NatureScot Research Report 1190 - Observer Variation in the Use of a Method of Assessing Current Herbivore Impacts in Woodland

The Woodland Herbivore Impact Assessment Method (WHIA) was developed as a means of assessing the impact of all species of large herbivores on woodlands. The aim was to provide a standard range of indicators, and standard ways of assessing herbivore impacts on those indicators. The method is based on observations, rather than measurements, of impact levels on seven indicators at ten roughly 25 metre radius 'stops' located throughout a woodland. Assessments can be used to inform target setting in an adaptive management system so that herbivore numbers can be related to the desired habitat condition.  Due to the relative simplicity, low cost and speed of the WHIA method it is suitable for use by woodland, deer and stock managers as well as by professional surveyors.

Prior to the development of the Woodland Herbivore Impact Assessment Method (WHIA), assessments of herbivore impacts on woodlands were based on subjective judgement of a set of simplistic and qualitative indicators which were mostly to do with assessing the consequences of historic grazing pressure, rather than anything to do with current herbivore pressure. The method made no distinction between impacts on palatable and unpalatable species, so failed to identify the extent to which sustained overgrazing has modified habitat composition.  In contrast, the WHIA measures the impact of current pressure, so allowing the observer to relate changes in the habitat to current management and target setting.

Although the WHIA has become increasingly used for a range of purposes, its reliability for formal impact assessment is currently unknown due to a lack of information on observer variation. This study sought to address this lack by comparing the results obtained by fifteen surveyors assessing the same four sites.

Pages: 91
Published: 2021

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