Selection of scale for Everglades landscape models |
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Authors: | Jayantha Obeysekera Ken Rutchey |
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Institution: | (1) South Florida Water Management District, 33416 West Palm Beach, Florida, USA |
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Abstract: | This article addresses the problem of determining the optimal “Model Grain” or spatial resolution (scale) for landscape modeling
in the Everglades. Selecting an appropriate scale for landscape modeling is a critical task that is necessary before using
spatial data for model development. How the landscape is viewed in a simulation model is dependent on the scale (cell size)
in which it is created. Given that different processes usually have different rates of fluctuations (frequencies), the question
of selection of an appropriate modeling scale is a difficult one and most relevant to developing spatial ecosystem models.
The question of choosing the appropriate scale for modeling is addressed using the landscape indices (e.g., cover fraction, diversity index, fractal dimension, and transition probabilities) recently developed for quantifying overall
characteristics of spatial patterns. A vegetation map of an Everglades impoundment area developed from SPOT satellite data
was used in the analyses. The data from this original 20 × 20 m data set was spatially aggregated to a 40 × 40 m resolution
and incremented by 40 meters on up to 1000 × 1000 m (i.e., 40, 80, 120, 160 … 1000) scale. The primary focus was on the loss of information and the variation of spatial indices as
a function of broadening “Model Grain” or scale.
Cover fraction and diversity indices with broadening scale indicate important features, such as tree islands and brush mixture
communities in the landscape, nearly disappear at or beyond the 700 m scale. The fractal analyses indicate that the area perimeter
relationship changes quite rapidly after about 100 m scale. These results and others reported in the paper should be useful
for setting appropriate objectives and expectations for Everglades landscape models built to varying spatial scales. |
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