IPA Delineation

We downloaded Strategy plant observation data from NHNM Biotics on February 1, 2017 and intersected all Strategy species occurrences with a one-mile hexagonal grid covering the state of New Mexico. This resulted in about 3,000 occupied hexagons attributed by Strategy species composition. This dataset was the foundation for aggregating spatially proximal and compositionally similar hexagons into coherent IPAs.

Initial clusters representing incipient IPAs were created by visually grouping hexagons in close physical proximity to each other. We deliberately made the initial clusters small with the goal of combining initial clusters into larger clusters in later steps. Hexagons that were completely isolated (>5km from the nearest hexagon) were given their own group identities.

To reduce the number of small isolated hexagons, we removed any hexagons that fit the following criteria: (1) >5km from the nearest hexagon, (2) no more than 1 Strategy species occurring in the hexagon with a (2) NHNM G-rank of 4 or 5 and an S-rank of 3, 4, or 5. This effectively removed isolated hexagons with low species richness that lacked highly-ranked species.

We summarized plant occurrence data per initial group as simple presence/absence data for each of the Strategy species. We calculated the geometric centroid of each initial group by calculating the mean x and y coordinates of all hexagons within that group. We then calculated the physical distance between each initial group and every hexagon in the state. Additionally, we estimated the floristic distance between each initial group and every hexagon in the state by using a Euclidean distance metric based on all species. We flagged as potential outliers hexagons within a group that were further than 5,000 m from the geometric center of group and that had a floristic distance to their own group >50. For each of these hexagons, we estimated the next best grouping using a combination of physical and floristic distance and reassigned the hexagons as needed.

Final hexagon groupings were created using expert knowledge of local geography and general Strategy species habitat requirements, while taking into account pairwise floristic and physical distances. After assigning hexagons into final groups, we used Fixed r Local Convex Hulls in ArcGIS to define the final IPA boundaries. We estimated the rparameter individually for each group by calculating the median of all pairwise distances between hexagons within each group. This allowed a more inclusive wrapping for hexagons that were spread over a large geographic area and tighter, more exclusive wrapping for hexagons that were tightly clumped. We hand edited individual IPA boundaries to prevent adjacent IPAs from overlapping.

IPA Biodiversity Significance

The biodiversity significance of an IPA was characterized by an IPA Biodiversity Rank (IPA B-Rank) based Diversity Score (D-Score) modified as needed to account for species that are both highly localized and very rare (S1/G1 and S1/G2 species). The Diversity Score is computed as the inverse Global/State Status Score for a species times its percent occupancy in an a given IPA, summed for species in an IPA (Tables 2 & 3). The higher the value, the greater the biodiversity significance. For example, a S2/G3 species would have a GS Status Score of 4, and if 50% of the observations for that species occurred within the IPA, its Diversity Score would be 2. These scores are summed for all species in the IPA. Based on the sums, the IPAs are initially assigned B-Ranks per Table 1. In addition, approximately 10% of the IPAs were assigned a modified B-Rank based on expert opinion, federal status of the species occurring within an IPA, and overall rarity.

Table 3. Biodiversity Significance Ranks (B-Ranks).

Table 4. Global/State Status Score scoring matrix based NHNM/NatureServe (NS)species status ranks.

Table 5. Assignment table for IPA Biodiversity Ranks based on the IPA Diversity Score (D-Score).

Additional Information:

New Mexico Rare Plant Conservation Strategy 2017: http://www.emnrd.state.nm.us/SFD/documents/NMRarePlantConsStrategy_Final_reduced.pdf

NM State Forestry Division Rare and Endangered Plants: http://www.emnrd.state.nm.us/SFD/ForestMgt/Endangered.html