The spatial distribution and biogeography of invasive plants at a regional and local scale in California

The invasion of alien plant species has a multitude of negative impacts on natural communities including a reduction in the amount of light, water, nutrients and space available to native species. In addition, alien plant species alter hydrological patterns, soil chemistry and moisture-holding capacity, and change fire regimes. The objectives of this dissertation were to provide a comprehensive assessment of alien plant invasion in California. More specifically, I examined the environmental factors that influence the invasion of alien plant species at a regional and local scale in California and I assessed the use of remotely sensed imagery in studying this phenomena.; The distribution of alien plant species was positively correlated with alien plant species richness at a statewide to local (1m2) scale. At the statewide scale, I documented a total of 1,170 alien plants species in California. Of this, 73 (6.24%) are considered invasive, causing harm to natural communities. Low elevation and high road density were significant factors in explaining the variation in the distribution of alien plant species in the state of California. At the local scale, I found a total of 21 alien plant species at Leo Carillo State Park in the Santa Monica Mountains of California. Of this, 9 (4.2%) are considered invasive. Elevation, distance to coast, and distance to trails/roads were significant factors in the distribution of alien plant species at a local scale.; The Normalized Difference Vegetation Index (NDVI) was significantly correlated with invasion variables collected in the field. At sites with low NDVI values, invasion was higher. My results suggest there is a great deal of potential to be learned from in-depth studies assessing this relationship. In addition, my results indicate that the scale and aggregation levels of remotely sensed data may have a large impact on the results of distribution models in biogeography.