Urban Ecology最新文献

Urban trees provide both physical and esthetic benefits that are often related to the presence or absence of leaves. Periods of leaf development and leaf abscission and the duration of the leaf season were determined for twelve common urban tree species. Apple, Norway maple, and grey birch developed leaves earlier than other species. Green ash tended to lose leaves earlier than other species. Actual dates were not considered important, because of weather differences between years, but the order of phenologic stages should be similar each year. The average time during which crowns were 50% or more of full density ranged from 154 days for green ash to 192 days for apple. Most species that developed leaves early tended to retain them longer and to have long leaf durations. Green ash lost leaves first and had the shortest leaf season.

Both the amount of stormwater runoff and its rate of discharge are greatly influenced by urban development. But one of the many benefits afforded by urban vegetation is its amelioration of extremes in urban runoff regimes. Using data for a 6-h, 1-year storm event on surface cover types for the city of Dayton, OH, the specific role of vegetation in lessening urban impacts on runoff is assessed. Estimates of runoff are obtained for 77 of Dayton's 79 neighborhoods for three scenarios: one for existing cover types (artificial surfaces, exposed soil, herbaceous cover, and tree canopy cover); one in which trees are hypothetically removed; and a third that places exposed soil in vegetation and increases tree canopy cover to achievably greater amounts. For this intensive storm in which the role of vegetation is less readily apparent than for gentler storms, existing tree canopies alone work to lower potential runoff by about 7%. This could be increased to nearly 12% by modestly increasing canopy coverage of the land surface. Effects on potential peak runoff rates are found throughout the city. Results suggest that when these hydrologic impacts are coupled with tree and other vegetation impacts in the city, a city can justify increasing attention to planning and managing its urban vegetation resource.

Under clear skies, a mid-sized sugar maple tree (Acer saccharum Marsh.) reduced irradiance in its shade on a south-facing wall by about 80% when in leaf, and by nearly 40% when leafless. Reductions by a similar-sized London plane (Platanus acerifolia W.) were generally slightly smaller. The percentage reductions varied with the fraction (DR) of diffuse radiation, and could be approximated by regressions with DR² as the independent variable.

The significance of the irradiance reductions for building radiation climate was tested by using physical models of representative tree crowns (similar to sugar maple) and a representative house to evaluate shadow patterns, along with a mathematical model of average hourly solar radiation for an average day of each month. For a mid-sized tree with a 2-m clear bole located south of the house in a cloudy climate, the ratio of desirable insolation reductions during the cooling season to undesirable insolation reductions during the heating season was a low 0.74; whereas, with the same tree on the west, the ratio was a much more beneficial 4.6. In a sunny climate, the ratios were 0.55 and 3.3 for the tree on the south and west, respectively. A taller tree with a longer clear bole on the south produced more favorable ratios of cooling season to heating season insolation reductions than the tree with the short clear bole on the south.

Theories of human ecology provide a framework for integrating the natural and social sciences within the planning process. These theories can be incorporated into many inventory and analysis methods. The primary advantage of a human ecological perspective in planning is the increased feasibility of plans. Approaches for this type of planning are outlined and unique aspects are discussed.

Drinking has become a serious problem for as many as 15 million Americans. Previous research on this subject has shown that urban living is often strongly correlated with problem drinking, although the underlying causes are not well understood. This paper attempts to shed some light on these causes by identifying factors that are associated with a variety of indices of problem drinking. These relationships are examined in the context of four alternative models of alcohol use and abuse: these are a ‘blaming the victim model’; a ‘social opportunities model’; a ‘cultural integration model’; and a ‘distribution of consumption model’. The models are estimated using county-level data from Oklahoma for 1970, and the results indicate that although urban living is related to problem drinking, the case for the urban variable has probably been over-stated.

Thirty-eight sites, representing a wide range of habitat types in a representative urban area in Ohio, were sampled for their herbaceous vegetation. Ordination of the sites yielded several major axes: an inner city-rural dichotomy, a gradient related to soil compaction, and a gradient based on the nutrient status of the site. A classification of the sites by means of two-way indicator species analysis revealed the existence of three major community types (residual, managed, and ruderal) and a variety of minor community subtypes. Many of the communities, particularly those of a more ruderal nature. are American analogues of the plant communities common to urban areas in central Europe.