Abstract
Cumulative effects of increased forest harvesting, mountain pine beetle (Dendroctonus ponderosae; MPB) outbreaks, and wildfire in low-elevation lodgepole pine (Pinus contorta) forests could limit long-term winter habitat supply for the northern group of southern mountain caribou (Rangifer tarandus). In a 17 year longitudinal study of vegetation remeasurements at eight sites in north-central and west-central British Columbia (BC), we assessed responses of terrestrial caribou forage lichen abundances to nine forest harvesting treatments and one prescribed burn 8–14 years following treatment, as well as to MPB attack. Overall, after initially declining following forest harvesting, mean forage lichen abundance increased between 1 and 2 years post-harvest and 13 and 14 years post-harvest at 10 of 11 site/treatment combinations. Mean forage lichen abundance decreased following MPB attack at all sites. Biophysical factors influencing rates of lichen recovery post-disturbance include site type (transitional vs. edaphic), a reduction in favourable conditions for moss recovery, level of MPB attack, and both seasonal timing and method of forest harvesting. When considering effects of forest harvesting on forage lichens, objectives of silvicultural management strategies should focus on protecting and retaining terrestrial lichens at edaphic sites and on re-establishing terrestrial lichens at transitional sites.
Highlights
During winter, northern group caribou (Rangifer tarandus) in the threatened southern mountain caribou population in Canada [1] use low-elevation lodgepole pine (Pinus contorta) forests, where they forage for terrestrial lichens
We found that there was a negative relationship between level of mountain pine beetle (MPB) attack and relative change in total forage lichen abundance
In the northeastern portion of the Itcha-Ilgachuz caribou range, level of MPB attack at the beginning of this study was a strong predictor of terrestrial lichen abundance 3 years following attack [48]
Summary
Northern group caribou (Rangifer tarandus) in the threatened southern mountain caribou population in Canada [1] use low-elevation lodgepole pine (Pinus contorta) forests, where they forage for terrestrial lichens. [reindeer lichens and pixie lichens], Stereocaulon sp., Cetraria sp.; forage lichens) are slow growing [2,3], susceptible to physical disturbance, and can take decades to become abundant following disturbance [4]. They are poor competitors against vascular plants and mosses, and grow best where conditions are unfavourable for vascular plant and moss growth [4,5]. In forested habitats, forage lichens may be abundant during different stages of succession depending on site (soil, climatic) conditions [4,5]. Because forest harvesting methods in western North America employ a variety of methods to attempt to minimize ground-level disturbances (e.g., timing of harvest, differing site preparation intensities, and methods of removing felled trees), the interactions of canopy structure, presence and densities of ground-level vegetation combined with site conditions pre- and post-harvest require longitudinal studies in a variety of locations to better define forest practices minimizing long-term degradation of terrestrial lichen abundances in managed forests
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