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Spatiotemporal characteristics of Lepidium latifolium invasion of the San Francisco Bay/Sacramento-San Joaquin Delta

Andrew, M. and Ustin, S. (2008) Spatiotemporal characteristics of Lepidium latifolium invasion of the San Francisco Bay/Sacramento-San Joaquin Delta. In: Bay Area Lepidium Science and Management Symposium, 10 September, Suisun City, CA, USA.


Hyperspectral and LiDAR (light detection and ranging) remote sensing data have the potential to address a wide variety of ecological questions. We have used these remotely sensed data to study the demography of Lepidium latifolium (perennial pepperweed) at several sites in the Sacramento-San Joaquin Delta and susceptibility to further invasion at Rush Ranch, in Suisun Marsh. Hyperspectral image data has been used to map Lepidium distributions in several sites of the Bay/Delta annually over 2004-2007. Annual distribution maps allow quantification of Lepidium spread. For example, on Bouldin Island, existing infestations doubled in size over these three years, with annual rates of increase ranging from 0.94 to 1.70. In contrast, a new infestation that spread from small satellite patches grew 35-fold in just three years, with annual growth rates ranging from 2.58 to 5.22. Habitat suitability modeling at Rush Ranch was performed with presence/absence of Lepidium extracted from the hyperspectral distribution map, and predictor variables derived from a high resolution LiDAR DEM (digital elevation model). Aggregate decision tree models found L. latifolium to infest two zones: near the marshland-upland margin and along channels within the marsh. Topographical data, which is typically strongly correlated to wetland species distributions, was relatively unimportant to L. latifolium occurrence, although relevant microtopography information, particularly relative elevation, was subsumed in the distance to channel variable. The map of potential L. latifolium distribution reveals that Rush Ranch contains considerable habitat that it is at risk to continued invasion.

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