1. Purpose
Methods
Temporal & Spatial Analysis of Soil Chemistry Changes Following Prescribed Burns In a
Pine-Hardwood Forest
Kelsey Calvez, Caroline Miller, Forrest Chevaillier, Matt Duncan, Nathan Peavey
College of Geosciences, Texas A&M University, College Station, Texas 77840
Results Conclusion
Discussion
Introduction
This before-and-after-impact assessment study is an analysis into what frequency of
prescribed burning is most effective at allowing for significant changes in key soil nutrients
(potassium, phosphorus, and magnesium) and isotopic concentrations, thus positively
impacting the vegetation in a pine-hardwood forest.
Results
Turner et al., (1999) has shown that in forests fire severity is tied to forest recovery and alien
plant invasions. Fire severity has also been correlated with ecosystem responses including
species richness (Whelan, 1995).
Policy Implications
Future Work
Acknowledgements &
References
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Scatter plot identified a significant increase in nitrogen
isotope concentrations one most post burning, with
these levels rapidly declining to normal levels 2 months
and 6 month post burn.
This rapid decline in 15N of soil to pre-fire values
indicates that the depleted ash, containing
considerable amounts of total N, was readily
incorporated into the soil (Huber et al., 2013). Rapid
growth of herbaceous plants and significant increases
in plant storage of nitrogen has been observed to
follow sudden flushes of nitrogen in the soil (Kutiel and
Naveh, 1987).
The nutrient levels of potassium in the soil post-burn
increased in concentration to 30.523ppm from the
control level of 13.235ppm. This temporary increase
lasted less than a month as the 2 month burn showed
potassium levels that had returned to normal levels.
Potassium is an important nutrient that enhances
vegetation growth, regulates enzymatic processes,
and improves the plants ability to withstand extreme
temperatures, droughts, and pests.
The nutrient levels of phosphorus in the soil post-
burn increased in concentration to 30.921 from the
control level of 7.774ppm. This temporary increase
lasted less than a month as the 2-month burn site
showed phosphorus levels that had returned to
normal levels.
Phosphorus is an important nutrient that affects the
rate of vegetation growth and promotes strong root
systems in plants.
The nutrient levels of magnesium (Mg) in the soil
post-burn increased in concentration to 44.097ppm
from the control level of 30.401. This temporary
increase was sustained less than a month as the
2-month burn site showed magnesium levels that
had returned to normal concentration levels.
Magnesium is an essential element for plant
growth and vegetation development. It is used for
plants cell membrane stabilization and
carbohydrate conversion.
Wildfires & Prescribed Burning
● Wildfires and prescribed forest burns have significant effects on nutrient cycling, as well as
the physical, chemical, and biological properties of the disturbed soils. This is in part due to
the rapid combustion of the organic material and leaf litter (Debano et al., 2000).
● The primary nutrient changes include, but are not limited to, organic carbon, nitrogen (δ15N)
phosphorus, magnesium, and potassium.
Abundance N Isotope Ratio (δ15N)
● The natural abundance N isotope ratio (δ15N) is well known in plant ecology to affect the
spatial and temporal fractionation of N isotopes in ground cover vegetation and soil (Huber et
al., 2013).
● The use of natural abundance of 15N throughout soil, ash, and vegetation as a mean of
tracing the transformation of nitrogen concentrations during wildfires has established the
importance of combustion products as an important source of inorganic N for plants
regeneration following a wildfire (Huber et al., 2013).
● Non-biological phenomena that have been examined using δ15N and are intimately
associated with plant growth have included broad studies that investigate the patterns of
vegetation distribution in relation to continental and global climates, and changes along
environmental gradients (Huber et al., 2013).
Soil and Leaf Litter Collection
1) Soil sampling and ground litter collection took place mid-March
2) 1 month, 2 month, 6 month, and control burn sites
3) Four 70m transects were laid out and divided into 5m increments
4) Ground litter (30x30 inch frame), 7 inch soil core, and topsoil collected
5) 3 cups of soil gathered from the middle of each of the four transects
Isotopic Analysis
1) Soi, ash, and charred organic material oven-dried at 105 D Celcius
2) Material then ground to a fine homogenized powder using mortar and pestle
3) 5-20mg of soil and ash, and 5-6 mg of plant material was weighed
4) Samples carried to a mass spectrometer for dN15 and dC13 analysis
Leaf Litter Analysis
1) Four samples of pine needles and leaves were randomly collected every
10 meters, then dried and ground up using a labor intensive screening
process
2) Samples prepared and carried to mass spectrometer for dN15 and dC13
concentration measurements
Surface Soil Enrichment
● In this study, surface soil was enriched in δ15N immediately following a fire. Similar
results were found following wildfires in other ecosystems (Huber et al., 2000; Herman
and Rundel 1989).
● This pattern of increased δ15N concentrations generally fits with the hypothesis
proposed by Hogberg (1997), that great δ15N enrichment of plants post-fire is due to
fire consuming upper soil layers that are depleted in δ15N.
Fire Severity, Frequency, & Ecosystem Responses
● DeBano et al., (1998) determined that fire severity and magnitude are both key players
in assessing δ15N concentrations. During low severity fires some portion of the
nutrients contained in the affected organic matter are converted to inorganic forms,
which can be readily taken up by plants.
Surface Soil Chemistry Changes in Pine-Hardwood Forest
● W. G. Jones States Forest management inadvertently allows for nutrient enrichment of
nitrogen, along with many micronutrients, via low severity burning techniques.
Prescribed Burns in a Pine-Hardwood Forest (W. G. Jones State Forest)
● Prescribed burns display a minimal impact on some of the dC13 and soil nutrients
calcium, sulfur, and sodium. T
● the impacts on phosphorus, magnesium, and potassium levels, each a critical soil
nutrient, were statistically higher post-burn in comparison to the control site.
● Overall the moderate changes in ground litter and soil nutrient contents indicate that the
prescribed burning promoted nutrient cycling. The influence of fire on micronutrient
availability is useful to understand its effect on the post-fire recovery of soils and plants.