GIS5100 - Part 2

Modeling Black Bear Connectivity: A Least-Cost Corridor Analysis

This project focused on identifying optimal connectivity pathways for Black Bear (Ursus americanus) movement between two designated park areas. Utilizing a least-cost path analysis framework, we modeled a potential travel corridor by integrating ecological principles with advanced spatial analysis techniques in ArcGIS Pro. While some traditional tools are being superseded by newer, more efficient geoprocessing functions in modern GIS software, the core methodology remains robust.

The analysis workflow, conceptualized below, systematically progressed through the following stages:

1. Habitat Suitability Assessment: The foundational step involved creating a habitat suitability model, quantifying the relative "goodness" of the landscape for Black Bear movement. This was achieved by:

• Reclassifying key environmental variables: We transformed raw data for factors like land cover, elevation, and proximity to human infrastructure (e.g., roads) into a standardized suitability scale (1-10), where higher values indicated greater habitat suitability. For instance, dense forest cover would receive a high suitability score, while urban areas or large water bodies would receive low scores.

• Weighted Overlay Integration: These individual suitability layers were then combined using a Weighted Overlay technique. Each criterion was assigned a specific influence based on its ecological relevance to Black Bear movement (e.g., land cover received a higher weight due to its direct impact on cover and foraging opportunities). This process generated a comprehensive habitat suitability raster, illustrating areas of high and low quality for black bears across the study extent.

2. Cost Surface Generation: To identify the paths of least resistance, the habitat suitability model was transformed into a cost surface. This involved:

• Inversion of Suitability: We inverted the suitability scores such that areas of high habitat suitability became areas of low travel cost, and vice-versa. This is based on the ecological premise that animals prefer to move through favorable, less risky environments.

• Cost Calculation: The cost surface was calculated by subtracting the suitability score from a maximum value (e.g., Cost = 10 - Suitability Score). This resulted in a raster where the lowest values represented the most "desirable" and least "costly" pathways for bear movement.

3. Least-Cost Path and Corridor Delineation: With the cost surface established, the analysis proceeded to identify the most efficient routes between the two park areas:

• Cost Distance Accumulation: From each of the two designated park areas (our "source" locations), we calculated an accumulated cost distance raster. This raster quantified the least cumulative cost to travel from each source to every other cell in the landscape.

• Corridor Identification: The two accumulated cost distance rasters were then combined (typically summed) to reveal the least-cost corridor. This resultant raster highlighted areas where the combined cost of travel from both source areas was minimized, indicating optimal connectivity.

• Thresholding for Meaningful Corridors: A critical, and somewhat subjective, step involved applying a threshold value to the combined cost surface. This allowed us to extract only the cells representing the absolute lowest cost pathways, thus delineating the most ecologically meaningful and practical corridor(s) for Black Bear travel. This final raster visually represented the prime areas for maintaining or enhancing connectivity between the two park areas.

4. Model Visualization (Conceptual Model):

[Input Layers]
    |
    |-- Land Cover
    |-- Elevation
    |-- Roads (for Distance to Roads)
    |-- Park Areas (Source Polygons)

    V

[Reclassify Tools]
    |-- Reclassify Land Cover (to Suitability 1-10)
    |-- Reclassify Elevation (to Suitability 1-10)
    |-- Euclidean Distance (Roads) -> Reclassify Distance (to Suitability 1-10)

    V

[Weighted Overlay Tool]
    |-- Combine Suitability Rasters (Land Cover: 60%, Elevation: 20%, Distance to Roads: 20%)

    V

[Calculate Raster Tool]
    |-- Invert Suitability (e.g., Cost = 10 - Suitability) -> COST SURFACE

    V

[Cost Distance Tool]
    |-- Cost Distance (from Park Area 1, using COST SURFACE) -> Accumulation Raster 1
    |-- Cost Distance (from Park Area 2, using COST SURFACE) -> Accumulation Raster 2

    V

[Corridor Tool / Raster Calculator (Sum)]
    |-- Combine Accumulation Raster 1 + Accumulation Raster 2 -> CORRIDOR SURFACE

    V

[Con Tool / Reclassify by Range]
    |-- Apply Threshold to Corridor Surface (e.g., where Corridor Surface < Threshold) -> FINAL BLACK BEAR CORRIDOR

    V

[Output]
    |-- Visualized Black Bear Travel Corridor

Conclusion:

This analysis provides valuable insights for conservation efforts, highlighting key areas for protecting or restoring habitat connectivity essential for Black Bear population viability and genetic exchange. While some specific tool names may evolve in future ArcGIS Pro versions, the underlying principles of creating suitability models, cost surfaces, and applying least-cost path algorithms remain fundamental to effective wildlife corridor planning.