Margin Strips Research Articles

Disturbance effects on early succession of field margins along the shaded and unshaded side of a tree lane

Effects of light and disturbance on species diversity and vegetation succession were assessed during early succession of newly created sown and unsown field margin strips installed along the sunny and shady side of a tree lane. During succession, disturbance by farming operations was simulated by a single rotocultivation of the margin strip. Two years after the disturbance event, species richness was not significantly determined by light regime or disturbance level. However, shortly after the disturbance event, disturbance caused a temporary increase in species richness on the unshaded side due to introgression by annual species in created gaps. On the shaded side, species richness was significantly lower in disturbed plots. Disturbance caused a temporary increase in importance of spontaneous annuals, which were quickly replaced by perennial sown and unsown monocotyledons and to a lesser extent by perennial unsown dicotyledons. The importance of spontaneous species within functional groups increased, resulting in higher similarity between sown and unsown vegetation.

Evolution of the vegetation of mown field margins over their first 3 years

Abstract Early succession of newly created sown/unsown margin strips on ex-arable land, managed by two cuttings per year with/without removal of cuttings, was characterised by the replacement of annuals in favour of perennials, a steady increase in the importance of monocotyledons and a decrease in non-nitogen-fixing dicotyledons. Mowing with removal of cuttings delayed this succession pattern. Sorenson's qualitative similarity index revealed that species composition of the sown communities in terms of species occurrence became increasingly similar to the unsown plots. Furthermore, convergence in vegetation composition between sown and unsown plots occurred also in terms of species importance as assessed by Sorenson's quantitative index. Similarity, in species, importance was significantly enhanced by cutting with removal of cuttings. During the first three successional years, species diversity of sown and unsown communities converged in time, irrespective of mowing regime or location. The decrease in species diversity, number and density of sown wildflowers was more pronounced under a mowing regime without removal of cuttings. The annual addition of mown roadside herbage significantly enhanced species-richness, but not the importance of dicotyledons.

An indicator of plant species richness of semi-natural habitats and crops on arable farms

Abstract As a straightforward method of assessing on-farm biodiversity, plant species numbers were compared in a fixed sampling area for each type of habitat distinguished independent of farm size and applicable for comparing different farm strategies. Using the species–area relationship, the minimum sampling areas were determined. For ditch banks, crops and field margin strips sampling areas of 400 m2 (independent of the ditch bank width), 100 and 25 m2, respectively, were proposed. Indicator threshold values for conventional farms were defined based on the best 10% of the variation in species richness among farms. With appropriate farm management these targets could be achieved. In comparison to ditch banks, crops and sown field margin strips were relatively poor in plant species. The respective numbers of naturally occurring plant species found in crops and field margin were both significantly smaller than those found in ditch banks. In contrast, ecological management of ditch banks appeared to be a promising means of increasing species richness.

Agricultural Landscapes

SUMMARY Most agricultural landscapes are a mosaic of farmers' fields, semi-natural habitats, human infrastructures (e.g., roads) and occasional natural habitats. Within such landscapes, linear semi-natural habitats often define the edges of agricultural fields. This paper reviews the role and interactions within and between the flora and fauna of these elements. In temperate, intensive agriculture, such field margin habitats, which historically had true agricultural functions, now are important refugia for biodiversity. As man-made habitats, field margins may also have important cultural roles as part of landscape heritage, e.g., hedges in Britain. Although field margins are not usually specific or characteristic habitat types, they contain a variety of plant communities in a variety of structures. These may range from aquatic elements, to ruderal and woodland communities, with combinations of them over small spatial scales. Studies demonstrate a variety of interactions between fields and their margins. Some margin flora may spread into crops, becoming field weeds. Margins also have a range of associated fauna, some of which may be pest species, while many are beneficial, either as crop pollinators or as pest predators. Agricultural operations, such as fertilizer and pesticide application, can have adverse effects on the margins. The biodiversity of the margin may be of particular importance for the maintenance of species at higher trophic levels, notably farmland birds, at the landscape scale. Margins can also contribute to the sustainability of production, by enhancing beneficial species within crops and reducing pesticide use, though further research on the predictability of these effects is needed. In northwestern Europe, a variety of methods to enhance diversity at field edges have been introduced, including sown grass and flower strips. While minor conflicts exist, notably for the conservation of rare arable weed species and the spread of some pests and weeds, the impacts of well-managed field margins on weed flora and arthropods indicate mostly beneficial effects. Thus field margin strips offer a practical means of providing on-farm biodiversity and enhancing more environmental and sustainable production.

Effects of landscape context on herbivory and parasitism at different spatial scales

Local community structure and interactions have been shown to depend partly on landscape context. In this paper we tested the hypothesis that the spatial scale experienced by an organism depends on its trophic level. We analyzed plant‐herbivore and herbivore‐parasitoid interactions in 15 agricultural landscapes differing in structural complexity using the rape pollen beetle (Meligethes aeneus), an important pest on oilseed rape (Brassica napus), and its parasitoids. In the very center of each landscape a patch of potted rape plants was placed in a grassy field margin strip for standardized measurement. Percent non‐crop area of landscapes was negatively related to plant damage caused by herbivory and positively to the herbivores’ larval mortality resulting from parasitism. In a geographic scale analysis, we quantified the structure of the 15 landscapes for eight circular sectors ranging from 0.5 to 6 km diameter. Correlations between parasitism and non‐crop areas as well as between herbivory and non‐crop area were strongest at a scale of 1.5 km, thereby not supporting the view that higher trophic levels experience the world at a larger spatial scale. However, the predictive power of non‐crop area changed only slightly for herbivory, but greatly with respect to parasitism as scales from 0.5 to 1.5 km and from 1.5 to 6 km diameter increased. Furthermore, the effect of non‐crop area tended to be stronger in parasitism than herbivory suggesting a greater effect of changes in landscape context on parasitoids. This is in support of the general idea that higher trophic levels should be more susceptible to disturbance.

Plant-insect communities and predator-prey ratios in field margin strips, adjacent crop fields, and fallows.

The management of field margin strips for the enhancement of biodiversity of plant-insect communities and natural-enemy populations was studied on experimental farms near Göttingen (Germany). Young and old, sown and naturally developed field margin strips were compared and differences to large fallows established. The five types of field margin strips (around cereal fields) were: (1, 2) 1- or 6-year-old naturally developed strips, (3) strips sown with a Phacelia mixture, (4) strips sown with a mixture of 19 wild flower species, and (5) strips sown with winter wheat or oat as a control. The naturally developed vegetation of the field margin strips was dominated by aggressive weeds, presumably due to the intensive farming practices and the fertile soils. Cirsium arvense populations decreased, while Elymus repens populations increased with age of habitat. Sowings were suitable to suppress these aggressive weeds. Potted plants of mugwort (Artemisia vulgaris) and red clover (Trifolium pratense) were exposed in the field margin strips to study arthropod colonization of these experimentally standardized plant patches. Arthropod species richness did not differ between field margin types, reflecting the overall similarity in floristic diversity, but sprayed and strip-free edges of cereal fields had a reduced diversity. Dispersal of insect populations of red clover into the cereal fields decreased with increasing distance, but benefited from adjacent field margin strips. Populations of predators (mainly spiders) as well as predator-prey ratios were significantly larger in 6-year-old than in 1-year-old strips emphasizing the importance of habitat age for natural enemies and possible biological control. Predator-prey ratios were also higher on old than young fallows. Large fallows had greater predator-prey ratios than small field margin strips emphasizing the trophic-level hypothesis of island biogeography in that the relative importance of natural enemies increased with habitat area. Insect species richness was only marginally influenced by area and not by age. As species richness of predators did not increase with area and age, species diversity and the possible biological-control function did not covary.

The influence of sown margin strips, management and boundary structure on herbaceous field margin vegetation in two neighbouring farms in southern England

Field margins are refugia for many species in arable landscapes, but are also affected by adjacent farming operations and by margin management. Botanical diversity in 117 hedge-bottoms on two neighbouring farms in Yatesbury, Wiltshire, UK, were studied in relation to boundary structure, hedge management practices and adjacent features on the farm to which they belong. The farms differed with regard to field margin and hedge management practices, but soil type and cropping patterns were very similar. Attention was also paid to effects of sown grass strips, coppicing and gapping-up of hedges and different approaches towards field margin management. Results indicated that there were no significant differences in woody species richness between the two farms, with hedges of similar composition. There was significantly higher herbaceous species diversity on the farm with grass strips. Multivariate analyses indicated that community differences were present, with a number of annual and biennial plant species predominating on the farm without grass margins. Principal components analysis (PCA), redundancy analysis (RDA) with forward selection and associated Monte-Carlo permutation tests, and stepwise linear regression showed the following. (1) Sown grass and/or wildflower strips adjacent to the hedge-bottom have a positive effect on species richness of the hedge-bottom vegetation. They also reduce the abundance in the hedge-bottom of Anisantha sterilis, Galium aparine, Poa trivialis and Urtica dioica, all four considered to be pernicious weed species. (2) Coppicing in combination with gapping-up of hedges increases species richness of the hedge-bottom vegetation and has a positive effect on floral diversity in the landscape. (3) Diversity in management, boundary structure and adjacent features within one farm increases the floral diversity at the farm scale. Diversity in management, boundary structure and adjacent features between farms increases the floral diversity on a landscape scale.

Summer bird abundance and distribution on set‐aside fields on intensive arable farms in England

The abundance and distribution of breeding birds were compared on paired fields comprising one set‐aside field and one crop field, on 11 intensive arable farms in eastern and western England. A single observer made four visits to all set‐aside and crop fields between April and July and recorded all birds seen during standardised counts and transects.Rotational and non‐rotational set‐aside supported higher densities and more species of birds than fields of wheat, brassicas, root crops and seed rye. These differences in density, between set‐aside and crops, were evident across a suit of species including waders, gamebirds, pigeons and passerines and were particularly marked on rotational set‐aside. The majority of species recorded in fields away from boundaries would have been feeding rather than nesting there and higher bird densities on set‐aside compared with adjacent arable crops probably reflects greater food abundance in the former.The study is the first to demonstrate a clear habitat preference for set‐aside by a wide range of bird species throughout the breeding season and it allows a number of recommendations to be made concerning the development of cost‐effective agri‐environment measures. The fact that the majority of birds utilised the outer 5 m, or in some cases 20 m, margin of the field suggests that many of the benefits of whole field set‐aside may be derived from marginal strips. A slight, but not significant preference for rotational over non‐rotational set‐aside suggest such margins should be managed to maintain a patchy, relatively diverse sward of arable plants. A key feature of set‐aside is the scale at which it has been incorporated into the arable landscape. Agri‐enviromental schemes will only provide similar national benefits if they are implemented on a wide scale in such as way as to promote high uptake by farmers.

Landscape structure and biological control in agroecosystems

Biological pest control has primarily relied on local improvements in populations of natural enemies, but landscape structure may also be important. This is shown here with experiments at different spatial scales using the rape pollen beetle (Meligethes aeneus), an important pest on oilseed rape (Brassica napus). The presence of old field margin strips along rape fields was associated with increased mortality of pollen beetles resulting from parasitism and adjacent, large, old fallow habitats had an even greater effect. In structurally complex landscapes, parasitism was higher and crop damage was lower than in simple landscapes with a high percentage of agricultural use.

Attraction and retention of Episyrphus balteatus DeGeer (Diptera: Syrphidae) at an arable field margin with rich and poor floral resources

The abundance of a beneficial syrphid species along two strips of an arable field margin with contrasting floral richness were assessed to determine how the strips attracted and retained Episyrphus balteatus, whose larvae are aphidophagous. One margin strip was supplemented by eight species of flowering plants, planted between the hedgerow and the arable crop. E. balteatus was observed foraging on all eight species at this florally rich strip. A control strip had no additional floral resources other than those naturally present. E. balteatus was significantly more abundant at the rich strip over 21 trapping days. The effectiveness of each strip to retain. E. balteatus was assessed by observing and recording the time spent by paint marked individuals within each strip. The rate of dispersal of E. balteatus from each strip was determined from the percentage of marked individuals remaining in a strip over time. Data from trapping E. balteatus, and from determining their dispersal rates from the strips were used in a simple mathematical expression to show that E. balteatus were attracted into the rich strip more than the control strip on nine study days during the first half of the investigation. E. balteatus dispersed significantly more slowly from the rich strip on nine study days during the second half of the study. Managing hedgerows and fieldmargins to create florally rich habitats to attract and retain E. balteatus is an option farmers can consider if E. balteatus is to be encouraged into fields as part of a system of integrated pest management.

Arthropod abundance and diversity in differently vegetated margins of arable fields

Field margin strips, sown with either the main field crop, rye grass ( Lolium perenne), a grass and wild flower mixture, or left to natural regeneration, were established in replicated plots along three hedgerows and field edges. Pitfall traps were used to assess the carabid beetle fauna in mid-summer between 1993 and 1996. Suction sampling was used to assess a wider range of arthropod taxa in June 1994. Pitfall data showed no significant overall effects from plot-type although significant differences in carabid activity-density were found between fields and years. In contrast, suction sampling showed marked differences between the crop, the hedge and the plots with different vegetation structures. There was a significant positive correlation between faunal and floral diversity, with arthropod diversity lowest in the crop, low in the crop edge, higher in the more diverse sown plots and highest in the hedge. Studies of over-wintering arthropods from soil samples revealed similar trends, confirming that arthropods colonised sown margin strips within 11–15 months of establishment. The results indicate that the appropriate scale for using pitfall traps is at the field rather than the plot scale. The introduction of botanically diverse field margin strips is shown to be an important method of increasing the arthropod diversity of semi-natural habitat in farmland.

The effects of organic and integrated farming on rare arable weeds on the Forschungsverbund Agrarökosysteme München (FAM) research station in southern Bavaria

Since the compensation for unsprayed field margin strips was recently reduced in Germany, the area used in this way has rapidly declined. These experiences show that management restrictions for the sake of species conservation are only accepted when high compensation is paid and efficiency is regularly controlled. The aim of the present investigation was to determine if conservation of arable weeds could be reached by management systems without imposing such restrictions. Therefore, 110 ha farmland, situated in the Tertiärhügelland in southern Bavaria, was investigated to compare the effects of a change from conventional farming to an organic and an integrated cultivation system. Four years after the change to the integrated farming system, the number of rare species had decreased at 90% of all sampling points where they occurred. This development seems mainly to be caused by minimum tillage, which was applied to prevent soil erosion. In the organic management area, rare weed species were observed at 94 grid points. At 33% of them weeds decreased, at 41% they remained unaffected, and at 26% weeds increased in number. Among the species occurring often enough for a statistical analysis, four did not change significantly, while Legousia speculum-veneris was found more frequently. Investigations in the population development at selected points showed a differing response of individual species to these management changes. Nevertheless, frequencies as well as densities of the rare weeds stayed constant within the fields under organic management. This and the respective literature lead to the conclusion that the influence exerted on rare weed species by the organic cultivation system is neutral to positive. Thus, organic management could be at least a way to prevent further decline in rare weeds.

Impact of Nitrogen and Organic Manures on Yield, Botanical Composition and Herbage Quality of Two Contrasting Grassland Field Margins

ABSTRACT Grassland field margin strips, including hedge bottoms, may support a high diversity of wild flower and grass species. This diversity is threatened by applications of fertilizer nitrogen. Organic fertilizer, in the form of farm-yard manure and rain-diluted liquid slurry which only slowly release nitrogen for plant uptake, might prove less damaging. A 5-year experiment on two contrasting sheep grazed, species-rich grassland field margin sites adjoining a mature hedgerow in mid-Wales compared three levels of fertilizer N (0, 100 and 300 kg N ha−1 year−1) with farm yard manure (FYM) and rain-diluted slurry containing an average annual equivalent of 30–42 kg N ha−1 and 27–72 kg N ha−1 respectively. The aim was to assess the impact of treatments on the plant communities of the hedge bottom and field margin strip ecosystems, and to establish whether the species diversity contained within the strips could be encouraged without significantly undermining the quantity and quality of the herbage. By the end of the experiment, the forb component of both ecosystems had been drastically reduced by the high N treatment, to less than half of their original level. The organic treatments on the other hand, particularly FYM showed signs of developing species-rich communities, while at the same time providing a relatively high yielding and nutrient-rich field margin sward of high mineral content. The implications of FYM deposition, particularly in terms of nature conservation considerations are highlighted.

The effects of weed cutting upon the biota of a large regulated river

1. The effects of macrophyte removal from a regulated reach of the River Great Ouse, UK, were recorded. The relationship between macrophyte cover, zooplankton distribution and 0+roach Rutilus rutilus (L.) distribution, diet and growth, were compared before, directly after, and over several weeks following weed-cutting operations. 2. Both zooplankton and fish were significantly associated with the macrophyte zone before weed cutting. It is suggested that this zone provides high food densities and refuge during periods of elevated flows. 3. Removal of all but a 2 m marginal strip of the macrophyte zone led to a rapid decline in the mean densities of planktonic Cladocera, probably as a result of increased washout, fish predation and starvation. This was accompanied by a rapid decline in the growth rate of the roach, which were forced to feed on the less nutritious aufwuchs. 4. It is suggested that river management involving weed cutting adjacent to one bank in alternate years would be sufficient to prevent loss of channel capacity and would provide a refuge for fish and zooplankton.

Mikrographische Chirurgie Eine methodische Bestandsaufnahme

Micrographic surgery is one of the most effective methods in the treatment of basal cell carcinoma. In the last 20 years this method has been further developed and modified. Three kinds of micrographic surgery are now available: the Mohs method, the margin strip method ("Tübingen torte") and the "Munich" method. All three variants have the same goal; radical tumour removal with optimal sparing of surrounding tumour-free tissue. They differ, however, in the technique of tumour excision, the preparation of the histological specimens and the interpretation of the slides. In this paper the authors take stock of the methods available and describe the differences, advantages and disadvantages.

STRUCTURE, LIFE HISTORY AND SYSTEMATICS OF RHOICOSPHENIA (BACILLARIOPHYTA). V. INITIAL CELL AND SIZE REDUCTION IN RH. CURVATA AND A DESCRIPTION OF THE RHOICOSPHENIACEAE FAM. NOV.1

ABSTRACTThe initial epivalve of Rhoicosphenia curvata (Kütz.) Grun. differs from vegetative valves in having a strongly arched section, a wide hyaline marginal strip, no pseudosepta, an unthickened margin, and a terminal raphe fissure at the head pole. The initial epivalve is of the D type, with short raphe fissures. The epicingulum consists of three bands as usual, but they are narrower and more delicate than those of vegetative cells. The initial hypovalve and hypocingulum are similar in every way to those of vegetative cells, except for the rounded section of the hypovalve. During size reduction the almost isopolar outline of the initial valves and their immediate descendants gives way to an increasingly strong heteropolarity, and this is accompanied by changes in the relative lengths of the raphe slits and the shape of the central area. Different populations have different gametangium and initial cell sizes, suggesting the presence of races within the species. The structure of the initial cell indicates that Rhoicosphenia is less closely related to the monoraphid genera than to the gomphocymbelloid genera, confirming conclusions reached from studies of the vegetative cell and auxospore formation. Rhoicosphenia should therefore be separated into a new family, the Rhoicospheniaceae, which is described.

Fissidens traversii, a new species from Queensland, Australia

Abstract Fissidens traversii, a new species from Queenslahd, Australia, is characterised by the rounded leaf apex, costa papillose and finishing short of the apex, mamillose, multipapillose cells, short dorsal lamina and vaginant laminae (which usually have a marginal strip of transversely elongated calls in the lower half), reaching almost to the apex of the leaf.

Emplacement model for some “Tethyan” ophiolites

Detailed mapping of part of the Othris (=sub-Pelagonian) zone in east-central Greece has revealed the existence of a stack of thrust sheets of Early Cretaceous age. These have emplaced ophiolites onto a formerly stable Mesozoic continental margin from an ocean that lay to the west of the Pelagonian zone. Systematic facies changes from one thrust sheet to the next overlying thrust sheet suggest that the ophiolites originally formed part of an ocean adjacent to the inferred continental margin and were laterally continuous with it. Thus the ophiolites are regarded as parts of a tectonically emplaced marginal oceanic strip (this does not imply they were parts of a “marginal ocean basin” in the sense of Karig). It is speculatively suggested that prior to emplacement the mantle underneath this marginal strip had been serpentinized and raised to a much higher level. Such a process would overcome one of the problems of ophiolite emplacement–the necessity to postulate uphill movement of heavy oceanic crust and upper oceanic mantle. Serpentinization is attributed to water freed by dehydration reactions in a slab sinking beneath the marginal oceanic strip from a trench initiated at some distance from the continental margin.

Month in the Patent Office

Skin‐stressed aircraft bodies, hulls, or floats comprise a shell composed of a number of channel section strips assembled in sets with the channel flanges projecting inwardly, each set constituting a section of the skin and connected to the adjacent set by securing together outwardly directed flanges formed on or fixed to the marginal strips of the sets. A monocoque fuselage 1, Fig. 1, of substantially oval section tapering in width to the rear end 5 and provided with an engine supporting frame at the forward end, is divided at 10 into two parts, of which the forward is built up in two sections 22, 23 joined in a horizontal plane 24 and the after part is built up from sections 2, 3, Fig. 3, joined in the plane of symmetry. The latter sections each comprise a half‐bulkhead 2a, 3a respectively to which channel strips 6 are secured by engagement of side flanges 6a in peripheral slots 7 and by welding. The abutting flanges 6a of the several strips are additionally interconnected by riveting along their length. The half‐bulkheads together with their attached channel strips are interconnected by engagement of a rod 9 in tubular lugs 8 formed alternately on the edges of the parts 2a, 3a, and also by riveting or bolting together the marginal pairs of channel strips. These may be formed with up‐turned abutting flanges 11 which are faired by a split tube 13 slidden or otherwise engaged therewith. Adjacent fuselage parts may be interconnected by riveting or otherwise securing juxtaposed bulk‐heads. The channel strips 6 are shaped to correspond with the longitudinal changes in section of the fuselage and may be reduced in gauge toward the tail or be of varying gauge to suit localized stresses. In a modification in which annular frames 16 of channel or box‐section are substituted for bulk‐heads, Fig. 10, the flanges 6a of channels 6 are inwardly bent at 6b to rest on the frames and attachment is by angle members 17, of which one limb is secured to flanges 6a and one to a side wall of frame 16. Fig. 11 shows modified channel member, the flanges of which form on assembly a series of longitudinal stiffeners, 6c. Attachment to frame 16 is by bent‐up fittings 22 secured to the flanges by bolts 24 which connect them together.

The Diorites and Associated Rocks of the Glen Tilt Complex, Perthshire

The Glen Tilt Complex, one of the larger masses of the Newer Granites of the Central Highlands, is included in sheet 64 of the Geological Survey of Scotland. The greater part of this complex is a granite which is bounded on the south-west and southeast by an earlier series of intermediate and basic rocks. The granites described in this contribution are restricted to a small area at the south-eastern margin of the large granitic intrusion generally known as the Beinn Dearc granite. The smaller and independent intrusion of the Sron a ‘Chro’ granite and a number of smaller masses of granite associated with the marginal strip of diorites on the north-western side of Glen Tilt have also been examined. These small isolated areas appear to be contemporaneous with the intrusion of the main Beinn Dearc mass and have been intruded between the earlier diorites and the margin of the intrusion, a feature not uncommon in many of the other Scottish Newer Granites. A small independent mass of muscovite-biotite-granite intruded into quartz-mica-diorite occurs on Conlach Mhor. Although these rocks are completely isolated from both the biotite- and muscovite-biotite-granites of the main Beinn Dearc intrusion their essential similarity with the latter leaves no reasonable doubt of their common origin.