ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00069.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractDespite this nation's massive effort during the past 90 years to build levees throughout the upper Mississippi Basin, mean annual flood damage in the region has increased 140% during that time. These levees exacerbate the flood damage problem by increasing river stage and velocity. Thus, rather than continuing to rely on structural solutions for flood control, it is time to develop a comprehensive flood management strategy that includes using wetlands to intercept and hold precipitation where it falls and store flood waters where they occur. History testifies to the truth of this premise: it was the rampant drainage of wetlands in the nineteenth century that gave rise to many of today's water resources management problems. The 1993 flood verifies the need for additional wetlands: the amount of excess water that passed St. Louis during the 1993 flood would have covered a little more than 13 million acres —half of the wetland acreage drained since 1780 in the upper Mississippi Basin. By strategically placing at least 13 million acres of wetlands on hydric soils in the basin, we can solve the basin's flooding problems in an ecologically sound manne

ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00070.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to clarify the effect of grazing exclosures on the recovery and rehabilitation of overgrazed steppe vegetation on varying slope aspects in the Loess Plateau of northwest China. The annual precipitation in the area studied was 400–480 mm. Soil samples were taken on nine slopes in the five‐year exclosure and on five slopes outside the exclosure after a vegetation survey; they were then analyzed chemically. Mean number of species recorded per 0.25 m2was lower on the south‐facing slope than all other slopes. The reverse trend was observed for aerial biomass. Species diversity estimated by information content was higher in the grazing zone than in a 3200‐ha protected zone within an exclosure. From species ordination by principal component analysis, species with lower coverage in the grazing zone werePoa sphondylodes, Roegneria purpurascens, Hierochloe odorata, and Potentilla bifurca, which are all recognized as indicator species for rehabilitation efforts. In the soil surface layer, calcium contents were low, and the total contents of carbon and nitrogen were high on the north‐facing slope in the exclosure. The protection by exclosure of overgrazed steppe was seen to be effective because the accumulation of soil organic matter increased and water balance

ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00071.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractTheoretical work on population viability and extinction probabilities, empirical data fromCanis lupus(gray wolf) populations, and expert opinion provide only general and conflicting conclusions about the number of wolves and the size of areas needed for conservation of wolf populations. There is no threshold population size or proven reserve design that guarantees long‐term (century or more) survival for a gray wolf population. Most theoretical analyses of population viability have assumed a single, isolated population and lack of management intervention, neither of which is likely for wolves. Data on survival of actual wolf populations suggest greater resiliency than is indicated by theory. In our view, the previous theoretical treatments of population viability have not been appropriate to wolves, have contributed little to their conservation, and have created unnecessary dilemmas for wolf recovery programs by overstating the required population size. Nonetheless, viability as commonly understood may be problematic for small populations at the fringe of or outside the contiguous species range, unless they are part of a metapopulation. The capability of existing nature reserves to support viable wolf populations appears related to a variety of in situ circumstances, including size, shape and topography of the reserve; productivity, numbers, dispersion, and seasonal movement of prey; extent of poaching inside; degree of persecution outside; exposure to enzootica; attitudes of local people; and proximity to other wolf populations. We estimate that a population of 100 or more wolves and a reserve of several thousand square kilometers may be necessary to maintain a viable population in complete isolation, although 3000 km2or even 500–1000 km2may be adequate under favorable circumstances. In most cases, management intervention is probably necessary to assure the viability of relatively small, isolated populations. Because most reserves may be inadequate by themselves to ensure the long‐term survival of wolf populations, favorable human attitudes toward the species and its management must be recognized as paramount, and cooperation of neighboring management jurisdictions will be increasingly impo

ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00072.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractWe conducted an experiment with the dual aims of (1) examining the feasibility of establishing a species‐rich grassland using a commercially available grass and wild‐flower seed mixture and (2) examining the effects of different defoliation and fertilizer managements on the productivity, species richness, diversity, and composition of a species‐rich grassland established on a site reclaimed after opencast coal mining. The use of the seed mixture successfully established a sward of some 18–25 species per square meter. The species composition was enriched to some extent by recruitment of unsown species, principally from the soil seed bank. Hay‐type defoliation management produced greater dry matter yield and species richness than grazing defoliation, but grazing defoliation produced greater species diversity. Fertilizer application had no significant effect on dry matter production but reduced species diversity. Ordination analysis revealed that both defoliation and fertilizer management significantly affected species composition. The response obtained by individual species was explicable largely by their comparativ

ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00073.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00074.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractDieout ofAmmophila breviligulata— death of the major dune‐stabilizing plants — has been observed along the north and mid‐Atlantic coast of the United States for the past decade and a half. Pathogenic nematodes have been identified as the probable causal agents; they can bring about a complete dieout of sand dune vegetation, withAmmophila breviligulatabeing the first species to die. Typically, such an area would remain barren for up to five years before plants could be successfully introduced. Applications of fertilizer and dolomitic limestone were tested in the field as a possible management strategy to alleviate the vulnerability of a denuded dune to erosion by making it possible to plant such a site earlier than usual. These applications were also tested in an area of weakened and dying plants to determine if the vegetation could be saved before complete dieout occurred. By creating soil conditions conducive to vigorous plant growth, it was hypothesized that the plants could better withstand the stress of nematode attack. The addition of N‐P‐K macronutrient fertilizer resulted in increased growth and spread of plants introduced into a site where the grass had been dead for only one to two years. Results indicate that application of fertilizer would be necessary only every other year at most. Micronutrient application, at the concentration used in this study, had little or a somewhat detrimental effect. The addition of dolomitic limestone increased the survival of newly introduced plants. It was also found that the application of macronutrients to a site of moribund vegetation could not only rescue the plants in that site, but could also increase their growth, vigor, and spread, thereby preventing further loss of plant cover essential to dune st

ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00075.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractOur objectives were to evaluate the use of microcatchments in the establishment ofLeucaena retusa(little‐leaf leadtree) andAtriplex canescens(four‐wing saltbush) and their role in the initiation of autogenic landscape restoration processes on a shallow semiarid site. Three six‐month‐old seedlings of eitherLeucaena retusaorAtriplex canescenswere planted in 1.5‐m2microcatchments. An equal number of seedlings was planted in control plots (unmodified soil surface). The water collection effects on shrub survival, standing biomass, and the natural immigration of herbaceous vegetation were determined over 42 months. Planting in microcatchment basins doubledLeucaenaseedling survival and resulted in a five‐fold increase in standing biomass, compared to the control, during the first growing season. There was a significant increase in soil organic matter in the microcatchment basins within 32 months. At the same time, microcatchments planted withAtriplex canescensseedlings had a ten‐fold increase in seedling standing biomass compared to the control. Forty‐two months after transplanting, the herbaceous standing crop was significantly greater nearAtriplex canescensor in microcatchment basins than in plots with unmodified surface soil. Basins containingAtriplexproduced significantly more herbaceous vegetation than basins containingLeucaena, and empty basins produced the least herbaceous vegetation of three basin treatments. These data suggest that landscape‐scale procedures that concentrate scarce resources (water, organic matter, nutrients, and propagules), establish keystone species, and ameliorate microenvironmental conditions can initiate autogenic restoration of degraded se

ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00076.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Books reviewed in this article:World Soil Erosion and Conservation.D. Pimentel, editorEnvironmental Impacts of Mining: Monitoring, Restoration and Control.M. Sengupta

ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00077.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:1061-2971    

DOI:10.1111/j.1526-100X.1995.tb00078.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY