Resistance surface - A landscape connectivity analysis for the coastal marten (Martes caurina humboldtensis)

This dataset serves as the resistance surface that formed the basis of our coastal marten connectivity model.  It is comprised of several data layers that represent forested and non-forested land cover, waterbodies, rivers, roads, and serpentine soils.

Please refer to the metadata records for each composite data layer for additional information (as identified in 'Cross-References' section of this ServCat reference).

Once these component data layers were assembled, we used them to create a single “resistance surface” covering the entire modeled landscape (Zeller et al. 2012).  We assigned numerical resistance values to each distinct land cover type represented in each spatial data layer based on our assessment of how easily and safely coastal martens could pass through them, which in turn were derived from the key assumptions we used in constructing the overall model.  Because we lacked empirical data on how likely coastal martens are to move through various habitat types and other features on the landscape (especially while dispersing), we had to extrapolate from what is known about the species’ home range habitat selection and dispersal patterns.  This required a certain amount of estimation, and the exact resistance values and resulting cost-weighted distance estimates should be viewed with caution.  However, we are reasonably confident in the general patterns that we modeled for the resistance values and generally strove to keep them relatively simple in the absence of data on coastal marten movement pathways demonstrating more complex relationships.  Such extrapolation from incomplete data is a common practice in constructing resistance surfaces for habitat connectivity models needed to inform urgent conservation decisions (Aune et al. 2011, Zeller et al. 2012, Cushman et al. 2013).  

A complete listing of the data sources, raster values, class descriptions, and resistance values that comprised our final resistance surface are presented in the accompanying spreadsheet of resistance surface data sources and resistance values. 

We created a raster file for the resistance surface covering the entire coastal marten historical range as well as the buffer to east (Fig. 4F of report) using the Resistance and Habitat Calculator component of Gnarly Landscape Utilities (McRae et al. 2015), which is a set of spatial analysis tools associated with Linkage Mapper.  This required creating separate raster files for each of the spatial data layers (forested land cover, non-forested land cover, rivers, roads, waterbodies, and bays/estuaries).  We then used the tool to evaluate the suite of component data layers and assign the highest resistance value possible for a given pixel to the final combined resistance surface raster.  For example, if a given pixel had an OGSI of 5.0 (resistance value = 10) but was also included in the roads raster as including a “primary road” (resistance value = 25), that pixel would receive the higher resistance value (25) in the final resistance surface.  See Appendix 2 of the project report for finer scale maps of the final resistance surface and the layers used to create it.  See Appendix 3 of the report for discussion of sensitivity analyses we performed related to various aspects of developing the resistance surface. 

In the areas with serpentine soils that potentially supported favorable habitat (as described in report and in the metadata record for ResistancePostProcessing_Serpentine), we halved the normal resistance values for pixels receiving their maximum resistance from  one of the OGSI 0-10, OGSI 11-20, and OGSI 21-30 resistance classes in the forested landcover data layer (see Table 2 on P. 29 of the report).

This is an abbreviated and incomplete description of the dataset.  Please refer to the spatial metadata for a more thorough description of the methods used to produce this dataset, and a discussion of any assumptions or caveats that should be taken into consideration.

Tags: coastal-marten, connectivity-modeling, general-biology-at-risk-biota-te-species, general-biology-species-mammals, general-landscapes-landscape-dynamics, general-landscapes-landscape-ecology, general-management-habitat-management-habitat-models, general-management-landscape-management-landscape-connectivity, gnarly-landscape-utilities, humboldt-coastal-marten, humboldt-marten, least-cost-path-analysis, linkage-mapper, martes-caurina-humboldtensis, pacific-marten
Organization: Department of the Interior