model of the dispersal, establishment, and subsequent growth processes of trees in the forest-agricultural system. The model incorporates spatially realistic patterns of source populations of trees, seed dispersal kernels derived from wind frequency data, and survival and growth functions similar to those used in SWAMP (a JABOWA derivative). Furthermore, individuals exist in continuous space throughout the model landscape, as in SORTIE, but the effect of competition (and other environmental influences) are scaled to a grid of cells where the area of influence for each individual is calculated using ecological field theory. The model predicts that the observed tree invasion pattern can result from either limited seed dispersal or from spatially patterned environmental conditions that are harshest far from existing forest, but more amenable near forest. Further parametization of the model using experimentally derived estimates of seed dispersal and seedling establishment with maps of edaphic conditions will yield results that can be applied in the restoration planning process.

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This abstract is being presented at: 3:30 PM in session:
AGROECOLOGY