Linking invasive plant management, conservation, and restoration on Santa Cruz Island, California.

摘要

Invasive species management is expensive. While the precautionary principle advocates a proactive posture towards the eradication of such species, there is little empirical evidence to support this effort. Natural resource managers can not afford to waste financial resources on weed management protocols that promote unanticipated outcomes. By examining fennel (Foeniculum vulgare ) management on Santa Cruz Island, California, from three perspectives, I intend to advocate an ecological framework for weed management. First, a critical discourse analysis (CDA) of the Santa Cruz Island Primary Restoration Plan-Final Environmental Impact Statement revealed that the underlying scientific assumptions and personal bias related to the use of prescribed-fire and aerial herbicide application for fennel management failed to provide hypothesized results. Second, two long-term field studies, The Nature Conservancy's Central Valley Fennel Removal Experiment and the University of California at Santa Cruz's Natural History Field Quarter (NHFQ) Fennel Project, focused on the response of vegetation guilds of introduced and native origin to restoration disturbances that occurred over three and sixteen-year time frames, respectively. These two community ecology approaches followed changes in ecosystem structure and function as a result of different field manipulations to fennel. The NHFQ Fennel Project also evaluated the short- and long-term impacts to ecosystem structure and function by disturbance from feral pig presence and absence. Canonical Correlation Analysis determined that a significant relationship exists between fennel presence and increased soil fertility in the Central Valley of the Island. Weed seed bank analysis determined that fennel seed was still viable in the soil after five years suggesting that prescribed burns do not provide either the temperature intensity or duration required to terminate all fennel seeds in situ. Productivity of fennel declined when left alone for 16 years. Abundance and richness of introduced species increased when fennel was managed. Third, the allelopathic potential of fennel was evaluated against a suite of species from introduced and native origin. It was learned that allelopathic interference was most negative for growth of introduced species with little significance for introduced species germination, and allelopathic interference was most negative for germination of native species with little significance for native species growth.