I've used distance sampling in several situations, including trapping webs for flat-tailed horned lizards. Distance sampling isn't appropriate for the situation below. Distance sampling estimates density. Is that what is wanted? And distance sampling is best for objects of interest that have low detectability and/or are more or less sparsely distributed. It's a way to deal with detection probability issues. If det prob is not an issue, like detection of p/a of sedges in a plot is probably not an issue, then you don't need to use distance sampling. You could cram the situation below into a distance sampling framework but it would not be worth the effort. You'd probably find det prob equaling 100%. Amy's situation sounds like a simple choose your plots and count situation. To choose plots she could simpling choose random bearings and distances from the center of the plot if a few need to be chosen. Otherwise could divide the plots up somehow into 10cm square sub-quadrats, number them, and randomly choose from the numbered list.
Distance sampling has come far since the 1983 paper listed below. The standard references are Buckland et al. 2001 Intro to Distance Sampling and Buckland et al. 2003(?) Advanced Distance Sampling. Program DISTANCE is available for analysis. Numerous papers are out there using different flavors of distance sampling. Tyler Grant Fish and Wildlife Biologist ----- Original Message ----- From: "Michael Fuller" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Sunday, June 03, 2007 6:12 AM Subject: Re: Sampling vegetation for wildlife habitat purposes > Hi Amy, > Ahh, thanks for clarifying your approach. :-) As you are using > circular plots (and, it seems, a form of distance sampling), you > might consider adapting the "trapping web" design to your needs. > Trapping webs are often used for capture-recapture studies. The web > design uses spokes radiating out from the center of the circle. > Samples are then taken at specific intervals along the spokes. This > approach yields several subsets of samples that are equidistant from > the center (i.e. rings of samples, like pearls on a necklace). The > following paper describes the design as applied to capture-recapture > studies, along with statistical analysis. > > Anderson, D.R., K.P. Burnham, G.C. White, and D.L. Otis. 1983. > Density estimation of small-mammal populations using a trapping web > and distance sampling methods. Ecology 64:674-680. > > The above is an early paper on the topic. The authors have written > several related papers, including one that compares the web design to > grid designs (Parmenter et al. 2003. Ecological Monographs 73:1-26). > > All the best, > Mike > >> Date: Sat, 2 Jun 2007 11:57:37 -0700 >> From: Amy Williams <[EMAIL PROTECTED]> >> Subject: Re: Sampling vegetation for wildlife habitat purposes >> >> Thank you all for your many insightful responses. Perhaps I can >> clarify a >> little bit. The research is already designed to gather plot-level >> information on vegetation physiognomy (canopy height and density, >> DBH, tree >> condition, percent of plot that is meadow, forest, bare ground, >> downed wood, >> etc.), as well as soil attributes and hydrology. In addition, I did >> intend >> to use the 10-cm square sub-quadrats to represent single points to >> gather >> presence/absence of either species or type (sedge, forb, grass), >> and average >> height. Is there a systematic way to place a large number of these >> in a 15-m >> square circular plot, besides limiting them to orthogonal cross- >> transects? I >> will make sure to consult the texts recommended to me; maybe I will >> find my >> answers there. >> >> Again, thank you for the help! >
