Originally published November 22, 2015 written by Denis Lynn
On 4th November 2015, Edna Thomson (Vol. 17, Num. 21) expressed concern that development of Lot 3 “would really mean the eventual loss of possibly the entire Crippen Park” as a consequence of “weakening (the trees) via the loss of their root systems and complimentary structural support systems”. We are beginning to understand that the trees in our forests are indeed intimately connected, not by roots but by a complex network of fungal mycelia, which provide nutrients and water and transmit chemical signals between trees. Damage to these mycelia could indeed impact the health of the trees. Nevertheless, we should remember that much of the present forests on Bowen has regrown following significant logging in the early 20th Century. This regrowth is possible because ecological systems have evolved over millions of years to respond to changes, often catastrophic. An ecologically significant catastrophe in recent times in the Pacific Northwest was the eruption of Mount St. Helens on 18th May 1980. Its steamy blast blew down and scorched forest over more than 500 km2, leaving a seemingly lifeless landscape. And yet, these ecosystems are recovering. What is it about the behaviour of ecosystems that enables this recovery?
In 1973 Prof. C. S. Holling, University of British Columbia, proposed two kinds of ecosystem behaviour. One he called stability – “the ability of a system to return to an equilibrium state after a temporary disturbance”; ecosystems that rapidly return to the equilibrium state are more stable. The other he called resilience – “a measure of the persistence of systems and their ability to absorb change and disturbance and still maintain the same relationships between populations”. Prof. Holling discusses the spruce budworm community in eastern North America, which is a highly resilient, but unstable, community, characterized by periodic outbreaks and a sequence of recovery steps that leads to the next outbreak. Another example he mentions is the response of Wisconsin forest communities to fires – over time since the fire they “reconstruct” themselves until the next fire starts the process all over. To these, we might add the response of forest communities in the Northwest to fire and volcanoes.
The long-term study of the forest and other ecosystems after the Mount St. Helens volcano has lead to some important and unexpected findings. The timing of the eruption was significant – an early spring morning meant that nocturnal animals, like mice, were in their burrows while spots covered by spring snow and ice were protected from extreme heat, permitting seeds to survive and colonize the more impacted habitats. The number of ponds and lakes increased as lava flows and mudslides blocked rivers and streams, creating new aquatic habitats. Surprisingly, amphibians and other organisms rapidly colonized these, so that lakes and streams are again showing communities typical of this forested region. Terrestrial habitats have been slower to recover, although there is greenery covering most of the blast area. This vegetation has provided habitat, even in the significantly disturbed areas, to support the colonization by almost all small mammal species of undisturbed forests. On the other hand, the return of bird species has lagged correlated with the slower recovery in structural complexity of forest habitat.
As Bowenians, we can appreciate this slow recovery as the forests that we value today have taken years to recover from earlier deforestations. Mount St. Helens has provided another lesson here, for the quantity of living and dead trees remaining in areas has significantly influenced the rate of recovery of the forested areas. These “biological legacies” now provide a management tool for some foresters who, rather than clear-cutting for logging, will leave a certain portion of standing trees – a biological legacy – to enhance the recovery. The biological legacies left by Mount St. Helens and by typical forest logging practices are probably much less than 20% of the original forest. This impact of biological legacies has been modeled and shown to increase the resilience of forest ecosystems to the impact of fire, even when about 20% of the forest is left in remnant patches.
Lot 3 runs along the east side of Miller Road and behind the RCMP Detachment, north and east from the Trunk Road, for about 300 m. If all trees were logged from this lot, it would represent, I believe, about 20% of the area of Crippen Park between Miller Road and Cardena Road, leaving 80% of the forested area untouched. While this would be a significant “empty space”, it hardly approaches the 20% or less of the forest left standing by logging operations or volcanic eruptions. I would guess that Edna Thomson is correct that the trees and shrubs bordering Lot 3 would be impacted. However, as a biologist, I am confident that the 80% of forest remaining would be very resilient to this disturbance, and that the future of Crippen Park is not in danger.
Further Reading: Dale, Crisafulli, Swanson. 2005. Science 308:961; Holling. 1973. Ann. Rev. Ecol. Syst. 4:1; Seidl, Rammer, Spies. 2014. Ecol. Appl. 24:2063.
– Denis Lynn