An objective Method of Measuring the Vegetation Structure of Animal Habitats

Abstract

The importance of habitat structure has been illustrated for many groups of animals. A method to objectively measure the vegetation structure of animal habitats is presented. Factors contributing to the index are evaluated and an attempt is made to show how this index relates to other methods of measuring habitat structure. A technique to measure crop leaf area is adapted and applied to assessing structure (the vertical distribution of vegetation) in natural vegetation. A light meter is used to determine a vegetation index for each of several layers. The index is compared with projected cover, cover estimated with a cover board and cover repetition using pin contacts. All correlations are highly significant. In heath the dry weight of clipped vegetation contributed more to the vegetation index than did the leaf area, reflecting a greater contribution of woody stems and branches than of the small ericoid leaves. The technique has been successfully applied to the measurement of habitat requirements for small mammals and an example of such an application is included.

The Ecology of Small Mammals in Urban Habitats. I. Populations in a Patchy Environment

“…( (7-10) Vegetation density, V. This was measured by the attenuation of light by different levels of vegetation along quadrats in each patch (Fox 1979). Vat 0-20 cm was denoted as VEG 0-20; other variables were VEG 20-50, VEG 50-100 and VEG 100-150.…”

An improved method of microhabitat assessment relevant to predation risk

“…The QCM can be applied consistently by different observers, allows data to be collected quickly and inexpensively, and does not require equipment such as a sight board, camera, or light meter (e.g., MacArthur and MacArthur 1961;Fox 1979;Parent and Messier 1996;Sutherland and Predavec 1999;Langkilde et al 2003). By comparing the scores obtained while following an animal's path with those from a similar number of random points, the QCM may be used to test for selective use of visual cover.…”

“…We also compared our method with the use of a sight board (e.g., MacArthur and MacArthur 1961;Fox 1979;Fox and Fox 1984;Monamy and Fox 2000). Two of us (DS and AG) sampled 70 points, first using the QCM and then using a 500-cm 2 sight board as follows.…”

“…However, accurately quantifying vegetation density can be labor-intensive (Fox 1979) and can require specialized equipment such as incident-light meters (Parent and Messier 1996;Sutherland and Predavec 1999) or photographic imageanalysis software (Langkilde et al 2003). More rapid estimates can suffer from a lack of repeatability, particularly when multiple observers are involved (Cheal 2008).…”

A review of habitat selection by the swamp rat, Rattus lutreolus (Rodentia: Muridae)

“…Mossman (1955) was the first to make use of light meters to measure the penetration of light through vegetation, so that measurements above the vegetation and at ground level provided a means of estimating the density of the vegetation. The use of a light meter to measure light attenuation as a surrogate for vegetation is an excellent, efficient and objective way to do this (see Kearney et al 2007) and the index created to measure this has been shown to have 56% of the variance contributed by the dry weight of leaves and stems while 34% is contributed by leaf area index (Fox 1979b). Hence the stems contribute greatly to the vegetation density and in our experience it was the density of this lowest level of vegetation that was most important to R. lutreolus and P. gracilicaudatus in their selection of habitat Fox, Taylor & Thompson 2003) so it is of great importance when measuring vegetation density to include measurements of the density at ground level, rather than start at some level above ground level.…”