This dataset serves as the habitat surface that was used to derive coastal marten habitat cores for use in our connectivity model. Of note, the set of habitat cores that came from this habitat surface received additional modifications; see the report or the metadata record for PrimaryModel_HabitatCores for details.

The Old-growth Structure Index (OGSI) is the primary estimator of habitat quality and cost-weighted distance in the connectivity model. OGSI is a parameter derived by the Gradient Nearest Neighbor (GNN) model produced by the Landscape Ecology, Modeling, Mapping & Analysis laboratory in Corvallis, OR (LEMMA 2014a). The GNN model provides fine-scale spatially explicit data on forest structure across a vast area of California, Oregon, and Washington, and is one of the very few datasets available that provides such habitat information in a consistent manner across the CA/OR state border. GNN summarizes detailed data from thousands of forest survey points. It then uses a multi-step process to interpolate them to the unsurveyed areas on the landscape based on several explanatory datasets such as Landsat remote sensing imagery, elevation, climate, and geology (more information about this process can be found at https://lemma.forestry.oregonstate.edu/methods/methods, see also Ohmann & Gregory 2002). Like Landsat imagery, GNN has a spatial grain of 30mX30m (900 m2). OGSI is used to characterize the suitability of forest habitat conditions for old-growth obligate species and processes. It is scaled to specific regions and ecotypes, and is derived from a conceptual model that incorporates: (1) the density of large trees (2) and snags, (3) the size class diversity of live trees, and (4) the amount of down woody material (Davis et al. 2015). These seem well aligned with critically important features in forests inhabited by Pacific martens generally and Humboldt martens specifically, and a range of literature describes the use of habitat types that are consistent with the presence of these features.

We derived the habitat cores using a tool within Gnarly Landscape Utilities called Core Mapper (Shirk and McRae 2015). To develop a Habitat Surface for input into Core Mapper, we started by assigning each 30m pixel on the modeled landscape a habitat value equal to its GNN OGSI value (range = 0-100). In areas with serpentine soils that support habitat potentially suitable for coastal marten, we assigned a minimum habitat value of 31, which is equivalent to the 33rd percentile of OGSI 80 pixels in the marten’s historical range marten (for general details on our incorporation of serpentine soils, see the report section titled "Data Layers - Serpentine Soils"; for specific details on the development of this serpentine dataset, see the metadata record for the ResistancePostProcessing_Serpentine data layer, which was used to make these modifications to the habitat surface). Pixels with an OGSI value >31.0 retained their normal habitat value. Our intention was to allow the modified serpentine pixels to be more easily incorporated into habitat cores if there were higher value OGSI pixels in the vicinity, but not to have them form the entire basis of a core. As a parameter of the Core Mapper tool, we also excluded pixels with a habitat value <1.0 from inclusion in habitat cores. We then used Core Mapper to define a moving window and calculate the average habitat value within a 977m radius around each pixel (derived from the estimated average size of a female marten’s home range of 300 ha). Pixels with an average habitat value ≥36.0 were then incorporated into habitat cores.

Additional data for this project (including the Habitat Cores referenced above and the Moving Window Averages used to derive the Habitat Cores) can be found at: https://www.fws.gov/arcata/shc/marten