Island Ecology

Horehound (front right) seedhead, embedded with a bison hair clump.  Bison play a role in the dispersal of non-native plant species.

Non-native plants have been defined as any plant introduced to California after European contact. There are roughly 215 non-native plant species found on Catalina Island, and of those, less than a third are known to be invasive throughout California. An invasive plant is a non-native plant that can invade native ecosystems, which can lead to the alteration of natural ecosystem processes and/or displace native flora. Invasive plant species can have a competitive edge over native flora because invasive species lack the natural predators and diseases found in their native home range.

Unfortunately, the Catalina Island Conservancy does not have the resources to control all the invasive plant species found on Catalina Island. By prioritizing them, the Catalina Island Conservancy can use their limited resources most effectively to ensure the health of natural ecosystems.  In 2004 seventy-six invasive species were identified for mapping and control prioritization. Populations of these 76 species were mapped throughout the island’s 200-plus miles of roads, 50 miles of coastline, twelve inhabited areas, 233 major drainages, 200-plus ridgelines and corresponding hillsides. After mapping using a global positioning system (GPS), the data gathered was entered into a Geographic Information System (GIS) to produce maps for analysis. A literature review was conducted on each species to gather information on climactic preferences and biological characteristics such as: means of reproduction, flowering period, seed production and invasiveness, among others. Several invasive plant species have also been modeled to predict their invasiveness on Catalina Island using a climate model.

John Knapp surveyed the entire Island for non-native invasive species.

After carefully plotting the location, distribution, biological characteristics and climatic preferences for each species, a ranking index was used, weighing the following:

1. Alteration of ecosystem processes, invasiveness and amount of area infested.
2. Each watershed will be ranked for priority of control based on rarity of the habitat infested, the amount of each invasive species in that watershed, and the local ease of control.
3. The ranking system will produce a prioritized list of the 76 invasive plant species for the island as whole.

The survey for invasive plant species enabled the Catalina Island Conservancy to monitor the success of management strategies and control techniques and the status of each species over time by building on the database developed with this project.

Several grants have been obtained by the Conservancy from various Federal, State and local agencies and the control and eradication of the highest ranked weeds on the Island is well on its way.  Twenty-two species of invasive weeds are scheduled for eradication and 8 species targeted for reduction in 2006.  Additionally, 120 acres of invasive flax-leaved broom have been controlled.  This control work will continue over the next few years.