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1.
Jeffrey G. Holmquist Jutta Schmidt-Gengenbach Elizabeth A. Ballenger 《Environmental management》2014,53(6):1109-1118
Assessments of vertebrate disturbance to plant and animal assemblages often contrast grazed versus ungrazed meadows or other larger areas of usage, and this approach can be powerful. Random sampling of such habitats carries the potential, however, for smaller, more intensely affected patches to be missed and for other responses that are only revealed at smaller scales to also escape detection. We instead sampled arthropod assemblages and vegetation structure at the patch scale (400–900 m2 patches) within subalpine wet meadows of Yosemite National Park (USA), with the goal of determining if there were fine-scale differences in magnitude and directionality of response at three levels of grazing intensity. Effects were both stronger and more nuanced than effects evidenced by previous random sampling of paired grazed and ungrazed meadows: (a) greater negative effects on vegetation structure and fauna in heavily used patches, but (b) some positive effects on fauna in lightly grazed patches, suggested by trends for mean richness and total and population abundances. Although assessment of disturbance at either patch or landscape scales should be appropriate, depending on the management question at hand, our patch-scale work demonstrated that there can be strong local effects on the ecology of these wetlands that may not be detected by comparing larger scale habitats. 相似文献
2.
Biodiversity conservation and management of natural resources are the best options to restore and increase productivity of
degrading pastureland in dry areas. Hence, arthropod abundance, organic matter, respiration, and dehydrogenase activity were
measured in canopy zone soil of Prosopis cineraria (PC), Acacia nilotica (AN), Zizyphus nummularia (ZN), Capparis decidua (CD), and Acacia senegal (AS) associated with grasses with a view to establish interrelation for productivity enhancement of pastureland. Pure grass
bock outside tree canopy was control plot. Acari, Myriapoda, Coleoptera, Isoptera, Collembola, and other soil arthropods were
the major soil faunal groups. Integration of tree in pastureland enhanced population of soil arthropod by 9–65-fold in May
2001 and 8–13-fold in August/September as compared with control. The trends of changes in soil organic matter (SOM), soil
respiration (SR), and dehydrogenase activity (DHA) were similar to the changes in soil arthropod population, indicating the
role of soil fauna in facilitating biochemical processes and soil fertility. Two, eight, and nine times greater SOM, SR, and
DHA, respectively, in silvipastoral system than the values in control suggest the beneficial effects of trees on improvement
in biochemical processes and thus biodiversity in pastureland, as supported by negative values of relative tree effects (RTE).
Microbial activities were highest in the ZN system, which had highest abundance of soil arthropods. In the other systems,
CD and AS systems showed greater soil arthropod abundance and biological activities than with the PC and AN systems. Therefore,
Z. nummularia-, C. decidua-, and A. senegal-based silvipastoral systems and related soil fauna may be promoted for enhancement of biological activity and productivity
of pastureland in desert. The strategy may be adopted for developing a sustainable pedoecosystem in a region of the world
where agriculture is notoriously difficult. 相似文献
3.
Depletion of vegetation by overgrazing in arid environments has long-lasting effects on the environmental quality over extended
geographic areas. An adequate inspection of habitat changes requires scaled up procedures that would allow assessing end-points
of environmental status in broad areas that would be based on processes occurring at the plant canopy level. Our purpose was
to find indicators of land degradation–conservation status for use in land monitoring programs and in planning management
practices that would be amenable to further up-scaling for use with remotely sensed imagery. In several sites of the Patagonian
Monte differing in the impact of grazing management, we evaluated vegetation attributes at three spatial scales. At the population
scale, we found that the severity of grazing impact was characterized by the reduction of the palatable grass, P. ligularis, outside and inside shrub canopies. At the vegetation patch scale, we found that land degradation by domestic herbivore impact
was characterized by changes in attributes of patch shape (radius, height, internal canopy cover) and patch abundance. At
the plant community scale, we found that the structure of the plant canopy as described using Fourier analysis of cover data
changed after long-term grazing impact consistently with the modifications in plant population and patch structures. We present
a conceptual multiscale scenario of structural changes triggered by domestic herbivore impact, and quantitative indicators
of plant structure and processes useful to develop management strategies of the Patagonian-Monte that would conserve its natural
habitats. The developed end-points are also amenable for use in land conservation assessment through remotely sensed imagery. 相似文献
4.
Sampling data are provided and concepts discussed regarding soil and foliage arthropod communities in conventional and no-tillage soybean agroecosystems Soil arthropod communities from the two cropping systems were also compared with that from an adjacent old field. Biweekly arthropod samples were collected from conventional, no-tillage, and old-field systems Soil arthropods were sampled by quadrat and pitfall trap methods, foliage arthropods were collected by sweep net Quadrat sampling revealed that ground beetle number, species diversity, and biomass were significantly higher (P<0.05) in no-tillage than in conventional tillage systems. Pitfall trap data indicated higher densities and species diversity for most major soil macro-arthropod guilds Foliage arthropod guilds from no-tillage treatments showed higher species diversity throughout the growing season than those of conventional tillage, possibly because of greater structural diversity provided by weeds and litter in notillage systems No-tillage systems supported a larger and more diverse arthropod community than conventionally grown soybeans, suggesting a need for pest management strategies that simultaneously consider many variables. Both foliar grazing and leaf nitrogen content were higher in conventional than in no-tillage systems, indicating a possible causal connection between soil tillage and insect herbivory rates 相似文献
5.
We assessed the relationship between riparian management and stream quality along five southeastern Minnesota streams in 1995
and 1996. Specifically, we examined the effect of rotationally and continuously grazed pastures and different types of riparian
buffer strips on water chemistry, physical habitat, benthic macroinvertebrates, and fish as indicators of stream quality.
We collected data at 17 sites under different combinations of grazing and riparian management, using a longitudinal design
on three streams and a paired watershed design on two others. Continuous and rotational grazing were compared along one longitudinal
study stream and at the paired watershed. Riparian buffer management, fenced trees (wood buffer), fenced grass, and unfenced
rotationally grazed areas were the focus along the two remaining longitudinal streams. Principal components analysis (PCA)
of water chemistry, physical habitat, and biotic data indicated a local management effect. The ordinations separated continuous
grazing from sites with rotational grazing and sites with wood buffers from those with grass buffers or rotationally grazed
areas. Fecal coliform and turbidity were consistently higher at continuously grazed than rotationally grazed sites. Percent
fines in the streambed were significantly higher at sites with wood buffers than grass and rotationally grazed areas, and
canopy cover was similar at sites with wood and grass buffers. Benthic macroinvertebrate metrics were significant but were
not consistent across grazing and riparian buffer management types. Fish density and abundance were related to riparian buffer
type, rather than grazing practices. Our study has potentially important implications for stream restoration programs in the
midwestern United States. Our comparisons suggest further consideration and study of a combination of grass and wood riparian
buffer strips as midwestern stream management options, rather than universally installing wood buffers in every instance.
RID=" ID=" The Unit is jointly sponsored by the US Geological Survey, Biological Resources Division; the Minnesota Department
of Natural Resources; the University of Minnesota; and the Wildlife Management Institute. 相似文献
6.
Mark B. Bain 《Environmental management》1993,17(2):211-224
Introduced species have created environmental benefits and unanticipated disasters so a priori assessments of species introductions
are needed for environmental management. A checklist for assessing impacts of introduced species was developed from studies
of introduced species and recommendations for planning introductions. Sterile, triploid grass carp (Ctenopharyngodon idella) are just beginning to be used as a biocontrol agent for the management of aquatic vegetation in open waterways. Potential
impacts of grass carp in open systems were identified by reviewing grass carp biology relative to the impact assessment checklist.
The potential consequences of introduced grass carp were reviewed for one case study. The case study demonstrated that conclusions
about potential impacts and monitoring needs can be made despite incomplete information and uncertainty.
Indicators of environmental impact and vulnerability of host systems were grouped into six categories: population control,
hybridization, diseases and parasites, habitat alterations, biological effects, and management issues. Triploid grass carp
can significantly alter habitat and biological resources through the secondary effects of reductions in aquatic vegetation.
Potential impacts and significant uncertainties involve fish dispersions from plant control areas, inability to control vegetation
loss, loss of diverse plant communities and their dependent species, and conflicts with human use of the water resource. Adequate
knowledge existed to assess most potential consequences of releasing large numbers of triploid grass carp in Guntersville
Reservoir, Alabama. However, the assessment of potential impacts indicated that moderate, incremental stockings combined with
monitoring of vegetation and biological resources are necessary to control the effects of grass carp and achieve desirable,
intermediate plant densities.
Cooperators: Auburn University (Alabama Agricultural Experiment Station, Department of Fisheries and Allied Aquacultures,
Department of Zoology and Wildlife Sciences), US Fish and Wildlife Service, Alabama Game and Fish Division, and the Wildlife
Management Institute. 相似文献
7.
Arthropod communities in pear are conceptualized as hierarchically organized systems in which several levels of organization
or subsystems can be recognized between the population level and the community as a whole. An individual pear tree is taken
to be the community habitat with arthropod subcommunities developing on leaf, fruit, and wood subcommunity habitats. Each
subcommunity is composed of trophically organized systems of populations. Each system of populations is comprised of a functional
group or guild of phytophagous arthropods that use the habitat primarily for feeding but also for overwintering or egg deposition,
and associated groups of specialized predators, parasitoids, and hyperparasitoids. Several species move from one subcommunity
to another during the course of community development and thus integrate community subsystems.
Community development or change in organization through time is conceptualized as being jointly determined by the development
of the habitat and the organization of the species pool. The influence of habitat development on community development within
a species pool is emphasized in this research. Seasonal habitat development is expressed as change in the kinds and biomasses
of developmental states of wood, leaf, and fruit subcommunity habitats. These changes are accompanied by changes in the kinds,
biomasses, and distributions of associated community subsystems. 相似文献
8.
Toshihide Hamazaki Bruce C. Thompson Brian A. Locke Kenneth G. Boykin 《Journal of Environmental Planning and Management》2003,46(2):239-256
In developing conservation strategies, it is important to maximize effects of conservation within a specified land tract and to maximize conservation effects on surrounding area (ecological context). The authors proposed two criteria to select biotic entities for conservation foci: (1) the relative occurrence of fauna or flora in a tract is greater than that of an ecological context region; and (2) occurrence of the fauna or flora is relatively limited in the ecological context region. Using extensive spatial data on vegetation and wildlife habitat distribution, the authors identified strategic vegetation and fauna conservation foci for the 400 000 ha Fort Bliss military reservation in New Mexico and Texas relative to a 164 km radius ecological context region intersecting seven ecological zones and the predicted habitat distribution of 616 animal species. The authors set two specific criteria: (1) predicted area of a species' occurrence is <50% of the ecological context region; and (2) percentage of Fort Bliss intersecting the species' or vegetation community predicted areas in the ecological context region is >5% (Fort Bliss is 4.2% of the region). These criteria selected one vegetation class and 40 animal species. Further, these vegetation and animal foci were primarily located in two areas of Fort Bliss. Sensitivity analyses with other analytical radii corroborated the context radius used. Conservation of the two areas and associated taxa will maximize the contribution of Fort Bliss's conservation efforts in its ecological proximity. This relatively simple but information-rich process represents economical and defensible preliminary contextual analysis for detailed conservation planning. 相似文献
9.
Danelle M. Larson 《Environmental management》2014,54(6):1434-1444
Fire and grazing are common management schemes of grasslands globally and are potential drivers of reptilian and amphibian (herpetofauna) metacommunity dynamics. Few studies have assessed the impacts of fire and cattle grazing on herpetofauna assemblages in grasslands. A patch-burn grazing study at Osage Prairie, MO, USA in 2011–2012 created landscape patches with treatments of grazing, fire, and such legacies. Response variables were measured before and after the application of treatments, and I used robust-design occupancy modeling to estimate patch occupancy and detection rate within patches, and recolonization and extinction (i.e., dispersal) across patches. I conducted redundancy analysis and a permuted multivariate analysis of variance to determine if patch type and the associated environmental factors explained herpetofauna assemblage. Estimates for reptiles indicate that occupancy was seasonally constant in Control patches (ψ ~ 0.5), but declined to ψ ~ 0.15 in patches following the applications of fire and grazing. Local extinctions for reptiles were higher in patches with fire or light grazing (ε ~ 0.7) compared to the controls. For the riparian herpetofaunal community, patch type and grass height were important predictors of abundance; further, the turtles, lizards, snakes, and adult amphibians used different patch types. The aquatic amphibian community was predicted by watershed and in-stream characteristics, irrespective of fire or grazing. The varying responses from taxonomic groups demonstrate habitat partitioning across multiple patch types undergoing fire, cattle grazing, and legacy effects. Prairies will need an array of patch types to accommodate multiple herpetofauna species. 相似文献
10.
Ecologists are beginning to recognize the effect of heterogeneity on structure and function in arid and semiarid ecosystems.
Additionally, the influences of temperature on ecosystems are widely documented, but landscape temperature patterns and relationships
with vegetation are rarely reported in ecological studies. To better understand the importance of temperature patterns to
the conservation and restoration of native ecosystems, we designed an experiment to investigate relationships among soil surface
temperature, landscape heterogeneity, and grazing intensity. Grazing intensity did influence the vegetation structure and
composition. Heavy treatments had the greatest bare ground and the least vertical structure. Ungrazed treatments had the most
litter and live grass cover. However, average temperatures among the three grazing treatments were not different and ranged
less than 2°C during midday summer periods. The temperature difference between riparian and upland landscapes within grazing
treatments was 21°C. Landscape position (riparian vs. upland) did have a significant influence on soil surface temperature
and produced a variation in temperature 11 times greater than grazing intensities. Thermal heterogeneity did not differ among
grazing treatments. Lower soil surface temperatures (associated with riparian areas) may provide a critical thermal refuge
for many animals in arid and semiarid ecosystems on hot summer days, when air temperatures can exceed 37°C. Riparian zones,
specifically riparian vegetation, are an important component in ecosystem management. 相似文献
11.
Mosquito control ditches designed to increase tidal circulation are widely used as a physical control alternative to insecticidal applications The impact of such ditching on Pacific Coast marshlands was largely unknown before this five-year study of impact in two types of San Francisco Bay salt marshes, aSalicornia virginica (pickleweed) monoculure and a mixed vegetation marsh Results of our studies suggest that ditches cause less environmental disturbance than insecticidal applications The article describes the following environmental consequences of ditching for mosquito control: increased tidal flushing of soils occurs adjacent to ditches compared with that in the open marsh, thereby reducing ground water and soil surface salinities and water table height; primary productivity ofS. virginica, as determined by both the harvest method and infrared photographic analysis, is higher directly adjacent to ditches than in the open marsh, distribution of selected arthropod populations is similar at ditches and natural channels, although arthropod community response differs seasonally; aquatic invertebrate biomass is similar within ditched and natural ponds, but diversity is lower in ditched habitats, ditching increases fish diversity and density by improving fish access from tidal channels; ditches provide additional salt marsh song sparrow habitat, although ditches are less preferred than natural channels or sloughs. Management criteria can be used to design ditches that provide effective mosquito control and reduced environmental impact 相似文献
12.
Dry grasslands are one of the most species rich and endangered types of vegetation in Europe. In the Czech Republic, dry grasslands
are mainly of anthropogenic origin and were formed as a result of grazing after the clear-cutting of thermophilous oak woods.
Gradual changes in the farming landscape throughout the 20th century, particularly in the 1960s, resulted in the abandonment
of the relatively infertile habitats of dry grasslands. After abandonment, dry grasslands decline and degrade due to the gradual
overgrowth of woody species and expansion of perennial tall grasses. In the year 2000, a grazing management program was introduced
in the protected areas within the territory of Prague City to maintain the species diversity of dry grasslands. The responses
of the expansive grass species, Arrhenatherum elatius L. and multiple woody species (especially, Prunus spinosa L.) to differences in grazing periods were monitored for over a decade. Grazing in spring through the end of June had the greatest impact on the reduction of A. elatius and woody species. Grazing in the height of summer through autumn did not reduce the cover of these plants, and may support
the prosperity of both A. elatius and the woody species due to higher levels of nutrients. 相似文献
13.
Effects of sheep and goat grazing on the species diversity in the alpine meadows of Western Himalaya 总被引:3,自引:0,他引:3
This paper deals with effects of sheep and goat grazing on plant species diversity, species richness and species composition in two important conservation areas of the Western Himalaya; the Valley of Flowers (VOF) National Park and the Great Himalayan National Park (GHNP). The VOF is a completely Protected Area as it is devoid of livestock grazing whereas, 20,000 sheep and goats annually graze in GHNP. Both the National Parks possess sub-alpine and alpine vegetation that is distributed in 13 major habitat types. Present investigations indicate that all the habitat types in VOF are higher in plant species diversity and richness compared to habitat types in GHNP. Similarly, all three eco-climatic zones in VOF are higher in species diversity and richness compared to GHNP. Species diversity also decreases with increasing altitude in both the National Parks. The findings of this study are discussed in the light of the management and conservation of alpine meadows of the Western Himalayas. 相似文献
14.
Miguel A. Altieri 《Environmental management》1983,7(1):3-7
Insect habitats in anthropocentric ecosystems consist of crop plants or forest trees and the coexisting non-crop vegetation. The manipulation of the spatial and temporal arrangement of these plant communities can trigger direct or indirect effects on insect pest populations and their associated natural enemy complexes. In this article habitat management is viewed as a technique to design plant associations that support populations of natural enemies or that exert deterrent effects on herbivorous insects. 相似文献
15.
Public rangelands in North America are typically managed under a multiple use policy that includes livestock grazing and wildlife
management. In this article we report on the landscape level extent of grassland loss to shrub encroachment in a portion of
the Rocky Mountain Forest Reserve in southwestern Alberta, Canada, and review the associated implications for simultaneously
supporting livestock and wildlife populations while maintaining range health on this diminishing vegetation type. Digitized
aerial photographs of 12 km of valley bottom from 1958 and 1974 were co-registered to ortho-rectified digital imagery taken
in 1998, and an un-supervised classification used to determine areas associated with grassland and shrubland in each year.
Field data from 2002 were over-layed using GPS coordinates to refine the classification using a calibration-validation procedure.
Over the 40-year study period, open grasslands declined from 1,111 ha in 1958 to 465 ha in 1998, representing a 58% decrease.
Using mean production data for grass and shrub dominated areas we then quantified aggregate changes in grazing capacity of
both primary (grassland) and secondary (shrubland) habitats for livestock and wildlife. Total declines in grazing capacity
from 1958 to 1998 totaled 2,744 Animal Unit Months (AUMs) of forage (−39%), including a 58% decrease in primary (i.e., open
grassland) range, which was only partly offset by the availability of 1,357 AUMs within less productive and less accessible
shrubland habitats. Our results indicate shrub encroachment has been extensive and significantly reduced forage availability
to domestic livestock and wildlife, and will increase the difficulty of conserving remaining grasslands. Although current
grazing capacities remain marginally above those specified by regulated grazing policies, it is clear that continued habitat
change and decreases in forage availability are likely to threaten the condition of remaining grasslands. Unless shrub encroachment
is arrested or grassland restoration initiated, reductions in aggregate ungulate numbers may be necessary.
相似文献
Edward W. BorkEmail: |
16.
Anthropogenic fires in Africa are an ancient form of environmental disturbance, which probably have shaped the savanna vegetation more than any other human induced disturbance. Despite anthropogenic fires having played a significant role in savanna management by herders, previous ecological research did not incorporate the traditional knowledge of anthropogenic fire history. This paper integrates ecological data and anthropogenic fire history, as reconstructed by herders, to assess landscape and regional level vegetation change in northeastern Namibia. We investigated effects of fire frequency (i.e. <5, 5-10 and >10 years) to understand changes in vegetation cover, life form species richness and savanna conditions (defined as a ratio of shrub cover to herbaceous cover). Additionally, we analysed trends in the vegetation variables between different fire histories at the landscape and regional scales. Shrub cover was negatively correlated to herbaceous cover and herbaceous species richness. The findings showed that bush cover homogenisation at landscape and regional scales may suggest that the problem of bush encroachment was widespread. Frequent fires reduced shrub cover temporarily and promoted herbaceous cover. The effects on tree cover were less dramatic. The response to fire history was scale-independent for shrub, herbaceous and tree cover, but scale-dependent for the richness of grass and tree life forms. Fire history, and not grazing pressure, improved savanna conditions. The findings emphasise the need to assess effects of anthropogenic fires on vegetation change before introducing new fire management policies in savanna ecosystems of northeastern Namibia. 相似文献
17.
Mark Thompson Jan Vlok Mathieu Rouget M. T. Hoffman Andrew Balmford R. M. Cowling 《Environmental management》2009,43(4):585-596
Improved techniques for measuring and monitoring the state of biodiversity are required for reporting on national obligations
to international and regional conservation institutions. Measuring the extent of grazing-related degradation in semi-arid
ecosystems has proved difficult. Here we present an accurate and cost-effective method for doing this, and apply it in a South
African semi-arid region that forms part of a globally significant biodiversity hotspot. We grouped structurally and functionally
similar vegetation units, which were expert-mapped at the 1:50,000 scale, into four habitat types, and developed habitat-specific
degradation models. We quantified degradation into three categories, using differences between dry and wet season values of
the Normalized Difference Vegetation Index (NDVI) for the three succulent karoo habitats, and the difference between maximum
and mean NDVI values for the subtropical thicket habitat. Field evaluation revealed an accuracy of 86%. Overall, degradation
was high: 24% of the study area was modeled as severely degraded, and only 9% as intact. Levels of degradation were highest
for bottomland habitats that were most exposed to grazing impacts. In sharp contrast to our methods, a widely used, broad-scale
and snapshot assessment of land cover in South Africa was only 33% accurate, and it considerably underestimated the extent
of severely degraded habitat in the study area. While our approach requires a multidisciplinary team, and in particular expert
knowledge on the characteristics and spatial delimitation of vegetation types, it is repeatable, rapid, and relatively inexpensive.
Consequently, it holds great promise for monitoring and evaluation programs in semi-arid ecosystems, in Africa, and beyond. 相似文献
18.
Restoration of Mountain Big Sagebrush Steppe Following Prescribed Burning to Control Western Juniper 总被引:2,自引:0,他引:2
Western juniper (Juniperus occidentalis ssp. occidentalis Hook) encroachment into mountain big sagebrush (Artemisia tridentata spp. vaseyana (Rydb.) Beetle) steppe has reduced livestock forage production, increased erosion risk, and degraded sagebrush-associated wildlife habitat. Western juniper has been successfully controlled with partial cutting followed by prescribed burning the next fall, but the herbaceous understory and sagebrush may be slow to recover. We evaluated the effectiveness of seeding perennial herbaceous vegetation and sagebrush at five sites where juniper was controlled by partially cutting and prescribed burning. Treatments tested at each site included an unseeded control, herbaceous seed mix (aerially seeded), and the herbaceous seed mix plus sagebrush seed. In the third year post-treatment, perennial grass cover and density were twice as high in plots receiving the herbaceous seed mix compared to the control plots. Sagebrush cover and density in the sagebrush seeded plots were between 74- and 290-fold and 62- and 155-fold greater than the other treatments. By the third year after treatment, sagebrush cover was as high as 12 % in the sagebrush seeded plots and between 0 % and 0.4 % where it was not seeded. These results indicate that aerial seeding perennial herbaceous vegetation can accelerate the recovery of perennial grasses which likely stabilize the site. Our results also suggest that seeding mountain big sagebrush after prescribed burning encroaching juniper can rapidly recover sagebrush cover and density. In areas where sagebrush habitat is limited, seeding sagebrush after juniper control may increase sagebrush habitat and decrease the risks to sagebrush-associated species. 相似文献
19.
Degradation of warmwater streams in agricultural landscapes is a pervasive problem, and reports of restoration effectiveness
based on monitoring data are rare. Described is the outcome of rehabilitation of two deeply incised, unstable sand-and-gravel-bed
streams. Channel networks of both watersheds were treated using standard erosion control measures, and aquatic habitats within
1-km-long reaches of each stream were further treated by addition of instream structures and planting woody vegetation on
banks (“habitat rehabilitation”). Fish and their habitats were sampled semiannually during 1–2 years before rehabilitation,
3–4 years after rehabilitation, and 10–11 years after rehabilitation. Reaches with only erosion control measures located upstream
from the habitat measure reaches and in similar streams in adjacent watersheds were sampled concurrently. Sediment concentrations
declined steeply throughout both watersheds, with means ≥40% lower during the post-rehabilitation period than before. Physical
effects of habitat rehabilitation were persistent through time, with pool habitat availability much higher in rehabilitated
reaches than elsewhere. Fish community structure responded with major shifts in relative species abundance: as pool habitats
increased after rehabilitation, small-bodied generalists and opportunists declined as certain piscivores and larger-bodied
species such as centrarchids and catostomids increased. Reaches without habitat rehabilitation were significantly shallower,
and fish populations there were similar to the rehabilitated reaches prior to treatment. These findings are applicable to
incised, warmwater streams draining agricultural watersheds similar to those we studied. Rehabilitation of warmwater stream
ecosystems is possible with current knowledge, but a major shift in stream corridor management strategies will be needed to
reverse ongoing degradation trends. Apparently, conventional channel erosion controls without instream habitat measures are
ineffective tools for ecosystem restoration in incised, warmwater streams of the Southeastern U.S., even if applied at the
watershed scale and accompanied by significant reductions in suspended sediment concentration. 相似文献
20.
Radioactive contamination of agricultural land may necessitate long-term changes in food production systems, through application
of selected countermeasures, in order to reduce the accumulation of radionuclides in food. We quantified the impact of selected
countermeasures on habitat diversity, using the hypothetical case of two agricultural areas in Finland. The management scenarios
studied were conversions from grassland to cereal production and from grassland and crop production to afforestation. The
two study sites differed with respect to present agricultural production: one being predominantly cereal production and seminatural
grasslands, while the other was dominated by intensive grass and dairy production. Some of the management scenarios are expected
to affect landscape structures and habitat diversity. These potential changes were assessed using a spatial pattern analysis
program in connection with geographic information systems. The studied landscape changes resulted in a more monotonous landscape
structure compared to the present management, by increasing the mean habitat patch size, reducing the total habitat edge length
and reducing the overall habitat diversity calculated by the Shannon diversity index. The degree of change was dependent on
the present agricultural management practice in the case study sites. Where dairy production was predominant, the landscape
structure changes were mostly due to conversion of intensive pastures and grasslands to cereal production. In the area dominated
by cereal production and seminatural grasslands, the greatest predicted impacts resulted from afforestation of meadows and
pastures. The studied management changes are predicted to reduce biodiversity at the species level as well as diminishing
species-rich habitats. This study has predicted prominent side effects in habitat diversity resulting from application of
management scenarios. These potential long-term impacts should be considered by decision-makers when planning future strategies
in the event of radionuclide deposition. 相似文献