Grantee Research Project Results
Final Report: Chinese Tallow Invasions into the Endangered Coastal Prairie: Causes and Consequences
EPA Grant Number: R828903Title: Chinese Tallow Invasions into the Endangered Coastal Prairie: Causes and Consequences
Investigators: Siemann, Evan , Grace, James , Rogers, William
Institution: Rice University
EPA Project Officer: Packard, Benjamin H
Project Period: June 1, 2001 through May 31, 2004 (Extended to May 31, 2005)
Project Amount: $381,687
RFA: Exploratory Research to Anticipate Future Environmental Issues (2000) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Water , Aquatic Ecosystems
Objective:
The main objective of this research project was to understand how abiotic conditions interact with biotic factors to influence the likelihood, severity, and impacts of Chinese tallow tree invasions into coastal prairie. Specifically, we addressed the following questions:
1. How do fire (annual or periodic), soil fertility, and herbivores interact to influence tallow tree invasion?
2. How do changes in frequency of extreme rainfall events (such as those that may accompany changes in climate), soil fertility, and herbivores interact to influence tallow tree invasion?
3. How important is local recruitment limitation versus local conditions in determining the likelihood and severity of tallow tree invasion?
4. What are the effects of fire, changes in hydrology, and nutrient addition on the aboveground and belowground distributions of carbon and nitrogen?
5. What are effective methods for controlling tallow tree invasions and for restoring invaded prairies?
Summary/Accomplishments (Outputs/Outcomes):
Chinese tallow tree (Sapium sebiferum) is a major invader in the southeast United States that aggressively displaces native plants. Our research focused on the mechanisms that allow tallow tree to establish in endangered coastal prairies and transform them into biotically depauperate forests. We considered three main drivers in these experiments: the effects of variation in fire regimes, the effects of changing precipitation in future climate, and anthropogenic nutrient addition. We also examined the interactions among these drivers and how herbivore pressure may modify their effects on tallow tree invasion. This research also investigated the effects of changing abiotic conditions and the effects of tallow tree invasion on the diversity of native plants, diversity of arthropods, and distribution of nitrogen and carbon aboveground and belowground. We examined the utility of prescribed burns for management of tallow tree invasions and the feasibility of mechanical methods for restoration of heavily invaded prairies.
Summary of Overall Results
One of the main predictions for these experiments, that disturbance in general will facilitate exotic plant invasions, was not supported. Some disturbances, such as pulses of nutrients, strongly facilitated tallow tree invasion in all conditions in all experiments whereas others, such as changing hydrological conditions, influenced tallow tree success only at certain fertility levels. Both increased and decreased frequencies of extreme rainfall events reduced the intensity of tallow tree invasion in fertilized conditions. Similarly, low frequencies of fires increased tallow tree invasion relative to no fires, but frequent fires reduced invasion compared to no fires.
In terms of relative expected impact on tallow tree invasions, anthropogenic nitrogen addition has a strong positive effect on invasion independent of any other abiotic or biotic factors, whereas changes in frequency of extreme rainfall events have no effect or a negative effect on invasions depending on levels of nutrient loading.
As we had predicted, understanding the interaction of different abiotic alterations is critical for predicting their effects on native prairie communities and their vulnerability to invasion. In particular, changing fertility appears to change the responses to fire or changes in water regime, though the effects of nitrogen loading always increased invasion intensity. We had conjectured that in some conditions herbivores may have a strong effect on tallow tree recruitment, but we saw little effect of herbivores on tallow tree in any conditions including regrowth following a fire. Regulation of tallow tree by herbivores did not occur in any conditions in any experiment. Recruitment of tallow tree from seed to seedling was very low in all experiments. Tallow tree’s success would appear to be caused by a high rate of seed input and/or high per capita success as a seedling but not from a high probability of seeds becoming seedlings.
Ecosystem level effects of fertilization were dramatic with large increases in the carbon and nitrogen contained in vegetation with fertilization. In comparison, the effects of fire and changing water availability on carbon and nitrogen distribution over a period of 3 or 4 years were minor.
Based on the first results of the fire experiment, fire appears to be an excellent method of controlling tallow tree invasion into coastal tallgrass prairies if burns are frequent. Mechanical removal is an effective way to restore heavily invaded prairies that cannot be burned.
Summary of Project Future
All experiments are complete with papers published, in review, and in internal review prior to submission.
Management Implications of this Work
- Multivariate approaches are crucial to understanding ecological systems. Therefore, decision support tools are needed that allow managers to take into account a wide variety of factors, while weighing the costs and benefits of one strategy against another, before being able to make an informed decision concerning resource management. It is important to consider the interactions among multiple drivers. In these studies, there were important interactions among factors that would make it difficult to make robust predictions if a univariate approach was employed.
- Understanding how changing climate and other human caused disturbances impact the intensity of biological invasions is critically important. Managers must understand how invasions will respond to the ever-accelerating pace of anthropogenic global change to predict and prepare for changes that will occur in our lifetimes, and in generations to come.
At least for tallow tree invasions in coastal tallgrass prairies, anthropogenic nutrient additions appear to pose a particularly large risk.
Management Recommendations
- Techniques used to control invasive vegetation include biological, herbicidal, mechanical, or some combination of these. Although some use of herbicide is probably unavoidable for control of tallow tree when invasions are advanced because resprouting from stumps poses a danger for reinvasion, an integrated management program that includes prescribed burning, mowing, and selective herbicide applications is likely to be the most successful management strategy for preventing tallow tree invasions and limiting woody encroachment in coastal tallgrass prairies. Although this research did not focus on biological control of tallow tree, the low herbivore impacts we found in our studies do not contraindicate the introduction of biological control agents as a future method of control.
- Fire is an effective management technique for grassland invaders because the treatments that reduced woody encroachment also encouraged higher arthropod diversity. Thus, in the absence of concerns about particular species or information regarding the regional rarity of different taxa, preservation of high diversity per se may be a good strategy. The small scale of experimental burns used in these studies, however, suggests caution in extrapolating these results to larger scales.
Uses
- State agencies, coastal zone managers, and local resource managers can use information from this study for restoration planning.
- Data from this study can be included in decisionmaking models and ecological risk assessments.
- Because the dominant features of tallow tree invasions appear to be the same as for many other invasions, these results should give insights into the causes, consequences, and management of other invasions, especially for woody plants invading grasslands.
Fire Experiment
Status of Treatments. We laid out this experiment and began the semiannual fertilization treatments in spring 2000. We burned the annually burned plots in 2000, 2001, 2002, and 2003. Another set of plots was burned only in 2000. The tallow tree seed addition subexperiment was initiated in fall 1999 and spring 2000 and continued through the end of the 2003 growing season. We planted the tallow tree seedlings in spring 2000 and harvested them at the end of the 2002 growing season. We collected vegetation and soil samples at the end of the 2003 growing season.
Fire Temperature Data. In 2000 and 2001, we measured maximum heat at the ground surface inburned plots. In 2002, we measured maximum temperature at ground level, 0.5 m above the ground and 1 m above the ground.
Tallow Tree Seeds. We found very little germination in our tallow tree seed addition experiment. Even though approximately 30 percent of seeds germinated in greenhouse flats, less than one-quarter percent of seeds have germinated in any of the seed treatments. No frequency or timing of prescribed burns appears to facilitate tallow tree seed germination.
Vegetation Data. We collected data on relative cover by plant species in spring 2000, fall 2000, fall 2001, and fall 2002. We clipped vegetation at the end of the experiment to be used in C:N analyses and to determine plant biomass. At the same time, we collected soil samples for C:N analyses.
Tallow Tree Seedlings. Tallow tree invasion is accelerated by fertilization and reduced by annual burning. A single burn increased the success of tallow tree seedlings, which suggests that a single burn has the potential to favor tallow tree seedlings that germinate shortly after a fire. We have not been able to detect any significant effects of our mammal or insect exclusion subplot treatments. There does not appear to be any significant interaction of fire and herbivore damage.
Insect Data. Insect community diversity does not appear to be harmed by burn treatments. We have not been able to detect any direct negative effects of burning, whereas woody encroachment in unburned plots (especially with fertilization) is associated with low insect diversity. From the perspective of arthropod diversity, management of tallow tree is compatible with management to maintain animal diversity.
Ecosystem Results. Burning decreased the N in the vegetation in terms of percent N. Fertilization increased vegetation percent N. The total amount of aboveground N per m2 was higher in unburned plots because there were no changes in aboveground biomass, but there were increases in N concentration. Soil N did not depend on any treatments at any of the three soil depths in terms of percent N or total N per m2. The percent C in vegetation depended on fire (P < 0.05) with the highest percent C in unburned vegetation. These plots were dominated by woody plants. N fertilization increased the percent C in vegetation. The amount of C in vegetation increased with fertilization and decreased with burning.
Notable Changes in Procedure. The heterogeneity of the plots forced us to change our original vegetation sampling plan. We had originally planned to clip small areas of each plot. Instead we clipped areas that were 1 m x 3 m. We dried and weighed these large samples to get an accurate estimate of the vegetation biomass in each plot. We passed the samples through a rough sample grinder and took subsamples that we ground in a cyclone mill for nutrient analysis. Our soil sampling protocol also was modified. We originally planned to sample soils up to 50 cm depth. We found that there were no roots below 30 cm and sampled only to a depth of 38 cm (in three separate strata).
Flood Experiment
Status of Treatments. In the original proposal, we described an experiment with a two-level water treatment (control vs. flooded). We added another treatment in which water from extreme precipitation events is pumped out of the plots. The experimental design now addresses explicitly the range of variation that is present for the frequency of extreme precipitation events in the Gulf Coast in models of future climate. This is an expansion of the original objectives. We laid out this experiment and began the semiannual fertilization treatments in spring 2002. At this time we installed the water control structures and the subsurface pumps. We added tallow tree seeds for the recruitment limitation experiment in spring 2002. We planted tallow tree seedlings for the other subexperiment in spring 2002. In the last growing season we harvested seedlings, clipped vegetation, and collected vegetation and soil samples for C:N analyses.
Soil Moisture. We were able to lower soil moisture in the drought plots and increase soil moisture in the flood plots.
Seeds. We had extremely low seed germination—approximately one-quarter percent, which is similar to that which we observed in the fire experiment.
Seedlings. Fertilization increased tallow tree invasion intensity by increasing seedling survival, height growth, and biomass. Insect damage was low in all conditions, and insect suppression had little effect in any conditions.
Ecosystem Results. Vegetation mass was increased by fertilization in both of the modified rainfall treatments but not in the ambient moisture treatment. The amount of C and N in plants was increased by fertilization, especially in modified moisture plots. Soil C and N were independent to all treatments. These results suggest that tallgrass prairies are more likely to be impacted by nutrient loading, in terms of invasion severity and nutrient cycling, than by changes in the frequency of extreme rainfall events.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 30 publications | 9 publications in selected types | All 4 journal articles |
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Type | Citation | ||
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Bossdorf O, Auge H, Lafuma L, Rogers WE, Siemann E, Prati D. Phenotypic and genetic differentiation between native and introduced plant populations. Oecologia 2005;144(1):1-11. |
R828903 (Final) |
Exit Exit |
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Butterfield BJ, Rogers WE, Siemann E. Growth of Chinese tallow tree (Sapium sebiferum) and four native trees under varying water regimes. The Texas Journal of Science 2004;56(4):335-346. |
R828903 (Final) |
not available |
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Donahue C, Rogers WE, Siemann E. Effects of temperature and mulch depth on Chinese tallow tree (Sapium sebiferum) seed germination. The Texas Journal of Science 2004;56(4):347-356. |
R828903 (Final) |
not available |
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Donahue C, Rogers WE, Siemann E. Restoring an invaded prairie by mulching live Sapium sebiferum (Chinese tallow trees): effects of mulch on Sapium seed germination. Natural Areas Journal 2006;26(3):244-253. |
R828903 (Final) |
Exit Exit |
Supplemental Keywords:
animal, ecological effects, ecology, Gulf Coast, soil, prairie, tallgrass, tallgrass prairie, terrestrial, ecosystem protection, environmental exposure and risk, biology, chemical mixtures, human health, ecological indicators, ecological risk assessment, ecosystem, assessment, indicators, forestry, state, exploratory research, environmental biology, Chinese tallow, tallow tree invasions, abiotic, bioindicator, biopollution, carbon, invasive plants, invasive species, nitrogen,, RFA, Scientific Discipline, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Forestry, Ecological Effects - Environmental Exposure & Risk, Ecological Risk Assessment, Ecology and Ecosystems, Exp. Research/future, Futures, bioindicator, ecological effects, ecological exposure, Tallow Tree invasions, forest, carbon, Texas, biopollution, East Texas, prairie, tall grass prairie, abiotic, exploratory research, Texas (TX), tallgrass, terrestrial, terrestrial habitat loss, invasive species, invasive plants, Chinese Tallow, futures researchProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.