Natural Elements, NRCan's Monthly Newsletter

Nature Lends Hand in Regeneration of Beetle-Impacted Pine Stands

An aerial view of the dead pine canopy.

Sometimes it’s best to just let nature run its course. That was the finding of recent Natural Resources Canada (NRCan) research on best practices for managing forests impacted by the mountain pine beetle infestation.

Aerial views of beetle-affected regions typically show an unbroken canopy of dead pine. But beneath this canopy frequently lives a secondary structure of trees — usually smaller, slower-growing spruce or fir — that have survived the beetle’s attack. And research conducted by Phil Burton, Northern Projects Manager for NRCan’s Canadian Forest Service (CFS), shows that pine forests stocked with these other, living conifers may be more widespread than previously thought.

This discovery opens up a new approach to the management of beetle-affected areas. Previously, in cases where it was not profitable to harvest the dead pine, all the trees —alive as well as dead — were cleared and seedlings were planted. But now that it is known that secondary, living populations can be substantial, it may often be more effective simply to leave such stands to recover on their own. 

“When clear-cutting stands that have a significant non-pine component — as much as 60 years of spruce growth — all that advanced growth is lost, and we start over from square one,” explains Phil. “So from an economic as well as an ecological perspective, it makes more sense to leave living trees standing so the area can go through its natural recovery process.”

Underneath the tall, dead pine lives the secondary structure of smaller, slower growing fir or spruce.

Economically, this approach makes sense because the forest manager does essentially nothing. Since dead pines don’t draw water or nutrients from soil, the competition for these resources is reduced. Also, as the taller, dead pines lose their needles and topple, the smaller, living trees receive more sunlight. These favourable conditions allow the secondary structure to flourish and maintain forest cover in the area. And since these secondary trees have a 20- to 60-year head start on new seedlings, they will be ready for harvest sooner.     

This approach can be widely applied. “From our experience, and based on data from multiple sources, we think that 40 to 60 percent of the pine-dominated stands out there could be reforested naturally,” Phil says. He also notes that it would be a straightforward matter to use some fill-planting to ensure that these stands return to optimal density. 

The let-it-grow approach also has a potential long-term benefit: namely, the trees may become more resistant to climate change. Dead pine stands are often simply replanted with more pine, which was well suited for the growing conditions of 100 years ago. Today, however, conditions have changed, with wetter summers and milder winters more prevalent. As a result, where nature has already established a new crop of trees, letting that crop mature improves the chances that future forests will be well suited to the new growing environment.

Changes in the complexion of Canada’s western forests are already under way. “For some of B.C.’s pine forests, conditions are now, or soon will be, better for spruce or subalpine fir in some places, better for Douglas fir in others,” says Phil. 

Research on the let-it-grow approach continues and is now turning to some important and related questions: the rates of growth for the secondary stands in the coming years; how these stands will affect forest carbon balance; and how they can help fill the timber supply gap left by the rapid elimination of mature pine stocks. 

More information can be found in Phil’s detailed articles published in Canadian Silviculture and the BC Journal of Ecosystems and Management. To learn about other CFS projects, visit their Forest Research home page.