Sample size, power, and analytical considerations for vertical structure data from profile boards in wetland vegetation

Abstract

Profile boards are commonly used to estimate vertical cover of herbaceous vegetation in the evaluation of wildlife habitat. However, data from this technique are seldom collected or analyzed in a consistent manner. Therefore, we investigated and evaluated methods of profile-board data collection and analysis using univariate and multivariate techniques. We collected 11,056 samples of vertical-structure data (percent cover) at 2,764 points in 8 playa wetlands in the Southern High Plains of Texas during 1989 and 1990, Visual obstruction data were collected along 5 transects in each playa, with 4 subsamples taken at each point. Data from strata of a profile board rarely followed a normal distribution. Observations among strata were correlated. initial analysis with a multivariate technique to simultaneously test data from all strata is recommended to control experiment-wise error rates. Only when a significant effect is determined in initial analyses should other multivariate techniques or univariate analyses follow to assess differences. Collecting > 1 observation per sampling point (i.e., subsanapling) did not affect analysis and is only necessary when subsamples are not con-elated. Sampling should be stratified throughout a habitat to account for structural variation within a habitat. Transforming percent cover into scores reduced differences among habitat units and may result in a misrepresentation of the data due to the potential for an indication of plant cover despite no vegetation occurring. When estimating a population mean, we recommend a minimum sample size of 20 points/habitat unit and arcsine transforming percent data to achieve acceptable type 1 error rates. When comparing 2 or more habitats or experimental treatments, aresine transformation of percent data is not necessary. General procedural recommendations for use of profile board are (1) use a board that is relative in height and strata size to vegetation/ animal of interest, (2) use equally spaced strata to avoid biasing results to certain stratum, (3) determine the distance from which to read the board by calculating the distance that results in the most variation in cover values, and (4) use one observer or randomize observers among expcrimental units.

Avian response to vegetative pattern in playa wetlands during winter

“…We used a profile board (Nudds 1977) 2.4 m high, and 15 cm wide, divided into 6 40-cm × 15-cm sections to determine vertical cover. A single observer estimated percent cover in each section of the profile board at a distance of 5 m from each of the 4 cardinal directions (Haukos et al 1998).…”

Salt Marsh Canopy Architecture Differs With the Number and Composition of Species

“…Assess more than plant cover.-We recommend measuring canopy height and layering when monitoring or assessing restored or created wetlands (Haukos et al 1998). We recognize that the relationships between canopy variables and target animal species need to be tested, and we encourage further research in this area.…”

Within-Stand Selection of Canada Lynx Natal Dens in Northwest Maine, USA

“…We chose a sampling protocol that would discriminate between multiple types of CWD because we hypothesized that larger CWD that was above-ground and solid would provide better den structure than smaller CWD that was on the ground and decayed. We estimated visual obscurity using a 2-m cover pole with 2 readings each from random azimuths at 10 m and 5 m from plot center (Nudds 1977, Griffith and Youtie 1988, Haukos et al 1998. We estimated hardwood and softwood stem density at each site within 2 15-m 3 0.5-m plots originating from plot center (Litvaitis et al 1985) and groundcover using 1m 2 plots at 3-m intervals along 2 15-m transects, counting projecting plants at intersections of small frames (10 3 10 cm) at 0.5-m height (Ferron and Ouellette 1992).…”