NE Resilience Report - Conservation Gateway

To assess the density of wetlands, we created a wetland grid for the region by combining the National
Wetland Inventory, NLCD (2001) wetlands, and Southern Atlantic GAP programs wetlands datasets
(http://www.basic.ncsu.edu/segap/index.html). We revised this source wetland dataset using the landform
models to identify and remove erroneously mapped wetlands on summits, cliffs, steep slopes, and
ridgetop landforms. To match the 100-acre scale of landform variety and elevation range, we generated
the percent of wetlands within a 100-acre circle for each 30-meter cell in the region using a focal sum
function in GIS. Additionally, to gauge the wetland density of the larger context, we generated the percent
of wetlands of an area one magnitude larger (1000 acre circle) around each 30-meter cell in the region
(Note: for the coastal areas where much of the area within the 100-acre or 1000 acre circles was actually
ocean, the percent of wetlands was based on only the percent of the land area, not ocean area, within the
100-acre or 1000 acre circle around each cell).
To summarize the wetland density for each cell, we combined the values from search distances, weighting
the 100-acre wetland density twice as much as the 1000 acre wetland density and summing the values into
an integrated metric. Lastly, we log-transformed the values to approximate a normal distribution and
divided by the maximum value to yield a dataset normalized between 0-100 (Map 3.3, Figure 3.4d). Raw
scores for each cell ranged from 0 to 100 percent with a mean of 7.1 percent and a standard deviation of
15.6 percent for the 100-acre search radius and a mean of 7.1 percent and standard deviation of 12.4
percent for the 1000 acre radius. The combined weighted value had a mean of 10.5 and standard deviation
of 21.1. Finally, wetland density metrics were only applied to cells that had close to zero slope as defined
by their landforms (hilltop flat, gentle slope, wetflat, dry flat, and valley/toe slope).
Landscape Complexity Combined Index: To create a standardized metric of landscape complexity (LC)
we transformed all three indices (landform variety (LV), elevation range (ER), and wetland density (WD)
to standardized normal distributions (“Z-scores” with a mean of 0 and standard deviation of 1) then
combined them into a single index.
In the combined index we weighted landform variety twice as much as the other two values because of
the importance of this feature in creating well defined microclimates (Map 3.4). Further, wetland density
was only added when the setting was a flat landform (dry flat, wet flat, slope bottom flat). The final index
was:
Landscape Complexity
Flats = (2 LV + 1 ER + 1WD)/4
Slopes = (2 LV + 1 ER)/3
24 Resilient Sites for Terrestrial Conservation in the Northeast and Mid-Atlantic Region
The Nature Conservancy • Eastern Conservation Science • Eastern Division • 99 Bedford St • Boston, MA 02111