Declines in riparian willow (Salix spp.) communities in Rocky Mountain National Park, Colorado, USA , coincident with a large increase in elk (Cervus elaphus L.) populations, has raised concerns about the future of willow communities. To identify possible constraints on willow establishment in two heavily browsed riparian areas, in 2000 and 2001, we examined seed dispersal phenology, germinability, and the spatial patterns of aerial seed rain, quantified the effects of soil surface relief, texture, and moisture on seed entrapment, and examined natural patterns of seedling emergence in relation to seed source proximity. All species dispersed seeds following peak streamflow and exhibited high germination rates (85%–99%). Total seed rain differed between years, although broad spatial patterns were similar. Seed rain density as high as 7650 seeds/m2 occurred in reference areas but declined by over two orders of magnitude in heavily disturbed areas and by >90% within 200 m of seed sources. Seed entrapment rates varied significantly with soil moisture and surface relief, but not with texture, and were low (<30%) regardless of treatment. Seedling density declined with distance from seed sources, suggesting that propagule availability may limit initial seedling establishment. Without a change in elk population or behavior, or intervention by park managers, degradation of willow communities will likely continue.Key words: Salix, riparian, dispersal, ungulates, elk.

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To help inform urban water conservation and planning, we evaluated spatial patterns and correlative relationships among physical land cover properties, socioeconomic and demographic characteristics, and single-family outdoor residential water use in Aurora, Colorado, a rapidly-growing suburb in the semi-arid Colorado Front Range. Using high resolution land cover maps and lidar-derived vertical structural data, we quantified land cover composition and vertical structural characteristics for detached, single-family residential parcels. These data were combined with socioeconomic and demographic datasets from the 2010 US Census and local government agencies and used in Random Forest analyses of outdoor water use estimated from residential water meter records, with separate analyses conducted using parcels and census block groups as sampling units. Conditional variable importance measures from Random Forest analyses and comparisons of the predictive accuracy of models developed using subsets of explanatory variables were used to assess the relative importance of physical and socioeconomic variables in predicting outdoor water use. Models developed using the subset of land cover variables had the highest predictive accuracy, followed by vertical structural variables, and lastly, socioeconomic/demographic variables. At both the parcel and census block group scale, there was significant spatial clustering in outdoor water use as indicated by various spatial statistical analyses. Our approach demonstrates the value of high resolution land cover and structure data for understanding urban water use patterns and can be used for targeting water conservation efforts.