Abstract

1. Boreal forests provide numerous ecological services, including the ability to store large amounts of carbon, and are of significance to global biodiversity. Increases in industrial activities in boreal landscapes since the mid-20th century have added to concerns over biodiversity loss and climate change. Boreal forests are home to dwindling populations of boreal caribou (Rangifer tarandus caribou) in Canada, a species at risk that requires large, undisturbed landscapes for persistence. In 2012, the Canadian government defined critical habitat for boreal caribou by relating calf recruitment to disturbances. Some have questioned whether the recruitment-relationship can be extrapolated beyond the environmental conditions represented in the analysis.

2. We examined the effects of human disturbances and fire (alone and in combination) on variation in recruitment and adult female survival using data from 58 study areas in Canada. Top models were used in aspatial scenarios of landscape change to evaluate the efficacy of the critical habitat definition in achieving the recovery objectives for boreal caribou in two contrasting landscapes: Little Smoky, dominated by high levels of human disturbances, and SK1, dominated by fire.

3. The top recruitment model suggested the negative effect of fire was 3-4 times smaller than human disturbances. The top adult female survival model included human disturbances only. These results re-affirm that human disturbances are the primary factor contributing to boreal caribou declines.

4. Our aspatial scenarios suggested that undisturbed habitat would have to increase to ≥68% for Little Smoky to maintain a self-sustaining population of boreal caribou with some degree of certainty. In contrast, the SK1 population was self-sustaining with 40% undisturbed habitat when fire disturbance predominates, but could become vulnerable with increases in human disturbances (8–9%). 5. Policy implications: Our results suggest that the 65% undisturbed critical habitat designation may serve as a reasonable proxy for achieving boreal caribou recovery in landscapes dominated by human disturbances. However, some populations may be less or more vulnerable, as illustrated by the SK1 scenarios. Continued population monitoring will be essential to assessing the effectiveness of land management strategies developed for boreal caribou recovery, especially with climate change.

Estimates of disturbance were calculated for 58 study areas with demographic data on boreal caribou. We derived estimates of anthropogenic disturbances, buffered by 500 m, from maps prepared by Environment and Climate Change Canada (Environment Canada, 2011; Pasher et al., 2013; Environment and Climate Change Canada, 2018). Provincial and territorial jurisdictions provided the fire data. Fire disturbance was characterized as unbuffered areas burnt 40 years prior to the first year of available demographic data used in the analyses.

Variable names correspond to those described in Table 1 of the journal article.