Visual Obstruction. Section 6.2.6, U.S. Army Corps of Engineers Wildlife Resources Management Manual.

Abstract : A report on visual obstruction as a vegetation sampling technique is provided as Section 6.2.6 of the U. S. Army Corps of Engineers Wildlife Resources Management Manual. This technique can be used by the Corps District or project biologist to estimate percentage horizontal cover of understory communities. Topics covered include guidelines for technique selection and study design, preparation for sampling, and procedures for data collection, recording, and analysis. The visual obstruction technique is a rapid method for measuring the structural profile of understory vegetation. Designed to measure horizontal foliage density, this technique is useful for estimating the amount of screening cover available to ground-dwelling wildlife species. It allows the measurement of horizontal cover by estimating the percentage of a 2-m profile board that is visually obstructed by vegetation. Equipment is inexpensive, data collection can be conducted by either 1 or 2 field personnel, and the method is applicable in a wide range of habitat types. Detailed instructions are given for recording and analyzing data; these are accompanied by numerical examples that illustrate each step of recording and data analysis. A reproducible form is also provided for recording and calculating visual obstruction data.