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NHESP
BioMap Supporting Natural Landscape - June 2002
OVERVIEW
Supporting Natural Landscape
is one of two datalayers resulting from the BioMap biodiversity mapping
project (also see the NHESP BioMap Core Habitat datalayer
description). The Supporting Natural Landscape buffers and connects
Core Habitat polygons, which depict the most viable habitat for rare species
and natural communities in Massachusetts, and identifies large, naturally
vegetated blocks that are relatively free from the impact of roads and
other development. The quality of undeveloped land considered in the landscape
analysis was evaluated based on four major components:
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natural vegetation patch characteristics;
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size of relatively roadless areas;
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subwatershed integrity;
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and contribution to buffering BioMap
Core Habitat polygons for plants and exemplary communities.
These components were represented in
seven Factor Maps in 30-meter x 30-meter raster datasets:
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size of natural vegetation patch;
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distance from development;
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forest history;
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size of individual roadless blocks;
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size of aggregated roadless blocks;
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subwatershed integrity;
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and distance to BioMap Core Habitat.
A weighted overlay was performed on
these Factor Maps using the Model Builder extension of Spatial Analyst
in ArcView 3.2a to produce the Supporting Natural Landscape datalayer.
This single statewide layer is stored
in the State library; its coverage and layer name is BIOSNL.
PRODUCTION
Supporting Natural Landscape
is a product of the weighted and additive overlays of seven Factor Maps.
The Factor Maps are derived from both external and internal sources. External
data includes the National Land Cover
Data (U.S. Geological Survey and U.S. Environmental Protection Agency),
Massachusetts
Highway Department Roads (USGS, Roads Digital Line Graphs, and the
Massachusetts Highway Department), Land Use (MassGIS),
1830’s-era Land Use (Harvard Forest),
Ecoblocks (The Nature Conservancy), and
Drainage Sub-basins (MassGIS). Internally-created
data, based on external data, includes Developed Lands and Natural Vegetation,
or Undeveloped Land, from the National Land Cover Data. For each Factor
Map, each grid cell received a score, ranging from 0 (no quality) to 9
(high quality). The categories for each Factor Map were derived with reference
to scientific literature where possible and otherwise on expert opinion.
Individual Factor Maps were then assigned weights to reflect their relative
importance in determining ecological value relative to other maps. All
the overlay processes were done per eco-region.
In the first weighted overlay process,
the following Derivative Intermediate Maps with 0 to 20 classes were created:
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Natural Vegetation from size of natural
vegetation patch, distance from development and forest history;
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and Roadless Blocks from size of individual
roadless blocks and size of aggregated roadless blocks.
Finally, a weighted overlay of the Natural
Vegetation and Roadless Block Derivatiave Maps along with the Subwatershed
Integrity produced the final scaled weighted overlay map. Then, using an
additive overlay this final Factor Map was combined with the Distance to
BioMap Core Habitat produced the Supporting Natural Landscape.
The selection of Supporting Natural
Landscape was determined by selecting a total of 40% to 50% per ecoregion
by the combination of BioMap Core Habitat with Supporting Natural Landscape.
The most highly ranked grid cells in each ecoregion were selected for inclusion
in BioMap, and thus the highest quality remaining habitat is represented
in each ecoregion. As the amount of Core Habitat varies from ecoregion
to ecoregion, the amount and the quality of Supporting Natural Landscape
also varies. All the cells selected by ecoregion were then merged together
to form a statewide map. Performing the landscape analysis by ecoregion
created gaps in the Supporting Natural Landscape across ecoregional boundaries.
The nearest neighbor interpolation technique filled in these artifacts
by assigning new values. Finally, the raster layer was converted to vector
format. Polygons that were not contiguous with BioMap Core Habitat and
polygons that were less than 2,500 acres were deleted from the final map
because the main intention was to buffer and connect Core Habitat polygons
and to identify the largest remaining patches of undeveloped land. Isolated
polygons larger than 2,500 acres that were not highly fragmented were retained.
As a final step, the Supporting Natural Landscape polygons were compared
with 1:5,000 digital orthophotos (1992-1999) and
recent areas of development were deleted.
ATTRIBUTES
The BIOSNL.PAT (polygon
attribute table) contains the following items:
BIOSNLID |
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16 |
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16 |
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C |
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NHESP Unique identifier |
BIOSNLPOLY |
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1 |
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1 |
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I |
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1 = SNL polygons
0 = "interior" polygons
(not SNL) |
USAGE
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· The legend that MUST accompany this
datalayer on ALL maps is:
"NHESP BioMap
Supporting Natural Landscape".
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Please note that Supporting Natural Landscape
polygons were designed for use at a regional or town scale. For accurate
portrayal, the data should be displayed at scales of less than 1:25,000
(e.g. 1:30,000).
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This datalayer is intended for conservation
planning purposes only- it has no regulatory purpose. The NHESP layers
designed for regulatory use are produced in the Natural Heritage Atlas.
MAINTENANCE
In June 2002 a few very small natural commuities
were removed from the BioMap Core Habitat layer, and this layer was updated to reflect those changes.
Questions about this datalayer should be directed to NHESP at 508-792-7270 x300.
ADDITIONAL REFERENCES
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The BioMap Core Habitat
datalayer was designed to delineate most viable habitat for rare species
and natural communities in Massachusetts. See the metadata for that
datalayer for more detail.
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The
Natural Heritage and Endangered Species Program has published two reports:
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‘BioMap: Guiding Land Conservation for Biodiversity
in Massachusetts’, a full color report on the BioMap project
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‘The BioMap Technical Report’, which presents
much greater technical detail on the methodology used to develop the BioMap,
along with the scientific basis for these methods.
See http://www.state.ma.us/dfwele/dfw/nhesp/nhbiomap.htm
for information on receiving these two reports for more detail on the criteria
and methodology involved in producing the Surrounding Natural Landscape
datalayer.
Last Updated 6/13/2003
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