Channel Islands National Park: Terrestrial vegetation monitoring annual report—2019

Williams, Cameron; Rodriguez, Dirk

doi:10.36967/2306141

Long-term ecological research is critical for evaluating past resource management actions and guiding future decisions. This report presents the data collected at Channel Islands National Park (CHIS) in 2019 as part of its terrestrial vegetation monitoring program. The program’s objective is to document long-term trends in the park’s vegetation communities consistent with the Mediterranean Network that also includes Santa Monica Mountains National Recreation Area and Cabrillo National Monument. Monitoring at CHIS began in 1984 to observe vegetation recovery after the removal of nonnative ranched animals. In 2019, field data were collected from 132 out of the 144 transects scheduled. Analyzing all years of data together showed that annual rainfall correlated positively with percent cover of vegetation, and an apparent long-term decline in average percent cover of vegetation that started in the mid-1990s continued in 2019. Analyzing the 2019 dataset by itself provided more nuanced results. Seablite scrub and valley/foothill grassland had consistently low proportions of absolute cover and native richness, respectively, as well as relatively low overall richness. These communities may have been more susceptible to browsing/grazing in the past and currently resistant to passive recovery; both communities could benefit from targeted restoration efforts. Vegetation was, on average, tallest at Santa Cruz and Santa Rosa Islands due to the presence of tree-dominated communities. Perennial plant species achieved significantly higher percent cover at Santa Cruz, Santa Rosa, and San Miguel Islands compared to Santa Barbara Island. Native plant species attained significantly higher percent cover at Santa Rosa Island compared to Santa Barbara Island. Adult shrub density was significantly higher at Santa Cruz, Santa Rosa, and San Miguel Islands compared to Santa Barbara Island. Islands at more northwesterly positions generally supported higher biodiversity. The tendency for vegetation height, cover of perennials and natives, shrub density, and biodiversity to each decline along a gradient from northwest to southeast indicates that moisture limitation is a strong driver of vegetation recovery after the removal of ranched animals. Moreover, moisture limitation at the park’s most southwesterly islands may interact with poor soils at Santa Barbara Island and seabird abundance at Anacapa Island to further inhibit recovery. Therefore, Santa Barbara and Anacapa Islands may benefit greatly from targeted native plant restoration. Santa Barbara Island’s high total cover contributed by a high proportion of nonnative species may render this island particularly resistant to recovery since a range of species responses to environmental disturbance can stabilize ecosystem processes.

Channel Islands National Park: Terrestrial vegetation monitoring annual report—2019

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