Saving old forests

Sustainable forestry aims to maintain wood supply whilst preserving biodiversity and the integrity of the ecosystem. Research shows that boreal forests, like those across much of Northern Europe and Canada, have higher levels of variability in their structure and dynamics when unmanaged, improving their biodiversity and the stability of their ecosystems. These unmanaged forests also have a higher proportion of older trees than those used in industrial forest rotation – around 70-100 years in Canadian boreal forests.

Why should we maintain old forests?

Old forests are important in terms of sustainability, as larger trees have a more complex structure, and provide more dead wood vital for certain aspects of the ecosystem. Old forests are gradually decreasing across the world as demand for wood supply increases, and the majority are located in boreal and temperate regions of the Northern Hemisphere. Many species of these forests are red-listed in Fenno-Scandinavia, partly because intensive silviculture has eliminated most of the old forests in these areas.

North American boreal forests

In North America, the increased demand for wood products has led to the expansion of commercial logging activities towards fire-sensitive northern boreal regions. Despite recognition of the importance of preserving old forests, forest management in these regions still predominantly employs clear-cut harvesting – a method of forestry in which all the trees in an area is cut down – with short rotations relevant to the average intervals between natural disturbances. However, it is unlikely that these forest ecosystems will be able to sustain these rates of logging and fire disturbances. According to current research, if rates of both continue, by 2050 the proportion of old forests could reach a minimum level rarely or never seen in the natural landscape in the past.

Impact of climate change

The situation is set to become even more critical, as with current rates of climate change, in the best case scenario, fire activity is projected to double. Indeed, the predicted global climate will not only be warmer, but also more prone to summer drought events. With an earlier thaw in spring, higher summer temperatures, and changing levels of precipitation, soil will be drier for longer and therefore more prone to fires. These conditions also increase the likelihood that fires will burn hotter, and for longer, increasing the amount of damage caused. Climate change will therefore probably reduce the trade-off space currently existing between supply targets for profitable forest industry and biodiversity conservation. However, further results indicate that with the current rate of harvesting, the predicted decrease in old forest has more to do with clear-cutting than increased fire activity. Maintaining old forests to a minimum sustainable value would require significant reductions of clear-cut harvesting, which will have an important economic impact.

Old forest as insurance

Not only are old forests important for biodiversity, they also decrease the risk of regeneration failure following fire events. The passage of fire often triggers boreal forest trees to undergo seed release. As a result, the trees need time to replenish their aerial seed banks, the seed stored in a plant’s canopy. Management practices that rejuvenate forests frequently increase the probability that a fire occurs before trees have produced enough cones, which leads to regeneration failure. In view of this, maintaining parts of the landscape as old forest could serve as an insurance policy in an uncertain future.

Moving towards a solution

Mitigating solutions will involve changes in the way forestry is planned, taking into account both wood production and ecosystem durability. Fortunately, it is not too late and several potential solutions exist: increasing rotation length, implementing diversified silviculture, using a fire-smart approach to decrease fire hazard, or improving the balance between intensive management and conservation of old forests. However, current management plans include very few alternatives to clear-cutting. We advocate the rapid implementation of alternative management strategies which would begin to reverse the projected decrease in the proportion of old forests. Without these strategies in place, we may face a future of costly restoration in order to maintain the health of the boreal forest industry.

Featured image credit: Old forest by Henry Ziegler. Used with permission.