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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules
TABLE 4ESTIMATED AREAS OF CURRENT DIRECT AND INDIRECT IMPACTS, BY IMPACT SOURCE, AND THE PROPORTION
OF THE TOTAL AREA OF THE SHORT-GRASS/CRP ECOREGION ESTIMATED TO BE IMPACTED SEE TABLE 1 FOR TOTALSContinued Impacts are not necessarily cumulative because of overlap of some impacted areas by more than one impact source.
Short-Grass/CRP Ecoregion Impact sources Wind Energy Development
Transmission Lines
Woody Vegetation Encroachment
Roads

145,963
436,650
284,175
1,075,931

Total Ecoregion Area

Based on population reconstruction methods, the mean population estimate for this ecoregion increased from a minimum of about 14,000 males in 2001
and peaked at about 21,000 males in 2011 Hagen et al. 2017, pp. 810; see also Service 2021, Figure 3.3.
Aerial surveys since 2012 indicate that the Short-Grass/CRP Ecoregion Figure 3.4 has the largest population size Nasman et al. 2020, p. 21 of the four ecoregions. Average estimates from 2015 to 2020 are 16,957 birds 90
percent CI: 13,605, 35,350, making up
Percent of ecoregion
Acres
about 62 percent of the rangewide lesser prairie-chicken total Table 2.
Much of the Mixed-Grass Ecoregion was originally fragmented by homesteading, which subdivided tracts of land into small parcels of 160320 ac 65130 ha in size Rodgers 2016, p.
17. As a result of these small parcels, road and fence densities are higher compared to other ecoregions and, therefore, increase habitat fragmentation and pose higher risk for collision mortalities than in other ecoregions Wolfe et al. 2016, p. 302.

2
7 5
17

6,298,014

Fragmentation has also occurred due to oil and gas development, wind energy development, transmission lines, highways, and expansion of invasive woody plants such as eastern red cedar.
A major concern for lesser prairiechicken populations in this ecoregion is the loss of grassland due to the rapid westward expansion of the eastern redcedar NRCS 2016, p. 16. Oklahoma Forestry Services estimated the average rate of expansion of eastern red-cedar in 2002 to be 762 ac 308 ha per day Wolfe et al. 2016, p. 302.

TABLE 5ESTIMATED AREAS OF CURRENT DIRECT AND INDIRECT IMPACTS, BY IMPACT SOURCE, AND THE PROPORTION
% OF THE TOTAL AREA OF THE MIXED-GRASS ECOREGION ESTIMATED TO BE IMPACTED SEE TABLE 1 FOR TOTALS
Impacts are not necessarily cumulative because of overlap of some impacted areas by more than one impact source.
Mixed-Grass Ecoregion Impact sources Cropland Conversion
Petroleum Production
Wind Energy Development
Transmission Lines
Woody Vegetation Encroachment
Roads

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Total Ecoregion Area

Using our geospatial analysis, we were able to explicitly account for habitat loss and fragmentation and quantify the current condition of this ecoregion for the lesser prairie-chicken.
Of the sources of habitat loss and fragmentation that have occurred, encroachment of woody vegetation had the largest impact, with conversion to cropland, roads, and petroleum production also having significant impacts on land cover in this ecoregion Table 5. Based on our nearest neighbor analysis, we estimated there are approximately 994,483 ac 402,453 ha or 12 percent of the ecoregion, that is potentially available for use by lesser prairie-chicken Table 1.

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The Mixed-Grass Ecoregion historically contained the highest lesser prairie-chicken densities Wolfe et al.
2016, p. 299. Based on population reconstruction methods, the mean population estimate for this ecoregion in the 1970s and 1980s was around 30,000
males Hagen et al. 2017, pp. 67.
Population estimates declined in the 1990s and peaked again in the early 2000s at around 25,000 males, before declining and remaining at its lowest levels, <10,000 males in 2012, since the late 2000s Hagen et al. 2017, pp. 67.
Aerial surveys from 2012 through 2020 Service 2021, Figure 3.6 indicate this ecoregion has the second highest population size of the four ecoregions
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Percent of ecoregion
Acres
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1,094,688
859,929
191,571
576,713
2,047,510
1,732,050

13
10
2 7
24
20

8,527,718

Nasman et al. 2020, p. 21. Average estimates from 2015 to 2020 are 6,135
birds 90 percent CI: 1,719, 11,847, representing about 22 percent of the rangewide total Table 2. Results show minimal variation in recent years.
Prairies of the Sand Sagebrush Ecoregion have been influenced by a variety of activities since European settlement of the Great Plains. Much of these grasslands have been converted to other land uses such as cultivated agriculture, roads, power lines, petroleum production, wind energy, and transmission lines. Some areas have also been altered due to woody vegetation encroachment. Only 26 percent of historical sand sagebrush prairie is
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