Mean Field Size Research Articles

Conterminous United States crop field size quantification from multi-temporal Landsat data

Abstract Agricultural field size is indicative of the degree of agricultural capital investment, mechanization and labor intensity, and it is ecologically important. A recently published automated computational methodology to extract agricultural crop fields from weekly 30 m Web Enabled Landsat data (WELD) time series was refined and applied to a year of Landsat 5 Thematic Mapper (TM) and Landsat 7 Enhance Thematic Mapper Plus (ETM +) acquisitions for all of the conterminous United States (CONUS). For the first time, spatially explicit CONUS field size maps and derived information are presented. A total of 4,182,777 fields were extracted with mean and median field sizes of 0.193 km 2 and 0.278 km 2 , respectively. The CONUS field size histogram was skewed; 50% of the extracted fields had sizes greater than or smaller than 0.361 km 2 , and there were four distinct peaks that corresponded closely to sizes equivalent to fields with 0.25 × 0.25 mile, 0.25 × 0.5 mile, 0.5 × 0.5 mile, and 0.5 × 1 mile side dimensions. There were discernible patterns between field size and the majority crop type as defined by the United States Department of Agriculture (USDA) National Agricultural Statistics Service (NASS) cropland data layer (CDL) classification. In general, larger field sizes occurred where a greater proportion of the land was dedicated to agriculture, predominantly in the U.S. Wheat Belt and Corn Belt, and in regions of irrigated agriculture. The results were validated by comparison with field boundaries manually digitized from Landsat 5 and Google-Earth high resolution imagery. The validation was undertaken at 48 approximately 7.5 × 7.5 km sites selected across a gradient of field sizes in each of the top 16 harvested cropland areas in U.S. states that together cover 76% of harvested U.S. cropland. Conventional per-pixel confusion matrix based measures that assess pixel level thematic mapping accuracy, and object extraction accuracy measures, were derived. The overall per-pixel crop field classification accuracy was 92.7% and the overall crop field producer's and user's accuracies were 93.7% and 94.9%. Comparing all the reference and extracted field objects, 81.4% were correctly matched and the extracted field sizes were on average underestimated by 1.2% relative to the reference field objects.

The diet of Danish red foxes (Vulpes vulpes) in relation to a changing agricultural ecosystem. A historical perspective

Rodents and especially voles (Microtus agrestis or arvalis) make up the basic diet of foxes (Vulpes vulpes) in Denmark. As the abundance of voles and mice may have decreased as a result of modern agricultural procedures, this study investigates potential changes in the diet of Danish red foxes over the past 4 decades in relation to a changing agricultural landscape. Our study compares the stomach contents of foxes collected in Jutland during the years 2012–2014 with a similar study from 1965 to 1970. The results show that small rodents occur in the stomachs of foxes with the same frequencies today (73 %) as 40–50 years ago (67 %), while the frequency of European brown hare (Lepus europaeus) has decreased from 7 to 3 % and the frequency of roe deer (Capreolus capreolus) has increased from 3 to 18 %. The changes in the occurrence of brown hare and roe deer in the diet of foxes during the past 40 years most probably reflect changes in the populations of the two species. By comparing digitised orthophotos of six agricultural areas (3.5 × 3.5 km) of the past 1974/1975 and present landscapes, it was revealed that the total area of crop fields, small natural habitats, hedgerows and grasslands have remained almost unchanged. However, mean field size has increased by 48 %, and the mean size of small natural habitats has increased by 15 %; meaning that the length of field boundaries and the number of small natural habitats have decreased by 65 and 33 %, respectively. The distance between natural habitats in the cultivated areas has become larger during the past 40 years. Overall, the areas of natural biotopes have remained the same in Denmark during the past 40 years. Field boundaries on the other hand which are known to be important vole habitats have become fewer in the cultivated areas. Despite this, small rodents still occur in high frequencies in the diet of nowadays foxes. As voles are sensitive to fragmentation, narrow stipes of permanent grass should be maintained or even re-established in the cultivated areas to improve life conditions for small rodents and other wildlife.

Farmlands with smaller crop fields have higher within-field biodiversity

Simple rules for landscape management seem elusive because different species and species groups are associated with different land cover types; a change in landscape structure that increases diversity of one group may reduce diversity of another. On the other hand, if simple landscape–biodiversity relationships do exist despite this complexity, they would have great practical benefit to conservation management. With these considerations in mind, we tested for consistent relationships between landscape heterogeneity and biodiversity in farmland (the cropped areas in agricultural landscapes), with a view to developing simple rules for landscape management that could increase biodiversity within farmland. Our measures of farmland heterogeneity were crop diversity and mean crop field size, where increases in crop diversity and/or decreases in mean field size represent increasing landscape heterogeneity. We sampled the abundance, and alpha, gamma and beta diversity of birds, plants, butterflies, syrphids, bees, carabids and spiders, in crop fields within each of 93 1km×1km agricultural landscapes. The landscapes were selected to represent three gradients in landscape composition and heterogeneity: proportion of the landscape in crop, mean crop field size and Shannon crop type diversity of the farmland. We found that mean crop field size had the strongest overall effect on biodiversity measures in crop fields, and this effect was consistently negative. Based on our results we suggest that, if biodiversity conservation in crop fields is a priority, policies and guidelines aimed at reducing crop field sizes should be considered.

SU‐F‐BRE‐07: Experimental Validation of a Lung SBRT Technique Using a Novel, True Volumetric Plenoptic‐Plastic‐Scintillator Detector

Purpose:Lung SBRT is being used by an increasing number of clinics, including our center which recently treated its first patient. In order to validate this technique, the 3D dose distribution of the SBRT plan was measured using a previously developed 3D detector based on plenoptic camera and plastic scintillator technology. The excellent agreement between the detector measurement and the expected dose from the treatment planning system Pinnacle3 shows great promise and amply justify the development of the technique.Methods:The SBRT treatment comprised 8 non‐coplanar 6MV photon fields with a mean field size of 12 cm2 at isocentre and a total prescription dose of 12Gy per fraction for a total of 48Gy. The 3D detector was composed of a 10×10×10 cm2 EJ‐260 water‐equivalent plastic scintillator embedded inside a truncated cylindrical acrylic phantom of 10cm radius. The scintillation light was recorded using a static R5 light‐field camera and the 3D dose was reconstructed at a 2mm resolution in all 3 dimensions using an iterative backprojection algorithm.Results:The whole 3D dose distribution was recorded at a rate of one acquisition per second. The mean absolute dose difference between the detector and Pinnacle3 was 1.3% over the region with more than 10% of the maximum dose. 3D gamma tests performed over the same region yield passing rates of 98.8% and 96.6% with criteria of 3%/1mm and 2%/1mm, respectively.Conclusion:Experimental results showed that our beam modeling and treatment planning system calculation was adequate for the safe administration of small field/high dose techniques such as SBRT. Moreover, because of the real‐time capability of the detector, further validation of small field rotational, dynamic or gated technique can be monitored or verified by this system.

Interplay effect of angular dependence and calibration field size of MapCHECK 2 on RapidArc quality assurance.

The purpose of this study is to investigate an effect of angular dependence and calibration field size of MapCHECK 2 on RapidArc QA for 6, 8, 10, and 15 MV The angular dependence was investigated by comparing MapCHECK 2 measurements in MapPHAN‐MC2 to the corresponding Eclipse calculations every 10° using 10 × 10 cm2 and 3 × 3 cm2 fields. Fourteen patients were selected to make RapidArc plans using the four energies, and verification plans were delivered to two phantom setups: MapCHECK 2/MapPHAN phantom (MapPHAN QA) and MapCHECK 2 on an isocentric mounting fixture (IMF QA). Migration of MapCHECK 2 on IMF was simulated by splitting arcs every 10° and displacing an isocenter of each partial arc in the Eclipse system (IMFACTUAL QA). To investigate the effect of calibration field size, MapCHECK 2 was calibrated by two field sizes (10 × 10 cm2 and 3 × 3 cm2) and applied to all QA measurements. The γ test was implemented using criteria of 1%/1 mm, 2%/2 mm, and 3%/3 mm. A mean dose of all compared points for each plan was compared with respect to a mean effective field size of the RapidArc plan. The angular dependence was considerably high at gantry angles of 90° ± 10° and 270° ± 10° (for 10 × 10/3 × 3 cm2 at 90°, 30.6% ± 6.6%/33.4%± 5.8% (6 MV), 17.3% ± 5.3%/15.0% ± 6.8% (8 MV), 8.9% ± 2.9%/7.8% ± 3.2% (10 MV), and 2.2% ± 2.3%/‐1.3% ± 2.6% (15 MV)). For 6 MV, the angular dependence significantly deteriorated the γ passing rate for plans of large field size in MapPHAN QA (< 90% using 3%/3 mm); however, these plans passed the γ test in IMFACTUAL QA (> 95%). The different calibration field sizes did not make any significant dose difference for both MapPHAN QA and IMFACTUAL QA. For 8, 10, and 15 MV, the angular dependence does not make any clinically meaningful impact on MapPHAN QA. Both MapPHAN QA and IMFACTUAL QA presented clinically acceptable γ passing rates using 3%/3 mm. MapPHAN QA showed better passing rates than IMFACTUAL QA for the tighter criteria. The 10 × 10 cm2 calibration showed better agreement for plans of small effective field size (< 5 × 5 cm2) in MapPHAN QA. There was no statistical difference between IMF QA and IMFACTUAL QA. In conclusion, MapPHAN QA is not recommended for plans of large field size, especially for 6 MV, and MapCHECK 2 should be calibrated using a field size similar to a mean effective field size of a RapidArc plan for better agreement for IMF QA.PACS numbers: 87.55.km, 87.55.Qr, 87.56.Fc

Predicting species diversity in agricultural environments using Landsat TM imagery

Maps based on classified Earth observation (EO) imagery have been used to model biodiversity, but errors associated with the classification process itself and the resulting discretization of land cover may ultimately limit such efforts. Among other issues, discrete land cover maps can often be costly to produce and validate. Alternatively, the original continuous spectral information in EO imagery can be used. The primary objective of this study was to compare predictors based on continuous and discrete information derived from Landsat TM imagery for modeling biodiversity in agricultural landscapes. In 46 landscapes throughout Eastern Ontario, Canada, landscape metrics (mean field size, the percentage of landscape in agriculture, and crop diversity) derived from a discrete image classification, along with several measures of crop productivity based on the continuous Normalized Difference Vegetation Index (NDVI), were used as predictors of field-based measures of species diversity for birds, butterflies, and plants. Using an Information-Theoretic approach for model-averaging and inference, we compared and interpreted the magnitude and direction of model-averaged coefficients, model evidence ratios, and overall fit of model-averaged predictions. Our findings indicate that when using Landsat TM imagery in agricultural environments, models using predictors derived from continuous information consistently outranked models based on discrete information derived from classified imagery.

Agronomic evaluation of Rice Production Systems of Sawah Ecotechnology in the Inland valley of Central Nigeria

In promoting increase productivity in rice production system in the Inland valley of central Nigeria, Sawah Eco-technology was introduced to rice farmers around Bida in central Nigeria. The technology involves levelled basin and improved bunding with inlet and outlet for irrigation and drainage to achieve full water control. In assessing the superiority of this technology over the conventional rice production system by the farmers, a survey in conjunction with field agronomic evaluation were conducted in rice growing communities where sawah was introduced. Three communities were chosen for the survey exercise. These are Ejeti, Emitsudadan and Shaba Maliki. Structural questionnaires were administered to all categories of farmers. That is those practicing sawah and those that are not. For the field agronomic evaluation, three rice communities where sawah was newly introduced were chosen. The communities were Musa, Army barrack and Ekpagi. In each of these communities, rice was cultivated using sawah technology and at the sametime there are those that are not cultivated using sawah. Survey results indicated that the mean field size of farmers using sawah was 1 ha while those that are not having a range of between 0.4 to 1.0 ha field sizes. Paddy yield for sawah compliance was between 2.0 to 2.4 t/ha and those of non compliance were between 1.0 to 1.7 t/ha. Agronomic evaluation indicated higher paddy yield in all the sawah fields compared to those of non sawah areas. Yields increased down the valley in all cases with the highest paddy yield of 4.6 t/ha obtained at the valley bottom of Army barrack site.

Comparing open and closed molecular self-assembly

We study theoretically in the present work the self-assembly of molecules in an open system, which is fed by monomers and depleted in partial or complete clusters. Such a scenario is likely to occur for example in the context of viral self-assembly. We provide a general formula for the mean-field size distribution which is valid both at equilibrium in a closed system, and in the stationary state in an open system. This allows us to explore in a simple way out-of-equilibrium features for self-assembly and compare them to equilibrium properties. In particular, we identify a region of parameter space for which the out-of-equilibrium size distribution in the presence of external fluxes is equal to the equilibrium size distribution in the absence of external fluxes, up to a constant renormalization factor. The range of validity of this result and its consequences are discussed.

Farmland Heterogeneity Benefits Birds in American Mid-west Watersheds

It is now well known that biodiversity in agricultural landscapes can be increased by converting production lands (i.e., farmland) into more natural habitat. However, it remains relatively unknown to what extent biodiversity can also be enhanced by changing the composition and configuration of farmland per se. We examined relationships between farmland structure and avian biodiversity in six watersheds representing a gradient in rowcrop intensity in the American Mid-west. We used canonical correspondence analysis (CCA) to model relationships at the site (0.8 ha), field (21 ha), section (165 ha) and watershed (4000–18,000 ha) extents to explore these questions: (1) At what spatial extent do birds respond most strongly to farmland structure? (2) Which farmland variables are most important? (3) Does avian biodiversity increase with increasing farmland heterogeneity? Most variation in bird assemblages was explained at the field versus the site or section extents. Of the top 20 field-extent variables in CCA, most important were: % woodland, an index of compositional heterogeneity (the modified Simpson's evenness index, MSIEI), % rowcrop, % core pasture (i.e., away from an edge), and edge density. Eighteen species were associated with woodland; their richness increased with woodland from 0% to 10%. Nine species were associated with rowcrop; their richness decreased two-fold with a change in rowcrop from 80% to 3%. Twelve species were associated with farmland heterogeneity; their richness increased four-fold with more field cover heterogeneity (MSIEI) and decreased three-fold with increasing mean field size from 1.2 to 7 ha. Field-extent α and β species richness were significantly higher than expected in the null model in the two most heterogeneous watersheds and lower in the two most intensely farmed watersheds. Differences among watersheds were significant and evident in the CCA ordination plot. Our results show empirically that policies to influence farmland heterogeneity could provide a conservation benefit to avian biodiversity.

REDDENING AND EXTINCTION TOWARD THE GALACTIC BULGE FROM OGLE-III: THE INNER MILKY WAY'SRV∼ 2.5 EXTINCTION CURVE

We combine VI photometry from OGLE-III with VVV and 2MASS measurements of E(J-K_{s}) to resolve the longstanding problem of the non-standard optical extinction toward the Galactic bulge. We show that the extinction is well-fit by the relation A_{I} = 0.7465*E(V-I) + 1.3700*E(J-K_{s}), or, equivalently, A_{I} = 1.217*E(V-I)(1+1.126*(E(J-K_{s})/E(V-I)-0.3433)). The optical and near-IR reddening law toward the inner Galaxy approximately follows an R_{V} \approx 2.5 extinction curve with a dispersion {\sigma}_{R_{V}} \approx 0.2, consistent with extragalactic investigations of the hosts of type Ia SNe. Differential reddening is shown to be significant on scales as small as as our mean field size of 6', with the 1{\sigma} dispersion in reddening averaging 9% of total reddening for our fields. The intrinsic luminosity parameters of the Galactic bulge red clump (RC) are derived to be (M_{I,RC}, \sigma_{I,RC,0}, (V-I)_{RC,0}, \sigma_{(V-I)_{RC}}, (J-K_{s})_{RC,0}) = (-0.12, 0.09, 1.06, 0.121, 0.66). Our measurements of the RC brightness, brightness dispersion and number counts allow us to estimate several Galactic bulge structural parameters. We estimate a distance to the Galactic center of 8.20 kpc, resolving previous discrepancies in distance determinations to the bulge based on I-band observations. We measure an upper bound on the tilt {\alpha} \approx 40{\deg}. between the bar's major axis and the Sun-Galactic center line of sight, though our brightness peaks are consistent with predictions of an N-body model oriented at {\alpha} \approx 25{\deg}. The number of RC stars suggests a total stellar mass for the Galactic bulge of 2.0*10^{10} M_{\odot}, if one assumes a Salpeter IMF.

Effects of landscape, conspecifics and heterospecifics on habitat selection by breeding farmland birds: the case of the Calandra Lark (Melanocorypha calandra) and Corn Bunting (Emberiza calandra)

The aim of habitat selection studies is to understand the effect of the different factors affecting the spatial distribution of individuals. Within this framework, the aim of this study was to evaluate the relative contributions of landscape features and conspecific and heterospecific interactions to habitat selection by two sympatric species, the Calandra Lark Melanocorypha calandra and the Corn Bunting Emberiza calandra, during the breeding season. During the 2008 breeding season, the population of both species was censused in three Central Spanish locations by means of transects (N = 58). A model-averaging approach was used to determine the weight and effect of landscape and interaction variables in each species’ habitat selection using abundance as the dependent variable. Deviance partitioning was used to determine the unique and shared contributions of these two sets of variables to the variation explained by the models. Calandra Lark was positively associated with mean field size, which reflects its preference for relatively simplified landscapes with a low density of field margins and, consequently, small land-use diversity. Corn Bunting selected areas with high land-use diversity, namely, a highly heterogeneous landscape with a high density of field margins. Attraction between conspecifics was found in both cases. Calandra Lark seems to negatively respond to the proximity of Corn Buntings, which indicates a partitioning of space and food resources. However, Corn Bunting responded positively to the proximity of Calandra Larks, which reflects a higher tolerance of Corn Buntings to the presence of other species nearby. Deviance partitioning showed that interactions were more important for Calandra Lark, while Corn Bunting was equally affected by both components. An appropriate management should combine the requirements of both species to achieve effective conservation at the bird assemblage level.

Effects of irrigation and landscape heterogeneity on butterfly diversity in Mediterranean farmlands

Irrigation effects on biodiversity are poorly known, particularly in Mediterranean agro-ecosystems. In this study we analyzed irrigation effects on butterfly species richness, abundance and diversity as well as on species composition in a farmed landscape under Mediterranean climate. The study area consisted of four contiguous agricultural sub-areas with a decreasing degree of intensification: irrigated, mixed (dry and irrigated), dry and environmentally protected (i.e. Special Protection Area, SPA) dry farmland. Forty one km-transects (ten per sub-area) were searched for butterflies in 2008 and 2009. Contrary to expectations, species richness (alfa, beta and gamma diversity) was highest in both years in the most intensified sub-area (i.e. irrigated) followed by SPA, dry and mixed sub-areas. Landscape characteristics accounted for most of the between-subareas differences in species richness. Species richness was negatively related to mean field size at the landscape level and positively related to the number of trees and large shrubs along transects. Therefore, the higher number of butterfly species recorded in the irrigated farmland could be due to a more complex landscape. In contrast, butterfly abundance was highest in cereal steppes (i.e. dry and SPA sub-areas), with abundance being negatively affected by mean field size. Inter-annual change in butterfly abundance was much sharper in rainfed (i.e. dry and SPA) than in irrigated (i.e. irrigated and mixed) sub-areas. Irrigated farmland may provide more favorable conditions for butterflies by buffering the (year-to-year and summer) drought periods characterising Mediterranean climate. Species composition differed among sub-areas, with differences being partly explained by field size and number of trees and shrubs along transects. Our study suggest an important role of landscape characteristics in boosting butterfly biodiversity in intensively managed irrigated croplands and emphasizes the importance of encouraging studies on farmland butterfly diversity in different (bioclimatic) regions allowing the design of region-specific agri-environmental schemes.

A study of the relationship between peak skin dose and cumulative air kerma ininterventional neuroradiology and cardiology

A study of peak skin doses (PSDs) during neuroradiology and cardiology interventionalprocedures has been carried out using Gafchromic XR-RV2 film. Use of mosaics made fromsquares held in cling film has allowed doses to the head to be mapped successfully. Thedisplayed cumulative air kerma (CAK) has been calibrated in terms of cumulative entrancesurface dose (CESD) and results indicate that this can provide a reliable indicator of thePSD in neuroradiology. Results linking PSD to CESD for interventional cardiologywere variable, but CAK is still considered to provide the best option for use asan indicator of potential radiation-induced effects. A CESD exceeding 3 Gy isconsidered a suitable action level for triggering follow-up of patients in neuroradiologyand cardiology for possible skin effects. Application of dose action levels definedin this way would affect 8% of neurological embolisation procedures and 5% ofcardiology ablation and multiple stent procedures at the hospitals where theinvestigations were carried out. A close relationship was observed between CESD anddose–area product (DAP) for particular types of procedure, and DAPs of 200–300 Gy cm2 could be used as trigger levels where CAK readings were not available. The DAP valuewould depend on the mean field size and would need to be determined for eachapplication.

Influence of agricultural factors on weed, carabid and bird richness in a Mediterranean cereal cropping system

Using a multimodel inference approach, the most relevant field-level and landscape context factors explaining the simultaneous variability of bird, carabid and weed species richness were identified and interpreted in a low-intensity cereal farming system in central Spain. Weed species richness was negatively influenced by sowing density, herbicides and surrounding mean field size. Carabid species richness was negatively related to applied nitrogen, but positively to surrounding land cover diversity and applied phosphorous. Bird species richness was positively influenced by focal field size, but negatively by surrounding land cover diversity, sowing density and amount of potassium applied. Although all three biological groups reflected the influence of intensification factors operating at different spatial scales, the most relevant factors were specific to each particular group. These results have implications in terms of the selection of targets for agri-environmental measures aiming at reversing the impacts of agricultural intensification on biodiversity.

Conservation reserve enhancement program fields: Benefits for grassland and shrub-scrub species

Almost 30,000 ha (74,100 ac) of grassland were created in south-central Pennsylvania through the USDA Conservation Reserve Enhancement Program (CREP) from 2000 to 2004. To assess the use of these fields by grassland and other birds and to develop region-specific management guidelines, we conducted transect counts of singing birds in 103 CREP fields during 2002 to 2004 and measured within-field vegetation and landscape characteristics. Thirty-two bird species were found on fields during the breeding season. Red-winged blackbirds (<i>Agelaius phoeniceus</i>) were most numerous, followed by three shrub-scrub species. Grassland obligate species were rare and were most abundant on larger fields with a lower density of vegetation and a predominance of cool-season grasses. Abundances of shrub-scrub species were highest on smaller fields with a higher density of vegetation and a higher proportion of warm-season grasses. Avian use of CREP fields in Pennsylvania differs from Midwestern Conservation Reserve Program fields in a number of important ways. Shrub-scrub species were more common, which may be due to the small mean field size and the more forested landscape. In addition, grassland obligates were found in greater densities on fields of cool-season grasses than in fields of warm-season or mixed grasses. Targeted enrollment and management of large fields or those adjoining other grasslands for grassland birds and small fields or those adjoining woodlands for shrub-scrub species may be the best approach to maximize the benefits of CREP for a range of bird species.

Bone Fractures Following External Beam Radiotherapy and Limb-Preservation Surgery for Lower Extremity Soft Tissue Sarcoma: Relationship to Irradiated Bone Length, Volume, Tumor Location and Dose

To examine the relationship between tumor location, bone dose, and irradiated bone length on the development of radiation-induced fractures for lower extremity soft tissue sarcoma (LE-STS) patients treated with limb-sparing surgery and radiotherapy (RT). Of 691 LE-STS patients treated from 1989 to 2005, 31 patients developed radiation-induced fractures. Analysis was limited to 21 fracture patients (24 fractures) who were matched based on tumor size and location, age, beam arrangement, and mean total cumulative RT dose to a random sample of 53 nonfracture patients and compared for fracture risk factors. Mean dose to bone, RT field size (FS), maximum dose to a 2-cc volume of bone, and volume of bone irradiated to >or=40 Gy (V40) were compared. Fracture site dose was determined by comparing radiographic images and surgical reports to fracture location on the dose distribution. For fracture patients, mean dose to bone was 45 +/- 8 Gy (mean dose at fracture site 59 +/- 7 Gy), mean FS was 37 +/- 8 cm, maximum dose was 64 +/- 7 Gy, and V40 was 76 +/- 17%, compared with 37 +/- 11 Gy, 32 +/- 9 cm, 59 +/- 8 Gy, and 64 +/- 22% for nonfracture patients. Differences in mean, maximum dose, and V40 were statistically significant (p = 0.01, p = 0.02, p = 0.01). Leg fractures were more common above the knee joint. The risk of radiation-induced fracture appears to be reduced if V40 <64%. Fracture incidence was lower when the mean dose to bone was <37 Gy or maximum dose anywhere along the length of bone was <59 Gy. There was a trend toward lower mean FS for nonfracture patients.

The impact of landscape structure and sown grass margin strips on weed assemblages in arable crops and their boundaries

SummaryA paired‐field study was made in southern England in arable fields, each with or without sown 6‐m wide grass margin strips. Seven field pairs were located in each of small, intermediate and open landscapes, which were based on mean field size. Ground cover, plant species diversity and assemblages were assessed in crop centres, crop edges and non‐crop field boundaries. The data were used to test for effects of sown grass margins, differences in field location, impacts on rare weed species and for landscape effects on weed assemblages. Significantly higher plant species diversity was found in boundaries protected by buffer strips. Annual weeds associated with field edges, notably Anisantha sterilis, were found at lower cover where perennial grass strips were present. Sown grass strips enhanced boundary plant diversity, particularly by increasing polycarpic species. Margin strips had a small influence on the weed flora of the crop edge, possibly reducing weed cover, but had no influence on floras of field centres. Field size and landscape context did not affect weed assemblages, which show marked field‐to‐field variability, though crop type was an important influence. Grass margins did not enhance rare arable weed species and may be a threat to them, if margins are sited where such species are known to occur in the seedbank. With this exception, grass strips are a positive influence on boundary flora diversity and reduce margin weeds in arable landscapes.

A method to search for optimal field allocations of transgenic maize in the context of co-existence

Spatially isolating genetically modified (GM) maize fields from non-GM maize fields is a robust on-farm measure to keep the adventitious presence of GM material in the harvest of neighboring fields due to cross-fertilizations below the European labeling threshold of 0.9%. However, the implementation of mandatory and rigid isolation perimeters can affect the farmers' freedom of choice to grow GM maize on their fields if neighboring farmers do not concur with their respective cropping intentions and crop plans. To minimize the presence of non-GM maize within isolation perimeters implemented around GM maize fields, a method was developed for optimally allocating GM maize to a particular set of fields. Using a Geographic Information System dataset and Monte Carlo analyses, three scenarios were tested in a maize cultivation area with a low maize share in Flanders (Belgium). It was assumed that some farmers would act in collaboration by sharing the allocation of all their arable land for the cultivation of GM maize. From the large number of possible allocations of GM maize to any field of the shared pool of arable land, the best field combinations were selected. Compared to a random allocation of GM maize, the best field combinations made it possible to reduce spatial co-existence problems, since at least two times less non-GM maize fields and their corresponding farmers occurred within the implemented isolation perimeters. In the selected field sets, the mean field size was always larger than the mean field size of the common pool of arable land. These preliminary data confirm that the optimal allocation of GM maize over the landscape might theoretically be a valuable option to facilitate the implementation of rigid isolation perimeters imposed by law.

Agricultural landscape connectivity for the meadow brown butterfly ( Maniola jurtina)

The relationships between movements of the meadow brown butterfly ( Maniola jurtina) and landscape features were examined at different scales in three hedgerow network landscapes of western France. Of the 4174 and 1474 individuals marked in the three landscapes in 1998 and 1999 respectively, a total of 1057 and 285 were recaptured at least once. Partial least squares (PLS) regression was used to model the number of butterflies moving between herbaceous patches within the landscape. The model predictors were related to (i) the distance separating the patches, (ii) the characteristics of the landscape between the patches and (iii) the characteristics of the departure and arrival patches, including the number of individuals marked in each patch. Site effects were tested by fitting separate models on each site and scale effects were tested by varying the extent of the windows in which landscape variables were extracted. The fits yielded models with R 2 values ranging from 0.22 to 0.64. Whatever the site, the distance between both patches and the number of individuals marked in the departure patch, exhibited significant and consistent effects on butterfly movements. Mean field size and direction of green network elements (hedges, field margins) were also relevant in some cases.

Factors affecting changes in grey partridge population dynamics in a French arable farmland over an eleven-year period

The grey partridge Perdix perdix is of conservation concern owing to habitat heterogeneity losses and the negative impact of other environmental factors, e.g., pesticide use, predators, weather or shooting pressure, which are known to be associated with population decline. By an 11-year-period study in an intensively cultivated farmland located in the Paris basin, we aimed to relate the changes in grey partridge population dynamics with the changes in agriculture, monthly rainfall and shooting pressure. Summer drought occurred at the middle time of the study period. At the start of our study, a new cultivation, winter-wheat broadcast in maize-stubble fields, was introduced that probably improved the habitat. But in the next years, there was a loss in habitat diversity due to the disappearance of pastures dedicated to sheep rearing, removal of non-cropped areas and field boundaries and increase in the mean field size. Shooting was annually adjusted to what the owner believed to be a wise harvest. In post-breeding coveys, both percentages of hens with young among total hens and young-to-successful hens ratios first increased and then decreased. The mean brood size was rather weak during the dryness incident. The number of pairs in a more heterogeneous sector was always greater than in a less one. In both sectors, spring abundance first increased and then decreased. In the second half of the study period, the shooting quotas were reduced, especially when the mean brood size fell down. Low hatching rates of clutches and low chick survival rates explain the population decline, as the results are convincing. To stop the population decline in intensive arable farmland, good breeding success is needed. This can be provided by favourable habitats for hens to nest and for chicks to feed.