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1.
Assessing the potential impacts of alternative landscape designs on amphibian population dynamics 总被引：2，自引：1，他引：2
An individual-based, spatially explicit population model was used to predict the consequences of future land-use alternatives for populations of four amphibian species in two central Iowa (midwest USA) agricultural watersheds. The model included both breeding and upland habitat and incorporated effects of climatic variation and demographic stochasticity. Data requirements of the model include life history characteristics, dispersal behavior, habitat affinities, as well as land use and landcover in geographic information systems databases. Future scenarios were ranked according to change in breeder abundance, saturation, and distribution, compared to baseline conditions. Sensitivity of simulation results to changes in model parameters was also examined. Simulated results suggest that while all four species modeled are likely to persist under present and future scenario conditions, two may be more at risk from future landscape change. Although the study species are all widespread generalists regarded as having a low conservation priority, they depend on wetlands and ponds, increasingly endangered habitats in agricultural landscapes. Broader conservation strategies in the region would ensure that these currently common organisms do not become the endangered species of the future.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
2.
Properly calibrated, single storm event, model simulations can be valuable quantitative tools for evaluating the effectiveness of grassed waterways (GWWs) and identifying a threshold length for an effective GWW. Current specifications for GWW lengths in Iowa are lacking. The key objective of this study is to employ the well-established Water Erosion Prediction Project model (WEPP) for determining an effective (or threshold) GWW length for reducing runoff and sediment yields under a wide range of hydrologic and management conditions in an agricultural Iowa watershed, namely Clear Creek, IA. The advantage of this physically based, distributed-parameter model is its ability to replicate processes at the hillslope scale where GWW performance is mostly evaluated. Overall, 84 WEPP runs were performed for assessing (i) the effect that GWW length has on reducing runoff and sediment yields within a representative test hillslope, and (ii) the effect of the gradient of the drainage area on GWW efficiency. Results show that the GWW efficiency for all GWW lengths is governed by hydrology, expressed as Qpeak. The results suggest that the threshold length for an effective GWW is 500 m for the hydrologic conditions in this study and for a representative drainage area of approximately 27 ha. For all storm events, a threshold drainage area gradient of approximately 3% was found above which the GWW efficiency was independent of topographic steepness. The results demonstrate similar trends to other studies although the relative increases in reduction in runoff and sediment delivery differ between sites and are very much dictated by Qpeak and hydrologic soil group. The effectiveness of models to evaluate GWW efficiency for nearly saturated conditions and shallow flows is discussed. 相似文献
3.
Landscape pattern indices are common tools of landscape ecologists, affording comparisons of different study areas, or the
same study area at different times. Since the advent of popular index-calculating software, more landscapes can be analyzed
in short amounts of time, yet the behaviour of landscape pattern indices can vary for different contexts or data characteristics,
complicating interpretation. I applied a selected set of landscape pattern indices to fine-resolution (3 m) data representing
a highly fragmented landscape – Corn Belt Iowa agriculture – to investigate the performance of landscape pattern indices.
Indices measured pattern attributes that affect the viability of small mammal populations, namely habitat proportion and connectivity
and landscape grain size and heterogeneity. Results showed that the performance of indices for fine-resolution data can be
highly variable, depending upon data and contextual issues like the presence of linear elements and the amount of habitat.
For these Corn Belt landscapes good habitat proportions and patch sizes were small (commonly less than 10% and less than 1 ha,
respectively), and connectivity was variable depending on the measure. Aggregation and mean nearest neighbour indices performed
better than other connectivity indices. Fine-resolution data representing highly fragmented landscapes can raise difficulties
for indices of landscape configuration. Landscape pattern indices require improvement to perform better for increasingly available
fine-resolution data representing common landscape types. 相似文献
4.
Soil apparent electrical conductivity (EC) as measured by electromagnetic induction (EM) using the Geonics® EM-38 has shown promise as a soil survey tool in Iowa and other parts of the American Midwest. Surveys made with the EM-38 often take place in the fall after harvest or in the spring prior to planting. Because of this, and because use of conservation tillage and other techniques that leave crop residues on the soil surface is prevalent in many parts of the United States, it is common for fields to have crop residues covering the soil surface when EM surveys are conducted. These residues might alter the soil EC values obtained with the EM-38. To test this possibility, soil EC was determined at two sites with three different types of residue cover (corn (Zea mays L.), soybeans (Glycine max L.), and durum wheat (Triticum turgidum L.)). The residue cover at each site was then brushed aside, and the soil EC was determined with bare ground exposed to the EM-38. On average, soil EC readings were 0.2mS/m higher when the EM-38 was exposed to bare ground, and 68% of the bare ground readings were higher than the corresponding readings through crop residues. However, the 0.2mS/m average difference is not significant when compared to the natural variation found in soil EC readings within any given soil series. Therefore, the results of this study indicate that soil EC values obtained with the EM-38 through crop residues are valid representations of the actual soil EC value. 相似文献
5.
T. B. Moorman C. A. Cambardella D. E. James D. L. Karlen L. A. Kramer 《Soil & Tillage Research》2004,78(2):225-236
Knowledge of the long-term effects of tillage on soil organic carbon is important to our understanding of sustainable agricultural systems and global carbon cycles. In landscapes susceptible to erosion, tillage can exacerbate losses of soil and C by increasing erodibility and stimulating microbial respiration. We measured long-term changes in soil carbon and soil loss in three small watersheds located in southwest Iowa, USA. The following soil series were formed on deep loess hills: Ida and Dow (Typic Udorthents), Napier and Kennebec (Cumulic Hapludolls) and Monona (Typic Hapludolls). All watersheds were cropped to continuous corn (Zea mays L.) and two were moldboard plowed and disk tilled while the third was ridge-tilled. The ridge-tillage system had greater C contents in the surface soil than the disk tillage soils, but ridge-tillage was not different from the conventional tillage in carbon retention over time. The ridge-tillage system, however, was more effective in retaining soil within the watershed. Microbial respiration by soil microorganisms accounted for 97% of the carbon loss in the ridge-tilled watershed compared to carbon loss in eroded sediment (3%). Terrain analysis was used to segment the landscape into landform elements. Less total carbon was present in the soil profiles of backslope elements than in footslope or toeslope elements, reflecting the combined effects of soil erosion and deposition within the watersheds. Profile C content was also positively correlated with the wetness index, a compound topographic attribute, that identifies areas of the landscape where runoff water and sediment accumulate. 相似文献
6.
Michael S. Carolan 《Agriculture and Human Values》2006,23(3):325-339
This paper examines sustainable agriculture’s steady rise as a legitimate farm management system. In doing this, it offers an account of social change that centers on trust and its intersection with networks of knowledge. The argument to follow is informed by the works of Foucault and Latour but moves beyond this literature in important ways. Guided by and building upon earlier conceptual framework first forwarded by Carolan and Bell (2003, Environmental Values 12: 225–245), sustainable agriculture is examined through the lens of a “phenomenological challenge.” In doing this, analytic emphasis centers on the interpretative resources of everyday life and the artful act of practice – in other words, on “the local.” Research data involving Iowa farmers and agriculture professionals are examined to understand how social relations of trust and knowledge are contested and shaped within and between agricultural social networks and organizational configurations. All of this is meant to further our understanding of what “sustainable agriculture” is and is not, who it is, and how these boundaries change over time.
Michael
S. Carolan
is an Assistant Professor of Sociology at Colorado State University. His areas of specialization included environmental sociology, sociology of science and knowledge, sociology of food systems and agriculture, and the sociology of risk. Some of his recent writings have focused on the theorizing of nature–society relations, epistemological issues related to agriculture (and sustainable agriculture in particular), and the processes by which knowledge claims are constructed and contested in response to environmental threats. 相似文献
7.
The movement towards precision agriculture has led to calls for soil maps that are more detailed and accurate than those offered in standard NCSS soil surveys. Studies have shown that soil variability can be greater than depicted in soil surveys; in fact, delineations that contain at least 50% of the soil mapped are considered satisfactory for soil survey purposes. Lacustrine plains are relatively flat and often have parent materials with uniform properties. Because soils are usually mapped using soil–landform relationships one might expect soil maps in these areas to be less accurate than average; it is difficult to delineate between map units using soil–landform relationships in such subtle landscapes. We grid-mapped a field containing lacustrine-derived soils in central Iowa and used the grid to evaluate the soil survey for accuracy. Two major and two minor soils, as determined by the area they occupy in the field, were present. For the field as a whole, the two major soils were correctly identified by the soil survey at least 63% of the time. The two minor soils were correctly identified 33% of the time or less by the soil survey. Large-scale soil mapping is expensive because of the time involved to create them in the field and in the office. Therefore, it is only economically beneficial to produce a detailed map if the map leads to significant alterations in the way a field is managed. In fields that may have uniform soil properties, it may be more cost-effective to conduct a reconnaissance survey first and then decide if more detailed mapping is required. 相似文献
8.
The gradient of water vapor pressure between soil and air controls the rate of evaporation from soil, but it has not been possible to determine the humidity at the soil surface. We have devised an instrument to measure the surface humidity in the field. Thermocouple psychrometry is used to monitor air equilibrated with the soil surface in a chamber placed briefly on the soil. A programmable data logger scans the thermocouples and stores the data. We calibrated the instrument over saturated salt solutions, and over soils whose relative humidity was calculated from measured water potentials. The instrument worked well, but underestimated slightly at relative humidities above 90%. It can be used to distinguish between stage 1 and stage 2 evaporation for soils. In field trials, the surface psychrometer was used to monitor diurnal and day-to-day changes in soil surface humidity during the drying cycle after irrigation. The cumulative vapor pressure difference between the soil surface and the air at 1.5 m was highly correlated with soil evaporation from microlysimeters set between crop rows. Changes in the cumulative difference in vapor pressure were also closely related to the changes in the evaporation component of measured evapotranspiration, as estimated with a simulation model. 相似文献
9.
Lateral migrations of river meanders create transient, spatially transgressive edges where the advancing cutbank edge encroaches upon interior floodplain forest communities. This spatial movement of edge toward the forest interior should initiate directional changes in species composition within a forest plot as it is affected by a changing microclimate and hydrological regime. We found that cutbank edge and forest interior sites in an Iowa floodplain contained markedly different plant assemblages. Species commonly associated with later stages of succession dominated interior sites while cutbank edge sites favored secondary, successional species. Assuming that the cutbank edge sites once contained vegetation similar to that surveyed in the floodplain interior, the observed changes in community structure accompanying channel migration are suggestive of retrograde succession, or retrogression. To link cutbank erosional processes with retrogressional processes, we modified a computer simulation model already in use for floodplain environments. We incorporated the changing edge effects and compared model projections with the data collected from the field sites using detrended correspondence analysis. Without changes, the simulation projected a site compositionally similar to the sampled interior forest. When the changes were initiated, the simulated site progressively took on compositional characteristics similar to the riparian edge sites. Because we included only those forcing functions that would be initiated by cutbank erosion, the model supports the hypothesis that the spatially progressive edge effect results in a directional change in forest community composition analogous to retrogression. Our results demonstrate an interesting linkage between successional and fluvial-geomorphic processes and indicate that site dynamics may be controlled differently in landscapes where sites are progressively created and destroyed than where recurrent disturbances affect the same site. 相似文献
10.
Landscape,community, countryside: linking biophysical and social scales in US Corn Belt agricultural landscapes 总被引：1，自引：1，他引：0
Understanding the interplay between ecological and social factors across multiple scales is integral to landscape change initiatives
in productive agricultural regions such as the rural US Corn Belt. We investigated the cultural context surrounding the use
of perennial cover types—such as stream buffers, wetlands, cellulosic bioenergy stocks, and diverse cropping rotations—to
restore water quality, biodiversity, and ecosystem function within a Corn Belt agricultural mosaic in Iowa, USA. Through ethnographic
techniques and 33 in-depth interviews, we examined what was most important to rural stakeholders about their countryside.
We then used photo elicitation to probe how interviewees’ assessments of farm practices involving perennial cover types were
related to their sense of place. Our interviewees perceived their rural “countryside” as a linked social and biophysical entity,
identifying strongly with the farming lifestyle and with networks of people across the landscape. While most interviewees
approved of perennial farm practices on marginal agricultural land, implementation of these practices was neither a priority
nor strongly assimilated into rural experience and ethics. We identified three scale boundaries in our interviewees’ perception
of place which present key challenges and opportunities for landscape change: landscape-community, individual-community, and
community-institution. In all cases, community social norms and networks—exhibited at landscape spatial scales—may be instrumental
in bridging these boundaries and enabling networks of perennial cover types that span privately owned and operated farms.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献