Remove, Reduce or Manipulate?

Dillon Fogarty1, Casey Matzke2, Morgan L. Treadwell2, Carol Baldwin3, Jared Beaver4, Laura Goodman5, Torre Hovick6, Annie Overlin7, J. Derek Scasta8, Allison Thompson5, and Dirac Twidwell1

1University of Nebraska, 2Texas A&M AgriLife Extension Service, 3Kansas State University, 4Montana State University, 5Oklahoma State University, 6North Dakota State University, 7Colorado State University, and 8University of Wyoming

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Key Takeaways 

• Guidelines for brush management promoted by agencies and Extension in the past have been conflicting and ambiguous for several species. 

• Woody plant species most likely to cause an undesirable transition from grassland to woodland (state transitions) should be removed from Great Plains grasslands.

Eastern Redcedar | Honey Mesquite | Chinese Tallow | Ashe Juniper | Redberry Juniper 

• In grasslands, there is no ‘tolerable’ level of these woody species. Resource management planners should use updated management guidance based on new research to minimize grassland exposure to seeds of these species. New guidance can be found at https://cedarliteracy.unl.edu.

Remove, reduce or manipulate?

Confusion over whether to remove, reduce, or manipulate woody plants is one of the greatest shortcomings of brush management as a conservation practice in grasslands and rangelands. Past brush management guidance from Extension and agencies addressed the symptoms of woody encroachment, rather than the root cause of the problem [1]. Selective removal and manipulation of woody plants may achieve short-term and local objectives but does not contain the threat of aggressive woody invaders. Today brush management is increasingly expected to contribute to collective efforts to confront the loss of grasslands at county, state, and biome scales [2]. This requires clarity on which woody species warrant complete removal versus species whose presence can be reduced or manipulated to meet local and regional objectives without threat of grassland loss. This factsheet introduces a list of woody species that should always be removed from Great Plains grasslands given their potential to cause large-scale state transitions and negatively impact human well-being (Table 1).

What is the current brush management standard? 

The current standards for brush management are designed to achieve a desired plant community based on species composition, structure, density, and canopy cover or height. Removal, reduction, or manipulation of targeted woody plants, including those that are invasive and noxious, is accomplished by mechanical, chemical, burning, or biological methods applied singularly or in integrated combinations [3]. 2

Table 1. Classification of woody plant species based on their potential to cause state transitions at various scales in Great Plains grasslands and corresponding recommendations for brush management standards. The list for species that cause large-scale state transitions is comprehensive, whereas representative examples are provided for other categories. 

aReduction and manipulation not recommended. Other species like Rocky Mountain juniper (Juniperus scopulorum), oneseed juniper (Juniperus monosperma), and huisache (Vachellia farnesiana) are also known to cause large-scale state transitions, but have limited geographic distributions in the Great Plains. 

bRemoval generally recommended but exceptions occur based on site history/objectives. 

cDecisions to remove, reduce, or manipulate may all be appropriate depending on site/landscape objectives. 

Why does Extension guidance and brush management standards need to be changed?

The lack of clarity on whether to remove, reduce, or manipulate woody plants, as well as the species and circumstances in which different tactics apply, has led to ambiguity in how to use brush management in Great Plains grasslands. The result is widespread use of brush management tactics that leave behind aggressive woody invaders that drive rapid reinvasion and prevent sites from achieving the desired plant community [1,4]. In addition, the most aggressive invaders continue to be planted in grasslands due to a lack of clarity on the relative risk that native and non-native species pose to Great Plains grasslands. 

Why recommend the removal of species that cause large-scale state transitions? 

We recommend the removal of woody species that cause large-scale state transitions because these species disproportionately account for severe consequences of woody encroachment in Great Plains grasslands, including:

Lost forage production. Great Plains grasslands lose 22.4 million tons of forage for livestock every year to woody encroachment. This equates to an annual economic impact of $323 million and continues to increase every year [5,6]. 

• Heightened wildfire danger. The number and severity of wildfires are increasing due to the large-scale expansion of volatile woody fuels in the Great Plains [7-9].
• Reduced water quantity and quality. Woody encroachment in grasslands can reduce stream flow and aquifer recharge, while increasing pollutant and sediment concentrations [10,11]. 
• Higher risk of soil erosion. Woody encroachment reduces grassland plants and increases bare ground cover, resulting in a higher risk of erosion during rainfall events [12]. 
• Less funding for public education. School lands generate income from grazing leases to support public education. Woody encroachment decreases the profitability and future school funding from these grazing leases [13]. 
• Vector-borne disease risks. Woody encroachment increases the risk of vector-borne diseases like West Nile virus and Rocky Mountain spotted fever in grasslands [14].
• Increased allergen potential. Pollen from woody plants contribute to seasonal allergies and threaten human respiratory health [15]. 

In addition, large-scale state transitions from grassland to woodland are cost-prohibitive and difficult to reverse. In fact, there are no examples of restoring large-scale grasslands after transitioning to woody dominance, despite significant investments in brush management.

Summary

• This factsheet provides clarity to improve Extension and agency guidance on what species should be removed with brush management versus those species that can be reduced or manipulated in grasslands. 
• Woody species that should be removed from Great Plains grasslands are those that cause large-scale state transitions and negatively impact human well-being.
• Five woody species meet the criteria of causing large-scale state transitions and disproportionately account for the negative impacts and collapse of Great Plains grasslands due to woody encroachment. 
• There is no ‘tolerable’ level of woody species that cause large-scale transitions from grassland to woody dominance. Species like eastern redcedar and honey mesquite should not be managed like sagebrush and oak. Rangeland managers should use brush management differently for these species and act as soon as possible to remove them. 
• Apply Twidwell’s (2021) guide for understanding risk and vulnerability to sustain brush management investments, prevent reinvasion, and avoid long-term costs and consequences of woody transitions [19].

References

[1] S. R. Archer, K. W. Davies, T. E. Fulbright, K. C. Mcdaniel, B. P. Wilcox, and K. I. Predick, “Brush management as a rangeland conservation strategy: A critical evaluation,” in Conservation benefits of rangeland practices: assessment, recommendations, and knowledge gaps, D. D. Briske, Ed. US Department of Agriculture, Natural Resources Conservation Service, 2011, pp. 105–170.

[2] N.R.C.S. (NRCS)., “A framework for conservation action in the Great Plains Grassland Biome.,” Washington, D.C., 2021.

[3] N.R.C.S. US Department of Agriculture, “Natural Resources Conservation Service conservation practice standard: Brush management,” Washington, DC, USA, 2017.

[4] D. T. Fogarty, C. de Vries, C. Bielski, and D. Twidwell, “Rapid re-encroachment by Juniperus virginiana after a single restoration treatment,” Rangel. Ecol. Manag., vol. 78, pp. 112–116, Sep. 2021.

[5] S. L. Morford et al., “Herbaceous production lost to tree encroachment in United States rangelands,” J. Appl. Ecol., vol. 59, no. 12, pp. 2971–2982, Dec. 2022.

[6] D. T. Fogarty et al., “Rangeland production lost to woody encroachment in Great Plains grasslands,” Gt. Plains Grasslands Ext. Partnersh., no. GPGEP-UNL-01, 2023.

[7] V. M. Donovan, D. T. Fogarty, and D. Twidwell, “Spot-fire distance increases disproportionately for wildfires compared to prescribed fires as grasslands transition to Juniperus woodlands,” PLoS One, vol. 18, no. 4, p. e0283816, Apr. 2023.

[8] V. M. Donovan, C. L. Wonkka, D. A. Wedin, and D. Twidwell, “Land-use type as a driver of large wildfire occurrence in the U.S. Great Plains,” Remote Sens., vol. 12, no. 11, p. 1869, Jun. 2020.

[9] V. M. Donovan, C. L. Wonkka, and D. Twidwell, “Surging wildfire activity in a grassland biome,” Geophys. Res. Lett., vol. 44, no. 12, pp. 5986–5993, Jun. 2017.

[10] C. Zou et al., “Impact of eastern redcedar proliferation on water resources in the Great Plains USA—current state of knowledge,” Water, vol. 10, no. 12, p. 1768, Dec. 2018.

[11] Y. Kishawi, A. R. Mittelstet, T. E. Gilmore, D. Twidwell, T. Roy, and N. Shrestha, “Impact of Eastern Redcedar encroachment on water resources in the Nebraska Sandhills,” Sci. Total Environ., vol. 858, p. 159696, Feb. 2023.

[12] F. B. Pierson, J. D. Bates, T. J. Svejcar, and S. P. Hardegree, “Runoff and erosion after cutting western juniper,” Rangel. Ecol. Manag., vol. 60, no. 3, pp. 285–292, May 2007. 

[13] D. Lally et al., “Eastern redcedar invasion threatens funding for Nebraska’s public schools,” University of Nebraska, Beefwatch, Lincoln, Nebraska, Aug. 2016.

[14] S. R. Loss, B. H. Noden, and S. D. Fuhlendorf, “Woody plant encroachment and the ecology of vector-borne diseases,” J. Appl. Ecol., vol. 59, no. 2, pp. 420–430, Feb. 2022.

[15] M. Flonard, E. Lo, and E. Levetin, “Increasing Juniperus virginiana L. pollen in the Tulsa atmosphere: long-term trends, variability, and influence of meteorological conditions,” Int. J. Biometeorol., vol. 62, no. 2, pp. 229–241, Feb. 2018.

[16] L. L. Nackley, A. G. West, A. L. Skowno, and W. J. Bond, “The nebulous ecology of native invasions,” Trends Ecol. Evol., vol. 32, no. 11, pp. 814–824, Nov. 2017.

[17] P. Wells, “Postglacial vegetational history of the Great Plains,” Science., vol. 167, pp. 1574–1582, 1970.

[18] D. I. Axelrod, “Rise of the grassland biome, central North America,” Bot. Rev., vol. 51, no. 2, pp. 163–201, 1985.

[19] D. Twidwell, D. T. Fogarty, and J. R. Weir, “Reducing woody encroachment in grasslands: A risk and vulnerability guide,” Oklahoma Coop. Ext. Serv., no. E-1054, 2021.