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991.
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993.
Several scholars have claimed that small-scale agriculture in which farmers sell goods to the local market has the potential to strengthen social ties and a sense of community, a phenomenon referred to as “civic agriculture.” Proponents see promise in the increase in the number of community supported agriculture (CSA) programs, farmers markets, and other locally orientated distribution systems as well as the growing interest among consumers for buying locally produced goods. Yet others have suggested that these novel or reborn distribution mechanisms are still primarily means of instrumental economic exchange and that optimistic characterizations of a renewed sense of community emerging from these practices are unfounded. This study provides an empirical assessment of the extent to which these community-based agriculture markets are associated with connection to community, volunteerism, and civic and political activities. In order to assess the relationship between civic agriculture and community engagement, we surveyed over 1,300 people in the Mid-Hudson region of New York State. The study design includes “civic agriculture participants” as the unit of analysis, defined as CSA farm members, shoppers at independent health food stores, and farmers market patrons. For comparison, a telephone survey of randomly selected residents of the region’s general population was also conducted. Unlike studies that focus solely on the perceptions of certain civic agriculture participants (e.g., CSA members), by comparing the perceptions and behaviors of those engaged in a range of civic agriculture practices, we are able to identify the effects of different forms of participation. The results demonstrate higher levels of voluntarism and engagement in local politics among civic agriculture participants relative to the general population. In addition, we found variation among those engaged in different forms of civic agriculture, with those immersed in more socially embedded forms of exchange demonstrating greater community and political involvement. These findings lend empirical support to the civic agriculture thesis.  相似文献   
994.
Crop wild relatives (CWR) and wild harvested plant species (WHP) constitute an important element of a nation’s plant genetic resources (PGR) available for utilisation. Although their natural populations are threatened like other wild species by habitat lost and fragmentation, little attention has generally been paid to their systematic conservation. The development of checklists and inventories is considered by the convention on biological diversity (CBD) and the global strategy for plant conservation (GSPC) as the first step in any national strategy for conservation and sustainable use of plant diversity. Methodological approaches to the development of a national inventory of wild PGR are discussed in the light of a case-study for the CWR and WHP growing in mainland Portugal. The resultant inventory comprises 2319 taxa, of which 97.5% are CWR, 21.4% are WHP and 19.0% are both CWR and WHP. Approximately 6.1% are endemic to mainland Portugal; 24.1% occur in 1 to 4 Portuguese administrative regions; 15.6% are threatened, but only 5.9% are covered by legislative protection. Taxonomic misalignments and the dispersed nature of biological literature were the major impediments to the production of the national inventory, but once the inventory was established it has proven to be a powerful tool in conservation management.  相似文献   
995.
Lentic wetlands are usually regarded as the most important natural freshwater sources of methane (CH4) and nitrous oxide (N2O) to the atmosphere, and very few studies have quantified the importance of lowland streams in trace gas emissions. In this study, we estimated fluxes of CH4 and N2O in three macrophyte-rich, lowland agricultural streams in New Zealand, to place their trace gas emissions in context with other sources and investigate the value of minimising their emissions from agricultural land. All three streams were net sources of both gases, with emission of CH4 ranging from <1 to 500 μmol m?2 h?1 and of N2O ranging from <1 to 100 μmol m?2 h?1 during mid-summer. For CH4, both turbulent diffusion across the surface and ebullition of sediment gas bubbles were important transport processes, with ebullition accounting for 20–60% of the emissions at different sites. The emissions were similar on a per area basis to other major global sources of CH4 and N2O. Although small on a catchment scale compared to emissions from intensively grazed pastures, they were significant relative to low-intensity pastures and other agricultural land uses. Because hydraulic variables (viz. depth, velocity and slope) strongly influence turbulent diffusion, complete denitrification can best proceed to N2 as the dominant end-product (rather than N2O) in riparian wetlands, rather than in open stream channels where N2O fluxes are sometimes very large.  相似文献   
996.
Shawn W. Laffan  Brian G. Lees 《Geoderma》2004,120(3-4):241-258
In this paper we assess the utility of mapping regolith properties as continuously varying fields using environmental correlation over large spatial areas. The assessment is based on a comparison of results from spatially global and local analysis methods.

The two methods used are a feed-forward, back propagation neural network, applied globally, and moving window regression, applied locally. These methods are applied to five regolith properties from a field site at Weipa, Queensland, Australia. The properties considered are the proportions of oxides of aluminum, iron, silica and titanium present in samples, as well as depth to the base of the bauxite layer. These are inferred using a set of surface measurable features, consisting of Landsat data, geomorphometric indices, and distances from streams and swamps.

The moving window regression results show a much stronger relationship than do those from the spatially global neural networks. The implication is that the scale of the analysis required for environmental correlation is of the order of hundreds of metres, and that spatially global analyses may incur an automatic reduction in accuracy by not modelling geographically local relationships. In this case, this effect is up to 45% error at a tolerance near half of a standard deviation.  相似文献   

997.
Fumonisins were monitored in corn grain collected from Bt hybrids grown in 107 locations across the United States in 2000-2002. Bt corn hybrids contain the Cry1Ab protein from Bacillus thuringiensis that controls European corn borers and other stalk-boring pests. Fumonisin levels were frequently lower in grain from Bt hybrids grown in field trials under conditions of natural (FACT trials) or manual insect infestation (university trials). Over three years of FACT trials, there were 126/210 comparisons when fumonisin levels in grain from control hybrids were >2 ppm, exceeding U.S. FDA guidance levels of 2 ppm for human food. Grain from Bt hybrids was at or below 2 ppm of fumonisins for 58 of the 126 comparisons. The use of Bt hybrids can increase the percentage of corn grain that would be suitable for use in food and feed.  相似文献   
998.
Objective evaluations of wildlife reintroductions are vital for increasing the success of future efforts to re-establish endangered species. Attempts to reintroduce one of the most endangered mammals in North America, the black-footed ferret (Mustela nigripes), have been ongoing for 18 years with no quantitative assessment of factors related to reintroduction success. We examined relationships between ferret reintroduction success and factors associated with disease outbreaks, release strategies, and the distribution and abundance of their primary prey, prairie dogs (Cynomys sp.), at 11 reintroduction sites. The most important factor related to ferret reintroduction success was a cumulative metric incorporating both size of the area occupied by prairie dogs and density of prairie dog burrows within that area. Each of the four successful sites had prairie dog populations that occupied an area of at least 4300 ha. No sites with <4300 ha of prairie dogs were successful in maintaining ?30 adult individual ferrets over multiple years without augmentation even if they had a high prairie dog burrow density. The overarching importance of the availability of high-quality habitat suggests managers should prioritize actions that maintain and enhance the availability of large areas with high prairie dog burrow density, which are becoming increasingly rare due to anthropogenic impacts and disease outbreaks.  相似文献   
999.
1000.
Bounty records from Montana (1902-1930) were used to better understand spatial and temporal response of wolves (Canis lupus) and cougars (Puma concolor) to an eradication program. Number of payments for wolves declined from a high of 4116 in 1903 to 0 by 1928. Numbers of cougar pelts fluctuated, but generally declined from 177 in 1908 to 2 in 1930. An inverse spatial relationship existed between density of payments for wolves and cougars. Payments for wolves were greatest in the Prairie ecoregion, while payments for cougars were greatest in the Montane. The ratio of pup to adult wolves also was greatest in the Prairie ecoregion and least in the montane. If distribution and frequency of bounty payments were a reflection of the distribution and abundance of wolves, populations were highest and most productive in areas where they currently do not occur.  相似文献   
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