This is the result of a two month student collaboration, under the instruction of Dr. William Platt, Biology, LSU, at Chappapeela Sports Park, Hammond, Louisiana where, in 2011 Pastorek Habitats, LLC, helped to design, and then build and manage a couple of fine prairie gardens for all the world to see. Enjoy the paper, but without graphs and charts, the graphics……. and go see the gardens, ya’ll!
Hunter Blalock, Matthew Blanchard, David Clark, Trent Davidge, Ian Elliott, Justin Ellis, Victoria Hutson, Paris Lee, Grant Raphael, Chad Rathcke, Clay Tucker, Tyler Viator, Christopher Welch BIOL 4017, Section 01 May 6, 2015 RESTORING A PRAIRIE ECOSYSTEM: PRESCRIBED FIRE EFFECTS ON TOTAL BIOMASS AND FORB DIVERSITY AT CHAPPAPEALA SPORTS PARK, HAMMOND, LOUISIANA Abstract Fire ecology is a major part of the savanna ecosystem, as it causes a disturbance in plants by burning them, which leads to open space for new recruitment. Therefore, areas that had been burned more recently should have higher biodiversity than areas that have not been burned. We tested fire’s effect on forb diversity and abundance as well as biomass in retention ponds surrounded by seeded prairies. We predicted that forb diversity would increase after the fire due to a lack of competition from larger plants that burned during the fire. We collected biomass using a smaller plot area (6.0 in2). We analyzed our data using ANOVA, t-tests, and a Shannon-Weiner Index. The results of this experiment showed that the unburned pond had a higher mean abundance of Baptisia spp. (p < 0.001) and a mean plant abundance (p < 0.001) than the burned pond. Possible errors are that data could be masked due to not enough time studied over the course of the experiment. The study suggests further study of fire ecology in relation to biomass and biodiversity in prairie systems to better understand the cyclic process of regrowth post fire. Introduction Fire has been a part of pine savannas ecology since the Eocene period (Noss et al. 2015). Investigating tree rings in pines shows that fires occurred in one to three year intervals. In the past, the fires were caused by lightning that occurred from frequent thunderstorms during the spring/summer transition (Noss et al. 2015). The native vegetation is resistant to fire and also has pyrogenic characteristics (Platt 1999). Many of the endemic species have rhizomes on their roots that allow them to resprout after a fire. Pines have thick bark that contains rosin, which lowers the combustion rate thus preventing heat from reaching the vascular cambium. Plants have not only developed resistances to fire, but also promote it. Savannas contain many grasses and forbes that ignite easily during a fire. Pines drop a large number of needles during the year that lose their resins and burn at high intensity on the ground (Platt 1999). These needles stay on the ground for a long time because of a low decomposition rate, which accumulate to further promote fire. Fire is a necessary ecological disturbance for pine savannas (Noss et al. 2015). Some species do not produce flowers or viable seeds until after a fire (Platt 1999). The survival rate and growth of juvenile pines are increased after a fire. This is due to the nutrients that fire puts into the ground. Savanna soil is typically low in nutrients, and fire helps to decompose the ground cover/litter and replenish the soil nutrients (Platt 1999). The adaptability of the endemic species to fire has created a defense to invasive species. Fire opens up the savanna’s surface, which helps native diversity, but does open the savanna to invasive species. The frequency of the fires is the defense against invasive species. The rate at which fires occur does not allow for non-native species to take hold because of their lack of adaptation to fire. Fires help promote the growth of native species, while defending against invasive species. Although fire is a tool for regrowth, intensity in fire can have some effect on the seedling establishment and soil heating can negatively effect on plants that are selected for fire (Tyler 1995). Davis et al. (1989) reported that although fire did enhance the germination in some species of plants, this occurred in canopy gaps where soil temperature was lower. This suggests that fire intensity and its effect on soil heat could harm the root system of plants adapted to fire. Also, another study by Moreno and Oechel (1991) reported that total number of herbs decreased with increasing fire temperature. That study correlates with the finding in the study by Tyler (1995) that there was a significant difference in emergence related to the intensity of the fire. They reported that there was a negative relationship between fire intensity and plant emergence, suggesting that even though fire is essential to these habitats, the buildup of flammable materials may damage the system. In this study, we observe the difference in vegetation between burned plots and unburned plots. In order to investigate this relationship, we conducted our experiment on the banks of two retention ponds at Chappapeela Sports Park (CSP) in Hammond, LA. These banks were seeded with native species that were planted by Marc Pastorek in the spring of 2013. One pond was burned in 2014, the other has never been burned. Native species of forbs include Baptisia solidago (golden rod), and Boltonia asteroides, and other common pine savanna groundcover species. In a previous study at CSP, three different fuel types (control[none], pine straw, bluestem grass hay) were compared to study the differing effects of fire intensity on biomass, abundance, and diversity two weeks later. Our study is a continuation of that research. Our research objectives include the following:
- How does fire affect vegetation in a newly seeded prairie?
- How is prairie vegetation affected by fire intensity one year after the fire?
We predict that biomass would decrease on the burned banks because fire destroys any vegetation opening the floor for new species. We also predict that forb diversity would increase after the fire because of lack of competition from large plants that burned during the fire. Methods For the first half of our experiments, we continued a study done by the 2014 conservation biology lab class. In that study, different fuel sources were used to manipulate fire temperatures in an attempt to discover the effects of accelerants on fires as well as the effects of fire on foliage. Refer to (Achord et al. 2014) for a full description of their methods. We continued use of 15 previously placed 1.0 m2 plots around a retention pond in Chappapeela Sports Park located in Hammond, LA which had been burned the previous year. This pond will be referred to as pond 1. Data was collected for three groups of plots treated with either hay, pine straw, or a control with no accelerant. Each group had five replicate plots. A 6.0 in2 area biomass sampling was collected for each of the 15 plots. The biomass clippings were separated into three groups: grasses, litter, and forbs. Once back at the lab, the sample bags were opened and placed into a drying oven for two days to remove any moisture. After drying, all biomass samples were weighed (in grams) in their respective bags. The contents of each bag were then removed and the empty bags were weighed. Weight of the empty bags was subtracted from the total weight of biomass samples plus their bags to determine the weight of just the biomass. Abundance and diversity of all forbs were counted in each of the 15 plots. All data was analyzed using two way ANOVA tests and T-tests: assuming equal variance as well as a Shannon-Wiener Index calculation for each plot. Dependent variables for this experiment were forb abundance, diversity, and total biomass. Independent variables for analysis include the accelerants used for burning. All analyses were performed in Microsoft Excel. The second half of our experiment required an additional retention pond in CSP which had been seeded at the same time as the first, but had never been burned. We will refer to this pond as pond 2. We looked at the overall effect of fire on abundance, diversity, and biomass of newly seeded prairie landscapes. Fifteen 1.0 m2 plots were placed around pond 2 in a similar fashion to the first retention pond. Flags were placed to mark the plots and metal tags used to label each plot. A 6.0 in2 area of vegetation around the plot perimeter was clipped for each plot to determine the biomass. Collected samples were once again separated into three groups: grasses, litter, and forbs and weighed in similar fashion to biomass samples from pond 1. Abundance and diversity of all forbs were collected for each plot. Data collected from all 15 plots in pond 1 was grouped together and analyzed with data collected from the 15 plots in pond 2. Forb abundance, diversity, and total biomass were our dependent variables and analyzed through t-tests: assuming equal variance. The independent variable was a prescribed fire 1 year prior. All analyses were performed in Microsoft Excel. Results Baptisia abundance and dominance was measured in pond 1 and pond 2. Baptisia spp. species were used for initial results because they are a dominant forb species in our plots and their presence or lack thereof matched with total forb abundance and diversity. Figure 1 shows the results for the mean Baptisia abundance. Abundance in pond 1 was 8.73 + 8.25 (mean + standard deviation) and pond 2 was 26.5 + 10.6 (n=30; df=28). There was a significant difference in the two ponds for Baptisia abundance (p-value= p < 0.001; t-stat= -5.14; df=28). Figure 2 shows the results for average Baptisia dominance, or the percentage of Baptisia spp. in plots. The average Baptisia dominance for pond 1 was 0.259 + .170, and pond 2 was 0.341 + .161. There is no significant difference in mean Baptisia dominance between the two ponds (p = 0.188; t-stat= 1.35; df=28). Plant diversity and total abundance was measured in pond 1 and pond 2, shown in Figures 3 and 4 respectively. The result shows that the average plant diversity in pond 1 was 6.6 + 2.38 (mean + standard deviation) (n=30; df=28) and pond 2 was 8.13 + 2.33. There was no significant difference in the two lakes for diversity (p = 0.085; t-value=1.78; df=28). However, this p-value is suggestive of a significant relationship. It is possible that undersampling contributes to a high p-value. A higher number of samples may make this relationship significant. The average total abundance in pond 1 was 30.5 and pond 2 was 89.9 (n=30; df=28). There was a significant difference in the two ponds for total abundance (p < 0.001; t-value=4.39; df=28). Analysis was completed for biomass variables as well (Figure 5). The only significant result to emerge from this analysis was that litter biomass was higher in pond 2 than in pond 1 (p < 0.001; df=28; t-stat=-5.09). Figure 1: Mean Baptisia spp. abundance of 1.0 m2 plots (N=15) from pond 1 and pond 2. Error bars represent the standard deviation in the data set for each pond. (p < 0.001, df= 28, T-statistic= -5.14). Figure 2: Mean Baptisia spp. dominance of 1.0 m2 plots (N=15) from pond 1 and pond 2. Error bars represent the standard deviation in the data set for each pond. (p = 0.188, df= 28, T-statistic= 1.35). Figure 3: Mean plant diversity of 1.0 m2 plots (N=15) from pond 1 and pond 2. Error bars represent the standard deviation in the data set for each pond. (p = 0.085, df= 28, T-statistic=1.78). Figure 4: Mean plant abundance of 1.0 m2 plots (N=15) from pond 1 and pond 2. Error bars represent the standard deviation in the data set for each pond. (p < 0.001, df=28, T-statistic= 4.39). Figure 5: Mean biomass (grams) of forbs, grasses, and litter of each 1.0 m2 plot (N=15) in pond 1 (red) and pond 2 (blue). Error bars represent the standard deviation in the data set for each pond. Discussion Before our experiments, we predicted the burned bank surrounding pond 1 would have less biomass and greater diversity relative to the unburned bank surrounding pond 2. The mean Baptisia spp. dominance (Figure 2) and mean forb diversity (Figure 3) were not statistically different between the two ponds. However, the mean Baptisia spp. abundance (Figure 1) and mean forb abundance (Figure 4) were statistically different between the two ponds. Mean Baptisia spp. abundance and mean forb abundance were greater on the bank of pond 2. From this information we can conclude that the unburned bank surrounding pond 2 had greater forb diversity than burned bank surrounding pond 1. We hypothesized that forb diversity would increase after the fire because of lack of competition from large plants that burned during the fire, which contradicts our results. Thus, we reject our research hypothesis regarding biodiversity. Additionally, we hypothesized that biomass would decrease on the burned banks of pond 1 because fire destroys vegetation. We rejected this hypothesis also because the results of our experiment did not yield statistically significant differences between the banks of the ponds. Reasonable explanations for the discrepancy between our diversity hypothesis and results are that it may take more than one year of succession or more than one burn cycle for the plants to show a significant response to fire. Furthermore, the diversity in a given plot will not decrease unless plants experience the deleterious effects of other plants. The growth of certain plants a year after seeding may not allow them to overcrowd other plants. When they do overcrowd other plants, the diversity will decrease due to their ability to out compete other plants. Plant diversity has increased in some Australian grasslands for 5-7 years before a significant decline in plant diversity. The optimal burn frequency is 4-6 year intervals for long term maximal diversity in this environment. (Morgan 1999) After 11 years, a single burn in this grassland was not sufficient to return the soil to its optimal level. Thus, more frequent fires were beneficial to sustain an optimal band of diversity within this ecosystem. (Morgan 1999). After a fire, factors such as burn season, timing, weather conditions, and animal disturbances affect the distribution of grass and forbs (Brown 2000). A continuation of our study would be beneficial to determine whether more burn cycles, more time after seeding, or more burns would yield significant results in terms of diversity. The analysis of our biomass data revealed that the mean biomass of litter was affected by fire. Litter had a significantly higher mean biomass in pond 2 compared to pond 1. We anticipated that this condition would contribute to higher levels of diversity on the burned banks of pond 1 because often burns litter. We believed that higher levels of litter would crowd out growth. Yet, retention pond #1’s lower levels of litter biomass did not result in higher biodiversity. The effects of litter accumulation over a year may not have been substantial enough to hinder growth. Increasing the duration of this experiment could provide insight to the role of litter on biodiversity. Fire’s effect on the biomass of forbs and grass was statistically insignificant. In total, the sum of the mean biomasses of forbs, grass, and litter did not differ in a statistically significant way between the plots on the burned bank and the unburned bank. The disparity between our hypothesis and results could have stemmed from an overestimate of the fire’s intensity and/or an understatement in the plant’s ability to respond. Fire acts as an important catalyst for reproduction to many adapted plants. The plant’s natural rejuvenation could have been aided by the fire’s characteristics and timing. Fires of low severity are followed by a stronger resprouting response when compared to fires of high severity (Turner et al. 1997). Also, the state of vegetation when the fire was started could have allowed recuperation of lost biomass faster (Miller 2000). As a general rule, burned areas tend to return to the same flora that existed previously (Brown 2000). However, we did not account for their rapid regrowth. These factors could account for the sudden resurgence of vegetative biomass on the bank of pond 1. In many ecosystems, fire is a necessary component of a stable environment. Inhabiting organisms benefit greatly from its role in ecological processes, and fire is essential to promoting biodiversity, which provides stability to our ecosystems. Conclusion Our study shows that a pond that was burned 1 year after seeding had significantly less Baptisia spp., forb diversity, and forb abundance. Litter biomass was much lower in the burned pond than in the unburned pond. No other tests were significant. We believe that burning a newly seeded prairie within 1 year of seeding had a negative effect on forb species diversity and abundance. However, burning does reduce biomass, especially in litter, opening the floor for new growth. This is likely an important part of creating a healthy and natural prairie ecosystem. In future restoration, we believe that prairies should not be burned within 1.5 years of seeding to allow for establishment of as many species of possible. Additionally, native species are necessary for producing a natural habitat. Next, including gallery forest species (such as Magnolia grandiflora) and hydrophilic species (such as Typha spp.) may reduce the effects of building a natural habitat. An additional important factor in providing a natural habitat is letting native canopy species dominate. For example, allowing nearby Pinus spp. to infiltrate the prairie ecosystem may promote a more natural habitat. Lastly, for future research, we believe that one pond should be burned annually and the other burned biannually. We believe that abundance and diversity were lower in the burned pond, not because of fire introduction, but because of the fact that the fire was started prior to establishment of a healthy, natural system. By studying the frequency of fire (annually vs. biannually) the true effects of fire may be seen. Suggestions for Restoration (Marc)
- Let the pine trees grow and get rid of magnolias (to enhance a natural savanna habitat)
- Stagger burning cycles for future research (annual for pond 1 and biannual for pond 2)
- Do not burn future newly seeded prairies within at least 1.5 years of seeding; burning too soon likely does not allow plants to become established
- Pay attention to individual species and/or cattail as invasive species
Suggestions for Future Studies (2016 class)
- burn pond 1 annually; burn pond 2 biannually (next burn in 2017)
- Look at 1 year burns compared to 2 year burn cycle
- Fire frequency effects on abundance, diversity, and biomass
- We expect lower abundance, diversity, and biomass in an annually burned pond than a biannually burned pond and the results of this study support that prediction
- Look at patterns of establishment
- Find out what Marc did not plant
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