Thanks Tyler, You make several important points about distance sampling. And I agree that Amy's study is not a distance sampling problem. But are you saying that the use of a web layout for sampling points (spokes radiating from a center) is inappropriate for taking veg samples? I don't see why. One can use any layout regardless of whether it involves a distance sampling problem. I was not suggesting Amy use distance sampling techniques, only that she consider the web as an approach to systematic sampling.
Mike On Jun 4, 2007, at 1:58 AM, Tyler Grant wrote: > 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! > >
