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Given the relatively small size of the Camp Adair training area, a systematic sampling design was chosen consisting of a uniform distribution of sample points over the entire area. These sample points were spaced 250m apart in a grid oriented toward magnetic north. This spacing corresponds to the minimum distance between avian point counts recommended by Ralph et al. (1995). The grid system resulted in 41 intersection points on Camp Adair which were used throughout the study for avian point counts, habitat measurements, and as reference points for incidental observations and opportunistic small mammal sampling.
In early April 1998, we began locating and marking the intersection points. A starting point was chosen and marked on an aerial photograph of the site, and grid lines drawn. In the field, a two-person team used a measuring tape and a compass to walk a magnetic course for a distance of 250m from the chosen starting point. At the end point, the aerial photograph was checked to verify that the location was correct by referencing recognizable landmarks such as fence lines, road intersections, and prominent tree stands. (The topography of the area rises to the west, and using a two dimensional approach resulted in some degree of distortion of actual ground distance between points, but we always maintained a minimum ground distance of 250m.) A wood stake with a plastic identification tag was placed at each intersection point. The tag contained the point’s (x, y) coordinates with the (1, 1) point occurring in the southwest corner of the grid. A non-differentially corrected GPS fix was obtained for each point and written on the identification tag. Subsequent checks with an independent differentially corrected receiver showed that the accuracy of the original receiver was acceptable within 0.05 minutes latitude/longitude.
Habitat Characteristics
Basic habitat structural characteristics were recorded at all grid intersections prior to conducting avian point counts in the spring, on each small mammal transect in the fall, and within each small mammal trap plot during both spring and fall trapping sessions. Since each small mammal plot was more or less homogeneous in habitat structure and was selected to represent a larger and frequently occurring plant community, we recorded habitat structural characteristics at a random location within the plot, avoiding the plot boundaries. The following endpoints were measured at woodland sites: general plant community, percent canopy closure, maximum vegetation height, percent ground cover/type, an index of visual obstruction, and an estimate of coarse woody debris in the fall. In grassland areas, general plant community, maximum vegetation height, percent ground cover/type, and an index of visual obstruction were recorded.
The general plant community, percent ground cover, and height of dominant vegetation were estimated for the area within a 50m radius of the sample point. In areas of grassland where large trees remained outside of the 50m radius, but obviously influenced the character of the site, both grass height and adjacent tree height were recorded. Percent canopy cover was estimated using a spherical densiometer and recorded as the average percent canopy closure over the observer’s position facing three directions, each 90E apart, i.e., readings facing 090E, 180E, and 270E magnetic. Visual obstruction, or horizontal shrub cover, was estimated using a Nudd’s board, after the methods of Griffith and Youti (1988). The device consisted of a white panel,
60cm wide x 200cm high, with 50cm partitions inscribed horizontally on the face. The board was observed from a distance of 10m and the percent of each 50cm panel partition that was concealed by vegetation was recorded. The procedure was repeated for three bearings at 90E intervals and the values averaged. Care was taken to not walk along the site line thus influencing the density of horizontal cover prior to measurement. A general assessment was also made as to the type of concealment encountered, i.e., ferns, shrubs, stumps, etc.
Line-transect sampling was conducted within wooded habitats after the methods of Bury and Major (1997) to characterize physical properties and general volume estimates of coarse woody debris which can be especially important for small mammals, reptiles, and amphibians. A series of one to three 100m line transects were established within or adjacent to the survey areas by placing a 100m tape at ground level along each amphibian or small mammal transect, or two 50m tapes placed along two non-adjacent plot grid lines within small mammal plots. All woody ground cover greater than 10cm diameter intersected by the line transect was measured for volume, and classified to species and decay class (modified from Franklin and others, 1981; Maser and others, 1979), and the information recorded on data sheets. Decay classes of coarse woody debris were grouped into 3 categories: A : Branchy, bark completely intact, log solid (Decay Class 1 & 2); B : Short branch stobs, pieces of bark off, 2/3 solid core (Decay Class 3); C : Branchless, often barkless, punky with little/no solid core (Decay Class 4 & 5). Coarse woody debris measurements were also conducted at randomly located points outside the small mammal plots, but within the same coarse scale plant community to determine variability and to examine how well each plot represented the immediate surrounding area.
incorrect use of the data described and/or contained herein.