REGIONAL ASSESSMENT STATELINE SOLAR FARM PROJECT BLM CASE FILE NUMBER CACA-48669 Prepared for: Prepared by: Desert Stateline, LLC NatureServe 525 Market Street 4600 North Fairfax Drive 15th Floor 7th Floor San Francisco, California 94105 Arlington, Virginia 22203 Date: 27 July 2012 Cover photo credit: Geoffrey Hammerson NatureServe Project Team Mary Harkness Patrick Crist Conservation Planner/Project Manager Director, Conservation Planning and Ecosystem Management Ian Varley Jacquie Bow Conservation Planner GIS Analyst Jon Hak Geoffrey Hammerson Ecologist/Senior GIS Analyst Research Zoologist Suzanne Young Conservation Biologist and Data Analyst Suggested citation: NatureServe. 2012. Regional assessment: Stateline solar farm project. Technical report prepared for Desert Stateline, LLC. NatureServe, Arlington, VA. Regional Assessment: Stateline Solar Farm Project Page 2 of 94 1 Introduction .......................................................................................................................................... 8 1.1 Purpose and overview of assessment ........................................................................................... 8 1.2 Assessment approach ................................................................................................................... 8 1.3 Assessment areas and context ...................................................................................................... 8 1.3.1 Ivanpah Valley Watershed .................................................................................................... 8 1.3.1.1 Land management and uses ........................................................................................... 13 1.3.2 Desert tortoise subpopulation cluster geography .............................................................. 16 1.3.3 Mojave Basin and Range Ecoregion .................................................................................... 18 2 Desert Tortoise: Overview and Demographic Summary .................................................................... 20 2.1 Desert tortoise taxonomy and status ......................................................................................... 20 2.2 Habitat ........................................................................................................................................ 21 2.3 Threats ........................................................................................................................................ 22 2.4 Genetic population structure ...................................................................................................... 23 2.5 Range-wide population trends ................................................................................................... 23 2.6 Ivanpah Valley Watershed population........................................................................................ 24 2.6.1 Density estimates ................................................................................................................ 24 2.6.2 Other demographic estimates ............................................................................................ 28 3 Ecological Health Assessment ............................................................................................................. 31 3.1 Cumulative impacts assessment approach ................................................................................. 31 3.1.1 Landscape condition-based approach ................................................................................ 31 3.1.2 Categorical response approach........................................................................................... 32 3.2 Data and information inputs ....................................................................................................... 33 3.2.1 Data ..................................................................................................................................... 33 3.2.2 Landscape condition index .................................................................................................. 33 3.2.3 Scenarios of current and future conditions ........................................................................ 39 3.2.4 Estimating ecological integrity ............................................................................................ 40 3.2.4.1 Estimating landscape condition of tortoise habitat ........................................................ 40 3.3 Current and projected status of tortoise habitat and other habitats ......................................... 41 3.3.1 Condition of tortoise habitat .............................................................................................. 41 3.3.1.1 Current tortoise habitat condition .................................................................................. 43 3.3.1.2 Tortoise habitat condition with projected infrastructure............................................... 43 3.3.1.3 Interpreting condition results ......................................................................................... 49 3.3.2 Compatibility of ecological systems .................................................................................... 51 4 Desert Tortoise Habitat Connectivity Assessment.............................................................................. 52 4.1 General approach........................................................................................................................ 52 4.1.1 Modeling scales: spatial and temporal ............................................................................... 52 4.1.2 Modeling tool and data inputs ............................................................................................ 52 4.2 Landscape-scale connectivity modeling ..................................................................................... 53 4.2.1 Approach ............................................................................................................................. 53 4.2.2 Data sources, model inputs and methods .......................................................................... 54 4.2.2.1 Tortoise habitat ............................................................................................................... 54 4.2.2.2 Conductance surfaces ..................................................................................................... 56 4.2.3 Circuitscape set-up and outputs ......................................................................................... 56 4.2.4 Results and discussion ........................................................................................................ 57 4.2.4.1 Current conditions: potential tortoise habitat connections ........................................... 58 4.2.4.1.1 Potential areas of viable connection ........................................................................ 58 4.2.4.1.2 Areas of questionable connection ............................................................................ 59 4.2.4.1.3 Areas of connection identified by the model that are unlikely to be viable tortoise habitat connections .................................................................................................................... 59 4.2.4.2 Stateline Alternatives B and D and other infrastructure: potential tortoise habitat connections ..................................................................................................................................... 60 4.2.4.2.1 Potential areas of viable connection ........................................................................ 60 4.2.4.2.2 Areas of questionable connection ............................................................................ 60 4.2.4.2.3 Areas of connection identified by the model that are unlikely to be viable tortoise habitat connections .................................................................................................................... 60 4.2.4.2.4 Impacts of Stateline alternatives on landscape-scale connectivity .......................... 61 4.2.4.3 LSTS and connectivity ...................................................................................................... 65 4.2.4.4 Interpreting the landscape-scale connectivity results: considerations, recommendations, and limitations ................................................................................................. 68 4.3 Local connectivity modeling ....................................................................................................... 69 4.3.1 Approach ............................................................................................................................. 69 4.3.2 Data sources, model inputs and methods .......................................................................... 69 4.3.2.1 Habitat patches and points ............................................................................................. 70 4.3.2.2 Conductance surfaces ..................................................................................................... 70 4.3.2.3 Short circuit layer ............................................................................................................ 70 Regional Assessment: Stateline Solar Farm Project Page 4 of 94 4.3.3 Circuitscape set-up and outputs ......................................................................................... 70 4.3.4 Areas of connectivity..........................................................................................................