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Site Attributes (site + attribute)

Distribution by Scientific Domains

Humanities and Social Sciences	25%

Selected Abstracts

LANDSCAPE ATTRIBUTES AS CONTROLS ON GROITHD WATER NITRATE REMOVAL CAPACITY OF RIPARIAN ZONES,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2001
Arthur J. Gold
ABSTRACT: Inherent site factors can generate substantial variation in the ground water nitrate removal capacity of riparian zones. This paper examines research in the glaciated Northeast to relate variability in ground water nitrate removal to site attributes depicted in readily available spatial databases, such as SSUIRGO. Linking site-specific studies of riparian ground water nitrate removal to spatial data can help target high-value riparian locations for restoration or protection and improve the modeling of watershed nitrogen flux. Site attributes, such as hydric soil status (soil wetness) and geomorphology, affect the interaction of nitrate-enriched ground water with portions of the soil ecosystem possessing elevated biogeochemical transformation rates (i.e., biologically active zones). At our riparian sites, high ground water nitrate-N removal rates were restricted to hydric soils. Geomorphology provided insights into ground water flowpaths. Riparian sites located on outwash and organic/alluvial deposits have high potential for nitrate-enriched ground water to interact with biologically active zones. In till deposits, ground water nitrate removal capacity may be limited by the high occurrence of surface seeps that markedly reduce the time available for biological transformations to occur within the riparian zone. To fully realize the value of riparian zones for nitrate retention, landscape controls of riparian nitrate removal in different climatic and physiographic regions must be determined and translated into available spatial databases. [source]

Racial Wage Differences among Young Male Job Changers: The Relative Contribution of Migration, Occupation Change, Site Characteristics, and Human Capital

GROWTH AND CHANGE, Issue 1 2006
AMY M. WOLAVER
ABSTRACT We demonstrated racial differences in the relationship between migration, location, and predicted wages for young male workers who have changed employers. An Oaxaca decomposition allowed a measuring of the contributions of migration, occupation change, site features, and human capital to the racial wage gap. Migration decreases black,white wage differences, and wage compensation for site attributes favors white householders. Constraints on occupation choice and migration dampen the ability of blacks to improve wages. Because most job changes occur in the first ten years of a career, these results on young workers give important general insights into the origins and persistence of racial wage gaps. [source]

Go climb a mountain: an application of recreation demand modelling to rock climbing in Scotland

JOURNAL OF AGRICULTURAL ECONOMICS, Issue 1 2001
Nick Hanley
In this paper, we apply random utility modelling techniques to rock-climbing in Scotland. Attributes relevant to choices over rock-climbing sites were identified from focus groups with climbers, along with a categorisation of principal climbing areas. A survey of climbers yielded 267 responses, which were then used as the basis for modelling. We compare a standard multi-nominal logit model with a random parameters approach, and look at seasonal differences in behaviour, and at the implications of different treatments of travel time. The random utility models showed that most of the attributes selected were significant determinants of choice. Welfare estimates of changes in site attributes are presented, which are relevant to policy choices currently facing land managers. [source]

A Nested Logit Approach to Household Mobility

JOURNAL OF REGIONAL SCIENCE, Issue 1 2001
Thomas A. Knapp
This study analyzes personal and site characteristics in a model of intraMSA and interMSA mobility. Households are assumed to choose a single type of move, intraMSA or interMSA, while simultaneously choosing a central city or suburban destination. We demonstrate that a nested logit model is appropriate on both theoretical and empirical grounds. The sample consists of intrametropolitan and intermetropolitan movers drawn from the 1990 U.S. Census PUMS. Personal characteristics drawn from the PUMS are matched to numerous site characteristics (climatic measures, other amenities, state and local fiscal characteristics, and other urban quality measures) drawn from a variety of sources. Nested logit direct and cross elasticities are presented for a number of site attributes. [source]

LANDSCAPE ATTRIBUTES AS CONTROLS ON GROITHD WATER NITRATE REMOVAL CAPACITY OF RIPARIAN ZONES,

Tree growth in an African woodland savanna affected by disturbance

JOURNAL OF VEGETATION SCIENCE, Issue 3 2006
R.M. Holdo
Abstract: Questions: How does tree growth in a tropical woodland savanna vary as a function of size, and how is it affected by competition from neighbours, site attributes, and damage caused by disturbance? Location: western Zimbabwe. Methods: Trees of common species were tagged, mapped, and measured annually between 2001 and 2003 in a Kalahari sand woodland savanna. Diameter increments were analysed with mixed model regressions for the largest ramet in each genet. Stem diameter and damage, soil texture, and indices of competition at multiple spatial scales were used as covariates. Results: Stem diameter increased initially and then declined as a function of size in undamaged trees, which grew faster than damaged trees. Growth in damaged trees declined with size. No site differences were detected, and there was evidence for between-tree competition on growth only in the fastest-growing species, Brachystegia spiciformis. In several species the growth rate of the largest ramet increased as a function of the basal area of secondary ramets, contrary to expectations. For many species, the growth models showed poor explanatory power. Conclusions: Growth in Kalahari sand savanna trees varies as a function of size and changes in tree architecture caused by disturbance agents such as fire, frost, and elephant browsing. Disturbance may thus play an important role on vegetation dynamics through its effects on growth in the post-disturbance phase. Growth is highly stochastic for some species in this system, and more deterministic in others. It is hypothesized that this dichotomy may be driven by differences in rooting depth among species. [source]

A long-term record of Nothofagus dominance in the southern Andes, Chile

AUSTRAL ECOLOGY, Issue 1 2005
William Pollmann
Abstract The general model of regeneration dynamics in Nothofagus forests of southern South America could have value in community ecology if predictive relationships between disturbance history, functional traits and site attributes could be identified. Examined here is the proposal that on favourable sites shade-intolerant Nothofagus are likely not to survive in competition with shade-tolerant, broad-leaved evergreen taxa of temperate rain forests, and persistence, thus, is dependent on periodic coarse-scale disturbance. Comparison of stand dynamics of three old-growth Nothofagus forests at different elevations in the southern Andes, Chile where deciduous Nothofagus alpina dominates the upper canopy, and examination of the life history trade-offs of this variation were made. Stem density of all stems ,5.0 cm d.b.h. was 233,303 stems per hectare, and basal area was 123.9,171.0 m2ha,1. Maximum lifespan of N. alpina was found to be greater than ca 640 years, exceeding all previously reported ages for this species in the region. Forests had a stable canopy composition for this long-term, but some appeared to lack effective regeneration of N. alpina in recent years. Regeneration of N. alpina was generally greater in disturbed stands and higher elevation than in undisturbed stands and at lower elevation. Recruitment emerged to be strongly affected by competitive over- and understorey associates. There was a gradient of increasing dependence of N. alpina on disturbance towards the more productive end of the environment gradients, and hence less dependence of N. alpina on disturbance for its regeneration towards higher elevation. The study confirms that changes in forest composition may be explained by processes occurring in accordance with the predictions of the existing model of Nothofagus regeneration dynamics, providing stronger evidence specifically directed at mid-tolerant N. alpina, and by factoring out regeneration dynamics on favourable sites. Thus, for N. alpina, trait differences probably contribute to the competitive advantage over its associates in productive habitats, and may be linked to small-to-intermediate-sized disturbances which inevitably occur as older trees die, enabling N. alpina to persist in forests and therefore maintain species coexistence for the long-term. [source]

Species richness,environment relationships within coastal sclerophyll and mesophyll vegetation in Ku-ring-gai Chase National Park, New South Wales, Australia

AUSTRAL ECOLOGY, Issue 4 2003
Andrew F. Le Brocque
Abstract Patterns in species richness from a wide range of plant communities in Ku-ring-gai Chase National Park, New South Wales, Australia, were examined in relation to a number of environmental variables, including soil physical and chemical characteristics. Total species richness and richness of three growth-form types (trees, shrubs and ground cover) were determined in duplicate 500-m2 quadrats from 50 sites on two geological substrata: Hawkesbury Sandstone and Narrabeen shales and sandstones. Generalized linear models (GLM) were used to determine the amount of variation in species richness that could be significantly explained by the measured environmental variables. Seventy-three per cent of the variation in total species richness was explained by a combination of soil physical and chemical variables and site attributes. The environmental variables explained 24% of the variation in tree species richness, 67% of the variation in shrub species richness and 62% of the variation in ground cover species richness. These results generally support the hypothesis of an environmental influence on patterns in total species richness and richness of shrubs and ground cover species. However, tree species richness was not adequately predicted by any of the measured environmental variables; the present environment exerts little influence on the richness of this growth-form type. Historical factors, such as fire or climatic/environmental conditions at time of germination or seedling establishment, may be important in determining patterns in tree species richness at the local scale. [source]