Retrospective Analysis of Soil Heat Index in
Areas Impacted by Wildfire
Nicole Kurhanewicz
Mentors: Dr. Elizabeth Sulzman1 and Jim Kennedy2
1Dept.
of Crop and Soil Science, 2Dept of Food Sci and
Technology, Oregon State University, OR, USA
Funding: USDA Forest Service, Pacific Northwest Research Station, Corvallis, OR, USA,
and HHMI
Background
Booth and Bear Butte Fire Complex
August 19th-September 26th, 2003
Deschutes National Forest, Oregon
B & B Complex Fire - Satellite image on 8-27-03
Over 90,000 acres were burned
Hwy 20
B&B Fire, Deschutes National Forest
Photos
taken
from Fire
Fighters Website
Significant portion within the Mt. Jefferson Wilderness Area
Jefferson Wilderness Study Site
Background
•
The B&B fire (summer 2003)
burned over 90,000 acres,
creating a mosaic of forest
disturbance in the cascade
range of Oregon. The impact
of the fire on the soil, and
consequently on the
belowground ecosystem, is of
special concern to future forest
recovery.
•
Currently, burn severity is
determined by field
observation; a more objective
approach would be helpful to
more accurately compare
data across sites.
•
Previous work has indicated
that concentrations of certain
phenolic compounds are
higher in severely burned than
in less severely burned soils
(Alcaniz et al., 1994; Certini,
2005)
B&B Burn Perimeter
Research Goal
To relate current soil chemistry (phenolic concentrations) to
stand-specific fire intensity within the 2003 B&B complex.
Objectives
Objective 1: Verify that tannin compounds can be identified
in recent Douglas fir and Ponderosa pine litter.
Objective 2: Establish a method to quantify tannin in soils.
Objective 3: Determine the relationship, if any, between fire
temperature and tannin content of soils
Objective 4: Quantify the tannin content of soils from each of
the study stands within the B&B Fire Study (PIs Smith and
Sulzman), and create a map of likely fire intensity.
Why do this research?
1. Fire intensity is a vital factor to take into consideration when analyzing post
fire data. A more objective approach to classifying burn intensity would
provide more accurate results when comparing data across sites.
2. Better forest management yields more productive, longer lasting forests
3. This study will provide knowledge critical to understanding the effects of
burn severity on soil productivity in mixed conifer forests with sandy loam
and loamy sand soils in central Oregon.
*photo from http://www.orww.org/B&B_Complex/index.html
Part of a Larger Research Effort
This research is a part of a cooperative
effort by the USDA Forest Service,
Forest Mycology Team to determine
the functional diversity of fungi and the
effects of disturbance, whether natural
or man-made, on microbial
community structure and ecosystem
function, as well as soil productivity
and recovery.
Tannins
• Tannins are naturally occurring plant
polyphenols that bind and precipitate
proteins.
• Proanthocyanidins, or condensed tannins,
are polymeric flavonoid compounds that are
widely distributed in the plant kingdom.
• In evergreen plants, tannins are evenly
distributed in all leaf tissues. They serve to
reduce palatability and, thus, protect against
predators.
Methods
1.
Collected soil and litter from each study site within the
larger B&B study. It was then dried, sieved, and frozen
for storage.
2.
Extraction and acid-catalyzed cleavage of tannin.
3.
The extracts were then analyzed for gravimetric
relationships, for UV absorbance at 280nm
(characteristic of phenolics), and by reverse-phase
HPLC.
Methods
1.
Collected soil and litter from study sites within the B&B
complex. It was then dried, sieved, and frozen for
storage.
2.
Extraction and acid-catalyzed cleavage of tannin.
3.
The extracts were then analyzed for gravimetric
relationships, for UV at A280m and by reverse-phase
HPLC.
Methods 1
• 9 sample sites were selected in
Deschutes National Forest near Sisters,
Oregon.
• Three repetitions were taken of each
treatment: severe burn, moderate
burn, and unburned
• A sample of forest litter was also taken
from an unburned site.
• The samples were then dried, sieved,
and frozen for storage.
Methods
1.
Collected soil and litter from each study site within the
B&B study. It was then dried, sieved, and frozen for
storage.
2.
Extraction and acid-catalyzed cleavage of tannin.
3.
The extracts were then analyzed for gravimetric
relationships, for UV at A280m and by reverse-phase
HPLC.
Methods step 2
Extraction:
The sample was combined with 2:1 acetone/water mixture to
form a slurry.
The slurry was then filtered, the excess acetone was boiled off,
and the remaining extract was freeze-dried
Acid-catalyzed cleavage of tannin:
The freeze-dried extracts were reacted with acid and
phloroglucinol in excess, and then with sodium acetate to stop the
reaction.
This process resulted in proanthocyanidin cleavage products to
be analyzed by HPLC.
Acid-catalyzed cleavage of tannin
Methods
1.
Collected soil and litter from each study site
within the B&B study. It was then dried,
sieved, and frozen for storage.
2.
Extraction and acid-catalyzed cleavage of
tannin.
3.
The extracts were then analyzed for
gravimetric relationships, for UV at A280m
and by reverse-phase HPLC.
(sample HPLC graph here--grape seed)
Results
1. Soil extract gravimetric data and absorption data.
% Mass Recovered
Average % Mass Recovered by Treatment
0.070
0.060
0.050
0.040
Severe Burn
Moderate Burn
0.030
0.020
0.010
0.000
Low to Unburned
Soil Treatment
Burn Severity
Absorption A280
Average Absorption at A280 by Treatment
0.450
0.400
0.350
0.300
0.250
0.200
0.150
0.100
0.050
0.000
Severe Burn
Moderate Burn
Low to Unburned
Soil Treatment
Results
1.
Initial results suggested some condensed tannin in forest litter
samples…Graph of soil litter HPLC here.
1.
Ran soil samples through HPLC and recovered no condensed
tannin.
Conclusions
Early analysis of the litter sample confirmed that condensed
tannins were present. However, evidence of those tannins could not
be found in the soil.
In the environment, tannins can be oxidized, as well as
degraded by microbial activity.
The results suggest that the tannins were modified in the soil
beyond recognition even before the fire (as the control soil sample
had no evidence of condensed tannin either).
The gravimetric relationship observed, as well as the absorption
data, suggest that there is some relationship between fire intensity
and phenolic content in soil. Unfortunately, quantifying that
relationship based on condensed tannin was not a successful
approach.
Acknowledgements
HHMI
USDA-FS Joint Fire Science Project
Dr. Elizabeth Sulzman
Dr. Jim Kennedy
Dr. Kevin Ahern
Tara Jennings
Burning Questions?