The Liberal Clause

Impacts of the Control of Dominant Invasive Species on the Native Species.


In most cases the removal of dominant invasive species is expected to lead to increases in native species richness and diversity through control experiments and arguments by scientific researchers. Baker. 1965 and Bazzaz.1986. Argue that, invasive species lead to native community habitat degradation and prevent the re-establishment of native species in invaded areas. E. Ogden and Rejma´nek, 2005. Therefore sort to conclusively give experimental evidence by testing the efficacy of different methods on the control of Foeniculum vulgare (fennel) and management effects on native species recovery, at Santa Cruz Island, California, in the early 1990s.

Various methods were used in the study;

Pilot tests, at first, he Nature Conservancy, owner and manager of 90% of the island at that time, to initiated small-scale fennel control experiments. Pilot studies were conducted in fennel-infested communities so as to find out the efficacy of a variety of treatments on the removal of fennel and its impact on native species richness and cover this evidenced that greatest decrease in fennel cover resulted to a significant increase in native species richness and diversity.

Experimental design, twenty blocks were established and placed in fennel dominated or grass dominated areas. Ten blocks were randomly placed in grasslands that did not contain fennel, and fifteen blocks were randomly placed in fennel-infested areas, five grassland blocks and five fennel blocks were untreated and designated as control blocks.

The necessary treatments such as, burning to remove dead standing fennel, aerial spraying, spring herbicide application which had no effect on native herbaceous dicots and soil analysis. Three plots were randomly selected within each block to collect species cover data and visual estimates of percent cover were taken for each species and averaged for the plots.

To evaluate results, statistical analysis using ANOVA and power analysis were performed using Statview 5.0.1 on  data, before treatment and after treatment to confirm that fennel cover, native species cover, and non-native species cover were not statistically different between fennel treated and untreated blocks and between grassland treated and untreated blocks due to spatial bias in the experimental design. Species diversity was also assessed using Hill.1973, indices of diversity.

As expected, fennel cover decreased significantly in the treated blocks, (P < 0.0001) as it did in the small pilot study plots. There was also, no resurgence of fennel cover with time in the large-scale experiment that occurred in the dry season herbicide application for the small-scale pilot Studies, native species cover, richness, and diversity increased significantly over time. Therefore, management of invasive species is a goal for many land managers and restoration ecologists although, eradication is often unattainable.


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