Forest Stewardship Spatial Analysis Project
Maryland Methodology
January, 2005
Project Summary
The purpose of the Spatial Analysis Project (SAP) is to create a series of GIS data layers
and tools for the state that represents various levels of potential benefit from, and
suitability for inclusion in the Stewardship Program as delivered by state forestry
agencies and the U.S. Forest Service. Private land programs and GIS staff from the four
states involved in the pilot SAP effort (Connecticut, Maryland, Massachusetts and
Missouri), along with U.S. Forest Service program identified 12 factors which help
identify the “Stewardship potential” of a given piece of land. The factors were
differentiated into two groups: resource potential and resource threats.
The resource potential factors include:
ƒ Riparian Zones
ƒ Priority Watersheds
ƒ Forest Patch Size
ƒ Natural Heritage Data
ƒ Public Drinking Water Supply Sources
ƒ Private Forest Lands
ƒ Proximity to Public Lands
ƒ Wetlands
ƒ Topographic Slope
The resource threat factors include:
ƒ Forest Health
ƒ Development Level
ƒ Wildfire Assessment
Certain lands within any state are not eligible for inclusion in the Forest Stewardship
program. Land use / land cover factors which identify these areas are open water,
industrial and urban areas. In Maryland open water was eliminated from the data sets and
a mask was created to exclude industrial and urban areas from the analysis. Publicly
owned lands were not entirely removed from Maryland’s considerations as some
programs could be applied under certain conditions. Those publicly owned lands that
were identified as not being eligible were removed from the data set through the same
process as the open water.
Once the 12 factors were identified, each state could determine the relative importance of
each of the criteria based on their state-specific conditions or treat all areas as equal
weights. Maryland Department of Natural Resources Forest Service staff decided to treat
each layers 30 meter grid resolution intersect as an equal weight of 1 for a hit or miss
summation model.
A weighted 32-layer model was also attempted during the early planning phases to
determine the feasibility of such an effort. It was determined to be too complex and
difficult to interpret by the reviewers in the Stewardship advisory committee and
Maryland DNR Forest Service staff. After reviewing the work of the other three states in
the SAP project Maryland returned to the basic 12 layer equal weighted model as
described above and used by the other project states.
The 12 layers were then combined in a GIS overlay analysis which took into account the
equal weight for each factor. The final product was a single data layer which represents
the suitability of the land for inclusion in the Forest Stewardship Program. Possible
values from this analysis range from 0 to 12, with a value of 12 representing the highest
level of suitability. Actual values for Maryland ranged from 0 to 12. A natural breaks
classification algorithm was used to break the values into low, medium and high classes.
The result is shown below.
Summary statistics were calculated and a series of maps were then created to display the
data as required by the U.S. Forest Service SAP project team.
While the process outlined above was taking place a parallel effort was occurring. In
order to understand where the Forest Stewardship Program has been previously
implemented, the centroids and property boundaries for ownerships with a Stewardship
plan were digitized.
For Maryland the centroids were the easiest to develop as we had 4,800 Stewardship
plans for the years 1990-2000. These plans existed only as hard copy records scattered
across 23 counties. In order to get this part of the task done no less than seven personnel
were hired during the projects operational period to collect and scan data on 4,800
potential plans. There was significant turnover in staff and only two of those staff remain
in service today. The centroid based database was completed Fall of 2003 and used in the
SAP project maps buffered to a size matching their acres of impact under the Stewardship
Programs.
The process of digitizing polygons to match the centroids began Summer 2003 and the
1990-1999 polygons were completed in November 2004 with the exception of those from
Mongomery County Maryland where record no longer used tax maps as the locator. This
difficulty made it hard to determine where exactly the polygons belong. Through an
intensive effort Montgomery County’s polygons were completed and incorporated into
the database in January 2005. This complete set of Stewardship plan polygons were
overlaid on the Stewardship potential layer to assess Stewardship efforts through 1999.
Plans and polygons for the period from 2000 through 2004 will be incorporated into the
Stewardship Database by December 31, 2005.
Data Development
Riparian Zones: Riparian zones were created by buffering (300 feet each side) the
streams data set from the Maryland Office of Planning 1:60,000 source scale files. The
buffers are shown in green.
Priority Watersheds: These watersheds are considered priorities for various reasons
including: non-point source pollution focus areas (SALT AgNIPS), presence of
threatened / endangered species, Farm Bill program focus areas, etc. Watershed polygons
were created by aggregating polygons from 12-digit Maryland DNR Watershed Services
Division shapefiles. Source scale for this data is 1:24,000. The priority watersheds are
shown in green.
Forest Patches: All forest cover used in this project was extracted from the early 1990s
National Land Cover Database (NLCD). This landcover classification was based on
Landsat Thematic Mapper 30 meter satellite imagery acquired in 1992 & 1993. Five
NLCD classes were used to create a "forest" layer: deciduous forest, coniferous forest,
mixed forest & woodland, shrubland, and woody wetlands (NLCD classes 41, 42, 43, 51,
91). Large roads create discontinuities in forest cover and reduce forest patch size for
some wildlife species. Accordingly, the state-maintained roads were buffered by road
type: 50 feet (each side) for interstates, 50 feet (each side) for U.S. and MD highways.
This buffered road layer was then erased through the private forest lands layer. The erase
process has the effect of cutting a hole in the forest layer wherever the buffered roads
occur. Minimum forest patch size was set at 50 acres. The result is the forest patch layer.
This 30m dataset was used in the analysis. Forest patches are shown in green.
Natural Heritage Data: Individual plant and animal records, and high quality community
records from the Maryland Natural Heritage Database were used to represent areas of
biological importance. Point and polygon records were both buffered by random amounts
by the Maryland DNR Wildlife and Heritage staff. Old, general historic records were not
used. Records are created using 1:24,000 scale USGS topographic maps as the base.
These areas are shown in green.
Public Drinking Water Supply Areas: Shapefiles from the Maryland Department of
Environment Public Drinking Water Program were provided per our request. Source
scale for this data is 1:24,000. Lake intakes and buffered (1 kilometer) surface and well
intake points were unioned into one file and clipped with the Maryland boundary
polygon. The MDE data set appeared to be missing some vital data areas but attempts to
obtain further information proved fruitless as MDE had reduced it’s GIS staff and seemed
unable or unwilling to comply with data requests over a two year period. Water resources
and their buffers are shown in green.
Private Forest Lands: All forest cover used in this project was extracted from the early
1990s National Land Cover Database (NLCD). This landcover classification was based
on Landsat Thematic Mapper 30 meter satellite imagery acquired in 1992 & 1993. Five
NLCD classes were used to create a "forest" layer: deciduous forest, coniferous forest,
mixed forest & woodland, shrubland, and woody wetlands (NLCD classes 41, 42, 43, 51,
91). Private forest land is created by erasing a public lands shape file through the forest
layer, creating "holes" in place of the public lands. This 30m dataset was then used in the
analysis. Private forest lands are shown in green.
Proximity to Public Lands: A single shapefile of all public land ownership in Maryland
was created by merging individual agency files for Federal, State and county land
holdings as maintained by the Maryland DNR and the Maryland Office of Planning. The
source scale for all the individual shapefiles is 1:24,000. The public lands were buffered
by 1000meters in an effort to show the priority to develop contiguous forest blocks
adjacent to public lands. These areas are shown in green.
Wetlands: Digital National Wetlands Inventory shapefiles originally compiled at
1:24,000 scale by the U.S. Fish and Wildlife Service were used by the Maryland DNR
Watershed Management Division as the source for this layer which was modified by new
data field sampled by state biologists and ecologists. All state designated wetlands classes
were used. These areas are shown in shades of pink to red based on the wetlands
importance.
Topographic Slope: A statewide 30 meter Digital Elevation Model (1:24,000 scale
source) from the National Elevation Dataset (USGS) was used to select areas where slope
is between 15% and 35%. 35% represents the general maximum operability limit for a
skidder operating in Maryland. Between 15% and 35% the Stewardship Program can be
used to help control soil erosion. These areas are shown in green.
Forest Health: The most extensive, addressable forest health concern occurring in
Maryland over the period addressed is Gypsy Moth. In future efforts, maps for southern
pine beetle, emerald ash borer (EAB), hemlock woolly adelgid (HWA) and sudden oak
death (SOD) may be considered for inclusion. Statewide data was collected from the
Maryland Department of Agriculture records for ten years of Gypsy Moth Treatment
from 1990-2000 showing treatment zones. The area described are shown in green.
Developing Areas: Based on U.S. Census Bureau 1990 and 2000 data. Census block
group polygons from 1990 and 2000 were unioned to deal with differing census
geography boundaries and the number of households per square kilometer was calculated.
The change in number of households / sq. km. from 1990 to 2000 was then calculated.
Block group polygons where the change was >= 1 and <= 8 households / sq. km. and not
in urban areas were selected. These areas are shown in green.
Wildfire Assessment: This layer is based on the Maryland DNR Forest Services
Geomatics Lab THARSFE Wildland Urban Interface (WUI) Fire Model. The model is a
composite of: wildfire risk based on wildland urban development level, wildfire hazard
fuels density and types of ground cover and wildfire sensitivity based on landuse and
perceived value. Fire equipment and fire response accessibility were used in the model to
show the ability of the local governments to deal with WUI fire. The WUI THARSFE
model was broken out originally by 12-digit watersheds and natural breaks of the
summed zones model values into five categories ranging from very low to extreme fire
impact. The high to extreme categories were used for SAP from the original assessment
to create the "1" or hit cells for this layer. These areas are shown in color based on level
of fire impact. Green is the least vulnerable and dark brown is the most vulnerable to
wildfire and are rated as follows: Green 1, Light Green 2, Yellow 3, light brown 4, dark
brown 5.
Analysis Mask: The analysis mask contains urban/developed areas that were not
considered in the analysis. Urban & developed areas were compiled from the urban and
industrial - commercial lands from the NLCD land cover classification. The final layer
was created by erasing the composite shape file of unavailable areas through the
Maryland state polygon, creating a state with holes in it corresponding to the unavailable
areas. The masked areas are shown in grey. All Maryland’s layers were clipped for open
water and those public lands not eligible for Stewardship.
Stewardship Plan Ownership Boundaries: Entire tract boundaries for which a
Stewardship Plan has been written since 1995 - 2000. Tract boundaries were compiled at
a source scale of 1:24,000. The Stewardship Plan tracts are shown in black.
Weighting
The twelve criteria identified as contributing to the potential Stewardship Program
benefit of a given piece of ground were each given an equal weight of 1 for where they
existed geographically and a 0 for where they do not exist. Each layer was converted into
a 30meter grid of 1 and 0 valued grid cells. The analysis summed the intersected grids
giving the analysis layer a range of grid values from 0 to 12 where 12 is the most
important for Stewardship efforts and 0 is of no importance or ineligible. The following
shows the layers and their weights for each factor.
Criterion
Riparian Corridors
Priority Watersheds
Forest Patches
Forest Health
Natural Heritage Sites
Drinking Water Supply
Private Forest
Public Land Adjacency
Wetlands
Slope
Development Risk
Wildfire Assessment
Weight
1
1
1
1
1
1
1
1
1
1
1
1
GIS Analysis
The GIS data representing each of the twelve factors was converted to the ESRI Grid
format with a cell size of 30 meters. The Grid of each factor was converted to a 0, 1
format. For example, all the 30m grid cells that fell within the riparian buffers were
coded as a “1”, while all the cells that were outside the areas of the riparian buffers were
give the value “0” in that layer.
The analysis process is relatively straightforward. Each Grid is multiplied by its weight
value, so that the cells coded as “1” take on the weight value while all the “0” cells retain
a value of 0. Because all twelve grids were derived from the same source, the grid cells of
each layer line up exactly with the cells from all the other layers. The overlay analysis
procedure uses this fact to create a final result Grid whose individual cell values equal the
sum of the values in the same location (on the same half-acre) from all twelve layers.
The maximum possible cell value in the final Grid is 12. Result Grid values for
Maryland could potentially range from 0 to 12. No single cell location was a “hit” in all
twelve data layers, though many were “misses” in all twelve layers.
The ESRI Spatial Analyst extension with model builder allows for the specification of an
analysis mask. The analysis mask layer described above was used in this capacity to
exclude areas of Maryland that don’t meet eligibility criteria for inclusion in the Forest
Stewardship Program (open water, public lands, urban areas, etc.).
To make interpretation of results easier and allow for computation of area statistics, three
data classes were established to group the continuous cell values: Low, Medium and
High Stewardship Potential. There are several possible methods for establishing class
breaks. The project group decided to use the Natural Breaks classification algorithm
available in ArcView. This was used by Maryland for Stewardship Potential maps and
Stewardship Threat maps.
The 12 data layer composite was grouped into three categories based on the number of
intersects in a given pixel as shown in the table below. Maryland staff decided this gave a
more useful picture as the ranges using natural breaks were quite small towards the low
and high with over 80% falling within the natural breaks medium range creating an
almost featureless image except around the Chesapeake Bay where the bulk of the high
range appeared.
Low
Medium
High
0-3
3-6
6-12
Creating a Maryland Stewardship Plan Database
with Associated Polygon Locations
Stewardship plans are not currently collected centrally in Maryland. Maps of each
Stewardship plan tract were digitized at 1:12,000 scale on a Digital Ortho Quarter Quad
based on the Stewardship plans written text description and the sketched maps based on
the Maryland ADC road map books which were collected from each Forestry office in
the state. Each tract was assigned a unique identifier based upon its legal description, and
a database of plan attributes is assembled. Title searches and tax records had to be
searched often to confirm the true location of the properties in question as often the
locations were poorly defined or paper maps were entirely unavailable. Maryland has a
high rate of mobile population which means tracts tend to change ownership often. This
adds to the difficulties involved in locating poorly recorded tract data when the main
source of location is the owners address and tax number. Often it was necessary to
determine who the new owners were to locate the property and any recent subdivisions.
Key Meetings And Project Genesis
Much of the genesis of the Stewardship Spatial Analysis Project can be traced to a
meeting on January 19, 2001 in Newtown Square Pennsylvania. At this meeting Steve
Koehn, Don Van Hassent and John Wolf from Maryland DNR presented preliminary
work on Maryland’s Strategic Forest Lands Assessment (SFLA), built on the
ecologically-based modeling methodology for Maryland’s Green Infrastructure Analysis
Project. USFS NA staff Susan Lacy and Mark Buccowich were present and could see the
significant value of this modeling approach, and how a similar analysis might be able to
benefit and focus Forest Stewardship efforts in the northeast. Maryland’s SFLA, funded
through the USDA Forest Service NA for $80,000 started on October 1, 1999 and was
completed December 31, 2003. With the seed planted, USFS staff sought to find other
states willing to participate in a pilot project to build a model capable of guiding
Stewardship efforts to areas where it would have the greatest benefit.
The first meeting of the four state pilot group occurred at Newtown Square Pennsylvania
on July 5-6, 2001. The meeting included representatives from the USDA Forest Service
NA, and state forestry representatives from Maryland, Massachusetts, Connecticut, and
Missouri. USDA FS funding for each of the four pilot states had already been secured
through the Northeastern area, with Maryland’s grant for $61,000 beginning on June 1,
2001. A subsequent meeting of the principles from each of the four states and Forest
Service staff was held in Annapolis, Maryland on November 1-2, 2001. Over the next
three years the group met numerous times and spend countless hours pouring over data,
evaluating rankings and honing the analysis.
Maryland Stewardship Committee Involvement
Maryland’s Stewardship Committee first received a briefing on the Stewardship Spatial
Analysis Project at their summer 2001 meeting. The group received briefings on both
SFLA and the exciting new SAP (than called Stewardship Initiative). During this
meeting committee members were promised the opportunity to have input on the ranking
process as it was developed for the SAP. In March 2003 the Stewardship Committee met
again and had the opportunity to comment on the layers and the suggested rankings used
in the SAP models. The Stewardship Committee felt strongly that the 32-layer approach
presented in that meeting was overly complex. Following the meeting Pat Patterson
revised the model to a 12-layer approach that was more closely aligned with the other
three pilot states. A presentation of the final draft model and an opportunity for comment
was provided at the December 17, 2004 meeting of the Maryland Stewardship
Committee.
Evolving and Potential Uses
The Maryland Forest Service Operations Team made up of the four Regional Foresters
and key headquarters staff met to discuss the potential use of the SAP analysis for
Stewardship Program implementation on November 9, 2004. A subsequent meeting of
the Regional Foresters and the rest of the Maryland Forest Service Leadership Team
occurred on December 9, 2004 with an agreement to fully analyze the potential of using
the SAP to prioritize Stewardship Program implementation in Maryland. The Leadership
Team also approved a new operations order that will require all future Stewardship Plans
and plan maps to be captured digitally and stored in the Stewardship Database. This new
process will likely capture all Stewardship Plans and the maps created beginning in 2005.
Maryland is also in the process of digitizing polygon maps for the Stewardship Plans
developed between 2000-2004. Those plans should be completely incorporated into
Maryland’s Stewardship Database by December 31, 2005.
A corollary effort is also underway in Maryland to incorporate SAP and a product from
Maryland SFLA, the Economic Model to build a decision support tool to help guide the
acquisition and protection of forestland in Maryland. The “Economic Parcel Evaluation
Tool” will use these two models to rank forest sustainability and justify the importance of
individual parcels as they are considered for protection through fee simple purchase or
conservation easement protection through Maryland Rural Legacy, Forest Legacy,
Agricultural Preservation, Maryland Environmental Trust or Program Open Space.
(Note: Questions about Maryland’s SAP Methodology should be addressed to Pat
Patterson or Jeff Horan of Maryland DNR Forest Service.)