Forest Stewardship Spatial Analysis Project
Iowa Methodology
December, 2005
Project Summary
One purpose of the Spatial Analysis Project (SAP) is to create a data layer for a state that
represents levels of potential benefit from, or suitability for inclusion in, the Forest
Stewardship Program as delivered by state forestry agencies and the U.S. Forest Service.
Private land program and GIS staff from the four states involved in the pilot SAP effort
(Connecticut, Maryland, Massachusetts and Missouri), along with Forest Service
program and GIS staff 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 (Forest Wildlife)
ƒ Public Drinking Water Supply Sources (Priority Watersheds)
ƒ Private Forest Lands
ƒ Proximity to Public Lands
ƒ Wetlands
ƒ Topographic Slope
The resource threat factors include:
ƒ Forest Health (Pest/Disease Risk)
ƒ Development Level
ƒ Wildfire Assessment
Iowa Identified and included three additional factors:
ƒ Forest Soils
ƒ Forested Landscapes
ƒ Historic Forest
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, urban
areas and publicly owned lands. A mask was created to exclude these areas from the
analysis. Once the 15 factors were identified, the Iowa Forest Stewardship Committee
determined the relative importance of each of the criteria and an average weight was
calculated for each.
The 15 layers were then combined in a GIS overlay analysis which took into account the
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 1, with a value of 1 representing the highest level of
suitability. 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 was then created to display the data.
In order to understand where the Forest Stewardship Program has been previously
implemented, the forest stands and property boundaries for ownerships with a
Stewardship plan were digitized. Stewardship plan polygons were then overlaid on the
Stewardship potential layer to assess Stewardship efforts to date.
Data Development
Forest Soils: This coverage is a 30 meter raster representation (in ESRI GRID format) of
soil mapping units from the published soil survey reports of Iowa. This GRID is a
compilation of the individual township-wide vector soil coverages. The original vector
versions of the soil surveys were digitized by the Iowa Cooperative Soil Survey (ICSS),
with township edge-matching, final editing and finishing assembled by the Iowa
Geological Survey, of the Department of Natural Resources. Minimum size delineation
of soils are 2 acres. The soil mapping values can be linked to the Iowa Soil Properties
and Interpretations Database (ISPAID) on the conoseq field.
For the purposes of the SAP project, a value of 1 was assigned to soils that
developed under forest as the native vegetation (NATIVEVEG = F). A value of 0.5 was
assigned to soils that developed under a transition from prairie to forest and often
supported savanna communities (NATIVEVEG = T).
Online_Linkage:
ftp://ftp.igsb.uiowa.edu/gis_library/IA_State/Geologic/Soils/soils.zip
Online_Linkage: http://www.igsb.uiowa.edu/nrgislibx/
Forest Wildlife: Following almost two years of work by more than 100 people, including
experts, agency and organization representatives and other interested individuals, a new
plan for Iowa’s wildlife is nearing completion, and a draft is now available for public
review and comment. Copies of the plan will be available as noted below.
This is the first attempt ever to enumerate most of the state’s wildlife and evaluate
the status of each species. It also examines stresses on wild creatures or their habitats and
lays out visions and strategies to conserve wildlife over the next 25 years. Also known as
the Iowa Comprehensive Wildlife Conservation Plan, the document identifies 999 species
of birds, mammals, fish, reptiles, amphibians, mussels (freshwater clams), land snails,
butterflies, dragonflies and damselflies. These groups were selected for inclusion because
there is sufficient data to identify all of the known species, or because DNR has statutory
authority for conservation and management of the listed groups. Fully one-third of all
species found in Iowa are of concern due to their decline across Iowa. Plants are not
listed because it is intended as a wildlife plan. However, plant communities are an
important part of the habitats for most of Iowa’s wildlife and are addressed in terms of
habitat throughout the plan. The draft plan is available on-line at the following link:
http://www.iowadnr.com/wildlife/files/IAcomprehensive_plan.html
The Iowa GAP Analysis project, part of the National GAP Analysis Program, developed
both habitat and species range maps for Iowa wildlife. Each of the grids represents a
species' predicted distribution based on habitat models derived from the IAGAP land
cover data and hexagon range maps derived from survey data and expert review. This
coverage was created to facilitate the vertebrate species habitat mapping portion of the
Iowa Gap Analysis Program. The naming convention for each of the predicted
distributions is based on a 4-letter code. A file called species_code.txt should accompany
the directory in which the predicted distribution files are found. The collection of grids
for individual species can be found at:
Citation_Information:
Originator: Iowa Gap Analysis Program
Publication_Date: 2002
Title: Iowa GAP Predicted Species Distributions
Online_Linkage: http://www.ag.iastate.edu/centers/cfwru/iowagap/
Online_Linkage: ftp://ftp.igsb.uiowa.edu/gis_library/IA_State/Biologic_Ecologic/
Online_Linkage: http://www.igsb.uiowa.edu/nrgislibx/
Existing Forest: The 2002 land Cover map was derived from 15 meter Landsat Satellite
imagery captured primarily in 2002. For the purposes of this project, land cover codes
for wet forest, coniferous forest, and deciduous forest were used to represent existing
Iowa forest. Details on individual scenes, processing steps, and individual land cover
categories can be obtained from the metadata available from the following links:
Online Linkage: http://www.igsb.uiowa.edu/nrgislibx/
OnlineLinkage:
ftp://ftp.igsb.uiowa.edu/gis_library/IA_State/Land_Description/Land_Cover/Land
_Cover_2002/lc_2002.zip
Forest Patch Size: This grid representing forest patch size was derived from existing
forest in the 2002 land cover map as described above. There is not a published, online
version of this map, but it can be recreated using tools available in ERDAS Imagine.
Iowa’s forest is highly fragmented, but larger areas of contiguous forest do
provide greater opportunities for forest stewardship activities. There is not a single
threshold value that adequately defines this relationship. Instead, a bottom limit of 20
acres was established, and four size ranges were included. A value of 1 was assigned to
forest patch sizes of 640 acres or more; a value of 0.75 was assigned to patch sizes from
160 to 639 acres; a value of 0.50 was assigned to patch sizes from 80 to 159 acres; and a
value of 0.25 was assigned to patch sizes from 20 to 79 acres.
Online Linkage: http://www.igsb.uiowa.edu/nrgislibx/
OnlineLinkage:
ftp://ftp.igsb.uiowa.edu/gis_library/IA_State/Land_Description/Land_Cover/Land
_Cover_2002/lc_2002.zip
Proximity to Public Land: This map was derived from a sub-set of Iowa’s public lands.
Much of Iowa was historically tall-grass prairie, and only approximately 1% of this
habitat remains today. Many public lands are managed for tall-grass prairie, and habitat
goals are aimed at increasing the percentage of grassland habitats in the landscape,
especially to support many of the grassland bird species that are experiencing long-term
population declines. For the purposes of this project, we have identified public lands
where forest habitat is one of the habitat and wildlife management goals using the
following criteria: More than 40 acres of forest and forest makes up at least 20% of the
public area. Public lands information is periodically updated by the various groups who
manage public lands in Iowa. We used the most complete versions available at the time
of this analysis. The most complete compilations that are publicly available can be found
at the locations listed below.
Online_Linkage for Iowa GAP Stewardship Lands: http://www.iowagap.iastate.edu
Online_Linkage for Iowa DNR Lands:
ftp://ftp.igsb.uiowa.edu/gis_library/IA_State/Admin_Political_Boundary/Public_Lands/D
NR_lands.zip
Priority Watersheds: Iowa has completed versions of 8-digit, 10-digit, and 12-digit
Hydrologic Unit Codes. In many cases, priorities are assigned to these watershed
boundaries. In certain cases, such as individual lake watersheds, the watersheds
contributing to these water bodies are considerably smaller, and specific watersheds have
been delineated for these features.
For the purposes of this project, a value of 1 was assigned to watersheds that meet
2 or more of the priority criteria, and a value of 0.5 was assigned to watersheds meeting
any one of the four listed criteria.
Online_Linkage for 12 Digit Hydrologic Units for Iowa:
<http://www.ftw.nrcs.usda.gov/HUC/huc_download.html>
Online_Linkage for Public Lakes Watersheds:
ftp://ftp.igsb.uiowa.edu/GIS_Library/IA_State/Hydrologic/Surface_Waters/public_lakes_
watersheds.zip
Topography: This map depicts slopes estimated from the National Elevation Dataset; a
statewide 30 meter Digital Elevation Model created from U.S. Geological Survey
1:24,000 topography maps. In Iowa, slope is a major determinant of land use and
susceptibility to erosion. Soils and general terrain relief of a region largely determine
land uses, and the negative environmental impacts of various land uses. For the purposes
of this project, steep slopes were identified using different minimum values in three
different sub-ecoregions of Iowa. The minimum slope threshold for each sub-ecoregion
was selected because land on more gentle slopes in Iowa is much more likely to be in
high value agricultural production and not likely for inclusion in the Stewardship
Program.
Online_Linkage for the National Elevation Dataset:
ftp://ftp.igsb.uiowa.edu/GIS_Library/IA_State/Elevation/NED/ned_ft.zip
Online_Linkage for Eco-regions of Iowa:
<ftp://ftp.igsb.uiowa.edu/gis_library/IA_State/Biologic_Ecologic/ecoregions.zip>
Development Risk: This map was derived from U.S. Census Bureau data summarized to
the block group level for the 1990 and 2000 national census. The specific shapefile used
for this analysis was provided by the U.S. Forest Service, SAP program staff.
Online_Linkage for the 1990 U.S. Census block groups:
ftp://ftp.igsb.uiowa.edu/GIS_Library/IA_State/Cultural_Demographic/Census_19
90/census_1990_block_group.zip
Online_Linkage for the 1990 U.S. Census block groups:
ftp://ftp.igsb.uiowa.edu/GIS_Library/IA_State/Cultural_Demographic/Census_20
00/census_2000_block_group.zip
Riparian Corridors: This map was derived from the Iowa Stream Order coverage. This
coverage contains selected arcs from the National Hydrogrophy Dataset which was
developed by the USGS and EPA. The selected arcs represent the centerlines of wide
streams, impoundments, reservoirs, and wetlands as well as the segments of single line
streams. An Arc/Info macro was run on the arc segments to calculate the Stralhler stream
order for each arc. Since floodplain information for most Iowa counties is not available
in digital format, stream order is the best indicator of potential for riparian habitat. First
order streams include grass waterways and other ephemeral drains that do not exhibit a
defined channel. Floodplain width tends to increase with stream order. Fifth order and
higher streams have broad floodplains capable of supporting larger stands of bottomland
forest. First order streams were not included and second order and higher streams were
buffered by 25 meters x the stream order. This results in a total riparian width of 50
meters for second order streams and 250 meters for fifth order streams.
Online_Linkage:
<ftp://ftp.igsb.uiowa.edu/gis_library/IA_State/Hydrologic/Surface_Waters/stream
_order.zip>
Pest/Disease Risk: Gypsy Moth and White Oak Decline demonstrated increased
presences in 2003. White Oak Decline: Rating reports from field foresters, field visits
by entomologists and pathologists, reports from forest industry personnel, and aerial
monitoring all concurred that white oak decline is increasing, especially in the 20
northeast Iowa counties depicted on this map. Gypsy Moth is not yet widespread as
viable breeding populations in Iowa. For over a decade, pheromone trapping to identify
early moth arrivals followed with treatments to eradicate early moth arrivals has kept
Gypsy Moths out of the area. Wisconsin entomologists report a quickening of movement
of gypsy moth westward, and this combined with the increase of 159 moth catches in
Iowa in 2003 pointed to the need to prepare for eventual infestation in Iowa. The 20
counties shaded on this map represent the area at highest risk to Gypsy Moth infestation
from Wisconsis populations. This information was published in the 2003 Iowa Forest
Health Highlights.
Online_Linkage:
http://www.fhm.fs.fed.us/fhh/fhh-03/ia/ia_03.htm
Forested Wetlands: This map depicts forested wetland habitats as defined by the
National Wetland Inventory (NWI) conducted by the U.S. Fish and Wildlife Service,
circa 1984. Areas on this map represent both forested wetlands as well as a 50 meter
buffer area. NWI data is stored in county-wide files so 99 files are needed to assemble
statewide information. Below is a link to the NWI data for Cerro Gordo County. Other
counties are available from different county directories at the same site.
Online_Linkage:
ftp://ftp.igsb.uiowa.edu/gis_library/Counties/Cerro_Gordo/NWI_17_poly.zip
Online_Linkage: http://www.igsb.uiowa.edu/nrgislibx
Oak regeneration: Loss of oak forest has been an increasing concern across Iowa. Since
1954, Iowa has lost more than 7,000 acres of oak forest annually. Managing native
vegetation communities in Iowa is a challenge because of the small and highly
fragmented acreages and near complete absence of historic disturbance regimes. Active
forest management is needed in many areas in order to favor regeneration of oaks in
aging forest stands. The above map showing high and moderate priority areas for oak
regeneration was produced by Paul Tauke, IDNR Forestry Services Supervisor. High
priority areas were assigned a value of 1 and moderate priority areas were assigned a
value of 0.5.
Forested Landscapes: Iowa’s landscape historically was dominated by grassland habitats
and is estimated to have been composed of 18% forest. Today, Iowa forests compose
about 8% of Iowa, and the remaining forest habitats exist in small, highly-fragmented,
stands. It is possible to quantify the density, or amount, of forest on a landscape scale in
order to differentiate areas that have more forest than others. More potential to benefit
from Forest Stewardship exists on both forested and non-forested areas in forested
landscapes than in areas where forest is only a minor component of the landscape. This
map assigns a value of 1 to landscapes containing the highest forest densities, comprising
13.5% of the state, and a value of 0.5 to landscapes with moderate amounts of forest,
which comprise an additional 21% of the state.
Online Linkage: http://www.igsb.uiowa.edu/nrgislibx/
OnlineLinkage:
ftp://ftp.igsb.uiowa.edu/gis_library/IA_State/Land_Description/Land_Cover/Land
_Cover_2002/lc_2002.zip
Historic Forest: This map depicts historic forest areas identified from the Government
Land Office Survey conducted in the 1860’s. A majority of the significant forested areas
today exist as fragments of the larger forests of the 1860’s. The historic forests provide a
footprint for focusing forest stewardship practices in order to improve the quality,
quantity, and connectivity of existing forest lands.
Online_Linkage:
ftp://ftp.igsb.uiowa.edu/gis_library/IA_state/biologic_ecologic/GLO_vegetation.z
ip
Online_Linkage: http://www.igsb.uiowa.edu/nrgislibx
Wildfire Risk: Areas of wildfire risk depicted on this map were taken from the
“Wildland Fire Assessment” report for the state of Iowa. The assessment was based on
historical data from the State Fire Marshall’s Office on wildfires occurring from 1994 to
1999. Natural vegetation and land use data was used to help predict future risks. This
report was produced y the Iowa DNR Forestry Bureau to be incorporated in the National
Fire Plan.
Hardcopy reports can be ordered from:
Gail Kantak
Fire Supervisor
2404 South Duff Ave.
Ames, Iowa 50010
Phone: 515-233-1161
Gail.Kantak@dnr.state.ia.us
Weighting
Of the fifteen criteria identified as contributing to the potential Stewardship Program
benefit of a given piece of ground, some will likely be more important than others. To
account for differing levels of importance, the Iowa forest Stewardship Committee (19
people total) ranked the fifteen criteria. Committee members were asked to rank each
factor from 1 to 15, with 1 being the most important. A mean response value was then
calculated for each of the 15 factors. In order to give the most important factor the
largest numerical value, the mean response for each factor was subtracted from the
highest possible rank (15). These inverse response values were then converted to relative
weights by dividing each by the sum of the inverse response values. The relative weights
were the values used in the analysis. The following shows the final weights for each
factor.
Criterion
Forest Soils
Forest Wildlife
Existing Forest
Forest Patch Size
Proximity to Public Land
Priority Watersheds
Topography (Slope)
Development Risk
Riparian Corridors
Pest/Disease Risk
Forested Wetlands
Oak Regeneration
Forested Landscapes
Historic Forest
Wildfire Risk
Weight
0.18
0.18
0.13
0.13
0.13
0.07
0.04
0.0315
0.03
0.021
0.02
0.014
0.01
0.01
0.0035
Grid Values
0.5, 1.0
0.5, 1.0
1.0
0.25, 0.5, 0.75, 1.0
1.0
0.5, 1.0
1.0
1.0
1.0
1.0
1.0
0.5, 1.0
0.5, 1.0
1.0
1.0
GIS Analysis
The GIS data representing each of the twelve factors was converted to the ESRI Grid
format with a cell size of 15 meters. The Grid of each factor was converted to up to 5
values from 0 to 1 (i.e., 0, 0.25, 0.50, 0.75, 1.0). For example, all the 15m 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. In the case of the
forest patch size grid, five grid values were assigned based on forest patch size (acres) as
follows: < 20 = 0; 20 to 79 = 0.25; 80 to 159 = 0.50; 160 to 639 = 0.75; and > 640 = 1.0.
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 fifteen 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 fifteen layers.
The maximum possible cell value in the final Grid is 1. Result Grid values for Iowa
ranged from 0 to 1.0. A total of 275 cells (only 15 acres) were a “hit” in all fifteen data
layers, though many were “misses” in all twelve layers (16,040 acres).
The ESRI Spatial Analyst extension allows for the specification of an analysis mask. The
analysis mask layer described above was used in this capacity to exclude areas of Iowa
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 Arc View. Class definition values for the Iowa final results data are:
Low
Medium
High
0 – 0.152
0.153 – 0.412
0.413 – 1.0
The final result grid was reclassified to an integer grid where 1 represents Low, 2
Medium, and 3 High.