The proposed sampling design attempts to balance the requirements of each of the following criteria:
1. This lichen survey involves four species, which share the common characteristic of being tolerant to air pollution. However, they have been found in a diversity of settings ranging from urban to rural and from moderately polluted to heavily polluted areas. As a result, we needed to balance broad geographical scope, which incorporates this habitat diversity, and sampling intensity, which will allow for effective "species capture" in the chosen sampling sites.
2. Second, the sampling sites should be well-defined areas which may be relocated on a map and revisited for future sampling. These sites need to be discrete areas with a high likelihood of still existing in a number of years.
3. We needed a survey strategy, which could be carried out within a little less than a month and with a work force consisting of 13-19 people (mainly students).
Our main sampling transect extended from Seattle, Washington along the Interstate Highway 5 (I-5) corridor to Eugene, Oregon. Sampling could easily be extended to other areas. Sites along this transect included the Seattle, Olympia/Tacoma, Centralia/Chehalis, Portland/Vancouver, Salem, Albany/Corvallis, and Eugene. Along this main transect we also sampled sites between cities but near I-5. In addition, a transect extending approximately 10-40 miles east from Portland will be sampled.
Arrangement of Sample Units
The total number of sites to be sampled was calculated based on the overall time available for sampling and the sampling time per site. These calculations resulted in a goal of approximately 30-50 sites to be sampled in this study (see note below).
A relatively large number of sites were sampled within Seattle and Portland because of their large area. In addition, sampling a number of sites within these cities allow for a more detailed account of lichen locations in the areas most likely to contain the target species. We sampled several sites each of the remaining urban areas.
Specific information on sampling sites was provided to surveyors in the form of written directions and marked maps. Site packets were created, containing the following: a map of the metropolitan area, a more detailed map of the area around the site which includes street directions and the general site layout, written street directions, sampling protocol, and data sheet.
Note on calculating sampling times and numbers: We expected each person to dedicate approximately 4 hours to sampling, not including driving time. With a minimum of 13 people as participants in the sampling, this gave us 52 hours of sampling time to work with. With sampling times of approximately 30 minutes, everyone in the class would be able to visit about 8 sites. Sites may be visited by solitary surveyors or surveying groups. Overall sampling time for a site will be a maximum of 60 person-minutes. At a minimum of ten trees per site, this requires no more than 6 minutes spent on a tree. If each area is sampled by more than one person, this would reduce the chance of sampling bias, and help with car pooling, etc. as well as giving plenty of time for finding the lichens. This would allow for sampling at approximately 30-50 different sites. The proposed sampling design was based, in part, on these approximate calculations. However, it incorporates a certain amount of flexibility by providing site choices and by depending on volunteers for the surveys of outlying sampling sites (such as Seattle and Roseburg).