A new index to measure roe deer (Capreolus capreolus) browsing pressure on woody flora

Abstract : To improve the management of cervid populations various indicators of ecological change have been formulated and notably the Index of browsing Pressure on the Flora (IPF), proposed to monitor roe deer, Capreolus capreolus, browsing pressure on woody vegetation. We show that the IPF (the browsing pressure defined for a series of sampling plots as the ratio of the total number of browsed plant species with respect to the total number of plant species present, pooled for aIl species over aIl plots) is not robust enough with regard to an observer effect and that this technique is difficult to apply where a rigorous monitoring over time is required. Moreover, the application of this index is hampered by the fact that presence and browsing of the different plant species do not occur independentIy of one another, which poses problems of statistical modeling. To make up for these various deficiencies, we propose a new index: the browsing index (BI) which is equal to the ratio of (1 + nc) to (2 + np), where nc = the number of " browsed " plots and np = the number of plots with woody vegetation, a plot being considered browsed if on this plot at least one shoot is found with traces of browsing, for any woody species. We also propose a method of statistical data processing for this new index through the application of Bayes' theorem which allows us to determine a confidence interval for the estimator. This new index has proved to be relatively independent with respect to the observer. Since the size of the sampling plot and the number of replications have an effect on the BI and its confidence interval, we propose a 1-m2 surface area and a minimum number of 150 plots for a forest stand of less than 1,500 ha. To monitor the individual-population-environment relationship, we recommend monitoring the browsing index, in combination with other indicators of ecological change, for subsequent implementation of appropriate measures of roe deer management.
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Nicolas Morellet, Philippe Ballon, Yves Boscardin, Stéphane Champely. A new index to measure roe deer (Capreolus capreolus) browsing pressure on woody flora. Game and Wildlife Science, 2003, 3, pp.155-173. ⟨hal-02350884⟩

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