Hilary Cooke
It’s fire season in Yukon and across the west. Our attention is, rightly, on the drier-than-normal forests, the record low water levels in our rivers, and the very real wildfire risk facing Yukon communities today.
As climate change dials up wildfires, it’s understandable to feel a sense of loss when vast boreal landscapes get consumed and spit out as charred trees and sooty ground. But, within a very short time after burning, that forest supports a new and unique mix of biodiversity.
In fact, many plant and animal species have evolved to be fully dependent upon stands killed by fire or insects or the early-successional growth that follows.
For example, black spruce is fire-adapted – seeds are released from cones under the heat of the fire. Aspen is a pioneer species, relying on it’s extensive underground root system to quickly occupy a site.
Insect life thrives in areas rich with dead or dying trees. Up to 25 per cent of boreal insects are saproxylic, meaning they are dependent on dead or dying wood for part of their life cycle. Pyrophilous — or fire-loving — beetles are some of the first organisms to colonize burned forests, sometimes even before the fire is completely out.
Linked to the fire-loving and deadwood-eating invertebrates are the woodpeckers that follow them. Two woodpeckers in particular, black-backed and American three-toed, are specialists of burned forests, taking advantage of the pulse of beetles for food as well as the standing dead trees that can be used for their tree cavity nests. As woodpeckers create new cavity nests each year, secondary cavity nesters, such as tree swallows and American kestrels, take up residence.
Over time, as the land becomes thick with willow shrubs and young aspen saplings, it becomes a hotspot for a key species of the boreal food web — the snowshoe hare — which thrives with the abundance of food and cover. Similarly, ungulates such as moose and elk are drawn to increased grazing and browsing opportunities, while patches of standing dead trees provide protective cover.
Burned and beetle-killed forests are important sources of fuelwood for Yukoners, and of biomass for our growing bioenergy production. But removing large numbers of trees over large areas can have a major impact on the biodiversity that depends on these disturbed forests.
The greatest impact of the removal of deadwood is on the beetles and woodpeckers that are dependent on them more than any other stage in the boreal forest cycle.
Post-disturbance logging can destroy plants that survived the initial disturbance or are in the early stages of regeneration. Damage to existing seedbeds can limit the recruitment of spruce seedlings. The first few years after a wildfire are critical for establishment of the growing forest.
Harvest activities can also lead to reduced growth of understory plants where soil is disturbed or compacted, or where removal of trees causes microclimate changes. This can lead to loss of forage and cover for snowshoe hares, moose, and other ungulates. And, new roads provide access and so put ungulates at greater risk from natural predators and hunting.
How to protect the biodiversity values of Yukon’s burned and beetle-killed forests while still meeting our needs for fuelwood and biomass?
First, protect large areas of new disturbances from road access.
Second, plan and manage harvest operations in a way that will minimize impacts. Particular attention should be paid to what, where, when, and how much removal of standing and downed deadwood a new disturbance can withstand before biodiversity is compromised.
To answer these questions, Wildlife Conservation Society Canada has just released a major report with specific recommendations for Yukon – from regional forest planning to the management of stands (available at WCSCanada.org).
With growing interest in using wood biomass for heat and energy production in Yukon, we need to think carefully about the consequences of additional – and different – harvest pressures. In comparison to harvest for personal fuelwood, biomass harvesting may include the removal of more small woody debris, such as small diameter tree limbs, that are important to soil building and nutrients.
It is the regenerating forest that will ultimately absorb the carbon released by such systems. And the time to carbon parity – when the process becomes carbon neutral – depends on the successful regeneration and growth of the forest.
Today we are most concerned with protecting our communities from a potentially significant fire season. And rightly so.
But once the fires are out, the beetles and woodpeckers will move in. The pioneer plants will emerge, and the natural process of boreal forest succession starts again.
These recently disturbed forests are not sites of devastation or wasted wood to be “salvaged.” They are as important to the natural ecology and biodiversity of our forests as the oldest stands of spruce, and they deserve to be protected and managed accordingly.
Hilary Cooke is an associate conservation scientist with Wildlife Conservation Society (WCS) Canada based in Whitehorse.