Climate change is causing species to shift their ranges northward in order to track cooler temperatures and more optimal conditions. This is known as a range shift, the process of a species moving its geographical range. Temperature is an important factor limiting the geographical range that species can inhabit. Oftentimes, the northern range edge of a species exists because of temperatures that are too low beyond the range edge, while southern range edges may exist because it is too warm beyond the range edge. There are a myriad of other biotic and abiotic factors that influence a species’ range (Dytham, 2009; Jameson et al., 2015; Kambo & Danby, 2018; Miller et al., 2020), but temperature is usually a strong factor that contributes to a species’ geographic distribution (Jeffree, 1955). Some species are dispersal-limited, meaning that they are restricted only because of their inability to migrate large distances but are capable of surviving and reproducing if transplanted beyond their occupied range (Cross & Eckert, 2021). However, there is no doubt that climate change is causing many species to migrate northward and to higher latitudes. One review found that the median rate of elevational migration is 11.0 metres/decade, while the median latitudinal migration rate is 16.9 km/decade (Chen et al., 2011). For this project, I will focus on how changing climatic variables will influence the geographic range of a species.

In British Columbia, big sagebrush (Artemisia tridentata) is a useful model species for studying range shifts, as there is a large amount of data on the species’ occurrences and it inhabits a large latitudinal range (GBIF, 2021). Big sagebrush is usually found in steppe communities, dry ecosystems that are shaped by disturbance events such as fires (Baker, 2006; Evers et al., 2013). Big sagebrush itself is an important part of these communities, providing valuable ecological roles such as food and habitat provision (Welch et al., 1991). However, due to increasing habitat fragmentation, species invasions, and urbanization, these ecosystems are exhibiting a decline in community biodiversity, and some local sagebrush populations have been extirpated (Davies et al., 2011). Despite the need to protect these ecosystems, conservation and recovery has proven to be challenging (Brabec et al., 2015; Schlaepfer et al., 2014). The range of big sagebrush stretches south from British Columbia across the western United States, as far as Baja California (GBIF, 2021). WIthin B.C., the species is found mostly in valleys within and around the Okanagan region. These occurrences in British Columbia are the individuals that compose the species’ most northern populations. Because they are likely locally adapted to cooler northern temperatures, these British Columbian populations may be the most well-suited for migrations beyond their northern range edge.

 

Using ArcGIS Pro’s Habitat Suitability Modeler, I project how habitat suitability of big sagebrush will change under different climate warming scenarios. Specifically, I aim to answer the following questions:

1. How will the habitat suitability of current British Columbian sagebrush populations change by the year 2080 under both low-warming conditions and high-warming conditions?
2. To what extent will habitat suitability change beyond the northern range edge of British Columbian sagebrush populations by the year 2080 under both low-warming conditions and high-warming conditions?

I will take into account a set of environmental variables, including elevation, slope, aspect, mean annual temperature (MAT) and mean annual precipitation (MAP) to determine the habitat preferences of big sagebrush within British Columbia. I will then use data on future temperature and precipitation conditions from climate model projections in order to determine how the suitable habitat of the species will change across the province. I predict that the current geographic range of big sagebrush will decrease in suitability under both warming scenarios, but will experience a larger decrease in suitability under the high-warming conditions, as temperatures will likely warm to levels above the plant’s thermal optimum. Additionally, I predict that northern regions of British Columbia will become more suitable for the plant as warming occurs because cold-stress will be alleviated. I expect this increase in habitat suitability beyond the northern range edge to be even larger under high-warming conditions compared to low-warming conditions.