Urban Ecology最新文献

Breeding bird communities were compared in three suburbs: a 70-year-old area of larhe houses along streets shaded by mature trees (MT), primarily oaks (Quercus) and elms (Ulmus); a 15-year-old area built upon open agricultural land with young maple (Acer) street trees (YT); and a 15-year-old area on which houses were built in small clearings within a second-growth oak-pine (Quercus-Pinus) woodland (OP). Bird censuses each year for 5 years revealed that YT supported the lowest total avian density of the three suburbs; OP supported the greatest variety and total density of insectivores, and the lowest number of ground-gleaning omnivores; and MT supported the highest total avian density, comprised primarily of ground-foraging seed eaters and omnivores. Among nesting guilds, OP contained the fewest ground/herb nesters, and MT the most. Also, OP had the fewest shrub nesters, and MT the most. Tree cavity and twig nesters were significantly more numerous in OP, and tree branch nesters fewer in YT than in either OP or MT. Analyses of habitat structure revealed that shrub maturity is more important than numbers of shrubs, and that planted trees, no matter how mature or abundant, do not replace natural forest stands as habitat for most insectivorous species.

Eleven studies of urban forest function are introduced in two general categories: factors influencing the evolution of the urban forest, and effects of the urban forest on human and faunal environments.

Relationships between street-tree characteristics, including habitat features, and use by urban birds were investigated from May to July 1980 in State College, Pennsylvania. Bird presence or absence was sampled in 1278 individual street trees of 24 species. Log-linear analysis of tree species, height class and bird occurence determined that pin oak (Quercus palustris), American elm (Ulmus americana) and honeylocust (Gleditsia triacanthos var. inermis) were used more frequently by birds (P<0.05), and there was a linear relationship between height class and bird occurrence. Relative use of tree species by a group of three exotic bird species was highly correlated with that of the remaining native bird species (P<0.01). Logistic-regression analyses of bird occurrence on 10 habitat variables and tree characteristics showed that tall street trees located in areas with little other deciduous tree cover were more attractive to both the native and exotic bird groups (P<0.05). In addition, native birds were observed more often in trees planted in residential areas with little vehicular traffic, whereas exotic birds were more frequent in business areas with greater traffic volume. Because of the interest in bird watching among urban residents, municipal arborists should be aware that street trees may differin their attractiveness to birds.

A 2-year study of the mammals in Syracuse, NY revealed the presence of 17 non-domestic species. Of the 13 species trapped in 20 greenspaces (Parks, greenbelts, private woodlots, etc.), white-footed mice (Peromyscus spp.), meadow voles (Microtus pennsylvanicus) and gray squirrels (Sciurus carolinensis) comprised 65% of the 1040 captures from 13 344 functional trapnights of effort. Species richness ranged from 3 to 9 species captured in the greenspaces, that varied in size from 2 to 22 ha. Three interspecific associations were identified, but several species were associated with similar habitat features. Using Spearman's rank correlation (univariate) and canonical correlation (multivariate), capture success of each species and various combinations were correlated with one or more of 31 physical, biotic or cultural variables obtained from on-site measurements, aerial photographs, and Bureau of Census reports. Generally, variables measured from aerial photographs accounted for more of the variability in mammal abundance among areas than did detailed measurements of on-site physical or biotic conditions. Area of water, area of grass or field, area of pavement or gravel, and total greenspace often were significant, whereas specific characteristics of a vegetative type such as size-class of trees, diversity of herb layer, or percentage of canopy closure in the understory had little effect on the mammalian community. Mammals that can exist in urbanized areas apparently respond to the mosaic of habitats and land uses in the general area rather than those conditions found within specific greenspaces.

A regression model was able to predict decline classes on the basis of crown density, small dead limbs and crown shape. The filtering of increment core data revealed three growth trends. One growth trend, termed responsive, generally followed fluctuations in climate. A second, termed nonresponsive, decreased over the time regardless of climatic fluctuations. A less common type, intermediate, showed no change in growth over the 20-year study period. The responsive growth trend was associated with the most healthy appearing trees. This early stage of decline was generally found in trees which had been subjected to root injuries following a drought stress period. Trees with advanced decline today had significantly reduced growth rates 15–20 years ago, indicating that Norway maple decline is a long-term multiple stress process.

Characteristics of presettlement forests at Menlo Park and South Lake Tahoe, CA were compared with the present characteristics of the urban forests in these cities. Urbanization of forest types in both cities led to decreased tree density (in Menlo Park from 279 to 43/ha; in South Lake Tahoe from 761 to 373/ha), decreased tree cover (in Menlo Park from 92 to 34%; in South Lake Tahoe from 57% to 19%). In contrast, urbanization of the oak savannas at Menlo Park has resulted in an increase in tree density (from 4 to 35/ha) crown cover (from 14 to 25%) and the number of species (from 3 to 130). The number of tree species has increased in both cities as a result of urbanization of presettlement forests (in Menlo Park from 5 to 145; in South Lake Tahoe from 1 to 6). The uneven-aged structure of presettlement oak savannas at Menlo Park has been modified to an all-aged structure as a result of tree planting and the mortality of older age classes. The all-aged structure of the presettlement oak forest at Menlo Park was not changed in the transition to the present urban forest. At South Lake Tahoe the even-aged structure of the presettlement Jeffrey pine forest has been modified into a uneven-aged structure by tree planting. Presettlement forest age structure is recognized as the most significant characteristic for the identification of possible management problems in the urban forest.

The fate of vegetation as three rural landscapes (each 25km²) in southeastern Wisconsin were urbanized was investigated using a spatial data base with time series of land use and vegetal cover for 1937, 1963 and 1975. Additionally, forest tracts in these landscapes were surveyed to assess types and intensity of disturbance.

Remnant natural vegetation and such semi-natural vegetation as tree-lined fencerows in rural landscapes undergo complex transformations during urbanization. Land use changes destroy some tracts of forest and savanna, while others are created in new locations offsetting losses. Forest and fencerows are resources for development of areas of street and yard trees. However, most such vegetal resources of rural areas are destroyed during urbanization, rather than being incorporated into urban vegetation.

A 5-year study of urban/suburban breeding birds in Amherst, Massachusetts, U.S.A., focused on the relationship between breeding birds and vegetation composition and structure. Over all habitats, and throughout the 5-year period, woody vegetation volume alone accounted for 50% of all the variation in breeding bird species number, and species richness kept increasing even at relatively high vegetation volumes. Sixty-five species of breeding birds were seen during the study, and these can be divided into three groups based on their overall abundance in the sample areas and on their amenability to management: one group is liable to occur anyway, whether or not woody vegetation volume is encouraged as a management strategy; the second group is liable to be well represented where vegetation volume is encouraged but not well represented where it is not, and is the group most suitably targeted for management; the last group consists of birds which are poorly adapted to built-up areas, and which — though detected in small numbers — are not judged likely to increase significantly even where vegetation volume is augmented.