In studies of forest fragmentatior~ a fundamental inconsistency exists in the distance criterion used to define the discreteness of forest fragmentx We examined three types of ubiquitous, narrow, forest-dividing corridors for effects that influence the relative abundance and community cornposition of forest.nesting birdg Fixed-radius (100-meter) point counts were conducted on 54 transects established along three width classes of corridors: unpaved roads (8 meters wide), paved roads (16 meters wide), and powerlines (23 meters wide). Transect locations were distributed equally among corridor edge forest margin 100 meters from corridor edge and forest interior 300 meters from corridor edge Forest-interior species of Neotropical migrants had significantly reduced relative abundances on edge transects along 16-and 23-meter corridorg compared with 8-meter corridors and with forest interior points along all three corridor-width classe£ At a landscape scal~ the consequences of corredores angostos divisorios del bosque pueden funcionar como trampas ecol6gicas para los migrantes neotropicales del interior del bosque. Sugerimos que estos corredores de amplia distribuci6n pueden ser poco conspicuos, pero contribuyentes importantes en la disminuci6n de las especies del interior de bosque en el este de Norte AmdricaL

We examined nest-site and nest-cavity characteristics for six species of cavitynesting birds in montane riparian and snowpocket aspen (Populus tremuloides) woodlan& in the northwestern Great Basin. Live trees and snags with DBH >24 cm were favored as nest sites by all species. Red-naped Sapsuckers (Sphy;apicus nuchalis) and Northern Flickers (Colaptes auratus) provided different sizes ofnest cavities for a suite of nonexcavator species. Flickers preferentially nested in snags; sapsuckers nested primarily in live trees, but used live trees and snags in proportion to their availabilities. Relative abundances of excavators and nonexcavators were associated positively with numbers of cavities. Nest-site variables overlapped extensively among species; Tree Swallows (Tachycineta bicolor) relied heavily on sapsuckers for provision of nest cavities, European Starlings (Sturnus vulgaris) and Mountain Bluebirds (Sialia currucoides) primarily used flicker-excavated cavities, and House Wrens (Troglodytes aedon) used nest cavities across the broadest range of nest-site characteristics. Compass orientation of nest-cavity entrances was strongly bimodal, with most facing east or southwest. Cavity entrances of species that foraged largely outside of riparian woodlands were oriented toward woodland edge, in contrast to nest cavities used by species that foraged largely within riparian woodlands. Snowpocket woodlands were much more extensive than riparian aspen, but birds strongly preferred riparian aspen stands as nesting habitats, presumably due to the scarcity of large aspen in snowpockets. Nest cavities appear to be a limiting resource with high potential for interspecific nest-site competition in these woodlands. Decades of livestock overuse and fire suppression have greatly diminished the availability of large aspen in riparian habitats throughout the region.

Riparian habitats are centers of biological diversity in arid and semiarid portions of western NorthAmerica, but despite widespread loss and degradation of these habitats there is little quantitative information concerning restoration of native riparian biota. We examined the recovery of a riparian meadow system in the context of long-term versus short-term release from livestock grazing. We compared the structure and dynamics of plant and avian communities on 1.5-ha plots inside a long-term ( Ͼ 30 years) livestock exclosure ("exclosure plots"), with adjacent plots outside the exclosure ("open plots") for 4 years following removal of livestock from open plots. Throughout the study, sedge cover, forb cover, and foliage height diversity of herbs were greater on exclosure plots; bare ground, litter cover, shrub cover, and shrub foliage height diversity were greater on open plots. Forb, rush, and cryptogamic cover increased on open plots but not on exclosure plots. Grass cover increased, whereas litter and bare ground decreased on all plots in conjunction with increased availability of moisture. Sedge cover did not change. Avian species richness and relative abundances were greater on exclosure plots; species composition differed markedly between exclosure and open plots ( Jaccard Coefficient ϭ 0.23-0.46), with exclosure plots dominated by wetland and riparian birds and open plots dominated by upland species. The appearance of key species of wet-meadow birds on open plots in the third and fourth years following livestock removal signaled the beginning of restoration of the riparian avifauna. We interpret the recovery of riparian vegetation and avifaunal composition inside the exclosure as a consequence of livestock removal, which led to a rise in the water table and an expansion of the hyporheic zone laterally from the stream channel. The lack of change in sedge and shrub cover on open plots suggests that restoration to a sedge-dominated meadow will not happen quickly.Hábitat y Recuperación de la Avifauna de Actividades de Pastoreo en un Sistema de Pradera Riparia en el Noroeste de Great Basin Resumen: Los hábitats riparios son centros de diversidad ecológica en porciones áridas y semiáridas del Oeste de Norte América, sin embargo, a pesar de la ampia pérdida y degradación de estos hábitats, existe muy poca información cuantitativa referente al restablecimiento de la biota riparia nativa. Examinamos la recuperación de un sistema de pradera riperia en el contexto de su liberación de actividades de pastoreo a largo plazo contra uno a corto plazo. Comparamos la estructura y dinámica de comunidades de plantas y aves en lotes de 1.5 ha. dentro de una zona exluyente de ganado por largo plazo (30 años) "lotes excluyentes" con lotes adyacentes fuera de la zona de exclusión "lotes abiertos" durante cuatro años después de que el ganado fuera removido de los lotes abiertos. A lo largo del estudio, la cobertura de ciperáceas, cobertura de hierbas forrajeras (diferentes a pasto) y la diversidad de la altura del follage de las hie...

Riparian habitats are centers of biological diversity in arid and semiarid portions of western NorthAmerica, but despite widespread loss and degradation of these habitats there is little quantitative information concerning restoration of native riparian biota. We examined the recovery of a riparian meadow system in the context of long-term versus short-term release from livestock grazing. We compared the structure and dynamics of plant and avian communities on 1.5-ha plots inside a long-term ( Ͼ 30 years) livestock exclosure ("exclosure plots"), with adjacent plots outside the exclosure ("open plots") for 4 years following removal of livestock from open plots. Throughout the study, sedge cover, forb cover, and foliage height diversity of herbs were greater on exclosure plots; bare ground, litter cover, shrub cover, and shrub foliage height diversity were greater on open plots. Forb, rush, and cryptogamic cover increased on open plots but not on exclosure plots. Grass cover increased, whereas litter and bare ground decreased on all plots in conjunction with increased availability of moisture. Sedge cover did not change. Avian species richness and relative abundances were greater on exclosure plots; species composition differed markedly between exclosure and open plots ( Jaccard Coefficient ϭ 0.23-0.46), with exclosure plots dominated by wetland and riparian birds and open plots dominated by upland species. The appearance of key species of wet-meadow birds on open plots in the third and fourth years following livestock removal signaled the beginning of restoration of the riparian avifauna. We interpret the recovery of riparian vegetation and avifaunal composition inside the exclosure as a consequence of livestock removal, which led to a rise in the water table and an expansion of the hyporheic zone laterally from the stream channel. The lack of change in sedge and shrub cover on open plots suggests that restoration to a sedge-dominated meadow will not happen quickly. Hábitat y Recuperación de la Avifauna de Actividades de Pastoreo en un Sistema de Pradera Riparia en el Noroeste de Great BasinResumen: Los hábitats riparios son centros de diversidad ecológica en porciones áridas y semiáridas del Oeste de Norte América, sin embargo, a pesar de la ampia pérdida y degradación de estos hábitats, existe muy poca información cuantitativa referente al restablecimiento de la biota riparia nativa. Examinamos la recuperación de un sistema de pradera riperia en el contexto de su liberación de actividades de pastoreo a largo plazo contra uno a corto plazo. Comparamos la estructura y dinámica de comunidades de plantas y aves en lotes de 1.5 ha. dentro de una zona exluyente de ganado por largo plazo (30 años) "lotes excluyentes" con lotes adyacentes fuera de la zona de exclusión "lotes abiertos" durante cuatro años después de que el ganado fuera removido de los lotes abiertos. A lo largo del estudio, la cobertura de ciperáceas, cobertura de hierbas forrajeras (diferentes a pasto) y la diversidad de la altura del follage de las hie...

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