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Traditionally, exurban lands in Colorado have been subdivided into a grid of parcels ranging from 2 to 16 ha. From an ecological perspective, this dispersed pattern of development effectively maximizes the individual influence of each home on the land. Clustered housing developments, designed to maximize open space, are assumed to benefit plant and wildlife communities of conservation interest. They have become a popular alternative for rural development despite the lack of empirical evidence demonstrating their conservation benefits. To better inform rural land-use planning, we evaluated clustered housing developments by comparing their spatial pattern with that of dispersed housing developments and by comparing their conservation value with that of both dispersed housing developments and undeveloped areas in Boulder County, Colorado. We used four indicators to assess conservation value: (1) densities of songbirds, (2) nest density and survival of ground-nesting birds, (3) presence of mammals, and (4) percent cover and proportion of native and non-native plant species. Clustered and dispersed housing developments did not differ on the majority of variables we examined. Both types of housing development had significantly higher densities of non-native and human-commensal species and significantly lower densities of native and human-sensitive species than undeveloped areas. More rigorous ecological guidelines and planning on a regional scale may help create clustered developments with higher conservation value.

Private lands in the American West are undergoing a land-use conversion from agriculture to ex- urban development, although little is known about the ecological consequences of this change. Some nongov- ernmental organizations are working with ranchers to keep their lands out of development and in ranching, ostensibly because they believe biodiversity is better protected on ranches than on exurban developments. However, there are several assumptions underlying this approach that have not been tested. To better inform conservation efforts, we compared avian, mesopredator, and plant communities across the gradient of inten- sifying human uses from nature reserves to cattle ranches to exurban developments. We conducted surveys at randomly selected points on each type of land use in one Colorado watershed between May and August of 2000 and 2001. Seven bird species, characterized as human commensals or tree nesters, reached higher den- sities (all p � 0.02) on exurban developments than on either ranches or reserves. Six bird species, character- ized as ground and shrub nesters, reached greater densities (all p � 0.015) on ranches, reserves, or both of these types of land use than on exurban developments. Domestic dogs ( Canis familiaris ) and house cats ( Felis catus ) were encountered almost exclusively on exurban developments, whereas coyotes ( Canis latrans ) were detected more frequently ( p � 0.047) on ranchlands than exurban developments. Ranches had plant com- munities with higher native species richness and lower non-native species richness and cover than did the other types of land use (all p � 0.10). Our results support the notion that ranches are important for protect- ing biodiversity and suggest that future conservation efforts may require less reliance on reserves and a greater focus on private lands. Biodiversidad a lo largo de un Gradiente de Uso de Suelo Rural Resumen: Los terrenos privados del oeste de America estan experimentando una conversion del suelo de un uso agricola a un uso urbano, aunque se conoce poco acerca de las consecuencias ecologicas de este cambio. Algunas organizaciones no gubernamentales estan trabajando con granjeros para que sus tierras permanez- can sin urbanizar, ostensiblemente porque piensan que la biodiversidad se protege mejor en tierras rurales que en urbanizaciones. Sin embargo, hay varios supuestos subyacentes a este modelo que no han sido com- probadas. Para informarnos mejor sobre los esfuerzos de conservacion, comparamos comunidades de aves, mesodepredadores y plantas a lo largo del gradiente de intensidad de uso humano de reservas naturales, granjas y zonas de urbanizacion. Realizamos muestreos en sitios seleccionados aleatoriamente en cada uso de suelo en una cuenca del Colorado entre mayo y agosto de 2000 y 2001. Siete especies de aves, caracteriza- das como comensales humanos o nidificantes arboreos, alcanzaron densidades mas altas (todas p � 0.02) en urbanizaciones nuevas que en granjas o reservas. Seis especies de aves, caracterizadas como nidificantes de suelo y arbustos, alcanzaron densidades mayores (todas p � 0.015) en granjas, reservas o usos mixtos del suelo que en las nuevas urbanizaciones. Se encontraron perros ( Canis familiaris ) y gatos ( Felis catus ) domes- ticos casi exclusivamente en nuevas urbanizaciones, mientras que se detectaron coyotes ( Canis latrans ) mas frecuentemente ( p � 0.047) en granjas que en nuevas urbanizaciones. Las granjas tenian comunidades de plantas con mayor riqueza de especies nativas y menor riqueza y cobertura de especies no nativas que en to- dos los demas usos de suelo (todas p � 0.10). Nuestros resultados apoyan la nocion de que las granjas son im

Residential development is occurring at unprecedented rates in the Rocky Mountain region of the United States, with unknown ecological consequences. We conducted our research in exurban development in Pitkin County, Colorado, between May and June in 1998 and 1999. Unlike suburban development, exur- ban development occurs beyond incorporated city limits, and the surrounding matrix remains the original ecosystem type. We surveyed songbirds and medium-sized mammals at 30, 180, and 330 m away from 40 homes into undeveloped land to examine the effect of houses along a distance gradient, and in developments of two different housing densities as well as undeveloped sites to examine the effect of housing density. We placed bird species into one of two groups for the house-distance effect: (1) human-adapted species, birds that occurred in higher densities close to developments and lower densities farther away and (2) human-sensitive species, birds that occurred in highest densities farthest from homes and in lowest densities close to develop- ment. For both groups, densities of individual species were statistically different between the 30- and 180-m sites. Six species were classified as human-adapted, and six were classified as human-sensitive for the house- distance effect. Dogs ( Canis familiaris ) and house cats ( Felis domesticus ) were detected more frequently closer to homes than farther away, and red foxes ( Vulpes vulpes ) and coyotes ( Canis latrans ) were detected more fre- quently farther away from houses. With respect to the effect of housing density, most avian densities did not differ significantly between high- and low-density development but were statistically different from undevel- oped sites. Six species were present in higher densities in developed areas, and eight species were present in higher densities in undeveloped parcels. Similar results were found for mammalian species, with dogs and cats detected more frequently in high-density developments and red foxes and coyotes detected more fre- quently in undeveloped parcels of land. From an ecological standpoint, it is preferable to cluster houses and leave the undeveloped areas in open space, as opposed to dispersing houses across the entire landscape.

We compared the plant communities on cliffs used for rock climbing with cliffs not used for climbing. Eighteen cliffs in Joshua Tree National Park, California (six each with no climbing, moderate climbing, and intensive climbing) were sampled for plant diversity and community structure. Plants were sampled on cliff faces and at the base of cliffs. The dominant taxa were Quercus cornelius-mulleri, Ericameria cuneata var. cuneata, and Bromus madritensis ssp. rubens. Plant species richness on cliff faces and at the base of cliffs was greater for cliffs with no evidence of climbing and lowest for cliffs with intensive use. Numbers of individual plants decreased with increased climbing use. Trees, shrubs, forbs, and cacti had greater relative abundances on cliffs without climbing than on cliffs with climbing. Plant cover on cliff faces decreased with increased climbing use. Adaptive management will be necessary to minimize the deleterious effects of rock climbing on plant communities associated with cliffs. Efectos de Alpinismo sobre las Comunidades de Plantas en Acantilados en el Parque Nacional Joshua Tree, California Comparamos las comunidades de plantas en acantilados usados para alpinismo contra acantilados no usados para esta actividad. Dieciocho acantilados del Parque Nacional Joshua Tree, California (seis con alpinismo, seis con alpinismo moderado y seis sin alpinismo) fueron muestreados para determinar la diversidad de plantas y la estructura de la comunidad. Las plantas fueron muestreadas en las caras y bases de los acantilados. Los taxones dominantes fueron Quercus cornelius-mulleri, Ericameria cuneata var. cuneata y Bromus madritensis ssp. rubens. La riqueza de especies en las caras y bases de los acantilados fue mayor en aquellos sin evidencia de alpinismo y menor para aquellos acantilados con uso intensivo. Los numeros individuales de plantas disminuyeron con un incremento en el uso para alpinismo. Arboles, arbustos, pastos y cactus tuvieron una abundancia relativa mayor en acantilados sin alpinismo que en aquellos con alpinismo. La cobertura de las plantas en las caras de los acantilados disminuyo con un incremento en el alpinismo. Sera necesario emplear un manejo adaptable para minimizar los efectos daninos del alpinismo en roca sobre comunidades de plantas asociadas con acantilados.

Wuerthner ( 1994) recently contrasted the environmental effects of agriculture and rural subdivisions and concluded that "Agriculture-both livestock production and farming-rather than being compatible with environmental protection has had a far greater impact on the western landscape than all the subdivisions, malls, highways, and urban centers combined." We suggest, however, that subdivisions can have profound impacts on the biodiversity of rural areas, particularly when they are adjacent to protected natural areas. In addition, we submit that much of the information required to evaluate the relationships between biodiversity and land-use patterns associated with agriculture and rural housing developments is still lacking. One of us recently completed a study of private landuse change in the Colorado mountains (Riebsame et al. 1994). The region's physical and political landscape limits private lands mostly to valley-bottom corridors that separate blocks of federal lands, including wilderness units. An assessment of the private-land corridors revealed repetitive patterns of land subdivision with negative ecological implications. Dense development (commercial strips, condominiums, and infrastructure) tended to encroach on riparian areas. Dispersed residential development occurred across valley bottoms and slopes, especially riparian areas, at forest edges (such as attractive building sites in aspen groves), and in the interior of coniferous forests (such as subdivisions carved from lodgepole pine [Pinus contorta] forests). Most of this dispersed development was not contiguous with existing town sites and other previous developments. A detailed mapping of subdivisions and roads in the East River Valley (from above Gunnison to Crested Butte, Colorado) showed that meadow, grassland, riparian, and sagebrush (Artemisia spp.) plant communities