THE WILDLIFE SOCIETY CONFERENCE 2015

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1 THE WILDLIFE SOCIETY CONFERENCE 2015 Evaluation of Desert Tortoise Habitat Suitability Model Predictions in the Soda Mountain Area, San Bernardino County Susanne Heim

2 Introduction Overview of Species Habitat Distribution Modeling Desert Tortoise Habitat Modeling used in the Desert Renewable Energy Conservation Plan (DRECP) Desert tortoise field survey results in the Soda Mountain area Comparison of field survey results to model predictions in the Soda Mountain area Recommendations for use of habitat suitability models in land use policy

3 What are habitat distribution models? Habitat distribution models are Bayesian statistical models Bayesian models use the data on hand to determine the probability distribution for a set of parameters Frequentist models require random sampling with defined parameters Extrapolate from the data that is available to define habitat suitability across a larger geographic area Maximum Entropy Model (Maxent) is a commonly used habitat distribution model Maxent uses species presence data only to predict habitat suitability (Phillips et al. 2006)

4 Applications for Habitat Distribution Models Habitat distribution models can generate information about habitats over a large geographic area where field surveys would be impractical or infeasible Example applications include: Habitat Conservation Plans Substantial modeling in the DRECP Land Use Planning Large-scale project planning Linear transportation projects that span a large area Long linear utilities

Desert Tortoise Habitat Suitability Model USGS used presence data from a large range of sources to predict habitat for desert tortoise in Mojave and Sonoran deserts Robust data set with 15,311

5 Desert Tortoise Habitat Suitability Model USGS used presence data from a large range of sources to predict habitat for desert tortoise in Mojave and Sonoran deserts Robust data set with 15,311 occurrence points Model grid resolution is 1 km 2 Used publicly available GIS data layers for model variables Source:Nussear, K.E., Esque, T.C., Inman, R.D., Gass, Leila, Thomas, K.A., Wallace, C.S.A., Blainey, J.B., Miller, D.M., and Webb, R.H., 2009, Modeling habitat of the desert tortoise (Gopherus agassizii) in the Mojave and parts of the Sonoran Deserts of California, Nevada, Utah, and Arizona: U.S.: Geological Survey Open-File Report , 18 p.

6 Parameters Used in USGS Model Precipitation Elevation Slope Aspect Roughness Average soil bulk density Depth to bedrock Average percentage of rocks >254 millimeters B-axis diameter Plant cover

Desert Tortoise Model Results Predicted habitat suitability across the model range This model was accurate in a wide range of circumstances Model outputs were binned into categories ranging from 0 to

7 Desert Tortoise Model Results Predicted habitat suitability across the model range This model was accurate in a wide range of circumstances Model outputs were binned into categories ranging from 0 to 1 A 0 value represents areas that approach 0 suitability and 1 represents areas approach 100% perfect suitability Mean score for grid cells where desert tortoise were known to occur is 0.84 Source: Nussear et al. 2009

Soda Mountain Valley Focus of our study is the Soda Mountain Valley Located in San Bernardino County 6 miles southwest of Baker Valley is at an elevation of

8 Soda Mountain Valley Focus of our study is the Soda Mountain Valley Located in San Bernardino County 6 miles southwest of Baker Valley is at an elevation of approximately 1,200 to 1,500 feet amsl Surrounding Soda Mountains are 2,400 feet amsl Baker Sink is located to the northeast and Mojave wash to the southeast of valley

9 Soda Mountain Valley

10 Desert Tortoise Surveys in the Soda Mountain Valley Year (timing) Area of Survey Survey Type 2001 (spring) 115 acres Opah Ditch Mine 2009 (spring) 6,770 acres in valley and zone of influence 2012 (fall) 220 acres and zone of influence 2013 (spring) 4,179 acres in valley; 446 acre canyon east of the valley 100% coverage 100% coverage in valley; transects in zone of influence 100% coverage of 220 acres at eastern and southern edges of the valley; transects in zone of influence 100% percent coverage

11 Survey Areas Majority of the valley was surveyed with 100% coverage surveys (black outline) Over 4,000 acres was surveyed twice at 100% coverage

12 Survey Results Survey Year Area acre Opah Ditch Mine ,770 acres in valley acres at south and east end of valley ,179 acres in valley and 446 acres in canyon Live Tortoise Scat Burrows Carcasses Rock Shelters (ZOI) (ZOI) (ZOI) ZOI: Zone of Influence

13 Survey Results

14 Desert Tortoise Model Results for Soda Mountain Valley Model predicted habitat values of 0.7 to 0.9 over the valley Lower probability predicted habitat values in the mountains Low probability habitat to the east and south in Soda Lake, Baker Sink and Mojave wash The values for the Soda Mountain Valley are in the range of the mean value (0.84) for areas where desert tortoise were present in the model Based on model output would expect desert tortoise throughout the valley Source: Nussear et al. 2009

15 Comparison of Desert Tortoise Model to Survey Results

16 Comparison of Desert Tortoise Model to Survey Results Sign in areas with high habitat suitability (0.8 to 0.9)is limited to three carcasses Would expect more desert tortoise throughout the valley based on model predicted habitat Areas in the valley with highest sign have lower habitat suitability than portions of the valley with no sign

17 Model Limitations The model did not account for anthropogenic impacts such as the four lane, divided highway I-15 Tortoise populations in the valley were likely impacted by the I-15 highway Bathtub effect where sign is more common near the mountains Low incidence of tortoise near the highway Model is constructed at a 1-square km grid Relies on GIS data for a large area Possible flaws in the underlying data layers No field work was conducted to verify the data layers

18 Anthropogenic Impacts in Soda Mountain Area

19 Implications and Cautions Habitat distribution modeling is useful for generating data over large landscapes where it would be impractical to collect field data The modeling may over- or underestimate species distribution and habitat quality in the model domain Additional caution should be used when working with models that are built on less robust data sets Consider anthropogenic effects Beware of sample bias when using modeling

20 Recommendations Large scale habitat models should not be used to determine species presence or habitat at a project scale Field surveys are needed to verify model outcomes at a project scale Land use policies that use habitat modeling should include flexibility to adapt to site-specific data collection There needs to be a process to revise designations as a result of new or better data Rule sets can be used to define the process for incorporating project-specific field survey data and revising site-specific designations or conditions

21 Conclusions The USGS developed a robust model to predict habitat suitability for desert tortoise in the Mojave and Sonoran desert The model did not accurately predict habitat within the Soda Mountain Valley The inaccurate predictions for the Soda Mountain Valley may be a result of anthropogenic impacts, which were not considered in the model Large-scale habitat modeling is best used for large-scale planning and more detailed field surveys should be conducted at a project scale

22 Questions

Analysis of Habitat Suitability and Connectivity in the Soda Mountain Area, San Bernardino County, California

Analysis of Habitat Suitability and Connectivity in the Soda Mountain Area, San Bernardino County, California Susanne Heim and Laurie Hietter August 2012 One Embarcadero Center, Suite 740 San Francisco,