Our results suggest that fires do impact the local conditions in tall grass prairies, particularly soil conditions and litter cover, which allows grasses to flourish. Prairies, though, are not diverse if only grasses are dominant. Therefore, fires should have a "patchy" effect, meaning their effects would best increase biodiversity if they only impact the local conditions of part of the prairie and only occur occasionally. This will result in a variety of local conditions for plant growth, allowing a variety of species to flourish.
How do we create "patchy" fires? Variable burning regimes. When managing a tall grass prairie, season of burn, burn intensity, frequency of burn, and area impacted by burn should be different from year to year.
In terms of diversity, Smokey is wrong. Fires are not inherently bad; instead, fire control by humans has disrupted an important factor of the prairie ecosystem. So while I don't recommend setting random wildfires, fire is an essential aspect of managing and reconstructing the endangered tall grass prairie ecosystem.
Friday, May 9, 2014
Thursday, May 8, 2014
The Effects of Prairie Burns
The effects of annual spring burns are displayed below. Significant results are marked with (*) and are bolded.
Table provided by Professor Jonathan Brown (Grinnell College, Biology 252).
As predicted, fire significantly decreased necromass (litter), which resulted in significantly increased soil temperature. Soil moisture was not significantly decreased; it had rained prior to our sampling, which made measurements of soil moisture unreliable. Diversity also increased in burned plots as expected.
There were several unexpected results. First, shoot density and above ground biomass were both significantly lower, not higher as hypothesized, on burned plots. We sampled plots very soon after the spring burn. There had not been enough time after disturbance for the colonizers shoots to begin to grow and any early shoots had been killed in the fire. On tall grass prairies, C4 grasses usually colonize burned plots because such grasses are better able to withstand the drier soil which results from burning. These C4 plants usually begin to grow in summer. These analyses should be repeated in a few weeks to determine if these unexpected results were simply temporal effects.
Soil organic matter was not significantly changed through fire. Therefore, changes in soil organic matter are not a major fire effect. Finally, below-ground biomass was not significantly changed by fire and did not increase in burned blots as hypothesized. As discussed earlier, new shoots had not begun to colonize the burned plots and add their below-ground biomass to the soil. Until the new shoots begin to grow and are impacted by the drier soil, below-ground biomass will not likely change on burned plots.
We are still waiting for the results of soil respiration.
As predicted, fire significantly decreased necromass (litter), which resulted in significantly increased soil temperature. Soil moisture was not significantly decreased; it had rained prior to our sampling, which made measurements of soil moisture unreliable. Diversity also increased in burned plots as expected.
There were several unexpected results. First, shoot density and above ground biomass were both significantly lower, not higher as hypothesized, on burned plots. We sampled plots very soon after the spring burn. There had not been enough time after disturbance for the colonizers shoots to begin to grow and any early shoots had been killed in the fire. On tall grass prairies, C4 grasses usually colonize burned plots because such grasses are better able to withstand the drier soil which results from burning. These C4 plants usually begin to grow in summer. These analyses should be repeated in a few weeks to determine if these unexpected results were simply temporal effects.
Soil organic matter was not significantly changed through fire. Therefore, changes in soil organic matter are not a major fire effect. Finally, below-ground biomass was not significantly changed by fire and did not increase in burned blots as hypothesized. As discussed earlier, new shoots had not begun to colonize the burned plots and add their below-ground biomass to the soil. Until the new shoots begin to grow and are impacted by the drier soil, below-ground biomass will not likely change on burned plots.
We are still waiting for the results of soil respiration.
The Experiment
We wanted to investigate some of the mechanisms by which fire acts as a disturbance on tall grass prairie ecosystems.
Ten 10mx10m plots were burned annually in the spring (experimental plots) and ten 10mx10m plots were left unburned (control plots) at Conard Environmental Research Center (CERA) in Jasper County, IA. These treatments have been maintained since 1997. A map of the treatments is shown below:
This study measured six different aspects of the prairie ecosystems to investigate how fire effects growth conditions to better understand the mechanisms fire disturbance. Plots were sampled on April 28, 2014.
The six measurements are explained in the table below. Hypothesized affects of annual spring fires (row 2) and methods (row 3) are also given for each measurement.
This picture was taken at CERA. The plot in the front of the picture is unburned while the plot behind is burned. The difference in necromass is quite obvious.
Photo supplied by Sue Kolbe (Grinnell College Biology Department).
Ten 10mx10m plots were burned annually in the spring (experimental plots) and ten 10mx10m plots were left unburned (control plots) at Conard Environmental Research Center (CERA) in Jasper County, IA. These treatments have been maintained since 1997. A map of the treatments is shown below:
This study measured six different aspects of the prairie ecosystems to investigate how fire effects growth conditions to better understand the mechanisms fire disturbance. Plots were sampled on April 28, 2014.
The six measurements are explained in the table below. Hypothesized affects of annual spring fires (row 2) and methods (row 3) are also given for each measurement.
This picture was taken at CERA. The plot in the front of the picture is unburned while the plot behind is burned. The difference in necromass is quite obvious.
Smokey the Bear and Theoretical Discussion of Fires in the Prairie Ecosystem
http://upload.wikimedia.org/wikipedia/commons/a/ae/Smokey3.jpg
Smokey the Bear taught us that fires are bad. Period. The longest running public service advertising campaign, Smokey posters have been calling for the prevention of wildfires since 1944. Fires, though, have been a natural part of all ecosystems for uncountable years; human regulation of fire has often removed this important contributor to maintaining ecosystem health.In tall grass prairies, fire contribues to biodiversity. By disturbing established community dynamics and productivity of individual species, fires modify the distribution of biomass and energy in ecosystems. In other words, fires change the local conditions of growth, allowing new species to recolonize the disturbed, burned regions and modifying species composition. Natural fires would occur at different frequencies and intensities and follow Connell's intermediate disturbance hypothesis demonstrated below:
Figure from Connell's "Diversity in Tropical Rain Forests and Coral Reefs" (1978)
His idea is that intermediate disturbance allows a mixture of colonizing species (the species that appear after a disturbance) and the best competitors (those that dominate communities long after disturbances), which promotes a high level of species diversity (represented as B in the diagram). Frequent disturbances only allow colonizers to flourish (represented as A) while infrequent disturbance allow the best competitors to dominate (represented as C).
Much research has been focused on understanding how fire acts as a disturbance. How does fire modify an ecosystem to promote biodiversity?
Hulbert (1969) demonstrated that the most important effect of fire is the removal of litter. Removing the layer of dead plant material has many implications. First, it allows a larger amount of sunlight to reach the ground, which should warm and dry the soil. This should promote the growth of species that are better suited to dry climates. By removing the litter, new shoots should have less competition and more sunlight. Therefore, burn plots should also have a higher amount of biomass, but this biomass should mostly consist of species with high growth rates (Connell's colonizers). Therefore, burning should allow grasses to infiltrate areas once dominated by forbs (better competitors). This prediction were confirmed by research by Abrams et al. (1986).
Therefore, fire promotes the growth of grasses while decreasing form dominance. How does this promote biodiversity? Following Connell's intermediate disturbance hypothesis, intermediate levels of fire will allow for a mix of colonizers and competitors (grasses and forbs). This leads us to an interesting question: What types of fires qualify as intermediate disturbances? Yearly? Bi-yearly? Understanding the mechanisms by which fire acts as an intermediate disturbance is important for conservation and reconstruction of tall grass prairies.
Sources used:
1. Abrams, Marc D., Knapp, Alan K., Hulbert, Lloyld, C. 1986. A Ten-Year Record of Aboveground Biomass in a Kansas Tallgrass Prairie: Effects of Fire and Topographic Positions. American Journal of Botany 73: 1509-1515.
2. Campaign History. Smokey Bear. http://www.smokeybear.com/vault/history_main.asp. 8 May 2014.
3. Connell, Joseph H. 1978. Diversity in Tropical Rain Forests and Coral Reefs. Science 199: 1302-1310.
4. Hulbert,
Lloyd C. 1969. Fire and Litter Effects in Undisturbed Bluestem Prairie in
Kansas. Ecology 50: 874-877.
Banner photo: http://www.kansassampler.org/siteassets/about/8%20Wonders/KonzaTrailSignWEB.jpg
Subscribe to:
Posts (Atom)