AN ASSESSMENT OF ECOLOGICAL THINNING FOR STRUCTURAL DIVERSITY IN COASTAL FORESTS OF THE PACIFIC NORTHWEST, USA
Abstract
Restoration for increased structural integrity is a relatively new strategy that is
being applied to protected areas in the Pacific Northwest. Not enough data has been
collected to determine how best to approach restoration, so the current projects have
made educated guesses about what the best approach might be to increase structural
diversity. My analysis seeks to determine the most effective thinning regime to increase
structural diversity.
The current stands which are undergoing restoration are young even aged plantations
which have been acquired by conservation organizations and government agencies. Ecologically,
these forests differ from the historical forests both in structure and species composition.
Restoration seeks to remove a portion of the overstory trees to allow the recruitment
of a new cohort of trees and increase the growth rate of the remaining overstory trees.
This approach essentially involves tunneling through the classic development curve
laid out by Odum (Odum, 1969).
I used a version of FVS ported into the R language to model the background forest
growth in the face of windthrow against 25 possible thinning types. I compared thinnings
across a range of intensity of tree removal (10-50% of trees removed per cycle) and
cycle length (10 to 50 years). I compared these results to a background scenario
consisting of windthrow disturbance with a 1% probability of occurring each year and
lognormally distributed impacts with low intensity damage more common than high intensity
damage.
My work has shown that removing 30 – 50 % of basal area every 30 to 50 years can help
forests achieve structural complexity before it would develop on its own accord.
Without restoration, natural forests achieve structure similar to old growth between
100 and 200 years of age depending on the frequency and intensity of windthrow. After
100 years of restoration, forests will achieve higher levels of structural complexity
and tree growth.
Type
Master's projectPermalink
https://hdl.handle.net/10161/8175Citation
Bubel, Ansel (2013). AN ASSESSMENT OF ECOLOGICAL THINNING FOR STRUCTURAL DIVERSITY IN COASTAL FORESTS OF
THE PACIFIC NORTHWEST, USA. Master's project, Duke University. Retrieved from https://hdl.handle.net/10161/8175.Collections
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