EPOW - Ecology Picture of the Week

Balancing Forestry and Ecology

"Variable Retention" Silviculture
Northern Vancouver Island, British Columbia, Canada

Explanation:  What an odd scene this is.  What could have formed these many tree-islands of varying shape and size?

This is the hand of variable retention silviculture.  It is a relatively recent invention, conceived by a meeting of the minds of biologists and foresters to help balance dual -- and often dueling -- objectives of forestry and ecology.

We are flying over the distant northern corner of Vancouver Island in British Columbia, Canada.  The forests here are largely managed by timber corporations and private land owners.  

In the recent past, such forestry has taken the form of clearcutting large swaths of mature forest.  This provides much merchantable timber, but ecological and wildlife studies have shown that such practices heavily degrade native biodiversity, contribute excessive sediment into fish-bearing streams, and essentially remove habitat for old-forest dwelling plants and animals.  Other effects of clearcutting include adverse changes in the local microclimate.   

Alternatively, variable retention silviculture (the science and practice of forest harvesting and management) was invented to help retain viable patches of native forest for a variety of plant and animal species.  On Vancouver Island, biologists Bill Beese and Glenn Dunsworth studied the influence of forest patch size and spacing on the persistence and successful dispersal of amphibians and other wildlife of the region.  They, and other researchers, thereby devised a series of variable guidelines for retaining the ecological values of forest cover while still providing for harvesting of timber for its economic value.

Unfortunately, for this patch of ground, the experiment -- although proven successful -- is over, and the forest has changed ownership with different goals in mind.  

In the Beese-Dunsworth system of variable retention silviculture,
small patches of forest cover are often retained as "anchors" to
local wildlife habitat features such as seeps, springs, and rock outcrops.

In the forests of Pacific North America, commercial conifer trees
often require direct sunlight to provide the best growth and timber yield.
So the question became, how to design a timber sale to meet that
requirement and also provide at least some minimal target cover
of retained forest for wildlife and biodiversity?
This was one answer.

Information:
     Beese, W. J., B. G. Dunsworth, K. Zielke, and B. Bancroft. 2003. Maintaining attributes of old-growth forests in coastal B.C. through variable retention. The Forestry Chronicle 79(3):570-578.
     Mitchell, S. J., and W. J. Beese. 2002. The retention system: reconciling variable retention with the principles of silvicultural systems. Forestry Chronicle 78(3):397-403.
     Sullivan, T. P., and D. S. Sullivan. 2001. Influence of variable retention harvests on forest ecosystems. II. Diversity and population dynamics of small mammals. Journal of Applied Ecology 38(6):1234-1252.
     Sullivan, T. P., D. S. Sullivan, and P. M. F. Lindgren. 2001. Influence of variable retention harvests on forest ecosystems. I. Diversity of stand structure. Journal of Applied Ecology 38(6):1221-1233.