Abstract
Methods: Field data
Increased tree establishment in subalpine parkland and an upward movement
of treeline are expected in a warming climate, and may already be occurring in
some ecosystems, but other factors, such as changing disturbance regimes,
have received less attention. We examined the effects of fire on subalpine
parkland with dominant tree species of Abies lasiocarpa, Larix lyallii, Pinus
albicaulis, and Picea engelmannii in the northern Cascade Range of
Washington. We used field data from two burned areas, 17 and 25 years after
fire, to investigate relationships between fire severity and post-fire
herbaceous species composition and tree regeneration across the subalpine
parkland ecotone. We sampled 68 and 45 plots within 1994 Butte Creek and
1985 Hubbard Creek fire perimeters, respectively, to assess herbaceous
species composition across a range of fire severities. We used plant
functional groups, classified based on growth form, to investigate how the
pre-fire setting (closed forest, open forest, alpine woodland, krumholtz, alpine
treeless vegetation) interacts with the severity of fire to affect the abundance
of plant functional groups. We also examined the influence of pre-fire
overstory tree structure and fire severity on post-fire seedling density and
composition, across 151 and 100 plots within Butte Creek and Hubbard Creek,
respectively.
Data was collected in 2012 within the 1985 Hubbard Creek
fire (n=100) and the 1994 Butte Creek fire (n=151).
Plant functional groups differed between burned and unburned sites and
along the gradient from closed forest to treeless alpine vegetation. We found
significantly more cushion plants in unburned sites than burned sites. Sites
that burned with high and very high severity had significantly more
graminoids, herbaceous perennials, and tall shrubs. Likewise, closed forest
and open forests had significantly more graminoids in burned than unburned
areas. Seedling density was positively associated with burn severity in areas
where there was a closed canopy forest before the fire, but showed
inconsistent relationships with fire severity and forest structure in open
forests and alpine parkland. Our initial results indicate that post-fire
succession dynamics in A. lasiocarpa forests in the eastern Cascades may be
strongly influenced by heterogeneous patterns of severity resulting in
heterogeneous survival of seedlings and overstory trees.
Results
Figure 2. Map of Hubbard Creek and Butte Creek study
areas
2. Post-fire seedling
establishment
Plot measurements
Used in this analysis:
• Burn severity (see below)
• Structural classes (see below)
• Seedling trees (<1.4m height)
• Herbaceous vegetation transect
Will be used in future analysis:
• Overstory trees (>1.4m height)
• Distance to nearest tree seed sources
Box-plots show post-fire seedling
densities (per ha) across all
species combined:
•
No significant difference in
seedling densities between
burned and unburned areas,
burn severity classes.
•
In combined models (severity *
pre-fire structural class)
differences in pre-fire structure
were stronger and more
significant than any differences
between burned and unburned
plots of severity classes.
•
In combined models there were
significant species-specific
responses to fire severity
within open forest and
parkland structural classes.
Table 1. Burn severity classes
Class
Class description
Unburned
No evidence of fire anywhere
Table 2. Structural classes
Very Low
Low burn severity; only small portion of area effected
Class
Class description
Low
Surface fire; few, if any trees killed
Closed forest
> 40% tree canopy cover
Moderate
Surface fire; 20-70 % trees killed
Open forest
10-40% tree canopy cover
High
50-100% of trees killed; >75% of surface fuels consumed
Parkland
5-10% tree canopy cover; trees often in clumps
Very high
100% of trees killed; >90 surface fuels consumed; soil altered
Alpine
No overstory tree cover. Krumholtz tress may be present
Pre-fire
Fire pattern
Post-fire
Figure 2. “State-transition models” provide a
conceptual framework for this research. The
probability of fire impacting different parts of the
alpine treeline ecotone is influenced by the prefire structural class and their position in the
landscape. Likewise the probability of a
persistent transition to a different structural type
is influenced by the severity of the fire and the
position on the landscape (e.g. environmental
stress at that location).
3. Structural class transitional probabilities
Table 3. Hubbard Creek (1985) structural
transitional probabilities
Pre-fire
Structural
class
Research questions
1.
2.
3.
How likely are different pre-fire structural classes to be impacted by fire of
burn at different severities?
How likely are different pre-fire structural classes transition to a different
structural class after fire?
How do seedling densities after fire differ among fire severity classes and
pre-fire structural classes
Closed
forest
Alpine
0.98
0.02
0
0
Parkland
0.32
0.68
0
0
Parkland
0.39
0.59
0.02
0
Open
forest
0.31
0.34
0.34
0
Open
forest
0.37
0.09
0.54
0
Closed
forest
0.26
0.22
0.3
0.22
Closed
forest
0.36
0.09
0.09
0.45
Future research


We will conduct similar analysis using data-driven classification of
pre-fire and post-fire plant structure and a continuous burn severity
index.
Additional topographical variables will be derived from DEMs and
used as predictors in models.
We will expand the analyses using field data from additional fires in
the Cascade Range (n=2) and Northern Rockies (n=2).
Models of burn severity probabilities and structural class
transitional probabilities will be expanded using a larger data set of
classified pre-and post-fire aerial photography.
Acknowledgements


Graminoids have a positive response to
fire, as frequency increased after high
severity fire in all forest classes.
Figure 1. Climate change will have direct impacts on tree establishment and
survival in the alpine treeline ecotone, as well as the annual area bend in
forested ecosystems. This research addresses uncertainties regarding the
direct effects of fire and post-fire successional dynamics in modern warming
climates in alpine treeline ecotones.
Open
forest
0
Plant species that have a cushion or
mat-forming growth form are less
frequent in severely burned plots,
primarily within the parkland structural
class.
GRAMINOIDS
HERBACEOUS
PERENNIALS
Parkland
0

Dwarf shrub species occur at low
frequency in closed forest and alpine
environments; we could attribute
differences in frequency due to forest
structural class, but not fire severity or
occurrence.
Alpine
0
Results: Herbaceous functional groups
DWARF SHRUBS
Closed
forest
Post-fire structural class
1

Background
Open
forest
Pre-fire
Structural
class
Parkland
Figure 4. Examples of pre-fire structural components: alpine, parkland, open forest, closed forest
CUSHION/MAT
Post-fire structural class
Alpine
Alpine
Climate change may increase area burned and frequency of fire in highelevation ecosystems, which could have long-term impacts on ecosystem
functions such as wildlife habitat use, hydrology, and nutrient cycling. Our
results provide a starting point for understanding the effects of fire on
herbaceous vegetation and post-fire forest succession in subalpine parkland.
Table 4. Butte Creek (1994) structural transitional
probabilities
Field & office assistants: J. Andreychuk, S. Hiebert, E. Banks, E. Driskill, S.
Erickson, E. Snoozy, E. Fales, K. Kingery, M. Tjoelker
Funding provided by US Forest Service, Pacific Northwest Research Station,
through a cooperative agreement with the University of Washington, School
of Forest Resources, the Western Mountain Initiative, and Joint Fire Science
Program Graduate Research Innovation Award
Author affiliations
We did not observe any difference in the
frequency of occurrence for herbaceous
perennials due to fire or structural class.
1
School of Forest Resources, University of Washington, Seattle, WA 98195-2100.
2 Pacific Wildland Fire Sciences Lab, USDA Forest Service, 400 N 34th Street,
Suite 201, Seattle, WA 98103.
Figure 5. Box plots of frequency of each
functional group within each severity class
For more information contact acansler@uw.edu
Website: www.cfr.washington.edu/research.FME/people/alina.htm