EFFECT OF SWISS NEEDLE CAST ON DOUGLAS-FIR CROWN
STRUCTURE AS IT RELATES TO FIRE RISK AND POTENTIAL FIRE
BEHAVIOR IN YOUNG PLANTATIONS OF WESTERN OREGON
Aaron Weiskittel1, Doug Maguire1, and Alan Kanaskie2
1Oregon State University, College of Forestry; 2Oregon Department of Forestry
The data indicated that both Douglas-fir
crown structure and morphology have
been significantly altered by the disease,
between SNC, Douglas-fir crown structure
and fire risk in the region.
METHODS
Using data from permanent monitoring
plots, 82 destructively sampled trees, and
150 litterfall traps, linear regression
models were constructed to test
hypotheses regarding the influence of
SNC on Douglas-fir crown structure as it
relates to fire risk. Vertical distribution of
crown dry matter was characterized by
fitting a β-distribution to each tree. Standlevel estimates of canopy bulk density and
canopy fuel load were constructed as the
Figure 1. Impacts of SNC on Douglas-fir in
Oregon Coast Range. Symptoms include
premature foliage loss, needle yellowing, and
reduced height and radial growth.
FHM posters home page
composite of individual sample trees and
litterfall. Canopy base height was defined
as the lowest height above which at
least 112.4 kg ha-1 of fuel was available.
0.20
0.15
0.10
0.05
•live wood moisture content was
significantly reduced by the disease
•work is currently being done on foliar
moisture content and in older stands
40
30
20
10
0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Foliage retention (years)
Figure 2. Relationship of foliage retention with canopy
bulk density (left) and canopy fuel load (right)
20
LOW SNC
15
HIGH SNC
10
5
0
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
Canopy bulk density (kg/m3)
due to the increased rates of crown
recession
•regardless of SNC level, a larger
proportion of foliage litterfall occurred in
the summer months and litterfall rates
were much higher when compared to
other similar studies (Figure 4)
50
0.00
Figure 3. Vertical distribution of canopy bulk density for
plantations with low SNC (solid line) and high SNC
(dashed line).
7000
0.7
Published data
This study
6000
0.6
5000
Proportion of litterfall
Douglas-fir, may be changing catastrophic
wildfire risk in this region. SNC may
intensify fire risk by enhancing vertical
continuity in ladder fuels, increasing rates
of fine fuel accumulation, and altering
combustion rates through changes in
crown bulk density and moisture content.
Currently, over 157,000 ha of Douglas-fir
forestland in western Oregon have
symptoms of SNC. This study was
initiated to examine the relationship
susceptibility to wildfire.
Specific objectives of the project include:
•describing quantitatively the changes in
crown structure and tree morphology
resulting from SNC;
•assessing the effects of SNC on stand
structure and litter dynamics;
•linking these tree and stand changes to
resulting alterations of fuel loads and
potential fire behavior in trees with varying
degrees of SNC damage;
•establishing the best procedure for rating
SNC damage and stand fire risk
which influenced several stand-level
attributes. Due to these changes, fire risk
and potential fire behavior, particularly
surface fire, have been modified in this
region. This is supported by the following
findings:
•both crown bulk density and canopy fuel
loads were significantly reduced by the
disease (Figure 2) due to the premature
loss of foliage and reductions in the size
and number of primary branches
•vertical distribution of canopy fuel was
shifted downwards with greater SNC
(Figure 3)
• canopy base heights were significantly
lower with greater SNC
•with increasing SNC, foliage litterfall
rates were lower than normal and fine
woody material litterfall rates were greater
60
0.25
Total stand litterfall (kg ha-1)
historically. In fact, some of the largest
fires in the state have occurred in this
region. Swiss needle cast (SNC), an
increasingly important foliar disease of
0.30
Canopy fueld load (Mg/ha)
RESULTS
The overall objective of this study was to
assess the degree to which young (10-30
yrs-old), Douglas-fir plantations impacted
by SNC experience an increased
Canopy bulk density (kg/m3)
OBJECTIVES
Catastrophic wildfires were an important
component of the Oregon Coast Range
Depth into the canopy (m)
INTRODUCTION
4000
3000
2000
Foliage litterfall
Woody litterfall
0.5
0.4
0.3
0.2
0.1
1000
0.0
0
15
20
25
30
35
40
2
45
50
Spring
55
Summer
Fall
Winter
Season
-1
Stand basal area (m ha )
ha-1)
Figure 4. Total litterfall (kg
over stand basal (left) and
seasonal distribution of litterfall for an average stand in
this study (right).
FHM 2004 posters