Forest Restoration on Haida Gwaii: Implications for Goshawk Habitat

Abstract

Haida Gwaii, a remote group of islands off the northwest coast of British Columbia, is home to an endemic species of Northern Goshawks (Accipiter gentilis laingi), at imminent risk of extirpation. The loss of old growth habitat due to industrial logging is the principal reason for the decline of goshawk populations on Haida Gwaii. The survival of the raptor is dependent on the abundance and accessibility of prey (such as red squirrels (Sciurus vulgaris) and red-breasted sapsuckers (Sphyrapicus ruber)) which are closely tied to the composition of the forest. Structurally complex forests with widely spaced trees and variable canopy heights, critical attributes for goshawk foraging, have been replaced by monocrop, over-dense conifer plantations that are not accessible to goshawks. In the spring of 2020, a silvicultural thinning treatment was completed to improve the accessibility of second growth stands along the Yakoun River for goshawk foraging. The treatment, part of a multi-year project, reduced the stand density of a 70.6-hectare area from 905 to 531 stems per hectare, while retaining standing dead trees for wildlife habitat. Plot data was collected to quantify the effectiveness of silvicultural treatments in mimicking the conditions of the forest structure and prey resource availability that support existing goshawk forage territory. Results from the 2020 treatment showed that the stand density was successfully reduced to the specifications outlined in the project prescription and that red squirrels were preferentially feeding around large diameter Sitka spruce trees. Results from the old growth control sites showed a lower stem density than the 2020 and 2019 treatment sites and a relatively higher abundance of red squirrels than red-breasted sapsuckers. Plot data from the 2019 treatment site showed a relatively higher abundance of red-breasted-sapsucker compared to red squirrels. Goshawk prey are present in the 2019 and 2020 treatment areas, and by improving the accessibility of the stand through thinning treatments, these forests may develop the necessary conditions for goshawk foraging. This initial field study has highlighted the need for rigorous scientific monitoring before and after thinning treatments to inform the location and implementation of future restoration projects, and to evaluate whether silvicultural treatments are effective in recruiting new goshawk foraging territory.