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CSX Relocation Study
A method for delineating areas of possible gopher tortoise
habitat.
CSX Relocation Study
What do we know about gopher tortoise?
1. They prefer areas of deep sandy soils for burrowing.
2. They forage primarily on prairie grasses with wiregrass
being a preferred food source.
3. They require open canopy for food and basking.
4. Landcover, soil and topography are key variables in
defining gopher tortoise habitat. Can we collect and
integrate these data in order to generally model possible
gopher tortoise habitat?
CSX Relocation Study
Study Area
Pearl River
Pearl River
Stone
Stone
Harrison
Hancock
Hancock
Harrison
Jackson
Jackson
CSX Relocation Study
Model Inputs: Soils
USDA SSURGO Finite
soils series maps provide
information on numerous
soil properties.
We know that gopher tortoise
prefer non-flooded, sandy soils
that support longleaf pine and
prairie grasses such as wiregrass.
CSX Relocation Study
Model limits
Model Inputs: Satellite Imagery
10 meter SPOT imagery gives a
useful overview of landcover.
Values in the image allow
discrimination between forested and
cleared areas.
A review of the data shows that
values below 12 counts indicate
bottomland hardwood or dense
mixed canopy. Values above 197
indicate disturbed/cutover/developed
areas. We believe areas valued
between 12 and 197 are candidates
for inclusion in gopher tortoise
habitat model.
CSX Relocation Study
Model Range
Model Inputs: Aspect
Aspect supplies the “sun face” of the
landscape.
We think that gopher tortoises
prefer S, SW, W facing slopes for
their burrows.
CSX Relocation Study
Model Range
Model Inputs: Slope
Slope is a derivative of elevation. Local
slope is given in degrees.
We believe that gopher tortoise prefers
areas with slopes that are above .2 degrees
and below 6 degrees- Not flat and
not too extreme.
CSX Relocation Study
GT Habitat Model Logic:
1.
If the Soil Class is “Escambia”, “Eustis”, “Lakeland”,”Latonia”,”McLaurin”, “Poarch”,
“Ruston”, “Saucier”, “Smithdale” or “Susquehanna”, there is habitat value because the soil
meets gopher tortoise preferences for non-hydric, sandy soil that supports pine and prairie grasses.
2.
If Satellite Imagery values are between 12 and 197, the indication is that landcover is neither
dense bottomland hardwood or disturbed/cutover/developed land.
3.
If topographic slope is between .2 degrees and 6 degrees (less than 10% slope), the
assumption is that the ‘micro-terrain’ will offer good burrow sites and access to forage sites.
4.
If topographic aspect is between 135 and 315 degrees, the “sun face” is opposite
the NW/NE quadrants. Burrow porches will provide better opportunities for sunning.
Every location in the study area will either conform to the model criteria or not. The modeling
method looks at every location and determines a degree of conformity with the criteria.
CSX Relocation Study
Here is an example of what the model instructions look like:
if(( Layer( SSURGO, compname:c ) == "POARCH" ||
Layer( SSURGO, compname:c ) == "SAUCIER" ||
Layer( SSURGO, compname:c ) == "BENNDALE" ||
Layer( SSURGO, compname:c ) == "NUGENT" ||
Layer( SSURGO, compname:c ) == "SUSQUEHANNA" ||
Layer( SSURGO, compname:c ) == "MCLAURIN" ) &&
( Layer( Satellite Imagery ) > 12 &&
Layer( Satellite Imagery ) <= 197 &&
Layer( Satellite Imagery ) != NO_DATA ) &&
( Layer( Aspect ) > 135 &&
Layer( Aspect ) <= 315 &&
Layer( Aspect ) != NO_DATA ) &&
( Layer( Slope ) > .2 &&
Layer( Slope ) <= 6 &&
Layer( Slope ) != NO_DATA )){
OD = 100.000000;
A location meeting all criteria will have an output
value of “100”. This indicates a good possibility
of gopher tortoise habitat.
CSX Relocation Study
Model Output
This is the result of the model run. It
shows all areas in the study region that
represent possible gopher tortoise habitat
classified as either “prime” or
“marginal”.
When corridors are planned, there will
be a “map” to guide transportation
planners in avoidance or impact
minimization.
Map can be used to quantify potential
impacts within selected corridor
alternatives.
Map can be used to plan verification
field work.
Map can be loaded on handheld, GPS
field systems like Pocket Dlog for
navigation and ground truth activities.
CSX Relocation Study
Prime GT Habitat
Marginal GT Habitat
Roads
Streams
USFS Field observation
Of GT burrows
There is observable correlation (spatially) between model output and empirical
data on GT communities.
CSX Relocation Study
Model Statistics:
Stone ~42,000 acres of prime
possibility and ~94,000 acres of
marginal possibility.
Pearl River ~10,000 acres of prime
possibility and ~21,000 acres of
marginal possibility.
Hancock ~27,000 acres of prime
possibility and ~64,000 acres of
marginal possibility.
Harrison ~63,000 acres of prime
possibility and ~94,000 acres of
marginal possibility.
Jackson ~28,000 acres of prime
possibility and ~49,000 acres of
marginal possibility.
CSX Relocation Study
Hypothetical Example of Corridor Analysis for Gopher Tortoise Habitat.
Planned corridor. How much habitat is
within corridor?
There are ~13,000 acres of prime possibility
and ~19,000 acres of marginal possibility in
a total corridor area of ~79,000 acres.
CSX Relocation Study
Conclusion:
1.
The method is based on a knowledge of species natural history and
field observations.
2.
The method is generally repeatable across regions given the same
sets of geo-spatial data.
3.
The method is extensible. It can be applied to habitat delineation
for other terrestrial plant and animal communities. We observe that
humans and trains have habitats too.
4.
The method can be improved. Higher resolution topography
(Lidar, OTF RTK) and MSS imagery can yield better spatial
definition. More information on species natural history and wider
field studies can contribute to model refinement.