Supplemental habitat cores (between 300 - 1500 hectares) - A landscape connectivity analysis for the coastal marten (Martes caurina humboldtensis)

This dataset contains additional "small" habitat cores that had a minimum size of 1 female marten home range (300ha), but were too small to meet the minimum size threshold of 5 female home ranges (1500ha) used to define cores in the Primary Model.  The description following this paragraph was adapted from the the metadata description for developing cores in the Primary Model.  These methods are identical to those used in developing cores in the Primary Model, with three exceptions:  (1) The minimum habitat core size parameter used in the Core Mapper tool was set to 300ha instead of 1500ha, (2) the cores that were included in the Primary Model (i.e. cores ≥ 1500ha) were removed from this dataset, and (3) there were no manual modifications to the habitat cores as was described in the metadata on developing cores in the Primary Model, as they were not applicable for this supplementary core dataset.  Thus, this dataset is a true supplement to the Habitat Cores dataset presented in the Primary Model, as there are no redundant cores included.  It should be noted that a single core in this dataset actually slightly exceeded the 1500ha threshold for its final area calculation but was not present in the Primary Model set of habitat cores.  We determined that this was because the "1500ha cutoff" in the tool was actually applied before the core was expanded by 977m to fill in interior holes and then subsequently trimmed back (In the Core Mapper tool, this is controlled by the "Expand cores by this CWD value" and "Trim back expanded cores" parameters).

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 (range = 0-100). In areas with serpentine soils that support habitat potentially suitable for coastal marten (see report for details), 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. Pixels with higher OGSI 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. We also excluded pixels with a habitat value <1.0 from inclusion in habitat cores. We then used a moving window to 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.

After conducting a sensitivity analysis by running a set of Core Mapper trials using a broad range of habitat values, we chose ≥36.0 as the average habitat value because it is the median OGSI of pixels within the marten’s historical range classified by the GNN as “OGSI 80” (Davis et al. 2015). It generated a set of habitat cores that were not overly generous (depicting most of the landscape as habitat core) or strict (only mapping cores in a few locations with very high OGSI). We then set Core Mapper to expand the habitat cores by 977 cost-weighted meters, a step intended to consolidate smaller cores that were probably relatively close together from a marten’s perspective. This was followed by a “trimming” step that removed pixels from the expansion that did not meet the moving window average so the net result was rather small changes in the size of the habitat cores, but filling in many individual isolated pixels with a habitat value of 0.

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