Habitat Mosaics in Dynamic Landscapes: Woodland Caribou in the Northwestern United States

HarleyJo  Holman

doi:10.7273/000007285

Because of rapid human encroachment and climate change, northern boreal forests (also referred to as Taiga) are one of the biomes most rapidly experiencing changes in ecological composition and biodiversity. One of the changes impacting boreal-adapted species most substantially is the gradual shift of suitable habitat. This shift has been seen across taxa and has been suggested to have been a contributing factor to the extirpation of groups such as the South Selkirk Mountain population of woodland caribou (Rangifer tarandus caribou). Quantifying the changes in this species’ suitable habitat and determining the suitability of remaining habitat in the species’ former range, may provide insight into what conservation actions would be most beneficial to mitigating the effects of habitat degradation. Based upon recent assessments of caribou habitat in British Columbia I hypothesized that semi-suitable habitat patches (defined as ≥50% on the Habitat Suitability Index created in this study) would be more abundant and larger in area than highly suitable patches (≥75% on the Habitat Suitability Index), that highly suitable patches would be limited by size (<150〖km〗^2) and elevation (>1800m), and that the semi-suitable habitat would have greater impact on overall landscape connectivity metrics than highly-suitable patches due to their larger size and increased abundance. After conducting a thorough literature review, I acquired spatially explicit data (i.e., Geographic Information system layers) for 12 habitat components that have been identified as promoting habitat use by woodland caribou: mean annual temperature, precipitation, and snow depth; slope; forest age; distance from water sources; distance from road, rails and frequented trails; distance from urban areas; and distance from agriculture. After standardizing each dataset, I developed a habitat suitability function that provided relative weights for each of these components and displayed them across four national forests (NF: Colville, Coeur d’Alene, Kaniksu, and Kootenai) to create a map of habitat suitability (referred to as the habitat suitability index or HSI). This analysis indicated that suitable caribou habitat was found in many small patches dispersed throughout the landscape. Based on this result, I chose to examine patch connectivity to make more effective proposals for future management. Using the HSI, I separated habitat patches into either semi-suitable or highly suitable categories and gathered information for both categories on metrics such as average patch size and total amount of habitat area. I then identified ten patches as potential focal patches for woodland caribou conservation: the five largest semi-suitable patches and the five largest highly suitable patches. I then created buffers of 3km, 5km and 15km around each patch to assess each patch’s ability to increase total habitat connectivity and increase in total habitat area based upon the likelihood of caribou dispersal at these distances. I used a in a One-Way ANOVA to examine the relationship between suitability category and connectivity metric. Finally, after quantifying the connectivity metric values, the ten patches were then ranked for overall influence on habitat connectivity. Most focal patches were identified in regions south of the last known location of woodland caribou from the Selkirk population. As I hypothesized, semi-suitable patches were larger and more abundant compared to highly suitable patches. Semi-suitable habitat patches had a significantly greater impact on the increase in total patch area, as well as the number of incorporated patches across all buffer distances. By increasing the connectivity and land protection of this region, potentially through a protected area network, future conservation efforts for woodland caribou may see greater success.

Habitat Mosaics in Dynamic Landscapes: Woodland Caribou in the Northwestern United States

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