Twenty-five years of tree demography in a frequently burned oak woodland: implications for savanna restoration

"Twenty-five years of tree demography in a frequently burned oak woodland: implications for savanna restoration"

This article was published Dec. 9, 2021 in the journal Ecosphere. This is an open-access journal.

Read or download the article from the journal using this permanent URL (DOI) (https://doi.org/10.1002/ecs2.3844)

Abstract

Due to decades of fire suppression, much of the Upper Midwest savanna habitat has converted to oak woodland. In efforts to restore oak savanna habitat, fire has been re-introduced in many of these woodlands. A primary purpose of these burns is to kill the fire-sensitive mesophytic tree species, which had established themselves during the decades of fire suppression, reduce the number of understory trees, and preserve the larger more widely spaced oaks. It is clear from ongoing efforts that restoring oak savannas will require frequent fires over decades, but frequent fires over the long term can also threaten the desirable oaks. Long-term demographic studies at savanna restoration sites experiencing frequent fires are necessary to determine the extent to the frequent burns are supporting and/or confounding restoration goals. Results presented here are from a twenty-five-year demographic study of an Upper Midwest bur oak (Quercus macrocarpa) savanna/woodland experiencing frequent fire, during which both the survival and growth of more than 9000 trees were documented. Survival was assessed annually and growth every five years.

In the face of frequent fires, stem survival was found to be strongly associated with tree species, stem size, and stem growth. In turn, stem growth was found to be related to tree species and stem size. Decades of frequent burning in this oak woodland have substantially reduced the abundance of unwanted trees, specifically mesophytic species and Quercus ellipsoidalis, the latter which outcompetes Q. macrocarpa in the absence of fire. While Q. macrocarpa mid-sized (10–25 cm dbh) and large (≥25 cm dbh) trees are quite resistant to fire and now dominate the savanna landscape, they are not immune from fire-induced mortality.

It is recommended that the number and density of these trees should be re-evaluated every few years to ensure that desirable numbers remain. If necessary, fires should be suspended for a period of time. This will give smaller Q. macrocarpa trees time to grow larger and become more fire-resistant, thereby ensuring successive generations of Q. macrocarpa.

Citation

Davis, Mark A. "Twenty‐five years of tree demography in a frequently burned oak woodland: implications for savanna restoration." Ecosphere 12, no. 12 (2021): e03844.

Recoupling cross-scale interactions in tall fescue-invaded tallgrass prairie

"Recoupling cross-scale interactions in tall fescue-invaded tallgrass prairie"

This article was published online Oct. 11, 2021 in Landscape Ecology.

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Abstract

Context

Vegetation quantity and quality influence the degree to which large grazers shape grassland structural heterogeneity. Invasive plants threaten the function of cross-scale interactions that exist when multi-scale effects such as fire and grazing interplay to form patterns of grassland structural heterogeneity.

Objectives

We investigated how grazing pressure and time since fire at the patch scale influenced patch utilization and production as well as forage quality in experimental grassland pastures dominated by an invasive grass, tall fescue (Schedonorus arundinaceous). We also assessed the response of tall fescue utilization and production to interactive fire-and-grazing under moderate and heavy grazing pressure.

Methods

We collected data on vegetation quantity and quality over two grazing seasons to evaluate the role of fire and grazing across time in shaping structural heterogeneity among patches in invaded tallgrass prairie in Iowa, USA. We anticipated greater initial patch-scale utilization in patches burned for the first time in two years than patches not burned in two years in our experimental pastures. We expected that greater utilization in recently-burned patches would reduce tall fescue production, mostly where grazing pressure was highest.

Results

The contrast in the availability of live herbage between patches was half the level typical for native-dominated tallgrass prairie. Under increased grazing pressure, the interplay between fire and grazing did not result in greater broad-scale heterogeneity (among-patch heterogeneity) or an invasive grass reduction in experimental pastures. Yet, increased grazing early in the season did promote native-grass production in this invaded grassland landscape.

Conclusion

Our results suggest that the dominance of tall fescue mediates the lack of structural heterogeneity induced by patch-level prescribed fire and grazing. Unlike native perennial grasses, tall fescue provides access to forage in unburned patches through its low-stature growth form. Diminished cross-scale interactions through a weak coupling of fire and focal grazing in invaded tallgrass prairie may facilitate structural homogenization of fire-dependent grassland.

Keywords:     Cross-scale interactions; Forage quality; Herbivore-plant interactions; Prescribed fire; Pyric herbivory; Schedonorus arundinaceus

Citation

Raynor, Edward J., Heidi L. Hillhouse, Diane M. Debinski, James R. Miller, and Walter H. Schacht. "Recoupling cross-scale interactions in tall fescue-invaded tallgrass prairie." Landscape Ecology (2021): 1-17.

Variation in prescribed fire and bison grazing supports multiple bee nesting groups in tallgrass prairie

This article was published July 30, 2021 in Restoration Ecology.

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Abstract

Fire and grazing are historic ecosystem drivers of tallgrass prairie and both are used for restoration management today. The effects of these drivers on animal taxa are still incompletely resolved, especially for wild bees, a growing conservation and restoration priority. Fire and grazing could affect wild bee communities through structural changes to nest site availability via changes to soil conditions, vegetative cover, and availability of plant stems. Here, we sought to determine how different bee nesting groups are affected by the combination of fire and bison grazing management strategies. We grouped bee species by nesting substrate (ground, stem/hole, large cavity) because we expect the availability of these substrates to vary with the application of prescribed fire and grazing. We collected bees in restored and remnant high-quality tallgrass prairie and analyzed whether the proportion of each nesting group within the total bee community was predicted by fire and/or grazing. Ground-nesting bees reached their greatest proportion in bee communities immediately after prescribed fire, but declined proportionally over time since the last burn. Stem-/hole-nesting bees reached their highest proportion in the bee community with infrequent fire (6-year interval) and differed in their response to fire depending on the presence/absence of bison. Sampling year affected bee nesting groups and we found that nesting groups did not change in concert (i.e. different nesting groups had different good and bad years from each other). Our results show that spatiotemporal variation of prescribed fire and bison grazing is essential for conservation of multiple bee nesting groups.

Citation

Bruninga‐Socolar, Bethanne, Sean R. Griffin, Zachary M. Portman, and Jason Gibbs. "Variation in prescribed fire and bison grazing supports multiple bee nesting groups in tallgrass prairie." Restoration Ecology (2021): e13507.

Fires slow population declines of a long-lived prairie plant through multiple vital rates

This article was published June 2, 2021 in Oecologia.

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Abstract

In grasslands worldwide, modified fire cycles are accelerating herbaceous species extinctions. Fire may avert population declines by increasing survival, reproduction, or both. Survival and growth after fires may be promoted by removal of competitors or biomass and increasing resource availability. Fire-stimulated reproduction may also contribute to population growth through bolstered recruitment. We quantified these influences of fire on population dynamics in Echinacea angustifolia, a perennial forb in North American tallgrass prairie. We first used four datasets, 7–21 years long, to estimate fire’s influences on survival, flowering, and recruitment. We then used matrix projection models to estimate growth rates across several burn frequencies in five populations, each with one to four burns over 15 years. Finally, we estimated the contribution of fire-induced changes in each vital rate to changes in population growth. Population growth rates generally increased with burning. The demographic process underpinning these increases depended on juvenile survival. In populations with high juvenile survival, fire-induced increases in seedling recruitment and juvenile survival enhanced population growth. However, in populations with low juvenile survival, small changes in adult survival drove growth rate changes. Regardless of burn frequencies, our models suggest populations are declining and that recruitment and juvenile survival critically influence population response to fire. However, crucially, increased seedling recruitment only increases population growth rates when enough new recruits reach reproductive maturity. The importance of recruitment and juvenile survival is especially relevant for small populations in fragmented habitats subject to mate-limiting Allee effects and inbreeding depression, which reduce recruitment and survival, respectively.

Citation

Nordstrom, Scott W., Amy B. Dykstra, and Stuart Wagenius. "Fires slow population declines of a long-lived prairie plant through multiple vital rates." Oecologia (2021): 1-13.

Potential impacts of prescribed fire smoke on public health and socially vulnerable populations in a Southeastern U.S. state

This article was published Nov. 10, 2021 in Science of the Total Environment

https://doi.org/10.1016/j.scitotenv.2021.148712

Abstract

Prescribed fire is an essential tool for wildfire risk mitigation and ecosystem restoration in the Southeastern United States. It is also one of the region's largest sources of atmospheric emissions. The public health impacts of prescribed fire smoke, however, remain uncertain. Here, we use digital burn permit records, reduced-complexity air quality modeling, and epidemiological associations between fine particulate matter concentrations and multiple health endpoints to assess the impacts of prescribed burning on public health across Georgia. Additionally, we examine the social vulnerability of populations near high prescribed burning activity using a demographic- and socioeconomic-based index. The analysis identifies spatial clusters of burning activity in the state and finds that areas with intense prescribed fire have levels of social vulnerability that are over 25% higher than the state average. The results also suggest that the impacts of burning in Georgia can potentially include hundreds of annual morbidity and mortality cases associated with smoke pollution. These health impacts are concentrated in areas with higher fractions of low socioeconomic status, elderly, and disabled residents, particularly vulnerable to air pollution. Estimated smoke-related health incidence rates are over 3 times larger than the state average in spatial clusters of intense burning activity, and over 40% larger in spatial clusters of high social vulnerability. Spatial clusters of low social vulnerability experience substantially lower negative health effects from prescribed burning relative to the rest of the state. The health burden of smoke from prescribed burns in the state is comparable to that estimated for other major emission sectors, such as vehicles and industrial combustion. Within spatial clusters of socially-vulnerable populations, the impacts of prescribed fire considerably outweigh those of other emission sectors. These findings call for greater attention to the air quality impacts of prescribed burning in the Southeastern U.S. and the communities most exposed to fire-related smoke.

Citation

Afrin, Sadia, and Fernando Garcia-Menendez. "Potential impacts of prescribed fire smoke on public health and socially vulnerable populations in a Southeastern US state." Science of The Total Environment 794 (2021): 148712.

Effects of fire seasonality and intensity on resprouting woody plants in prairie-forest communities

This article was published May 28, 2021 in Restoration Ecology

https://doi.org/10.1111/rec.13451

Abstract

Woody plant expansion is one of the greatest contemporary threats to fire-dependent ecosystems. Reducing woody plant prevalence is often a primary objective of prescribed burns, yet little attention has been given to understanding the efficacy of burning to reduce their abundance. Fire intensity characteristics and plant phenology/physiology, which are sometimes presented as competing hypotheses, influence how woody plants respond to a fire event. Little work has been done in the prairie-forest region of the upper Midwest to understand how fire characteristics interact with woody species phenology and/or physiology. Using a controlled field experiment, we examined effects of timing (seasonality) and intensity (temperature and duration) of fires on top-kill and resprouting of three invasive woody plants in this region (common buckthorn, Rhamnus cathartica; bush honeysuckles, Lonicera spp.; and a native species, northern pin oak Quercus ellipsoidalis). Honeysuckles and pin oak burned in the spring dormant period, a common practice in the region, resulted in low levels of top-kill and high levels of resprouting. Burning during the late growing season yielded highest levels of top-kill and lowest levels of resprouting for honeysuckles and pin oaks. However, there was no apparent effect of season or fire intensity treatment for buckthorn stems. Under all treatment combinations, buckthorn was easily top-killed but resprouted prolifically. Collectively, most prescribed burning in the Midwest appears to be conducted during the least effective season (early growing season), when top-kill is reduced and/or resprouting most pronounced. Our results indicate that fire use could be better prescribed in this region for controlling woody plants.

Citation

Meunier, Jed, Nathan S. Holoubek, Yari Johnson, Tim Kuhman, and Brad Strobel. "Effects of fire seasonality and intensity on resprouting woody plants in prairie‐forest communities." Restoration Ecology: e13451.

Watershed and fire severity are stronger determinants of soil chemistry and microbiomes than within-watershed woody encroachment in a tallgrass prairie system

This manuscript was accepted Nov. 27, 2021 and published in FEMS Microbiology Ecology, fiab154

https://doi.org/10.1093/femsec/fiab154

Abstract

Fire can impact terrestrial ecosystems by changing abiotic and biotic conditions. Short fire intervals maintain grasslands and communities adapted to frequent, low-severity fires. Shrub encroachment that follows longer fire intervals accumulates fuel and can increase fire severity. This patchily distributed biomass creates mosaics of burn severities in the landscape—pyrodiversity. Afforded by a scheduled burn of a watershed protected from fires for 27 years, we investigated effects of woody encroachment and burn severity on soil chemistry and soil-inhabiting bacteria and fungi. We compared soils before and after fire within the fire-protected, shrub-encroached watershed and soils in an adjacent, annually burned, non-encroached watershed. Organic matter and nutrients accumulated in the fire-protected watershed but responded less to woody encroachment within the encroached watershed. Bioavailable nitrogen and phosphorus and fungal and bacterial communities responded to high severity burn regardless of encroachment. Low severity fire effects on soil nutrients differed, increased bacterial but decreased fungal diversity, and effects of woody encroachment within the encroached watershed were minimal. High severity burns in the fire-protected watershed led to a novel soil system state distinct from non-encroached and encroached soil systems. We conclude that severe fires may open grassland restoration opportunities to manipulate soil chemistry and microbial communities in shrub-encroached habitats.

Keywords

Fire severity and history, woody encroachment, tallgrass prairie ecosystem, soil bacteria and fungi, soil chemistry, alternate ecosystem states

Citation

Mino, Laura, Matthew R. Kolp, Sam Fox, Chris Reazin, Lydia Zeglin, and Ari Jumpponen. "Watershed and fire severity are stronger determinants of soil chemistry and microbiomes than within-watershed woody encroachment in a tallgrass prairie system." FEMS Microbiology Ecology (2021)

The combined effects of an extreme heatwave and wildfire on tallgrass prairie vegetation

This article was published in the Journal of Vegetation Science March 22, 2019.

https://doi.org/10.1111/jvs.12750

Abstract

Questions

Climate extremes are predicted to become more common in many ecosystems. Climate extremes can promote and interact with disturbances, but the combined effects of climate extremes and disturbances have not been quantified in many ecosystems. In this study, we ask whether the dual impact of a climate extreme and concomitant disturbance (wildfire) has a greater affect than a climate extreme alone.

Location

Tallgrass prairie in the Konza Prairie Biological Station, northeastern Kansas, USA.

Methods

We quantified the response of a tallgrass prairie plant community to a 2-year climate extreme of low growing-season precipitation and high temperatures. In the first year of the climate extreme, a subset of plots was burned by a growing-season wildfire. This natural experiment allowed us to compare community responses to a climate extreme with and without wildfire.

Results

In plots exposed to the climate extreme but not wildfire, community structure, diversity, and composition showed minor to insignificant changes, such as a 20% reduction in grass cover and a slight increase in species diversity. Plots exposed to both the climate extreme and wildfire underwent larger changes, including an 80% reduction in grass cover, 50% increase in forb cover, and increased plant diversity. Two years after the climate extreme, structural shifts in burned plots showed little sign of recovery, indicating a potentially lasting shift in plant community structure.

Conclusions

Our results suggest that community responses to climate extremes need to account for climate-related disturbances — in this case, high temperatures, drought and wildfire. This response diverged from our expectation that heat, drought, and an additional fire would favor grasses. Although growing-season wildfires in tallgrass prairie have been rare in recent decades, they will likely become more common with climate change, potentially leading to changes in grassland structure.

Citation

Ratajczak, Zak, Amber C. Churchill, Laura M. Ladwig, Jeff H. Taylor, and Scott L. Collins. "The combined effects of an extreme heatwave and wildfire on tallgrass prairie vegetation." Journal of Vegetation Science 30, no. 4 (2019): 687-697.

Exploring the Potential Role of Ants as Pollinators in a Tallgrass Prairie Following Varied Prescribed Burns

This article was published Nov. 10, 2021, in Transactions of the Kansas Academy of Sciences 

https://doi.org/10.1660/062.124.0301

Abstract

Prescribed burns are used to restore the herbaceous plant communities of tallgrass prairies. Unfortunately, land-use change has driven declines in animal communities that use that habitat, including insect pollinators. Flowering forbs in tallgrass prairies likely depend on insect pollinators for their reproduction, suggesting that restoration efforts may be limited if insect pollinators continue to decline. Further, prescribed burns may lead to the direct mortality of insect pollinators. We thus explore whether Formica ants may be able to compensate for the loss of insect pollinators in tallgrass prairies by monitoring visitation rates of ants and insect pollinators to the milkweed Asclepias tuberosa. Using replicated experimental plots burned at different times (summer, fall, or spring), we found that ants were robust to the timing of prescribed burns and that they averaged 50% of all visits across plots. The distribution of ants and other insect pollinators may be regulated by competitive interactions, as there was a negative relationship between the two potential pollinator communities: the more ant visits, the fewer pollinator visits, and vice versa. The high visitation rates suggest ants may potentially compensate, especially as competitive interactions decrease, but whether that may occur likely depends on their efficiency as pollinators, current plant features, or subsequent plant adaptations to utilize ants.

Citation

Eckols, Tucker, Bethany Roberton, Brandon Clark, and Darren Rebar. "Exploring the Potential Role of Ants as Pollinators in a Tallgrass Prairie Following Varied Prescribed Burns." Transactions of the Kansas Academy of Science 124, no. 3-4: 155-164.

Assessing the Impacts of Prescribed Fire and Bison Disturbance on Birds Using Bioacoustic Recorders

This article was published Oct. 18, 2021 in The American Midland Naturalist 

https://doi.org/10.1674/0003-0031-186.2.245

Abstract

Grassland bird responses to grazing and prescribed fire are species-specific and are primarily known from systems with cattle as the predominant grazer. There is less knowledge of how grazing by bison impacts grassland birds, especially in sites restored and reconstructed from row-crop agriculture. Working at a tallgrass prairie site consisting of restored and remnant prairie in the years following bison reintroduction and ongoing prescribed burning, we assessed overall species richness and the relative detection frequency of five focal species (Grasshopper Sparrow, Henslow's Sparrow, Dickcissel, Eastern Meadowlark, and Brown-headed Cowbird). We used stationary bioacoustics recorders to record the soundscape during the summer breeding season in areas with and without bison from 2016 to 2018. Species richness and the detection frequencies of our focal species were not influenced by bison disturbance. Grasshopper Sparrow and Dickcissel detection frequency increased slightly in response to prescribed fire, whereas Henslow's Sparrow detection frequency decreased. Time since sites were restored was a predominant factor that influenced the variation in detection frequency of Henslow's Sparrows and Eastern Meadowlarks, likely due to vegetation differences in restored versus remnant sites and each species' vegetation structure preferences. Brown-headed Cowbird detection frequency was unaffected by bison presence, prescribed fire, or time since restoration, but varied among sampling years. Our focal species showed no response to bison disturbance 4 y after the bison reintroduction. This suggests there could be a time-lag for a response or that these species will not respond to the bison reintroduction at this study site.

Citation

Herakovich, Heather, Nicholas A. Barber, and Holly P. Jones. "Assessing the Impacts of Prescribed Fire and Bison Disturbance on Birds Using Bioacoustic Recorders." The American Midland Naturalist 186, no. 2 (2021): 245-262.