Cultivated Fields (cultivated + field)

Distribution by Scientific Domains

Selected Abstracts

Coexistence of natural enemies in a multitrophic host,parasitoid system

Michael B. Bonsall
Abstract., 1. This study explored the temporal and spatial aspects of coexistence over many generations in a multispecies host,parasitoid assemblage. 2. The long-term interaction between the cabbage root fly, Delia radicum (Diptera: Anthomyiidae), and two of its natural enemies, Trybliographa rapae (Hymenoptera: Fitigidae) and Aleochara bilineata (Coleoptera: Staphylinidae), in a cultivated field at Silwood Park over 19 years was explored. 3. Although time series showed that the populations were regulated, the impact of the natural enemies was highly variable. Within-year determinants showed that the spatial response of the specialist parasitoid, T. rapae, was predominantly independent of host density while A. bilineata acted simply as a randomly foraging generalist parasitoid. 4. These findings are compared and contrasted with an earlier investigation of the same system when only the first 9 years of the time series were available. This study demonstrated the potential of long-term field studies for exploring hypotheses on population regulation, persistence, and coexistence. [source]

Starling foraging success in relation to agricultural land-use

ECOGRAPHY, Issue 3 2002
Ola Olsson
Changes in agricultural land-use have been suggested to contribute to the decline of several bird species through negative effects on their food supply during breeding. One important change in land-use has been loss of pastures, especially permanent pastures. In this study we investigated how different forms of agricultural land-use affected foraging success of a declining bird species, the European starling Sturnus vulgaris. We let caged starlings forage in different forms of agricultural fields and determined time spent foraging and foraging success. The starlings' activity level (time spent actively foraging) as well as the number of prey caught per time unit was strongly related to the abundance of prey in soil samples. Also the body mass change during the experiment was positively related to activity level and prey capture rate. We found consistent differences in foraging variables between habitats. In spring sown grain starlings were least active and found fewer prey items at a lower rate than in any other habitat. The other three habitats differed less, but in general mowed hay fields appeared slightly more valuable than the cultivated and natural pastures. We did not find any differences between natural and cultivated pastures in foraging variables. Thus, starling foraging success is higher in grass-covered fields than in cultivated fields, but the management of the grass-covered fields mattered less. The results are consistent with starlings having higher population densities and breeding success in areas with higher availability of pasture. We suggest that the physical structure of the habitat (sward height) and moisture may be additional variables that need to be taken into account to explain starling breeding density and success in the agricultural landscape. [source]

Comparing the hydrology of grassed and cultivated catchments in the semi-arid Canadian prairies

G. van der Kamp
Abstract At the St Denis National Wildlife Area in the prairie region of southern Saskatchewan, Canada, water levels in wetlands have been monitored since 1968. In 1980 and 1983 a total of about one-third of the 4 km2 area was converted from cultivation to an undisturbed cover of brome grass. A few years after this conversion all the wetlands within the area of grass dried out; they have remained dry since, whereas wetlands in adjacent cultivated lands have held water as before. Field measurements show that introduction of undisturbed grass reduces water input to the wetlands mainly through a combination of efficient snow trapping and enhanced infiltration into frozen soil. In winter, the tall brome grass traps most of the snowfall, whereas in the cultivated fields more wind transport of snow occurs, especially for short stubble and fallow fields. Single-ring infiltration tests were conducted during snowmelt, while the soil was still frozen, and again in summer. The infiltrability of the frozen soil in the grassland is high enough to absorb most or all of the snowmelt, whereas in the cultivated fields the infiltration into the frozen soil is limited and significant runoff occurs. In summer, the infiltrability increases for the cultivated fields, but the grassland retains a much higher infiltrability than the cultivated land. The development of enhanced infiltrability takes several years after the conversion from cultivation to grass, and is likely due to the gradual development of macropores, such as root holes, desiccation cracks, and animal burrows. Copyright 2002 Crown in the right of Canada. Published by John Wiley & Sons, Ltd. [source]

Land use/cover changes and their implications on rural livelihoods in the degraded environments of central Tanzania

Richard Y. M. KangalaweArticle first published online: 3 FEB 200
Abstract This paper examines the changes in land use/cover types in the degraded environment of central Tanzania over the last 45 years, and how such changes have influenced agricultural and livelihoods sustainability, especially in the Irangi Hills. Changes of land use/cover were measured through aerial photographs interpretations, while local perceptions and description of change were addressed through household interviews and field observations. The results of this study show that there have been variations over the years in terms of both the areas and spatial distribution of cultivated fields. The total land cultivated increased from 31% in the late 1970s to 35% in early 1990s, mainly because of agricultural expansion to sandy watercourses and former grazing areas. Water courses shrank by 55% between late 1970s and early 1990s providing new areas for cultivation. Over the last 45 years, the open and wooded grasslands, and tree-cover types covered about 40% of the total land area, ranging from 29% in 1960 to 43,45% between late 1970s and early 1990s. Spatial and temporal distribution of the cultivated fields and other vegetation cover types were influenced by differences in the scale of land degradation, and the soil-conservation initiatives that have been implemented. With increasing pressure on the land, however, sustaining livelihoods through agricultural production in the area remains a critical challenge. [source]

Wheat field erosion rates and channel bottom sediment sources in an intensively cropped northeastern Oregon drainage basin,

G. N. Nagle
Abstract Sediment tracers were used to quantify erosion from cultivated fields and identify major source areas of channel bottom sediment within the Wildhorse Creek drainage, an intensively cropped tributary of the Umatilla River in northeastern Oregon, USA. Available data indicated that Wildhorse Creek was one of the largest sediment yielding tributaries of the Umatilla River. Carbon, nitrogen and the nuclear bomb-derived radionuclide 137Cs were used as tracers to fingerprint sediment sources. Sediment was collected from the stream bottom and active floodplain and compared to samples from cultivated fields and channel banks. Samples were characterized on the basis of tracer concentrations and a simple mixing model was used to estimate the relative portion of bottom sediment derived from cultivated surface and channel banks. The results indicate that the amount of bottom sediment derived from cultivated surface sources was less than 26,per,cent for the 1998 winter season, although this estimate has a high margin of error. Cesium-137 was also used to estimate surface erosion from three cultivated fields in the watershed. Annual estimates of erosion since 1963 from the three sampled fields were from 3 to 7,5,t,ha,1 yr,1. For the 1998 season, it appears that most channel-bottom sediment was of subsurface origin with much of it likely coming from channel and gully banks indicating that significant reductions in sediment in Wildhorse Creek might be accomplished by the stabilization of eroding riparian areas and swales on the lower slopes of agricultural fields. Published in 2004 by John Wiley & Sons, Ltd. [source]

Attacks on local persons by chimpanzees in Bossou, Republic of Guinea: long-term perspectives

Kimberley J. Hockings
Abstract Attacks on humans by nonhuman primates are one of the most serious causes of human,primate conflict, and strongly influence people's perceptions and tolerance of nonhuman primates. Despite their importance, systematic and extensive records of such attacks are rare. Here, we report the attacks that occurred on local persons by chimpanzees (Pan troglodytes verus) at Bossou, Republic of Guinea, from 1995 to 2009. There have been a total of 11 attacks during this period, the majority of which were directed toward children. They varied in their severity, but all were nonfatal. Attacks took place on a road and narrow paths that bordered the forest or in cultivated fields and orchards where opportunities for human,chimpanzee contact are high. Attacks occurred between the months of March and October, coinciding with wild fruit scarcity, increased levels of crop-raiding, and periods of human cultivation with likely increased human usage of paths. Although the families of attack victims felt angry and fearful toward chimpanzees after attacks, some drew on their traditional beliefs to explain why chimpanzees were respected, protected, and could not hurt them, even when attacks occurred. We provide suggestions for reducing future nonhuman primate attacks on humans in an effort to mitigate human,primate conflict situations. Am. J. Primatol. 72:887,896, 2010. 2009 Wiley-Liss, Inc. [source]