Boreal Caribou Can Coexist with Natural but Not Industrial Disturbances

Abstract

For species at risk, it is important that demographic models be consistent with our most recent knowledge because alternate model versions can have differing predictions for wildlife and natural resource management. To establish and maintain this consistency, we can compare predicted model values to current or past observations and demographic knowledge. When novel predictor information becomes available, testing for consistency between modeled and observed values ensures the best models are used for robust, evidence-based, wildlife management. We combine novel information on the extent of historical disturbance regimes (industrial and fire) to an existing demographic model and predict historical and projected demographics of woodland caribou (Rangifer tarandus caribou). Exploring 6 simulation experiments across 5 populations in Alberta, Canada, we identify the relative importance of industrial disturbance, fire, and population density to observed population size and growth rate. We confirm the onset of significant declines across all 5 populations began approximately 30 years ago, demonstrate these declines have been consistent, and conclude they are more likely due to industrial disturbance from the oil and gas sector within contemporary population ranges than historical fire regimes. These findings reinforce recent research on the cause of woodland caribou declines. Testing for consistency between observations and models prescribed for species recovery is paramount for assessing the cause of declines, projecting population trends, and refining recovery strategies for effective wildlife management. We provide a novel simulation method for conducting these tests.

Disturbance‐Mediated Apparent Competition Decouples in a Northern Boreal Caribou Range

“…However, caribou density was 2–3 times greater in comparison to averages reported for most other boreal caribou ranges in Canada (caribou density reported in orther areas ranged 4.3–18.7/1,000 km 2 ; Committee on the Status of Endangered Wildlife in Canada [COSEWIC] 2014). The SBS's high caribou density reinforces the hypothesis of Stewart et al (2020) that caribou can tolerate natural disturbance. In contrast, our density estimates for moose rival the lowest reported for populations where moose and wolves are sympatric in North America (Messier 1994, n = 33 study areas) and compared well with other northern boreal shield regions including the Pickle Lake and Nakina regions of Ontario (24 and 46 moose/1,000 km 2 , respectively; Kittle et al 2015).…”

Habitat loss accelerates for the endangered woodland caribou in western Canada

“…Historically, caribou have persisted in fire‐dominated ecosystems by expanding their home ranges and shifting their habitat in response to forest fires (Courtois, Ouellet, Breton, Gingras, & Dussault, 2007). Now, however, the combined effects of dynamic fire regimes (Brandt et al, 2013), linear features that allow predators to encroach in refugia (DeMars & Boutin, 2018), and increased forest harvest, have contributed to broad‐scale declines of boreal caribou (e.g., Hervieux et al, 2013; Stewart et al, 2020). Notwithstanding the fact that humans often initiate forest fires (Tymstra, Stocks, Cai, & Flannigan, 2020), subsequent management of large forest fires is difficult (Werth et al, 2011; Tymstra et al, 2020).…”

Predicting patterns of terrestrial lichen biomass recovery following boreal wildfires

“…The modeled threshold for lichen recovery is variable even within regions and stand types, and should be carefully considered when developing caribou habitat policies, especially given future climate scenarios and cumulative impacts from industrial development. Regional variation in disturbance regimes, both natural and anthropic, can influence caribou responses across range (Lafontaine et al 2019, Johnson et al 2020, Stewart et al 2020). Caribou can persist in a fire‐prone landscape, but added pressure from industrial development can have important consequences on short‐ and long‐term population dynamics (Johnson et al 2020, Stewart et al 2020).…”

“…Regional variation in disturbance regimes, both natural and anthropic, can influence caribou responses across range (Lafontaine et al 2019, Johnson et al 2020, Stewart et al 2020). Caribou can persist in a fire‐prone landscape, but added pressure from industrial development can have important consequences on short‐ and long‐term population dynamics (Johnson et al 2020, Stewart et al 2020). In northern SK and the NT, anthropogenic disturbance and forestry in particular are limited, and so have not been investigated here.…”

“…Boreal and barren‐ground caribou depend on lichen forage as an essential element of their diet, particularly in winter (Klein 1982, Thompson et al 2015). Although wildfire reduces the likelihood of lichens being present (Collins et al 2011, Pinno and Errington 2016), and may contribute negatively to caribou reproductive rate (Johnson et al 2020), caribou can coexist with this natural disturbance (Johnson et al 2020, Stewart et al 2020). Under a changing climate, fire regimes are expected to change as weather conditions become warmer and drier, changes that are already evident in northwestern Canada in the form of shortened fire return intervals, increased mean annual burned area, and increased fire severity (Boulanger et al 2013, Coops et al 2018).…”