Forest Stewardship Spatial Analysis Project
Vermont Methodology, September 2007
Project Summary
The Vermont Forest Stewardship Spatial Analysis Project (SAP) was developed to
determine the potential for stewardship of private forest lands in Vermont. Spatial
data were used to indicate non-industrial private forest (NIPF) lands where
stewardship could be encouraged or enhanced. Lands with high stewardship potential
are considered priority areas for the Forest Stewardship Program (FSP) of the USDA
Forest Service as well as for more concentrated conservation, management, and
associated planning efforts.
The pilot project for the SAP--by the states of Connecticut, Massachusetts, Maryland,
and Missouri--identified 11 factors that play a key role in influencing suitability for
forest stewardship. Depending upon the type of influence, the 11 parameters were
evaluated according to their ability to support or threaten forest resources.
Factors that threaten forest resources:
Development (conversion to non-forest uses)
Forest Health (risk and adaptability to change)
Fire (not used for Vermont analysis)
Factors that support the potential of forest resources:
Forest Patches
Slope
Natural Heritage (wildlife and biodiversity)
Riparian Corridors
Public Water Supplies
Wetlands
Priority Watersheds
Proximity to Publicly-Owned Lands
The analysis that was performed on private forest lands in Vermont used 10 of the
data layers (excluding fire). Using a raster-based GIS analysis, 30-meter by 30-meter
grid cells were assigned values based on the each of the 10 parameters to determine
their individual forest stewardship potential or threat. Then the importance of each
layer was determined as high, medium, or low by the SAP steering committee for
Vermont. The results were combined in a GIS overlay analysis. The final product is a
single data layer which represents the suitability of the land for inclusion in FSP and
for further stewardship efforts. In addition, the two forest threat layers—Development
and Forest Health—were combined into a composite map entitled Resource Threats. A
composite map of the eight forest potential layers entitled Resource Richness was
created as well. All three of these maps are found in the Vermont section of the U.S.
Forest Service SAP website (www.fs.fed.us/na/sap/products/index.shtml).
Spatial Analysis Project (SAP) for Vermont, September 2007
As the spatial representation of Vermont lands enrolled in the FSP and in Vermont’s
Use Value Appraisal Program become available, the SAP map will be compared with
them to determine areas that may receive special emphasis for forest stewardship.
Project Methodology
All map files imported, transformed, and created for the Vermont SAP were projected
to the Vermont State Plane Coordinate System of 1983 (NAD83) at 30x30 meter cell
resolution. All spatial data presented are for informational use only and are not
considered survey quality.
First a base map was created. Then factors influencing forests were represented
spatially through a series of mapped data layers. Finally computer analyses were
performed on lands in the base map using the factors influencing forestlands to create
three final maps.
Base Map
Computer analyses were performed on private forest lands with the exclusion of
private lands to which a conservation easement pertains. Further explanation is
offered below. Other lands or areas that are not eligible for inclusion in the Spatial
Analysis Project (SAP) and the Forest Stewardship Program (FSP) include publiclyowned lands, open water, and urban areas.
The privately-owned forested lands layer was created as follows:
•
Forested lands were selected first by extracting forest cover from the National
Land Cover Dataset 1992 (NLCD 1992), a lands classification based on Landsat
Thematic Mapper 30-meter satellite imagery from 1992-93. The result was the
exclusion of open water and most urban areas. The NLCD classes that were
selected are deciduous (41); coniferous (42); mixed (43); shrubland (51); nonnatural woody such as orchards (61); woody wetlands (91); and emergent
herbaceous wetlands (92).
•
Then private forested lands were selected by using the Conserved Lands
Database (CLD) of the University of Vermont’s Spatial Analysis Lab from
December 2004. Lands in the CLD were masked so that only those private
forest lands considered suitable for the analysis were selected. The CONSPRI
layer of the CLD was used because it contains conserved land holdings by both
public and private organizations or individuals. Private lands in CONSPRI are
owned by organizations dedicated to conserving land or other resources, or they
are private lands encumbered with conservation easements or other legalprotection mechanisms. The conservation status of these private lands dictates
that they be excluded from this SAP. See page 10 for additional metadata.
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Spatial Analysis Project (SAP) for Vermont, September 2007
Data Used to Indicate Factors of Influence
Factors that influence forests were chosen and represented through a series of maps.
These factors were later used to perform computer analyses on the private forestlands
layer (base map as described above). Of the 11 factors used for the pilot version of the
SAP, Vermont used 10 of them, as follows:
•
Two of the threats layers: Development and Forest Health; and
•
All of the forest potential factors: Forest Patches; Riparian Corridors; Public
Water Supplies; Priority Watersheds; Natural Heritage (biodiversity); Wetlands;
Proximity to Publicly-Owned Lands; and Slope.
Each state has some flexibility in determining whether the 11 factors are useful
measures for forests in the state. States are able to select the data that can best
represent the resource potentials and threats and also are free to select additional
data layers. Risk factors of fire to Vermont private forestlands were not used in this
analysis. Ideas for how to display such data were discussed. However, fire does not
pose a significant threat to private forestlands in the state at this time. The inclusion
of additional data regarding recreational uses on private lands in Vermont also was
discussed. There is interest in trying to display some recreational data in the future,
but this was not done for the SAP analysis.
For the purposes of the overlay model and additional composite maps described in the
GIS Analysis Section, the mapped results of each of the ten factors, which are
presented next, are considered important for forest stewardship. The data are used
this way despite the fact that there may be reasons why an inverse relationship might
be more appropriate. For example, the case might be made that forests in areas where
human population is predicted to increase are less suitable for stewardship. This
could be the case also for forests that show a higher risk for health problems,
suggesting these areas may be less likely to respond to forest stewardship practices.
However, those possibilities were not considered in this analysis, and all highlighted
areas are being regarded as suitable for forest stewardship.
In performing the computer analyses, the data layers representing the ten factors were
grouped together in different ways, depending upon the map and/or analysis to be
done. In this section of the report, they are presented in groups of high, medium, and
low importance.
Factors of High Importance (3)
For the purposes of the analysis, the SAP Steering Committee determined the following
three factors to be of high importance to Vermont forests: Forest Patch Size; Forest
Productivity; and Natural Heritage Resources.
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Spatial Analysis Project (SAP) for Vermont, September 2007
Forest Patches
The first model was engineered to yield forest patches greater than 200 acres in size.
Forests were selected by extracting forest cover layers from the National Land Cover
Database (NLCD). Roads were buffered to produce
fragmentation as follows:
Interstates – 600’ (each side)
US Highways – 300’ (each side)
State Highways – 300’ (each side)
Town Roads – 100’ (each side)
Class 4, private, and forest roads-0 (not
buffered)
Roads and their buffers were subtracted (erased)
from the forested NLCD to identify areas of
fragmentation. Forested NLCD cells were grouped to
create forested “patches,” and areas were calculated
for each patch. Patches with an area less than 200
acres were discarded. A raster calculation was
performed to exclude extraneous data from the
rectangular extents.
Slope, expressed as Productive Soils
The SAP pilot study used slope to represent forest
productivity. For the Vermont analysis, forest
productivity was represented by selecting certain
soils, especially those rich in carbonate. Soils for all
but one county were taken from the Soil Survey
Geographic Database (SSURGO), at the 1:20000
scale, indicating areas of at least three acres in size.
The three most productive soil layers for each county
were selected from the Top 20 Tables, as determined
by the Soil Potential Index (SPI) of Forest Values
Group (FVG). The SPI is a mapping system of the
Natural Resources Conservation Service that takes
into account soil characteristics including soil type,
slope, and operability. FVG’s 1-3 were identified as
1 = exists, while other soils were given no value or 0 =
does not exist (Binary).
Due to lack of digitized soils data, Essex County was
the exception. For this county the two most carbonate-rich rock layers were selected
from the state’s generalized bedrock geology map scaled at 1:300000. The inconsistent
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Spatial Analysis Project (SAP) for Vermont, September 2007
origin of the Essex County data compared with the other counties was not considered
a limitation due to the broad scope of the SAP.
Natural Heritage (wildlife and biodiversity), expressed as a
Natural Heritage Composite Map
Pertinent forest and wildlife related data layers were used to represent areas of
ecological importance. A single composite map was made by grouping the layers
together in Binary.
The Nature Conservancy’s (TNC) Tier 1 Forest Matrix (dominant forest types)
Blocks
These forest blocks are the result of a broad regional analysis (three ecoregional
analyses) that identifies these blocks as the best locations to conserve the dominant
forest types (matrix forests) and associated interior forest-dwelling species. Once the
overall matrix size criteria were set, TNC’s site selection process used five steps: 1)
Created a GIS data layer of road-bounded forest for each ecoregion; 2) Estimated a set
of all potential matrix sites based on a GIS analysis of road bounded blocks; 3)
Determined which blocks qualify for inclusion by assessing the condition of each
potential block through GIS and field analyses and expert opinion; 4) Assessed the
biophysical composition within each block based on Ecological Land Units (ELUs); and
5) Set priorities for blocks within each ELU group, first based on forest diversity and
condition and then proximity to other features, biodiversity value, complementarity,
feasibility, and threat.
Deer Wintering Areas
The polygon and line data for Vermont Deer Wintering Areas were created on various
dates from USGS topographic quadrangles at either 1:24000 or 1:25000. The final
layer used for the SAP was the most recent
statewide--posted in 1997.
Bear Wetlands and Bear Mast
The bear wetlands layer identifies locations of
wetland feeding areas critical to black bear in
Vermont as published in 2001. This layer
indicates sites of heavy bear use and grazing,
mostly located on or adjacent to state-owned
lands, as observed and recorded by Vermont
Department of Fish and Wildlife wardens and
biologists. The data are presented as points which
roughly identify the center of the wetland and
were originally collected in various years using
different methods.
The bear mast layer identifies locations of mast
stands critical to black bear as published in 2001.
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Spatial Analysis Project (SAP) for Vermont, September 2007
A mast stand is characterized as hard mast, either oak or beech, containing 15 or
more bear-scarred trees and other evidence of bear use. Vermont Fish and Wildlife
biologists compiled these data from field observations of wardens, foresters, and
wildlife biologists. The data are presented as points with accompanying description.
Point locations roughly represent the center of the mast stand. The data were
originally collected in various years using different formats.
Rare, Threatened, and Endangered Species, Species of Special Concern, and
Natural Community Occurrences
These data originate from the Nongame and Natural Heritage Program in the Vermont
Fish and Wildlife Department database of rare, threatened, and endangered species
and state significant natural (plant) communities in Vermont. The umbrella
organization for the data is NatureServe. The records that form the core of the
NatureServe database include location, characteristics, numbers, and condition of
species and communities that indicate biological diversity.
Vermont records are collected and maintained by the Vermont Natural Heritage
Program using a standardized methodology with at least a general 1.5 kilometer range.
Locations are plotted manually as vector data on 1:24000 USGS or by using a 1:5000
orthophotography base. Locations are buffered using guidelines for distance based on
level of locational uncertainty. Many scientists and institutions have collected and
submitted data for decades. The edition used for this SAP is 2007A.
Many areas of the state have never been thoroughly surveyed. As a result, the absence
of data in any particular geographic area does not necessarily mean that species or
ecological communities of concern are not present.
Factors of Medium Importance (4)
For the purposes of this analysis, the SAP Steering Committee determined the
following four factors to be of medium importance to Vermont forests: Forest Health;
Development; Wetlands; and Public Water Supplies.
Forest Health
A computer model depicting the sensitivity of soils to acid deposition in Vermont was
used to represent the risk of forest health problems. Why the forest sensitivity model
of calcium availability is a good proxy for risk to forest health will appear shortly in a
USDA Forest Service book about threats to U.S. forests (Schaberg, in press).
Digital data describing the exceedance of atmospheric deposition of sulfur and
nitrogen over the critical load for sulfur and nitrogen for forest ecosystems in Vermont
were developed by Ecosystems Research Group, Ltd. using the methods described in
Miller (2005). For purposes of the SAP, a categorical version (sensitive/not sensitive) of
the model was used (not the continuous layer, deposition index version).
6
Spatial Analysis Project (SAP) for Vermont, September 2007
Areas depicted on the map indicate where atmospheric deposition of sulfur and
nitrogen cause leaching of calcium, magnesium, and potassium from soils at a rate
greater than they can be replaced by natural soil processes (the weathering of primary
minerals in the soil). It is important to note that calcium limitation is only one element
of the total risk to forest health. As mapped data depicting threats to forests from
pests and pathogens become more readily available, these factors can be used as well.
Raster data layers developed for the model include soils weathering rate; and tree
species nutritional needs for base cations, including
site nutrient uptake and some harvesting data
aggregated on a county basis. The model assumed
that harvest removals remain similar to the countywide average removal rates (by forest type and
ownership class) during the 1990s. The model found
that these areas are at risk for forest health problems
in the future should sulfur and nitrogen deposition
remain constant. The model-based estimates used
generalizations of average soil depth (STATSGO).
Areas with greater than average soil depth might
have less risk than indicated, while areas with less
than average soil depth might have more risk than
indicated, depending on the parent material of the
soil.
The forest sensitivity assessment was conducted for
regional air quality planning purposes. The
interpretations of forest sensitivity for stand
management purposes could be improved by using SSURGO soils data or data
collected on-site instead of the STATSGO data. The data layers used in the current
assessment are most useful for broader scale analyses like the SAP.
Development
Development threats to Vermont forests were
represented by future population growth, as
determined by forecasting changes in housing
density. The model used for the SAP was developed
by Theobald (2005) and assumes that changes in
housing density will continue to occur at rates
similar to those between 1980, 1990, and 2000 for
U.S. Census blocks. The data were developed by
eliminating public lands and water from the 2000
Census block data layer and then calculating acres
per house.
The model is able to estimate potential development
on lands that are not urban and that are not
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Spatial Analysis Project (SAP) for Vermont, September 2007
protected, and are referred to as “exurban.” The values were classified in raster format
into five common housing density classes: undeveloped at value=1; rural at values=26; exurban at values=7-11; suburban at value=12; and urban at values 13-15. The
reclassified 2000 density values were then subtracted from the projections for 2030.
All resulting cells with a value greater than 0 were determined to be under pressure
for development.
Wetlands
Digital shapefiles of wetlands were taken from the
Vermont Significant Wetlands Inventory (VSWI) layer.
These wetlands often correspond with wetlands
represented on U.S. Fish and Wildlife Service National
Wetlands Inventory (NWI) maps. However, the Vermont
Agency of Natural Resources (ANR) determines which
wetlands are included in the VSWI, so there may be
differences between the two maps.
NWI maps were used by the Vermont ANR to create
this map. Nearly 2/3 of the wetlands were hand
digitized from RF 24000 scale NWI mylars. The rest of
the state was scanned from RF 24000 or RF 25000
scale mylars. These mylars were created by
transferring wetland polygon boundaries from RF
62500 scale NWI mylars to RF 24000 scale base maps.
Public Drinking Water Source Protection Areas (SPAs)
This data layer represents a composite of two polygon
data layers: the Groundwater Source Protection Area
layer and the Surface Water Source Protection Area
layer.
In Vermont, water systems serving 25 or more people
for at least six months of the year are regulated as
public water systems. Public water systems serving
non-transient populations, such as homes, schools,
and businesses, and bottled water providers, are
required to develop a Source Protection Area (SPA)
which is subject to public notice and state approval.
A SPA represents the estimated land area through
which water flows to a public drinking water source.
Contaminants released to the land surface or
subsurface within a SPA would be reasonably likely
8
Spatial Analysis Project (SAP) for Vermont, September 2007
to move toward, and reach, the drinking water source. SPAs are developed to help
water systems and land use officials to focus protection efforts on land areas most
likely to adversely impact public drinking water sources.
The Groundwater Source Protection Area data layer is composed of the state-approved
delineations of primary and secondary recharge areas for wells, springs, or
groundwater infiltration galleries permitted for active use by public water systems.
The Surface Water Source Protection Area data layer is composed of the stateapproved delineations of watershed boundaries or critical assessment zones for intake
structures and infiltration galleries at lakes, streams, and surface water
impoundments that are permitted for active use by public water systems.
Many of the SPAs in both the Groundwater and the Surface Water Source Protection
Area data layers are further subdivided into Zones 1, 2, and 3. These subzones
characterize degrees of expected impact to the source, with Zone 1 indicating the zone
of greatest expected impact and Zone 3 the least. For purposes of the SAP, the outermost SPA boundaries – and not the interior subzones, which were dissolved away – are
shown.
Factors of Low Importance (3)
For the purposes of the analysis, the SAP Steering Committee determined the following
three factors to be of low importance to Vermont forests: Priority Watersheds; Riparian
Corridors; and Proximity to Publicly-Owned lands.
Priority Watersheds
Priority Aquatic Features are aquatic sites in Vermont,
both standing water and running water, judged to be the
“best reference” or least impacted (exemplary) examples
of classes of aquatic organisms (VT Department of
Environmental Conservation 1998).
The data for the Vermont Biodiversity Project (Thompson
2002) were compiled in the 1990s. Spatial polygon vector
data were extracted from U.S. Geological Survey’s Digital
Line Graphs of RF 1:100000. These data represent a first
attempt to classify aquatic communities and identify
high quality sites. Further validation of the classification
and site assessments are pending further data gathering
and analysis.
The SAP Steering Committee determined the priorities of
each data source for this analysis. Committee members
9
Spatial Analysis Project (SAP) for Vermont, September 2007
agreed that watersheds are more important to the SAP than the low importance
designation would indicate. However, because suitable spatial data at a watershed
scale were not available, the Priority Aquatic Features data layer that was created for
the Vermont Biodiversity Project was used instead.
Riparian Corridors
The riparian corridors map was created by buffering, at
300 feet each side, perennial streams from the U.S.
Geological Survey 1:100000 source scale Digital Line
Graph files that had been combined into a single
statewide coverage by the Vermont Center for
Geographic Information.
Proximity to Publicly Owned Land
This data layer is intended to place emphasis on
areas in close proximity to lands that are considered
to be permanently protected and managed. Public
lands fall in this category as do private lands in a
permanently protected status via easements.
Privately-owned forests that are relatively close to
these types of lands are of particular interest for their
ability to supplement forest connectivity and to
preserve the integrity of the forest resources,
habitats, and the genetic pool across the landscape
through professional forest management methods.
The Proximity to Publicly Owned Land map depicts
600-foot buffers adjacent to the boundaries of
federal, state, and municipal public lands throughout
the state. Privately-owned lands for which public
access is mandated by easement are also included.
The minimum size for most parcels is two acres, with
exceptions for critical natural areas and state public
access areas.
10
Spatial Analysis Project (SAP) for Vermont, September 2007
This map was developed using the Vermont Conserved Lands Database (CLD) layer
CONSPRI as described on page 2. The CLD vector database is distributed by the
Vermont Center for Geographic Information. The edition of the public map used for the
SAP was from December 2004 as maintained by the Spatial Analysis Lab in the
Rubenstein School of Environment and Natural Resources at the University of
Vermont.
The base sources of conserved land parcel boundaries for the Vermont CLD vary
greatly and include survey maps measured in chains; digital town parcel coverages;
and RF 5000 orthophoto-based property boundary maps. The database is accurate
enough to be used for both state and town scale projects, with most analog source
maps RF 24000 or better. The CLD was designed to be continuously updated and
improved as new and better information becomes available. To facilitate this, several
attribute fields illuminate the accuracy of every line, or arc, and polygon in the
coverage so that the least accurate arcs or polygons can be replaced as improved data
become available.
GIS Analysis
Weighting of Factors of Influence
The SAP Steering Committee evaluated the 10 factors influencing Forest Stewardship
Potential in the state and assigned them a high, medium, or low value. However, due
to the quality, scale, and accuracy of the data that were available, the value assigned
to a few of the factors used for this analysis is not completely accurate. For example,
committee members agreed that the Priority Watersheds should be valued more highly
than the low value it was assigned. However the data that are easily accessed at this
time–Priority Aquatic Features–although important, are not useful for evaluating at the
watershed scale. So the Priority Aquatic Features layer is considered to be of low
importance at this time for the purposes of the Vermont SAP. In the future as more
appropriate data become available, it is likely that the values assigned to each data
layer in the SAP will change.
Overlay Model
The Potential for Forest Stewardship Program Benefits map is based on the values that
the SAP Steering Committee placed on the 10 factors influencing forest stewardship
potential for private forestlands in Vermont. As explained earlier in this report, the
mapped results of each of the 10 factors were considered important for forest
stewardship. The model was run via a raster-based GIS analysis using 30-meter by
30-meter grid cells.
First each group of factors—high, medium, and low--were summed separately,
reclassified, and assigned their corresponding weighting factor in a raster calculation.
11
Spatial Analysis Project (SAP) for Vermont, September 2007
•
Factors ranked of high importance and summed together were forest patch >
200 acres; productive soils; and natural heritage (wildlife and biodiversity). The
result was assigned an overall weighting factor of 4.
•
Factors ranked of medium importance and summed together were acid
deposition (forest health); projected growth in number of households
(development); wetlands; and public water Source Protection Areas. The result
was assigned an overall weighting factor of 2.
•
Factors ranked low in importance and summed together were priority
(exemplary) aquatic features; riparian corridors; and proximity to publiclyowned land. The result was assigned an overall weighting factor of 1.
The final overlay map represents these relative values through different shadings.
Values ranged from 0 (no factors met) to 7 (all factors were coincidental). These factors
were then reclassified into three categories (high, medium, and low). Areas of 0 were
excluded from the analysis and were considered not suitable for the Forest
Stewardship Program. Areas with the values 1-2 were reclassified as 1 (low); areas
with values 3-4 were reclassified as 2 (medium); and areas with values 5-7 were
reclassified as 3 (high). This single data layer indicates the relative degree of suitability
of the land for inclusion in FSP and for further stewardship efforts.
Additional Maps
For additional clarification, the U.S. Forest Service asked the states to show the
factors representing Resource Richness and Resource Threats in separate maps. The
two factors included in the Resource Threats map are housing threat and acid
deposition. The eight factors shown in the Resource Richness map are forest patches >
200 acres; productive soils; wildlife and biodiversity; riparian corridors; public water
Source Protection Areas; wetlands; priority aquatic features; and proximity to publiclyowned lands. Although not completely consistent with the analysis described in this
report, it is possible that the Resource Threats map could be used separately to
indicate areas where forest stewardship practices might be less effective. This could be
useful when comparing the suitability of various projects or parcels for forest
stewardship.
Each map was created by summing the pertinent data layers. The Jenks statistical
method was applied to the summed layers of each map so that areas where more
factors were present were assigned a high value, and areas with few or no factors were
given a low value.
Conclusions and Future Uses
Benefits of Vermont’s SAP assessment of forest values and threats include the
following:
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Spatial Analysis Project (SAP) for Vermont, September 2007
Improved understanding of priorities for forest management;
Increased ability to set management priorities for private forestlands; and
Assistance in setting priorities for distributing cost-share funds.
Vermont hopes to find the resources to map the boundaries of Forest Stewardship
Program parcels and Use Value Appraisal Program parcels, where property tax
incentives are offered in exchange for managing land for timber crops. This mapping
effort is referred to as Phase 2 or the historic parcels data for the SAP. With more than
10,000 parcels enrolled in the state, it will take a few years for this to be done.
However, once completed, this data layer can be overlaid with the maps produced for
the statewide analysis described in this report (Phase 1 of SAP).
The benefits of having the historic parcel data mapped include the following:
This layer will provide an important addition to Vermont’s Conserved Lands
Database; and
A computerized method of developing Forest Stewardship Plans through
WebDET offers the potential for greater efficiency in this regard.
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Spatial Analysis Project (SAP) for Vermont, September 2007
References
Miller, E.K. (2005) Assessment of Forest Sensitivity to Nitrogen and Sulfur
Deposition in New Hampshire and Vermont. Technical Report prepared for the
NH Dept. of Environmental Services and the Conference of New England
Governors and Eastern Canadian Premiers. 15 December 2005, 19pp.
http://www.ecosystems-research.com/fmi
Schaberg, P.G., Miller, E.K., Eagar, C. In press. Assessing the Threat that
Anthropogenic Calcium Depletion Poses to Forest Health and Productivity.
USDA Forest Service General Technical Report (a peer-reviewed, combined
publication of the Southern and Pacific Northwest Stations) and a chapter on
the web-based forestry encyclopedia: www.threats.forestencyclopedia.net
Theobald, D.M. (2005) Landscape Patterns of Exurban Growth in the USA from
1980 to 2020. Ecology and Society (10)1:32.
Thompson, Elizabeth H. (2002) Vermont’s Natural Heritage: Conserving
Biodiversity in the Green Mountain State. A Report from the Vermont Biodiversity
Project. 48 pp.
Vermont Department of Environmental Conservation (October 1998) A
Classification of the Aquatic Communities of Vermont. Waterbury, VT.
14