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Federal Register / Vol. 86, No. 243 / Wednesday, December 22, 2021 / Proposed Rules
areas unsuitable for future occupancy by pygmy-owls. Buffelgrass is now fully naturalized in most of Sonora, southern Arizona, and some areas in central and southern Baja California BurquezMontijo et al. 2002, p. 131, and now commonly spreads without human cultivation Arriaga et al. 2004, pp.
15091511; Perramond 2000, p. 131;
Burquez et al. 1998, p. 26.
Similar issues occur in Texas.
Buffelgrass is now one of the most abundant nonnative grasses in South Texas, and a prevalent invasive grass within the range of the pygmy-owl.
During the 1950s, federal and state land management agencies promoted buffelgrass as a forage grass in South Texas Smith 2010, p. 113. Buffelgrass is very well adapted to the hot, semiarid climate of South Texas due to its drought resistance and ability to aggressively establish in heavily grazed landscapes Smith 2010, p. 113. Despite increasing awareness of the ecological damage caused by nonnative grasses, buffelgrass is still planted in areas affected by drought and overgrazing to stabilize soils and to increase rangeland productivity. Prescribed burning used for brush control typically promotes buffelgrass forage production in South Texas Hamilton and Scifres 1982, p.
11. Buffelgrass often creates homogeneous monocultures by outcompeting native plants for essential resources Lyons et al. 2013, p. 8.
Furthermore, buffelgrass produces phytotoxins in the soil that inhibit the growth of neighboring native plants Vo 2013, unpaginated. With regard to pygmy-owl habitat, the loss of trees and canopy cover and the creation of dense ground cover resulting from buffelgrass conversion reduces nest cavity availability, cover for predator avoidance and thermoregulation, and prey availability. Overall, buffelgrass is the dominant herbaceous cover on 10
million ha in southern Texas and northeastern Mexico Wied et al. 2020, p. 47.
The impacts of buffelgrass establishment and invasion are substantial for the pygmy-owl in the United States and Mexico because conversion results in the loss of important habitat features, particularly columnar cacti and trees that provide nest sites. Buffelgrass invasion and the subsequent fires eliminate most columnar cacti, trees, and shrubs of the desert Burquez-Montijo et al. 2002, p.
138. This elimination of trees, shrubs, and columnar cacti from these areas is a potential threat to the survival of the pygmy-owl in the northern part of its range, as these vegetation components are necessary for roosting, nesting,
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protection from predators, and thermal regulation. Invasion and conversion to buffelgrass also negatively affect the diversity and availability of prey species in these areas Franklin et al. 2006, p.
69; Avila-Jimenez 2004, p. 18; BurquezMontijo et al. 2002, pp. 130, 135.
Buffelgrass is adapted to dry, arid conditions and does not grow in areas with high rates of precipitation or high humidity, above elevations of 1,265 m 4,150 ft, or in areas with freezing temperatures. Areas that support pygmy-owls south of Sonora and northern Sinaloa typically are wetter and more humid, and the best available information does not indicate that buffelgrass is invading the southern portion of the pygmy-owls range.
Surveys completed in Sonora and Sinaloa in 2006 noted buffelgrass was present in Sonora and northern Sinaloa, but the more southerly locations were noted as sparse or moderate Van Devender and Dimmitt 2006, p. 7. As such, this nonnative species only affects the northern parts of the pygmy-owls range.
Agricultural Production and Wood Harvesting Agricultural development and wood harvesting can result in substantial impacts to the availability and connectivity of pygmy-owl habitat.
Conversion of native vegetation communities to agricultural fields or pastures for grazing has occurred within historical pygmy-owl habitat in both the United States and Mexico, and not only removes existing pygmy-owl habitat elements, but also can affect the longterm ability of these areas to return to native vegetation communities once agricultural activities cease. Wood harvesting has a direct effect on the amount of available cover and nest sites for pygmy-owls and is often associated with agricultural development. Wood harvesting also occurs to supply firewood and charcoal, and to provide material for cultural and decorative wood carvings.
In Arizona, although new agricultural development is limited, the effects to historical habitat are still evident. Many areas that historically supported mesoand xeri-riparian habitat have been converted to agricultural lands and associated groundwater pumping has affected the hydrology of these valleys Jackson and Comus 1999, pp. 233, 249.
These riparian areas are important pygmy-owl habitat, especially within drier upland vegetation communities like Sonoran desertscrub and semidesert grasslands.
Habitat fragmentation as a result of agricultural development has also
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occurred within Texas. Brush clearing, pesticide use, and irrigation practices associated with agriculture have had detrimental effects on the Lower Rio Grande Valley Jahrsdoerfer and Leslie 1988, p. 1. From the 1920s until the early 1970s, over 90 percent of pygmyowl habitat in the Lower Rio Grande Valley of Texas was cleared for agricultural and urban expansion Oberholser 1974, p. 452. The Norias Division of the King Ranch in southern Texas has been isolated by agricultural expansion, which has restricted pygmyowl dispersal Oberholser 1974. This has resulted in loss of pygmy-owl habitat connectivity between pygmyowl population groups in Texas and in Mexico. Historically, agriculture in Sonora, Mexico, was restricted to small areas with shallow water tables, but it had, nonetheless, seriously affected riparian areas by the end of the nineteenth century. For example, in the Rio Mayo and Rio Yaqui coastal plains, nearly one million ha 2.5 million ac of mesquite, cottonwood, and willow riparian forests and coastal thornscrub disappeared after dams upriver started to operate Burquez and Martinez-Yrizar 2007, p. 543.
Other Mexican states within the range of the pygmy-owl show similar potential for habitat loss. For example, in Tamaulipas, area under irrigation increased from 174,400 to 494,472 ha 431,000 to 1.22 million ac between 1998 and 2004, with an area of 668,872
ha 1.65 million ac equipped for irrigation. However, agricultural development in the States of Colima, Jalisco, Nayarit, and Nuevo Leon had substantial decreases in the amount of irrigated lands over the same period FAO 2007, unpaginated. Although land continues to be converted to agriculture within the geographic range of the pygmy-owl, we do not know if the areas being converted currently support pygmy-owl habitat. Continuing destruction of pygmy-owl habitat for agricultural production is not occurring with the same intensity throughout the range of the pygmy-owl, and the area in agricultural production may be declining in some parts of its southern range.
Wood harvesting is also a potential threat to pygmy-owl habitat. Ironwood Olneya tesota and mesquite Prosopis spp. are harvested throughout the Sonoran Desert for use as charcoal, fuelwood, and carving Burquez and Martinez Yrizar 2007, p. 545. For instance, by 1994, 202,000 ha 500,000
ac of mesquite had been cleared in northern Mexico to meet the growing demand for mesquite charcoal Haller 1994, p. 1. Unfortunately, woodcutters
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