Our second survey, in the summer of 2002, was set
at the mesoscale and designed to decouple the correlation
between geographic distance and environmental
change observed in many similar studies. We used a
digital elevation model of the reserve in concert with
geographic information system (GIS) software to identify
potential sample sites (50-m2 circular plots), in
broadly defined environmental classes based on terrain
attributes (aspect, slope steepness, and slope position;
cf. Grigal et al. 1999). We took these physiographic
variables as indicators of a more comprehensive set of
environmental variables, which were to be sampled later.
In deciding potential sampling sites, we excluded
all water bodies and any sites situated within 10 m of
trails, the shore of Lac Hertel inside the reserve, or the
outer perimeter of the reserve. We selected sites so that
any correlation between site characteristics representing
the abiotic environment and distance would be
avoided in the data set. For example, we chose a southfacing,
steep, midslope site to have both environmentally
similar and dissimilar sites evenly distributed
across near to far distances. We also chose sites that
ensured the entire reserve was well represented. We
iteratively tested tentative sampling designs using
Mantel tests until there was no detectable correlation
between distance and site characteristics. We assessed
the selected sites in the field in the spring of 2002, and
used initial on-site estimates of slope, aspect, soil moisture,
and humus richness to again test the success of
our sampling design. Gilbert and Lechowicz (2004)
provide additional details on this survey.