COS 182-1 - Active restoration of tree cover on forest roads for caribou conservation in Quebec: planting tree establishment and soil constraints

Background/Question/Methods

Road construction for forest harvest leads to long-term ecosystem disturbance. In Quebec, the roads generated by the forest industry are particularly damaging to boreal woodland caribou, a threatened species in Canada. Indeed, the presence of forest roads is one of the main causes of the decline of this species since they facilitate movement of predators, and therefore their hunting efficiency, and they promote the regeneration of deciduous vegetation favorable to other species such as moose or black bear.

In order to improve caribou habitat, one of the measures being tested is the restoration of forest roads. A dismantling and reforestation of forest roads trial was undertaken in 2017 to test different approaches: Four species were planted (jack pine, black spruce, tamarack, green alder) combined with three soil preparation techniques (mechanical with bucket or teeth excavator for gravel roads, direct planting for winter roads). We carried out a follow-up two and three years after planting, in order to estimate tree establishment and to characterize the soil. The goal is to estimate which approach is the most promising for restoring the tree cover on forest roads and thus rapidly limiting the movement of caribou predators.

Results/Conclusions

Green alder established particularly well with 99% survival, and height and diameter growth much greater than conifers. Among the latter, jack pine stood out by an annual height increment 2 to 4 times greater than the other two species, as well as a much better general condition (less frost-heaving, less defoliation, etc.). In fact, black spruce and tamarack had difficulty in short-term establishment, represented among other things by very low height and diameter annual growth. We also observed that conifers planted on winter roads all had better annual height increment than those planted on gravel roads. This is probably due to the fact that winter road soil had a lower bulk density and a higher concentration of organic matter and nitrogen than gravel roads. Soil compaction is certainly one of the main constraints to vegetation re-establishment, which was on average two times higher compared to an undisturbed mineral forest floor.

Thus, the choice of planted species is decisive to ensure good tree establishment and rapid closure of the tree cover. Future studies should focus more on soil quality restoration, which seems to be a major constraint to re-establishment of vegetation on forest roads.