Research Summaries

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Parsons, C. T., P. A. Momont, T. Delcurto, M. McInnis, and M. L Porath. 2003.
Cattle distribution patterns and vegetation use in mountain riparian systems. Journal of Range Management 56:334-341.

To quantify the effects of season of use on beef cattle distribution relative to the riparian area, 52 cow-calf pairs were used to evaluate 1) early summer grazing (mid-June to mid-July), and 2) late summer grazing (mid-August to mid-September) during the summers of 1998 and 1999. Within a block, cow-calf pairs were used during early summer were also used during late summer grazing periods. Pastures were stocked to achieve 50% utilization of herbaceous vegetation after a 28-day grazing trial. Livestock location and ambient air temperature were recorded hourly during two-four-day periods in each season of use. Locations were transcribed to a geographical information system for the study area.

Ocular vegetation utilization estimates, forage quality, and fecal deposits within 1 meter of the stream were recorded post grazing. During early summer, cattle were further from the stream (P< 0.01) than late summer, averaging 161 and 99 meters, respectively. Cows were observed closer (P< 0.01) to the stream when ambient air temperature were higher. Fecal deposits within 1 meter of the stream were similar (P= 0.13) following early and late-summer grazing. Forage quality varied (P< 0.01) between seasons, with early summer forages having lower dry matter, greater crude protein, lower fiber, and greater in situ dry matter digestibility compared with late summer forages. Utilization of riparian vegetation was lower and use of upland vegetation greater during early summer that late summer (P< 0.05). In summary, season of use affected cattle distribution relative to the riparian area, with late summer pastures having more concentrated use of riparian vegetation.

 

Miller, J. R., J. A. Wiens, N. T. Hobbs, and D. M. Theobald.
2003. Effects of human settlement on bird communities in lowland riparian areas of Colorado (USA). Ecological Applications 13:1041-1059.

Riparian areas in western North America have been characterized as centers of avian diversity, yet little is known about the ways that native species in streamside habitats are affected by development nearby. To address this issue, we examined patterns of habitat use by birds during the 1995-1997 breeding seasons at 16 lowland riparian sites representing an urban to rural gradient. As development increased, riparian woodlands tended to have fewer native trees and shrubs, less ground and shrub cover, higher tree densities, and greater canopy closures. Bird species richness also declined as urbanization increased in the surrounding landscape. Cannonical correspondence analysis (CCA) revealed that measures of settlement intensity best explain variation of habitat use by riparian birds, although some residual was accounted for by differences in woodland understory features. Migrant and low nesting species were associated with lower than average levels of development, whereas resident and cavity nesting species tended to increase with urbanization. In partial CCA analysis, however, local habitat variables explained twice the variation that measures of settlement did. Nearly half of all explained variation could be attributed to local and landscape variables simultaneously. For avian guilds based on migratory, nesting, and foraging behaviors, regression analyses showed that the best variables for explaining patterns of habitat use were usually those that reflected levels of urbanization, particularly at broad scales. When the effects of local habitat variation were removed, however, the best variables for explaining residual variation in habitat use tended to describe insects or seeds. These species were also most sensitive to human trail use. Our analyses indicated that bird communities and local habitat conditions in riparian areas were both affected by development in the surrounding landscape. In may be possible to mitigate the negative impacts of human settlement on native birds in streamside woodlands by maintaining or restoring vegetation structure and composition and by imposing limits on human recreational activity in these habitats.