- Library Home /
- Search Collections /
- Open Collections /
- Browse Collections /
- UBC Theses and Dissertations /
- Landscape dynamics of the boreal mixedwood forest
Open Collections
UBC Theses and Dissertations
UBC Theses and Dissertations
Landscape dynamics of the boreal mixedwood forest Cumming, Steven G.
Abstract
The mixedwood forest is a broad transitional area of intermingled deciduous and ever-green coniferous forest found along the southern extent of the boreal forest in western Canada. Extensive timber harvesting is a recent development in the mixedwood region. This thesis contributes to the scientific foundation of sustainable forest management in the mixedwood by describing the natural dynamics of a 73,000 km2 study area in northeastern Alberta. Large scale patterns in species composition and in the age and size structures of forest stand populations show that the forest in not an equilibrial, or shifting mosaic steady state, landscape. The age structure of the forest and the relative abundances of aspen and white spruce are not constant over time. Trends in fire size distributions and in rates of fire extinguishment, and a re-gression of monthly area burned on monthly weather, imply that fire suppression has reduced the mean proportional area burned per annum (r) by a factor of three since the late 1970s, but had negligible effect before 1960. Statistical models of fire size and composition, developed from mapped fires, predict the total size and composition of all known fires from 1940-1993. Over this interval, and corrected for fire suppression, r — 0.004, or one fifth the previously accepted rate. I conclude that the forest is older than generally believed. Extreme fire years and "background" years are of approx-imately equal importance, in terms of total area burned, but fire years more strongly influence large scale landscape pattern. The rate r varies with forest cover type, from 0.0027 for aspen to 0.007 for some coniferous types. I conclude that fire hazard increases along some successional pathways, which may be the mechanism by which landscape disequilibrium is maintained. Accumulated adjacent stem mortality forms small canopy gaps in young aspen stands. The gaps exhibit elevated recruitment of aspen and other shade-intolerant hardwoods. The age and size structures of older aspen stands, and an analysis of extensive forest inventory data, show that uneven-aged aspen stands are abundant, a finding consistent with gap dynamics. Simulation studies, and the statistics of some age-verification data, show that unexpectedly old aspen stands probably exist, which is consistent with the analysis of fire history. In these stands, the mean or maximum age of canopy trees are negatively biased estimators of the time that has elapsed since a stand-initiating fire.
Item Metadata
Title |
Landscape dynamics of the boreal mixedwood forest
|
Creator | |
Publisher |
University of British Columbia
|
Date Issued |
1997
|
Description |
The mixedwood forest is a broad transitional area of intermingled deciduous and ever-green
coniferous forest found along the southern extent of the boreal forest in western
Canada. Extensive timber harvesting is a recent development in the mixedwood region.
This thesis contributes to the scientific foundation of sustainable forest management
in the mixedwood by describing the natural dynamics of a 73,000 km2 study area in
northeastern Alberta.
Large scale patterns in species composition and in the age and size structures of
forest stand populations show that the forest in not an equilibrial, or shifting mosaic
steady state, landscape. The age structure of the forest and the relative abundances of
aspen and white spruce are not constant over time.
Trends in fire size distributions and in rates of fire extinguishment, and a re-gression
of monthly area burned on monthly weather, imply that fire suppression has
reduced the mean proportional area burned per annum (r) by a factor of three since
the late 1970s, but had negligible effect before 1960. Statistical models of fire size and
composition, developed from mapped fires, predict the total size and composition of
all known fires from 1940-1993. Over this interval, and corrected for fire suppression,
r — 0.004, or one fifth the previously accepted rate. I conclude that the forest is older
than generally believed. Extreme fire years and "background" years are of approx-imately
equal importance, in terms of total area burned, but fire years more strongly
influence large scale landscape pattern. The rate r varies with forest cover type, from
0.0027 for aspen to 0.007 for some coniferous types. I conclude that fire hazard increases
along some successional pathways, which may be the mechanism by which landscape
disequilibrium is maintained.
Accumulated adjacent stem mortality forms small canopy gaps in young aspen
stands. The gaps exhibit elevated recruitment of aspen and other shade-intolerant hardwoods. The age and size structures of older aspen stands, and an analysis of
extensive forest inventory data, show that uneven-aged aspen stands are abundant, a
finding consistent with gap dynamics. Simulation studies, and the statistics of some
age-verification data, show that unexpectedly old aspen stands probably exist, which
is consistent with the analysis of fire history. In these stands, the mean or maximum
age of canopy trees are negatively biased estimators of the time that has elapsed since
a stand-initiating fire.
|
Extent |
13214419 bytes
|
Genre | |
Type | |
File Format |
application/pdf
|
Language |
eng
|
Date Available |
2009-04-03
|
Provider |
Vancouver : University of British Columbia Library
|
Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
|
DOI |
10.14288/1.0075285
|
URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
|
Graduation Date |
1997-11
|
Campus | |
Scholarly Level |
Graduate
|
Aggregated Source Repository |
DSpace
|
Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.