Ecological Restoration

by John Brouwer

A challenge for all ecologists is figuring out how trees live for hundreds and even thousands of years rooted in one place while having to withstand droughts, disease, fire, insects and all the things that humans do to their environment. Unlike most other organisms, a tree can't move to adapt to changing environments.

Evidently the key is in the surrounding forest and its diversity.

Forests moderate summer heat and drying winds to reduce stress on the individual trees. On a hot summer day the temperate in the forest will be five degrees cooler than in an open field. And the drying effect of wind is moderated as there is no wind on the forest floor. In the winter the interior of a forest is well-sheltered even though a winter storm may be raging. Individual trees are protected from climatic stress because they are part of the forest.

Diversity keeps the forest in ecological balance. The thousands of different organisms within a forest all work together to protect all the species. Each is dependent upon the other while protecting the whole.

This diversity keeps predator/prey relationships in balance. For trees this is important because the diversity ensures that no particular threat dominates to destroy the tree species. For example, a particular insect which could defoliate the tree, is kept in balance by the insect's predators who ensure that insect populations don't become dominant enough to destroy all the trees. The same principle, though much more complex, holds for tree diseases.

However when events occur to threaten and destroy diversity, trees lose their protection and become vulnerable because they cannot move to find a new location. Insects and disease can attack at will as there is no surrounding habitat which supports the insects' predators.

Ontario's forest ecology has been completely altered by human activity. The dominant impact has been in the key areas of ecological diversity and climate change. The result are species which have and continue to lose the protection which has sustained them over the centuries.

Without supporting diversity, trees become susceptible to defoliating and boring insects. Trees can withstand defoliating insects even for two or three seasons. Diversity would allow predators to establish themselves after a season and hold the defoliating insects in check by the second and third season allowing the trees to survive. Without diversity the insect can attack the tree and kill it over several seasons.

For example, boring insects live under the tree bark consuming the cambrium nutrient layer. These insects are susceptible to woodpecker species and parasites. But woodpeckers only survive in old growth forests which have old deteriorating trees hosting abundant insect populations. Without old trees woodpeckers populations are too low to control new boring insects. Hence the devastation being caused by the Asian longhorned beetle and the emerald ash borer.

It is questionable whether the current strategy of cutting thousands of healthy trees around an isolated infestation will control these beetles. All ash trees within a 10 km swath from Lake St. Clair to Lake Erie west of London have been cut and removed in an effort to keep the beetle within Essex and Kent counties. But the borer has now been found in two areas of Toronto. A better strategy may have been to leave the trees and encourage woodpeckers and related species and those parasites and predators which would attack the borer as it moves from tree to tree.

The objective of ecological restoration is habitat diversity since diversity stabilizes all the living things in the area.

We have a unique opportunity to foster habitat diversity this spring. A small group has received permission from the university to naturalize the grassed remnant area across the road between Pineridge and the creek. This area can become an ecological corridor between the conservation area and the university's environmental reserve. Ecologists now understand that a key strategy for supporting diversity is connections between existing natural areas so that the existing areas can function as one entity. The movement of animals, insects, pollen, and other living things through a connecting ecological corridor increases diversity in the natural system.

Sometime this spring we will organize a planting day when the native trees and shrubs growing in our garden tree nursery will be planted onto the creek bank. Lots of volunteers will be needed to make it a success. And assistance will be needed on a on-going basis to nurture the area until these trees and shrubs establish themselves and become dominate on the area. Let me know if you are interested in helping out.

This spring take the opportunity to walk along the Doreen Thomas trail alongside Bearinger Road into the old growth forest just past the creek (you may need to crawl through the hole in the fence) or at the sugar bush just before Laurel Drive. There are marvellous displays of trillium and the other Carolinian flowers for a couple of weeks before the trees leaf out and shade the forest floor.

And in early May the redbud which was planted four years ago within the emerging sugar bush between block two and Pineridge will be in blossom. Redbud is a native Carolinian tree which died out in Ontario two hundred years ago. This tree, and others not yet old enough to bloom, are part of a restoration program developed through the southern Ontario conservation areas.

March 2010