Arable Weeds Research Articles

Species but not genotype diversity strongly impacts the establishment of rare colonisers

Summary Understanding species coexistence and regulation of biodiversity are major research challenges, yet there is no consensus on the effects of diversity on diversity, including their mediation through plant–plant interactions. We examined how the diversity of recipient communities impacted on the establishment of colonising species. We ran a greenhouse‐based community experiment, creating artificial arable crop communities with varying levels of barley genotype and weed species diversity, analysed with structural equation modelling of responses across trophic levels. Colonising arable weed species establishment was significantly reduced when the recipient communities’ weed species richness, but not barley genotype richness, increased. Recipient plant communities with higher species richness occupied more total niche space and showed stronger competition with colonising species. In contrast, recipient plant communities with higher genotype richness, even though they had slightly greater niche space occupancy, had no significant effects on the colonisation of additional species. Responses were species specific: colonising common weed species establishment was less affected by the recipient plant communities than that of colonising rare weed species. Strong responses of colonising rare species were related to the abiotic rather than the biotic environment created by the recipient communities. The stronger response of colonising rare species suggests greater niche overlap with and competitive inferiority to the recipient plant community, whereas the relative independence of colonising common species indicates less niche overlap and/or competitive equality or superiority. We observed a negative species diversity effect on colonising species, with the effect size increasing with increasing rarity of the colonising species. This differential responsiveness of colonising rare and common arable weed species to the presence of and diversity in the recipient arable plant communities may be crucial in understanding rarity and may result from differential evolutionary pathways in response to interactions.

Living cover crops have immediate impacts on soil microbial community structure and function

Cover cropping is a widely promoted strategy to enhance soil health in agricultural systems. Despite a substantial body of literature demonstrating links between cover crops and soil biology, an important component of soil health, research evaluating how specific cover crop species influence soil microbial communities remains limited. This study examined the effects of eight fall-sown cover crop species grown singly and in multispecies mixtures on microbial community structure and soil biological activity using phospholipid fatty acid (PLFA) profiles and daily respiration rates, respectively. Fourteen cover crop treatments and a no cover crop control were established in August of 2011 and 2012 on adjacent fields in central Pennsylvania following spring oats (Avena sativa L.). Soil communities were sampled from bulk soil collected to a depth of 20 cm (7.9 in) in fall and spring, approximately two and nine months after cover crop planting and prior to cover crop termination. In both fall and spring, cover crops led to an increase in total PLFA concentration relative to the arable weed community present in control plots (increases of 5.37 nmol g−1 and 10.20 nmol g−1, respectively). While there was a positive correlation between aboveground plant biomass (whether from arable weeds or cover crops) and total PLFA concentration, we also found that individual cover crop species favored particular microbial functional groups. Arbuscular mycorrhizal (AM) fungi were more abundant beneath oat and cereal rye (Secale cereale L.) cover crops. Non-AM fungi were positively associated with hairy vetch (Vicia villosa L.). These cover crop-microbial group associations were present not only in monocultures, but also multispecies cover crop mixtures. Arable weed communities were associated with higher proportions of actinomycetes and Gram-positive bacteria. Soil biological activity varied by treatment and was positively correlated with both the size and composition (fungal:bacterial ratio) of the microbial community. This research establishes a clear link between cover crops, microbial communities, and soil health. We have shown that while cover crops generally promote microbial biomass and activity, there are species-specific cover crop effects on soil microbial community composition that ultimately influence soil biological activity. This discovery paves the way for intentional management of the soil microbiome to enhance soil health through cover crop selection.

Effet des dates de semis sur la performance agronomique de Lagenaria siceraria (Molina) Standl. (Cucurbitaceae) et Manihot esculenta Crantz (Euphorbiaceae) en culture associée

Description du sujet. L’association culturale est une pratique bénéfique largement utilisée dans les zones tropicales pour la gestion durable de la fertilité des sols, l’amélioration des rendements de l’agriculture traditionnelle et des revenus des petits producteurs. Objectifs. Évaluer l’effet de la culture associée et de la culture pure de la cucurbite Lagenaria siceraria, plante lianescente et du manioc Manihot esculenta var. ‘Bonoua blanc’, plante érigée, sur les différentes performances agronomiques de chacune de ces cultures. Méthode. Un dispositif expérimental en blocs complètement randomisés avec trois répétitions par traitement a été mis en place. Les traitements analysés sont, premièrement, des cultures associées M. esculenta var. ‘Bonoua Blanc’/L. siceraria avec les semis de la cucurbite à 0 (CAT0), 15 (CAT15), 30 (CAT30) et 45 (CAT45) jours après la mise en place du manioc ; deuxièmement, des semis de cultures pures de la cucurbite aux mêmes dates que pour les cultures associées (CPT0, CPT15, CPT30 et CPT45) et troisièmement, une plantation de culture pure de manioc à 0 jour (CP). Neuf caractères agronomiques chez la cucurbite et huit chez le manioc ont été analysés. Résultats. Les paramètres agronomiques évalués sont les composantes de rendement du manioc qui varient avec l’augmentation du temps de décalage de semis de la cucurbite. Cependant, les performances de la cucurbite diminuent avec cette augmentation du décalage de semis, que ce soit en culture associée ou en culture pure. Malgré une productivité élevée lorsque la cucurbite est simultanément semée avec le manioc, elle reste faible comparativement à la culture pure de la cucurbite. Conclusions. Dans une association cucurbite Lagenaria siceraria et manioc Manihot esculenta, la production n’est pas bénéfique aux cultures prises individuellement. Cependant, l’utilisation de la cucurbite comme plante de couverture en interculture permet de conserver l’humidité du sol et de gérer les surfaces cultivables et les adventices pour en faire bénéficier le manioc en association.

From Traditional Farming in Morocco to Early Urban Agroecology in Northern Mesopotamia: Combining Present-day Arable Weed Surveys and Crop Isotope Analysis to Reconstruct Past Agrosystems in (Semi-)arid Regions

ABSTRACTWe integrate functional weed ecology with crop stable carbon and nitrogen isotope analysis to assess their combined potential for inferring arable land management practices in (semi-)arid regions from archaeobotanical assemblages. Weed and GIS survey of 60 cereal and pulse fields in Morocco are combined with crop sampling for stable isotope analysis to frame assessment of agricultural labour intensity in terms of manuring, irrigation, tillage and hand-weeding. Under low management intensity weed variation primarily reflects geographical differences, whereas under high management intensity fields in disparate regions have similar weed flora. Manured and irrigated oasis barley fields are clearly discriminated from less intensively manured rain-fed barley terraces in southern Morocco; when fields in northern and southern Morocco are considered together, climatic differences are superimposed on the agronomic intensity gradient. Barley δ13C and δ15N values clearly distinguish among the Moroccan regimes. An integrated approach combines crop isotope values with weed ecological discrimination of low- and high-intensity regimes across multiple studies (in southern Morocco and southern Europe). Analysis of archaeobotanical samples from EBA Tell Brak, Syria suggests that this early city was sustained through extensive (low-intensity, large-scale) cereal farming.

Resurveying hedgerows in Northern Germany: Plant community shifts over the past 50 years

Resurveying is a powerful approach to investigate responses of plant species communities to a changing environment. We present a resurvey of hedgerows from the “Knick” landscape of eastern Schleswig-Holstein, Germany. The original survey was done by H. E. Weber in 1967 and new data from totally 51 semi-permanent plots was sampled in 2015. Hedgerows are a key near-natural habitat that can harbour a great biodiversity in otherwise agriculturally intensified landscapes.Our study reveals a distinct shift in the herbaceous species composition of the hedgerows over the past five decades. To understand the reasons for these changes, we compared the mean Ellenberg indicator values (EIVs) and measured pH values, as well as hedge shape parameters of the hedgerows between the recent and the original study. The main driver behind the change in species composition appeared to be the increase in nutrient supply. The hedge shape changed as well, indicating an altered hedgerow management. Interestingly, we found a contradictory relationship between measured pH values and mean EIVs for reaction: while the former showed a decrease over time, the latter suggested an increase.Species richness decreased in some groups (shrubs and herbaceous forest species) but increased in others (grass species and arable weed species), with an overall decline in species richness. An analysis of the species' changes in frequency in relation to their EIVs showed that species with higher nitrogen and temperature scores were more likely to have increased.

Plantemateriale frå jordprøver: uviss alder og ubrukt potensial?

The aim of this paper is to assess the assumptions we make about the age of carbonized and uncarbonized plant materialsfrom soil samples. By questioning the age and origin of plant remains, we investigate an unexploited potential of possiblearchaeological interpretations. As a case study, carbonized and uncarbonized plant remains from a house that dates to thetransition between the Pre-Roman Iron Age and the Roman Iron Age at Hove-Sørbø in Southwestern Norway are investigated. As opposed to the original assumptions based on the preservation conditions at the locality, a total of 1 062 uncarbonized seeds of the arable weeds fat-hen (Chenopodium album) and corn spurrey (Spergula arvensis) are shown to be contemporary with the house. This is a unique find in Norway, and it is assumed that the seeds are a by-product of crop processing, most likely residues from fine sieving of cereal grains. The literature discussing macro analysis and interpretation relevant for Norwegian archaeological contexts is scarce. This is partly due to the fact that analysis of macro remains from such contexts is inherently interdisciplinary, and therefore dependent upon the involvement of archaeologists as well as palaeobotanists for further method development and knowledge production.

Local and regional changes in taxonomic and functional diversity of arable weed communities in Burgundy (France) between the 1970s and the 2000s

Human activities lead to a process of homogenization of biotas in which specialist species are increasingly replaced by common and widespread species. Using a 30-year diachronic record of arable weed communities, we tested this hypothesis by quantifying changes in α- and β-diversity, using both taxonomic and functional diversity and by partitioning β-diversity into species replacement and richness differences. Arable weed communities were sampled in the same 158 fields of the Côte-d’Or region (northeastern France) between the 1970s and the 2000s. For each period, each field was characterized by crop types, soil characteristics and a High Nature Value (HNV) farmland index based on agricultural intensification at the landscape level. At the field scale, we observed a loss of 46% and 38% in α-taxonomic and functional diversity, respectively, which was in accordance with the decrease in the HNV farmland index over the same period. At the regional scale, there was an increase of 15% and 21% in β-taxonomic and functional diversity (across fields), respectively. Crop type and soil characteristics explained similar levels of variation in species replacement, and crop type explained much larger richness differences in the 2000s suggesting that crop and associated practices may exert a high filtering effect. Our results also highlighted a marked decline of common weeds; a process that is far from being counterbalanced by the few colonizing weeds. Rather than to biotic homogenization, this pattern of loss has led to a higher differentiation of arable weed communities. This could correspond to a fragmentation of suitable habitats for species that depend on weeds. This pattern was associated with a decrease of species richness per field; the loss of common species and their associated functions may be of greater significance for agroecosystem functioning.

Transmission of Tomato chlorosis virus (ToCV) by Bemisia tabaci Biotype Q and Evaluation of Four Weed Species as Viral Sources.

Tomato chlorosis virus (ToCV) is implicated in tomato yellows disease in many countries worldwide. It has a wide host range, including cultivated species as well as arable weeds, and it is transmitted in a semipersistent manner by at least five whitefly species or biotypes of the genera Trialeurodes and Bemisia. ToCV is not seed transmitted and more than 36 weed species have been recorded as natural reservoirs, acting as unique sources both for the virus and its vectors when susceptible crops are harvested. In this study, experiments were conducted to determine the transmission parameters of ToCV by biotype Q, the most abundant biotype of Bemisia tabaci in Greece. Results showed that biotype Q is an efficient vector of ToCV and it is able to retain the virus for at least 6 days. This vector was then used for the evaluation of four widespread weed species (Solanum nigrum, Sonchus oleraceus, Amaranthus retroflexus, and Chenopodium album) as ToCV sources through transmission experiments. Solanum nigrum was shown to be the most significant viral source among the tested weeds, followed by Sonchus oleraceus, A. retroflexus, and, lastly, C. album. Nevertheless, none of them was as efficient a ToCV source as tomato. This variation could be attributed to differences in virus concentration in each plant species or possible host preference by the whitefly vector.

The influence of crop tiller density on the breeding performance of a cereal‐nesting specialist

Summary In the pursuit of maximizing agricultural yields and profits, crop management under intensive agriculture has reduced the heterogeneity of crop sward structure within fields. Several farmland bird specialists that nest within arable crops have undergone marked population declines during recent periods of agricultural intensification. Understanding the mechanisms that link crop sward structure to demographic fitness and population change may be important for developing effective conservation solutions. We studied whole‐season breeding performance of a declining cereal crop specialist, the corn bunting Emberiza calandra, to test the relationships between crop sward structure and both nest site selection and reproductive output within intensively farmed landscapes. Experimental double‐drilling of cereal seed was used to manipulate crop sward structure and explain the observed within‐field nest distribution. The density of crop tillers (reproductive cereal stems) was a strong predictor of nest site selection and a disproportionate number of nests occurred close to (15–30 m) crop edges where regular seed sowing overlaps (operational double‐drilling) occurred during crop establishment. Nest survival was subject to a strong crop edge effect and re‐nesting rate increased with mean tiller density in the surrounding crop. Experimental double‐drilling that simulated seed sowing overlaps increased crop tiller density (by 25%) and corn bunting nest density (by 406%) compared to adjacent areas of operational double‐drilling. Corn buntings breeding in intensively managed cereal crops therefore place their nests in areas of high tiller density which under normal sowing practice tend to occur close to crop edges where nest survival is low. A simple population model indicated that productivity under conventional, intensive cereal management may be too low to sustain local populations in the absence of immigration. Modern cereal husbandry therefore creates an ecological trap for nesting corn buntings. Synthesis and applications. This study highlights a novel mechanism by which modern cereal crop management lowers the potential reproductive success of a conservation priority species nesting in intensively managed cereal crops. Unavoidable overlapping of cereal seed along crop headlands, close to crop edges, systematically produces patches of dense sward that attract nesting corn buntings. This creates an ecological trap because nests close to crop edges are subject to high predation rates, and this may be linked to the loss of arable weeds elsewhere within crops. When double‐drilled strips are intentionally provided adjacent to these areas, nesting preference switches to these strips, suggesting a potential conservation solution. Provision of mid‐field double‐drilled strips at least 100 m from crop edges, if similarly selected by nesting females, should raise nest survival rates and improve population trends. Such interventions are simple and cheap to implement, unlike most conservation measures in high‐value cropping systems.

A generalised individual-based algorithm formodelling the evolution of quantitative herbicide resistance in arable weed populations.

Simulation models are useful tools for predicting and comparing the risk of herbicide resistance in weed populations under different management strategies. Most existing models assume a monogenic mechanism governing herbicide resistance evolution. However, growing evidence suggests that herbicide resistance is often inherited in a polygenic or quantitative fashion. Therefore, we constructed a generalised modelling framework to simulate the evolution of quantitative herbicide resistance in summer annual weeds. Real-field management parameters based on Amaranthus tuberculatus (Moq.) Sauer (syn. rudis) control with glyphosate and mesotrione in Midwestern US maize-soybean agroecosystems demonstrated that the model can represent evolved herbicide resistance in realistic timescales. Sensitivity analyses showed that genetic and management parameters were impactful on the rate of quantitative herbicide resistance evolution, whilst biological parameters such as emergence and seed bank mortality were less important. The simulation model provides a robust and widely applicable framework for predicting the evolution of quantitative herbicide resistance in summer annual weed populations. The sensitivity analyses identified weed characteristics that would favour herbicide resistance evolution, including high annual fecundity, large resistance phenotypic variance and pre-existing herbicide resistance. Implications for herbicide resistance management and potential use of the model are discussed. © 2016 Society of Chemical Industry.

Impacts of short-term germination delay on fitness of the annual weed Agrostemma githago (L.)

AbstractTime of seedling emergence is an important step in the life cycle of annual plants because it may determine subsequent performance and success. Timing of emergence is especially critical to plant performance in habitats like arable fields which are subject to frequent disturbances. Within-season variation in timing of germination in the range of only a few days is typical for many arable weeds. However, since it is unclear whether such small deviations in germination date translate into fitness differences in the course of the life cycle, the aim of this paper was to quantify the effects of short germination delays on plant performance. We conducted two generalized randomized block experiments in an unheated greenhouse to study the impact of delayed germination (1, 2, 3 and 7 d) with and without competition, respectively, on the fitness of the arable weed species Agrostemma githago (L.). We expected that delayed germination significantly reduces fitness in terms of several life-history traits, and that the decrease of fitness is higher in the presence of competition. Under realistic conditions with competition through barley, Agrostemma plants with delayed germination of 7 d produced 54% fewer shoots, 57% less biomass, 52% fewer flowers, 36% lighter seeds and were 23% shorter as compared to control plants without delayed germination. Without additional stress through competition with barley this pattern was less pronounced. Thus, in the situation of interspecific competition, early emerging seedlings have biologically significant fitness advantages over later emerging seedlings of the same species.

Organic farming affects the potential of a granivorous carabid beetle to control arable weeds at local and landscape scales

AbstractOrganic farming not only increases plant diversity, but also simultaneously promotes biological weed control through provisioning of ample resources to seed predators.Harpalus affinis(Schrank, 1781) was collected from organically or conventionally managed winter‐wheat fields with high or low surrounding shares of organic fields, aiming to test the impact of agricultural management on its activity density, body size and nutritional condition. Body size and nutritional condition were then related to the arable weed seed predation of this granivorous carabid beetle.Activity density ofH.affiniswas 3.5‐fold higher in organically compared with conventionally managed fields, if these were primarily surrounded by conventional fields. Body size was larger in fields surrounded by large proportions of organically managed land, independent of local management. The nutritional condition of beetles was unaffected by local or landscape scale farming. Per capita seed predation significantly increased with body size, whereas nutritional condition had no effect.The results of the present study suggest that organic farming at local and landscape scales enhances the potential of species to control arable weeds by increasing activity densities and intraspecific body size. Seed predation therefore not only depends on local and landscape effects on the community composition of local guilds of granivores, but also on the contribution of individual species to this important ecosystem service.

Arable weed decline in Northeast Spain: Does organic farming recover functional biodiversity?

The comparison of the frequency, richness and weed cover of total species and functional groups of weeds, including those of interest for birds, pollinators and other invertebrates, and the subset of segetal and rare species from the 1950s to the present, has allowed to detect the consequences of the agricultural intensification in Catalonia (NE Spain) at regional and field scales. We analyzed field plots of conventionally managed cereal fields of the periods 1953–88 and 1996–99 while cereal fields assessed in the period 2005–07 were organic and conventionally managed. Our results indicate a remarkable reduction in weed frequency (58%), species richness (47%) and total weed cover (69%) from the 1953–1988 to 2005–2007 periods. The diminishing species richness was observed in species that are important for birds, pollinators and other invertebrates, but the most drastic decline was observed in the segetal and rare species subsets (75% and 87%, respectively). In current organic crops, the frequency, richness and total weed cover per relevé are significantly higher than in conventional crops, especially for those groups of species that are interesting for fauna and for segetal (more than twice) and rare species (4-fold). Nevertheless, the increase in arable weeds by current organic management is still insufficient to recover the highest plant biodiversity values that were observed before the widespread agricultural intensification in Catalonia.

Influence of conservation tillage and zero tillage on arable weeds in organic faba bean production

In den Erntejahren 2008, 2009 und 2010 wurden am Standort Reinshof (Auenboden/Vega, Sud-Niedersachsen) Feldversuche mit dem Fruchtfolgeausschnitt Sommergerste – Hafer-Sonnenblumen-Gemenge (Winter-Zwischenfrucht) – Ackerbohnen durchgefuhrt. Folgende Ziele wurden verfolgt: Reaktionen der Segetalvegetation auf unterschiedliche Bewirtschaftungsmasnahmen sowie Forderung der symbiotischen N2-Fixierung der Ackerbohnen durch N-Immobilisierung nach Zwischenfrucht-Anbau. Drei Varianten bezuglich der Bodenbearbeitung vor Aussaat der Ackerbohnen wurden miteinander verglichen Direktsaat mit Cross-Slot-Aussaattechnik, reduzierte Bearbeitung mit dem Flugelschargrubber mit Cross-Slot-Aussaattechnik und tiefwendende Pflugbearbeitung mit Einzelkorn-Aussaattechnik. Das Zwischenfrucht-Gemenge bildete im Herbst ausreichend Biomasse (bis zu 28 dt TM ha -1 ), um Ackerwildkrauter effektiv zu unterdrucken. Die Zwischenfruchte akkumulierten Stickstoff in hohem Mase (bis zu 65 kg N ha -1 ) und nachfolgende Ackerbohnen reagierten mit signifikanten Steigerungen (bis zu 10 %) der symbiotischen Stickstoff-Fixierung gegenuber der Kontrollvariante Schwarzbrache. Mit zunehmender Intensitat der Bodenbearbeitung stieg die Abundanz des Leitunkrautes Acker-Senf (Sinapis arvensis) in den Ackerbohnen-Bestanden signifikant an. Die von der Segetalvegetation gebildete Biomasse war Ende Mai/Anfang Juni nach Direktsaat hoher als bei reduzierter oder tiefgrundiger, wendender Bodenbearbeitung. Die Abundanz von Acker-Kratzdistel ( Cirsium arvense ) war im Jahr 2010 umso hoher, je geringer die Bodenbearbeitungsintensitat ausfiel. Die mittleren Korn-Ertrage der Ackerbohnen bewegten sich in den Erntejahren 2009 und 2010 auf niedrigem Niveau (im Mittel: 30 bzw. 24 dt TM ha -1 ). Influence of conservation tillage and zero tillage on arable weeds in organic faba bean production The field experiments were conducted in 2008, 2009 and 2010 on a Gleyic Cambisol near Goettingen, Lower Saxony, Germany. A crop sequence of summer barley, winter cover crops (intercropped oat and sunflower) and summer faba bean was examined under organic farming conditions. Emphasis was given to the studying of arable weeds in faba beans. However, enhancing symbiotic nitrogen fixation of summer faba beans by accumulation of soil-nitrogen by winter cover crops was a second objective in these experiments. The faba bean field plots had been cultivated with three different tillage systems: zero tillage, sowing with cross-slottechnique, conservation tillage (wing share cultivator, rotary harrow) sowing with cross-slot-technique and conventional tillage with mouldboard plough followed by rotary harrow, sowing with precision monoseeder. In plots with zero tillage preceding cover crops were left as mulch on the soil surface. Cover crops accumulated adequate nitrogen amounts and following faba beans reacted with significant increase (up to 10%) in symbiotic nitrogen fixation. Maximum of arable weed biomass was observed in zero tillage-plots at the end of May or early in June. The abundance of the predominant weed wild mustard ( Sinapis arvensis ) increased with tillage intensity, whereas the abundance of creeping thistle ( Cirsium arvense ) increased in 2010 with decreasing tillage intensity. Average grain yield of faba beans was low with only 3.0 and 2.4 t ha -1 in 2009 and 2010, respectively.

Arable weed flora in the Western Siberian grain belt

Between Ekaterinburg and Nowosibirsk, in the Western Siberian grain belt, spring wheat is grown on fertile Chernozem soils. Field and farm sizes are large but the land-use intensity per area is low compared to Central Europe. Fertilizers and pesticides are applied only in low to moderate quantities and yields range between 10 and 20 dt ha-1. We studied the arable weed flora in the northern forest steppe zone of Tyumen region using a randomized sampling design. Surprisingly, the species richness was only moderate, on average 9.8 ± 3.8 species per 100 m². Compared to weed communities of Bashkiria (Southern Ural) and less intensively used arable land of Central Europe these numbers are rather low. Moreover, most of the recorded species were cosmopolitans or widely distributed throughout the temperate zone. We suggest that the land use intensity was high enough to reduce the density of a number of weed species in a way that they were not registered by our random sampling design. The limited conservational value of the weed vegetation of large grain fields in Tyumen leads to the conclusion that if intensification of land use is unavoidable, it should be directed to arable land and not to ex-arable land or ancient grassland, which is of higher conservation value. Segetalvegetation des Westsibirischen Getreidegurtels Die fruchtbaren Schwarzerden im Westsibirischen Getreidegurtel zwischen Jekaterinburg und Nowosibirsk werden grosflachig mit Sommergetreide bestellt. Trotz des grosen Anbaumasstabes ist die Landnutzungsintensitat pro Flacheneinheit gering, wenn man sie mit Mitteleuropa vergleicht. Der Einsatz von Dungemitteln und Pestiziden ist niedrig, und die Ertrage liegen zwischen 10 und 20 dt ha-1. Die Verteilung der Probenflachen erfolgte mittels eines randomisierten Samplingdesigns mit 99 Probenflachen a 100 m² im Tjumener Gebiet des Getreidegurtels. Uberraschenderweise war der Artenreichtum mit einem Mittelwert von 9,8 ± 3,8 Arten niedriger, als bei der geringen Landnutzungsintensitat zu erwarten ware. Verglichen mit Ackergemeinschaften Baschkiriens (Sudural) und extensiv bewirtschafteten Flachen in Mitteleuropa sind diese Artenzahlen gering. Auserdem waren die meisten erfassten Arten Kosmopoliten oder in grosen Teilen der gemasigten Zone verbreitete Arten. Aus unseren Ergebnissen schlussfolgern wir, dass die Landnutzungsintensitat in Tjumen hoch genug ist, um die Dichten einer Reihe von Segetalarten so zu reduzieren, dass sie mit einem randomisierten Samplingdesign nicht mehr oder nur in geringen Stetigkeiten nachzuweisen sind. Die Unterschiede zum Artenreichtum Mitteleuropaischer Acker ergeben sich auch aufgrund des geringen Anteils von Archaophyten in der Flora von Tjumen. Hieraus folgt, dass, wenn eine Steigerung der Landnutzungsintensitat im Getreidegurtel Westsibiriens unvermeidbar ist, sie auf Ackerflachen stattfinden sollte und nicht auf Ackerbrachen oder Grunlandflachen, die einen hoheren naturschutzfachlichen Wert besitzen.

Positive diversity effects on productivity in mixtures of arable weed species as related to density–size relationships

Positive diversity effects on productivity in mixtures of arable weed species as related to density–size relationships

Methods to conduct and analyse weed surveys in arable farming: a review

Arable weeds always accompany arable farming; however, species and abundances vary in space and change in time. Surveys assess weeds on a large spatial scale. The regional and national importance, the abundances in which weeds occur, is derived from surveys. Environmental and management background data assist to explain the weed vegetation. Arable weed surveys can have an agronomic, a botanical or an ecological purpose—we approach the agronomic viewpoint. Scientific value results from spatial data about the arable weed vegetation for modelling the dependencies and predicting future changes on a large scale. Researchers, botanists, farmers, advisors, herbicide manufacturers and other industry players engaged in weed control can get rationale spatial impressions of trends in the weed vegetation. This review focuses on methodical aspects of weed surveys. Forty-three surveys on farmed fields, mainly but not exclusively undertaken in Europe, done in up to nine crops per survey covering periods of 1 to 67 years and including 59 to 4423 fields were excerpted for suitable methods to conduct and analyse surveys. The methods reflect agronomic and other targets, e.g. from vegetation science. When accessing existing data, the interdependencies of the layout and all targets should be handled with care. When setting up surveys for agronomic purpose, it is worthwhile to include 3 years and apply stratified sampling. We recommend assessing abundances rather than presence only. Weed survey data is most suitable for applying multivariate statistics. We recommend using proven methods, without discouraging to explore others. To collect sound explanatory data demands for robust contacts with land managers. Explanatory variables are important in survey analyses to extract knowledge about the drivers of the weed vegetation. We conclude that extra value can be obtained from existing weed survey data. We propose to setup public–private partnerships as a way to carry on with arable weed surveys.

The best of both worlds: Human impact and plant subsistence at the Middle and Late Neolithic semi-agricultural site of Hekelingen III (2900–2500 BC)

Abstract Archaeological sites of the Dutch Neolithic Vlaardingen group (ca. 3400–2500 BC) are known from a large variety of environments with both dryland and wetland settings and display a variety of site functions. However, large and interdisciplinary archaeobotanical data sets are still scarce, which restricts the understanding of the subsistence of this cultural group. This paper presents a reconstruction of the vegetation, an analysis of human impact and a reconstruction of plant exploitation at the Vlaardingen site of Hekelingen III (2900–2500 BC). The analysis is based on an unusually large data set of four pollen sequences and more than 100 macroremain samples, supported by wood and charcoal data. The pollen data allows a reconstruction of the vegetation before, during and after the Vlaardingen occupation, and shows that human impact was very modest. The macroremain data indicates that there is evidence of emmer wheat, naked barley and flax. Arable weed analysis provides indications of an import of naked barley during at least one occupation phase, which corresponds with the restricted palynological evidence of human impact. In addition, there is plenty of evidence for the exploitation of wild fruits, such as hazelnuts, acorns, crab apples, and water chestnuts, and possibly root tubers of Ficaria verna. Despite indications of long-lasting occupation and a large variety of activities at Hekelingen III, the evidence of the consumption of agricultural products rather than their production and of the collection of a wide range of fruits fits very well with further indications of hunting, fishing and fowling and the absence of heavy, permanent structures. Moreover, the site can be seen as being part of a settlement system in which also other Vlaardingen sites played a role, such as the nearby site of Hellevoetsluis, where permanent occupation was verified and crops were locally cultivated.

Perturbation Experiments in Community Plant Species during Recovery from Agricultural Abandonment in a Semi-Arid Region of Central-Western Spain

Background: Can high diversity mixtures of later succession plant species be able to suppress early successional (arable weed) species than low diversity species mixtures? Can the removal of plant functional groups have important consequences on the sys-tem stability? Location: The study area was located at 850 m a.s.l., fifteen kilometers (15 km) to the west of Salamanca city, Spain, in a dehesa-like woodland. Methods: The field experiment was installed in Spring 1996 (May). The plots represented former agricultural lands cropped with (a rotation of) monocultures and abandoned right at the beginning of the experiment after the last crop was harvested in 1995. Before in-stalling plots, the fields were harrowed and equalized. The treatments (NC-natural colonization, LD-low diversity seed mixture and HD-high diversity seed mixture) were randomly allocated to the plots in each block. The experiment was organised accord-ing to a block design with five replicate blocks. Within each block, four plots measur-ing 10 × 10 m were marked out and each of the three treatments was randomly as-signed to one plot. All plots were separated by 2 m walkways. Results: The competitive ability of the sown species in different mixtures in LD, valued on the basis of their performance in HD, is a good predictor of their ability to suppress the weed crops spe-cies. This was also corroborated by the high relationship between the efficiency of the sown species in both treatments of species mixture (R2 = 0.51, F (1, 33) = 34.56, P

Et monumentalt midtsulehus ved Nørre Holsted i Sydjylland

Et monumentalt midtsulehus ved Nørre Holsted i Sydjylland