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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules
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both the Northern and the Southern DPSs. These activities have resulted in decreases in population resiliency and species redundancy.
Woody Vegetation Encroachment As discussed in Background, habitat selected by lesser prairie-chicken is characterized by expansive regions of treeless grasslands interspersed with patches of small shrubs Giesen 1998, pp. 34; lesser prairie-chicken avoid areas with trees and other vertical structures. Prior to extensive EuroAmerican settlement, frequent fires and grazing by large, native ungulates helped confine trees like eastern red cedar to river and stream drainages and rocky outcroppings. The frequency and intensity of these disturbances directly influenced the ecological processes, biological diversity, and patchiness typical of Great Plains grassland ecosystems Collins 1992, pp. 2003
2005; Fuhlendorf and Smeins 1999, pp.
732, 737.
Following Euro-American settlement, increasing fire suppression combined with government programs promoting eastern red cedar for windbreaks, erosion control, and wildlife cover facilitated the expansion of eastern red cedar distribution in grassland areas Owensby et al. 1973, p. 256; DeSantis et al. 2011, p. 1838. Once a grassland area has been colonized by eastern red cedar, the trees are mature within 6 to 7 years and provide a plentiful source of seed so that adjacent areas can readily become infested with eastern red cedar.
Despite the relatively short viability of the seeds typically only one growing season, the large cone crop, potentially large seed dispersal ability, and the physiological adaptations of eastern red cedar to open, relatively dry sites help make the species a successful invader of grassland landscapes Holthuijzen et al.
1987, p. 1094. Most trees are relatively long-lived and, once they become established in grassland areas, require intensive management to remove to return areas to a grassland state.
Within the southernand westernmost portions of the estimated historical and occupied ranges of lesser prairie-chicken in Eastern New Mexico, Western Oklahoma, and the South Plains and Panhandle of Texas, honey mesquite is another common woody invader within these grasslands Riley 1978, p. vii; Boggie et al. 2017, entire.
Mesquite is a particularly effective invader in grassland habitat due to its ability to produce abundant, long-lived seeds that can germinate and establish in a variety of soil types and moisture and light regimes Lautenbach et al.
2017, p. 84. Though not as widespread
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as mesquite or eastern red cedar, other tall, woody plants, such as redberry or Pinchot juniper Juniperus pinchotii, black locust Robinia pseudoacacia, Russian olive Elaeagnus angustifolia, and Siberian elm Ulmus pumila can also be found in grassland habitat historically and currently used by lesser prairie-chicken and may become invasive in these areas.
Invasion of grasslands by opportunistic woody species causes otherwise usable grassland habitat to no longer be used by lesser prairie-chicken and contributes to the loss and fragmentation of grassland habitat Lautenbach 2017, p. 84; Boggie et al.
2017, p. 74. In Kansas, lesser prairiechicken are 40 times more likely to use areas that had no trees than areas with 1.6 trees per ac 5 trees per ha, and no nests occur in areas with a tree density greater than 0.8 trees per ac 2 trees per ha, at a scale of 89 ac 36 ha Lautenbach 2017, pp. 104142.
Similarly, within the Shinnery Oak Ecoregion, lesser prairie-chicken space use in all seasons is altered in the presence of mesquite, even at densities of less than 5 percent canopy cover Boggie et al. 2017, entire. Woody vegetation encroachment also contributes to indirect habitat loss and increases habitat fragmentation because lesser prairie-chicken are less likely to use areas adjacent to trees Boggie et al.
2017, pp. 7274; Lautenbach 2017, pp.
104142.
Fire is often the best method to control or preclude tree invasion of grassland. However, to some landowners and land managers, burning of grassland can be perceived as a highrisk activity because of the potential liability of escaped fire impacting nontarget lands and property.
Additionally, it is undesirable for optimizing cattle production and is likely to create wind erosion or blowouts in sandy soils.
Consequently, wildfire suppression is common, and relatively little prescribed burning occurs on private land. Often, prescribed fire is employed only after significant tree invasion has already occurred and landowners consider forage production for cattle to have diminished. Preclusion of woody vegetation encroachment on grasslands of the southern Great Plains using fire requires implementing fire at a frequency that mimics historical fire frequencies of 214 years Guyette et al.
2012, p. 330, further limiting the number of landowners able to implement fire in a manner that would truly preclude future encroachment.
Additionally, in areas where grazing pressure is heavy and fuel loads are
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reduced, a typical grassland fire may not be intense enough to eradicate eastern red cedar Briggs et al. 2002a, p. 585;
Briggs et al. 2002b, p. 293; Bragg and Hulbert 1976, p. 19 and will not eradicate mesquite.
As part of our geospatial analysis, we calculated the amount of woody vegetation encroachment in the current analysis area of the lesser prairiechicken. These calculations of the current analysis area do not include historical impacts of habitat loss that occurred outside of the current analysis area; thus, it likely underestimates the effects of historical woody vegetation encroachment rangewide on the lesser prairie-chicken. An additional limitation associated with this calculation is that available remote sensing data lack the ability to detect areas with low densities of encroachment, as well as areas with shorter trees; thus, this calculation likely underestimates lesser prairiechicken habitat loss due to woody vegetation encroachment. The identified areas of habitat impacted by woody vegetation are: About 5 percent of the total area in the Short-Grass/CRP
Ecoregion; about 2 percent of the total area in the Sand Sagebrush Ecoregion;
about 24 percent of the total area in the Mixed-Grass Ecoregion; and about 17
percent of the total area in the Shinnery Oak Ecoregion. Rangewide, we estimate about 3,071,000 ac 1,243,000 ha of grassland have been directly or indirectly impacted by the encroachment of woody vegetation, or about 18 percent of the total area. These percentages do not account for overlap that may exist with other features that may have already impacted the landscape. Further information, including total acres impacted, is available in the SSA report Service 2021, Appendix B; Appendix E, Figure E.5.
Woody vegetation encroachment is contributing to ongoing habitat loss as well as contributing to fragmentation and degradation of remaining habitat patches. The effects of woody vegetation encroachment are particularly widespread in the Shinnery Oak Ecoregion that makes up the Southern DPS as well as the Mixed-Grass Ecoregion of the Northern DPS. While there are ongoing efforts to control woody vegetation encroachment, the current level of woody vegetation on the landscape is evidence that removal efforts are being outpaced by rates of encroachment, thus we expect that this threat will continue to contribute to habitat loss and fragmentation, which has reduced population resiliency
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