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High-resolution maps of forest-urban watersheds present an opportunity for ecologists and managers
Citation:
Stueve, K., T. Hollenhorst, J. Kelly, L. Johnson, AND G. Host. High-resolution maps of forest-urban watersheds present an opportunity for ecologists and managers. LANDSCAPE ECOLOGY. Springer, New York, NY, 30:313-323, (2015).
Impact/Purpose:
To appreciate potential effects of green infrastructure at scales from neighborhoods to watersheds it is important to be able to observe and quantity the presence and spatial distribution of green infrastructure features that exist at scales of meters or even less. Moreover, these must be observable in patches and interfaces such as between land cover classes, riparian buffers, or on rooftops in mixed use forest-urban environments. To date, there are no methods to make these observations comprehensively and feasibly at an extent to the thousands of square kilometers needed for watershed classification. This paper presents a new method that used a set of variables, gathered remotely, using high-resolution aerial photography, visible/infrared spectral sensors, and microtopographic elevation data. The method demonstrated, calibrated, and validated new land classifications to sub-meter scales and allowed a look at the spatial pattern of distribution of green infrastructure-like features for a entire case study watershed.
Description:
Dense populations of people and abundant impervious surfaces contribute to poor water quality and increased flooding in forest-urban watersheds. Green infrastructure mitigates these effects, but precisely quantifying benefits is difficult because most land cover maps rely on coarse-resolution data. Hence, important questions concerning the effects of green infrastructure on water quality and quantity at different spatial scales remain unanswered. We used object-based image analysis to create high-resolution land cover maps and detect tree canopy overlapping impervious surfaces in a forest-urban watershed. Mapping accuracies approached or exceeded 90%. Impervious surfaces comprised ~24% of the watershed, tree canopy overlapped ~6% of impervious surfaces, and tree extent greatly exceeded baseline estimates. High-resolution land cover products provide ecologists an unprecedented opportunity to (1) quantify benefits of green infrastructure at different spatial scales and (2) model where future installations of green infrastructure and development are feasible, which could greatly improve the decision-making abilities of managers.
