San Juan Hydrologic Unit – Non-native Species Eradication Plan

This project developed a comprehensive program to remove non-native, invasive species from the San Juan Hydrologic Unit.

The San Juan Hydrologic Unit (SJHU) is a generally trapezoidal-shaped area of 500 square miles in Orange, San Diego and Riverside Counties. This project included the SJHU area within Orange County, which is comprised of approximately half the square miles, or about 173,319 acres.

The headwaters for this unit largely begin in the Cleveland National Forest in a rugged mountain environment, then enter a more level floodplain in the middle sections, before reaching their ocean outlets.

The SJHU has experienced a variety of natural and human-induced changes, which have caused economic damages and a significant decline in environmental resources. Invasive species reduce overall biodiversity within the various habitats they displace and degrade the natural functioning of many of these habitat associations and ecosystems. Removal and restoration of these areas is critical to the long term sustainability and ecological functionality within these ecosystems.

In the past it has been common for various interest groups to try and eradicate these species from a particular location within a watershed without having an understanding of where else in that watershed the species exist and where additional seed or other propagule sources may continue to come from once they have removed the existing vegetative biomass. While such efforts have generally been well intended, such programs are not without environmental impacts and, without a well-defined strategy, they may achieve short term successes at great expense and impact. With this in mind, this project aimed to develop a non-native species eradication plan, starting with removal at the headwaters, for the entire San Juan Hydrologic Unit.