Boreal forests are being clearcut faster than some of their wildlife and plant species can recover, with a few failing to return even 100 years after harvesting, according to University of Alberta-led research.
The comprehensive global analysis looked at how clearcutting - when all trees in an area are felled - affects birds, small mammals, spiders, insects, vascular plants, mosses and lichens in forests that are harvested for lumber or pulp and paper production. The researchers compared logged and unlogged areas over many decades, tracking how long it took to return to the biodiversity levels of a mature forest.
While some species came back within 30 years - soon enough to fall within typical 60- to 80-year logging cycles - others won't fit into that timeline, warns biologist Dr. Ellen Macdonald, a professor emerita in the Faculty of Agricultural, Life & Environmental Sciences and lead author on the study.
"If forestry operations continue on in the future with repeated cycles of the clearcutting practices they use now, some of these species are essentially never going to recover; they will start to disappear from the landscape."
The biodiversity provided by plant, lichen and animal - or biotic - communities is vital to forest health, adds ecologist Dr. Anne McIntosh, a professor at Augustana Campus and co-lead on the research.
"All of these species play important roles in their own ways," she says. "There are many types of interactions that occur, and when species are removed from a forest, there is a danger of losing that biodiversity and their interactions, with unknown consequences."
The first of its kind to examine such an extended timeline for recovery and a wide range of the biotic groups in boreal forests after clearcutting, the study analyzed 190 datasets across North America, Europe and Russia. The research looked at the biodiversity of communities within different forest types, including broadleaf trees like aspen or birch, coniferous trees like spruce or pine, and a mix of the two types.
In about half of the cases studied, the biodiversity of the forest communities returned to pre-logged levels in less than 30 years, particularly in faster-growing broadleaf forests, where vascular plants and mosses either weren't affected at all, or recovered within 12 to 25 years.
But in mixed and coniferous forests, recovery was much slower, taking more than 55 years for small mammals such as mice and voles, 85 years for flowering plants, 95 years for lichens and more than 100 years for mosses and liverworts. And beetles dependent on deadwood for survival showed no signs of recovery at all within the 16 to 29 years of existing data that was available to review.
The lengthy recovery times suggest that the varying forest types need to be managed in different ways, Macdonald says.
"We know that these conifer forests take longer than broadleaf forests to recover, so that provides an opportunity to be more targeted in management."
Using alternative practices to clearcutting, such as retention harvesting which leaves more live trees and deadwood in place, "would help provide the right kind of conditions to 'lifeboat' slow-growing lichens and mosses," McIntosh notes.
Lengthening the number of years between harvests and completely protecting some forest areas from logging are also measures that would help conserve biodiversity, Macdonald adds.
"These kinds of approaches are becoming more important, particularly for the organisms that take a long time to recover."
