Description
Streams and the riparian ecosystems that they support are valuable natural resources that filter out pollutants and contaminants while providing habitat for plants and animals. Understanding the environmental effects of anthropogenic changes to riparian ecosystems begins with understanding how the surrounding watershed has been altered. This study utilized remotely sensed data, including vegetation greenness from the Normalized Difference Vegetation Index (NDVI) and elevation data from Light Detection and Ranging (LiDAR), to determine if urbanization is a factor contributing to differences and changes in the abundance of riparian vegetation in semi-arid watersheds of San Diego County. NDVI was calculated for 15 50 m reaches downstream of watersheds with differing amounts of urbanization, with drainage areas between 1.5 km2 to 10.5 km2. Relationships between reach-average NDVI and five explanatory variables: 1) area of the watershed, 2) years since urbanization, 3) percent of area developed, 4) riparian width of the study reach and 5) slope of the study reach, were examined to interpret spatial and temporal changes in riparian vegetation. Mean NDVI of the study reaches correlated positively with the percent of watershed area developed and the amount of time since urbanization first began. Other watershed and reach characteristics (area, width, slope) were not significant predictors of NDVI, suggesting that human-related variables were most important in controlling intersite variability in riparian vegetation abundance. Understanding how riparian vegetation is affected by urbanization can help inform professionals for future watershed management and urban planning.
