Nature's own sustainable timber harvest rate

In the natural world, “consumptive” dynamics have been functioning for thousands or millions of years

Bruce Ellingsen

For the Cortes Island community, obtaining a community forest tenure on crown lands and managing it sustainably, while allowing for a modest timber harvest, has been a priority since the 1990s.

But how can we determine a rate of timber harvesting that will ensure the community forest is sustainable? On the surface this appears challenging, considering the complexities of forest ecosystems and the many different approaches to forest harvesting and management. However, if we step back and look at the underlying dynamics of any healthy ecosystem, we find that, large or small, complex or simple, all ecosystems must be able to acquire or generate the nutrients required to maintain their metabolic functions, plus a “surplus” to cushion the system through lean times.

Mature forests generate more than enough nutrients to thrive, with surpluses stored in the tissues of the trees or in the forest’s soil. Before colonization and industrialization, Pacific coast forests were sustainable, with harvesting levels that met the needs of Indigenous people. After, demands for timber grew, technology advanced, and harvesting rotation periods diminished, resulting in increasingly unsustainable extraction rates.

In BC, there is growing recognition that the impact of conventional forest management, made worse by the shortening of the “rotation age” (now often down to 30-60 years between harvests), is removing far too many nutrients from these forest landscapes for them to be sustainable.

As the forest regains old growth characteristics, it will become more biodiverse and resilient – boosting its ability to respond to the impacts of climate change.

Following a harvest, most of the nutrients needed by a regenerating young forest come from accumulations stored in the landscape from previous generations. Over time, a myriad of organisms re-establish themselves in complex, interdependant relationships that are increasingly able to generate the nutrients necessary to sustain a forest ecosystem.

Any healthy ecosystem can tolerate losing a portion of its accumulating nutrients, but requires most nutrients to remain in the system to ensure its ongoing health. Unless forest ecosystems are allowed to grow beyond the age when nutrients are being extracted by the growing forest, the forest will be degraded by each short-rotation harvest.

So the question remains: how much of the accumulating nutrients in the annual incremental growth of the ecosystem can be extracted in timber or biomass without reducing the forest’s ability to sustain itself?

Look to nature

It is difficult to find examples of “managed forests” that have proven sustainable over millennia. However, in the natural world, there are many “consumptive” dynamics that have been functioning for thousands or millions of years. These can provide clues as to what proportion of accumulating nutrients might be sustainably removed from our community forest.

Let’s look at some examples of sustainable relationships found in the natural world:

  • Biologists believe some 15 per cent of the leaf production of tropical forests is used by leaf-cutter ants as substrate for growing fungus for their food, according to a 1999 New York Times article.
  • Big cats on the Serengeti take about 16 per cent of the total prey biomass, according to research by Anthony Sinclair, zoology professor emeritus at UBC.
  • Polar bear expert and University of Alberta professor Ian Stirling found polar bear predation of ring seals (which make up 95 per cent of the bear’s diet) ranges between 15 and 22 per cent of the annual incremental growth of the seal population.
  • A long-running study on the relationship between peregrine falcons and ancient murrelets in Haida Gwaii found that the falcons hunt 15–20 per cent of the annual growth of the murrelet population, according to CBC’s Nature of Things.

See a trend? In nature, a consumptive rate between 15 and 22 per cent of the annual incremental growth of the consumed has been demonstrated.

Considering these examples and the fact that timber harvesting is not a “closed loop system” where nutrients remain within the ecosystem, the average harvest taken, over any five years, from the Cortes community forest should be limited to 15 per cent of the Mean Annual Incremental growth (MAI – a measure of the average yearly growth of the timber in the community forest).

Veteran forestry consultant Herb Hammond and Jerry Franklin, professor of Ecosystems Analysis at the College of Forest Resources at the University of Washington, both believe less than 25 per cent of the MAI is “surplus” to the needs of the ecosystem over the long term.

Benefits

Preserving 85 per cent of the annual accumulation of nutrients in the community forest ecosystem would form a simple, measurable foundation to managing Cortes Island’s community forest, ensuring the forest survives in perpetuity.

The timber harvested and available to local entrepreneurs for value-adding would increase in size and quality, just as competing timber sources diminish. This would provide a stable base for the local forest sector economy, with room for future development.

As the forest regains old growth characteristics, it will become more biodiverse and resilient – boosting its ability to respond to the impacts of climate change. The knock-down effects of a thriving forest would benefit salmon runs, as natural hydrological cycles throughout the landscape and streams of Cortes are re-established. Epiphytes and mycorrhizal fungi, potential major sources of nutrients for an older ecosystem, would have time to re-establish healthy populations.

Let’s demonstrate a dramatically different and justified-by-nature approach to management of Cortes’ community forest – for our community, and for visitors drawn to Cortes to see a forest managed sustainably.


Bruce Ellingsen is a 70-year resident of Cortes Island with a family background in forestry and a lengthy interest in sustainability.

Sponsored by Friends of Cortes Island


 

Read more: Restoration Forestry | Ecological forester Herb Hammond on the history, diagnosis, and cure for BC’s crummy forestry practices

“Like some giant machine that could not be turned off” | As BC’s logging and mining industries lay waste to wilderness, do our elected leaders have their hands on the wheel ?

And the Cut Goes On | Logging in West Kootenay watersheds continues unabated

 

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