Plant-Environment Interactions With Fire
In this blog I will be discussing
the interactions between plants and fire. Prescribed fires are commonly used to
promote plant growth and set back succession. Wildfires are fires that are
burning out of containment and can have various intensities. While some people
view fire as a detrimental thing to the environment, it can be very beneficial.
For example, the Great Smoky Mountain wildfire destroyed many homes and
businesses but it could result in the betterment of some of the ecosystems that
were burned. Many plant species rely on fire for their existence. These plants
have many adaptations that help them survive these fires. A few of these adaptations
include serotenous cones and thick bark. Fires also clear debris from the
soil’s surface allowing for seeds to be in contact with bare mineral soil. Fire
can have a major impact on the environment in many ways. Fire impacts the
environment through the change of soil nutrients available and soil erosion.
The change in vegetation caused by
fire can affect soil erosion in ways such as rill formation and sheet flow
(McNabb & Swanson 1990). Vegetation and leaf litter are very important in
the stabilization of soil. Without vegetation and leaf litter present, there is
an increase in soil erosion due to the increase of rainfall intensity hitting
the ground and the total amount of precipitation that comes in contact with the
ground (Kutiel & Inbar 1993). The severity of the fire is very important
when dealing with erosion. Fire severity can be measured either by the maximum
soil temperature, by the volume of fuel burnt, or by its effects on vegetation
and soils. (Walker et al. 1986). Low
intensity fires mostly burn the understory layer of vegetation, while high
intensity fires can burn every level of vegetation. Low intensity fires have a
minor effect on organic matter and soil structure, however high intensity fires
can create temperatures high enough to break down soil aggregates (Prosser
& Williams 1998). Fires cause the soil surface to be bare, thus increasing
the risk for runoff. The increased risk of runoff is caused by the burning of
organic matter and creates a loose soil surface. This organic matter is very
important because it aids in soil cohesion (Giovannini & Lucchesi 1983). There
are many factors that control erosion following a fire. Some of the main
factors that control erosion are soil type, ground litter, infiltration rate,
and vegetation cover (Prosser & Williams 1998). These factors that control
erosion are changed during and after the fire, but will return to their normal
state over time (Brunsden & Thormes 1979). It could take many years before
the vegetation and soil are back to normal. After the soil, ground litter, and
vegetation cover are back to their normal state following a fire, these factors
can become slightly more resistant to erosion and reduce the amount of runoff (Prosser
& Williams 1998). Ian Prosser and Lisa Williams performed a study on runoff
for areas that had been burned and had not been burned. Their results showed
that the burnt plots had more runoff. Their results help show that fire has an
impact on the amount of runoff produced.
Fire can also affect physical and
chemical soil properties. Fire intensity and frequency have an effect on the
amount of alteration of abiotic and biotic factors (Debano et al. 1977). An
intense fire that occurs in areas that have high erosion potential can cause significant
alterations in the environment (Swanson
1981). During low intensity fires, the amount of nitrogen lost at the soil’s
surface is less than fifty percent (Dunn & Debano 1977). On the other hand,
fire can increase the amount of elements in the soil. Some of the elements that
fire increases are K, Mg, Ca, and Na. The amount of phosphorus in the soil
following a fire is variable. Fire can also increase the amount of soil
exchangeable Ca^2+ and Mg^2+ (Murphy et al. 2005). If the fire becomes hot enough,
then phosphorus, potassium, and sulfur can be volatilized (Raison et al. 1985).
P. Kutiel and M. Inbar performed a
study to better understand the impacts of fire on soil nutrients and soil
erosion. They suggested that medium intensity forest fires and light could
cause an increase in soil fertility without causing a major difference in soil
erosion (Kutiel & Inbar 1993). Their results showed that there was a
significant increase in available forms of nitrogen. The available forms of nitrogen
were NH4-N and NO3-N. Below are graphs that show the changes in NH4-N (a) and
NO3-N (b) concentrations at the soil surface (0-5 cm) after a moderate wildfire
in a mature pine forest plantation (Kutiel & Inbar 1993).
Solid lines =
burnt soil; dotted line = Un-burnt soil.
Vertical lines
indicate standard deviations.
Vertical lines
indicate standard deviations.
So why do we care about the
plant-environment interactions with fire? The answer is simple. Fire impacts
soil nutrients and soil erosion. If a fire changes the amount of soil nutrients
available, then some plants may not have enough nutrients to grow. Plants need
a certain amount of nutrients to be able to grow and without these nutrients
those plants don’t stand a chance of surviving. We also need to care about soil
erosion. The studies that I have examined indicate that fire increases the
amount of soil erosion. An increase in soil erosion can have impacts on
watersheds and the loss of nutrient rich soil that plants need to grow in. Just
imagine a mudslide going into a river. Can you see all of all of the mud
dirtying up the water? This event can have a major impact on the river’s
ecosystem as well as the plant ecosystem. Soil erosion can cause sedimentation
in watersheds, which can kill aquatic vegetation and animals through the
decrease in oxygen levels that they need to live. Soil erosion can also
increase the amount of pollutants that are unwanted in certain areas. This can
be caused by the runoff collecting things such as herbicides and dispersing
them into other areas. Remember that fire can change the factors that control
soil erosion. The main factors that control erosion are soil type, ground
litter, infiltration rate, and vegetation cover (Prosser & Williams 1998).
It is very important to know how fire intensity plays a role in both soil
erosion and soil nutrients. A low intensity fire can cause little to no impact
on soil erosion and nutrients, while a high intensity fire can cause a
significant change on soil erosion and soil nutrients. Plants require nitrogen,
calcium, phosphorus, potassium, sulfur, and magnesium in order to live. If a
fire is hot enough it can eliminate phosphorus, potassium, and sulfur from the
soil surface. So if a fire is really hot it can eliminate half of the nutrients
that plants need to survive.
Fire impacts the environment
through the change of soil nutrients available and soil erosion. Fire can have
a major impact on the environment in both positive and negative ways. The use
of fire has been used as a management tool for hundreds of years. I have
personally used prescribed fires to burn around 2,000 acres, and I have seen
how many ecosystems strive after the application of fire. However, wildfires can
create a problem for the environment. I have found through my research that the
changes in soil nutrients and soil erosion are related to fire intensity.
Literature Cited
McNabb, D.H. & Swanson,
F.J.(1990): Effects of fire on soil
erosion. In: J.D. Walstad, S.R. Radosevich & D.V. Sandberg (Eds.), Natural
and prescribed fire in Pacific Northwest Forests. Oregon State University
Press, Corvallis, Oregon. 159-173.
Dunn,
P.H. & Debano, L.F. (1977): Fire's effect on biological and chemical
properties of chaparral soils. In: Proceedings of the Symposium on the
Environmental Consequence of Fire and Fuel Management Ecosystems. ESDA Forest
Service General Technical Report. WO-3, 75-84.
Debano, L.F., Dunn,
P.H. & Conrad, C.E. (1977): Fire's
effects on physical and chemical properties of chaparral soils. In: Proceedings
of the Symposium on the Environmental Consequence of Fire and Fuel Management
Ecosystems. ESDA Forest Service General Technical Report. WO-3, 65- 74.
Swanson, F.J. (1981): Fires and geomorphic processs. In:
Proceedings, Fire regimes and ecosystems conferences. Honolulu, 1979~ Gen.
Tech. Rep. WO-26 USDA, Washington, DC, 401--420.
Kutiel,
Pua, and Moshe Inbar. "Fire impacts on soil nutrients and soil erosion in
a Mediterranean pine forest plantation." Catena 20.1-2
(1993): 129-139.
Walker,
J., Raison, R. J., and Khanna, P. K. 1986. “Fire”, in Russell, J. J. and Isbell, R. F. (Eds), Australian Soils: The Human Impact. University
of Queensland Press, Brisbane. pp.
185-216.
Brunsden, D. and
Thornes, J. B. 1979. `Landscape sensitivity
and change', Trans. Inst.
Brit. Geogr., 4, 463±484.
Prosser, Ian P., and Lisa Williams.
"The effect of wildfire on runoff and erosion
in native Eucalyptus forest." Hydrological processes 12.2
(1998): 251- 265.
Raison, R.J.,
P.K. Khanna, and P.V. Woods. Mechanisms of element transfer
to the atmosphere during vegetation fires. Can. J. For.
Res. 1985. 15:132–140
Murphy,
J. D., et al. "Wildfire effects on soil nutrients and leaching in a Tahoe
Basin watershed." Journal of Environmental Quality 35.2
(2006): 479-489.
