Weed Species Richness Research Articles

Influences of long‐term different types of fertilization on weed community biodiversity in rice paddy fields

In order to provide a scientific basis for developing integrated weed management strategies in rice paddy fields, this study investigated the influences of different types of fertilization on weed biodiversity. The experiment was conducted at Long‐term‐located Monitoring Station for Soil Fertility, Agricultural Science Academy, of Jiangxi Province, China. Five fertilization treatments were set: no fertilization (NOF), PK, NP, NK, and NPK. The results showed that the influence of different fertilization treatments on weed community traits followed the models PK > NOF > NK > NP > NPK for species richness, PK > NOF > NK > NP > NPK for species diversity, NPK > NP > NK > NOF > PK for community dominance, and PK > NOF > NK > NP > NPK for community evenness. Under NPK (i.e. balanced fertilization), the weed species diversity and richness and weed community evenness were the lowest. The principal component analysis showed that the weed community was divided into three groups: (i) NK and a part of NOF; (ii) NP and NPK; and (iii) PK and NOF. The correlation analysis indicated that the influence of each macro‐element on the weed community followed the model N > P > K. The organic content in the paddy soil might have played an equally important role with the amount of available N in determining the weed community's characteristics. Regarding the way by which N, P, and K influenced the weed community, the amount of available P and K mainly influenced the organic content, while the amount of available N influenced both the organic content and light transmittance within the canopy, thereby enhancing the capacity of rice to compete with weeds.

Influence of crop rotation and meteorological conditons on biodiversity of weed communities in spring barley (Hordeum vulgare L.)

The paper presents the analysis of changes in weed biodiversity in spring barley cultivated in the years 1990-2004 in crop rotation with a 25% proportion of this cereal (potato - spring barley - sowing peas - winter triticale), when it was grown after potato, and in crop rotation with its 75% proportion (potato - spring barley - spring barley - spring barley), when it was grown once or twice after spring barley. In the experiment, no weed control was applied. Every year in the spring (at full emergence of the cereal) and before the harvest, the composition of weed species and numbers of particular weed species were determined, and before the harvest also their biomass. On this basis, the constancy of species in particular years, Shannon-Wiener species diversity indices and diversity profiles according to Rényi were determined. Weed species richness increased linearly at all plots during the 15-year period. <i>Chenopodium album</i> was a constant and dominant species in terms of weed species density and biomass year after year. The quality of the plot had no clear influence on the diversity of weeds in barley. Weed density and biomass showed high year-to-year variability and a positive correlation with the amount of precipitation and a negative correlation with temperature during the period of the study. The significance of the correlation between the productivity of barley and weed diversity was not confirmed.

Effects of fertilizer application on summer usage of cereal fields by farmland birds in central Hungary

Capsule Despite negative effects of inorganic fertilizer on weeds and invertebrates in cereal fields, impacts on bird usage were weak and non-linear. Aim To assess the effects of inorganic fertilizer application to winter cereals on breeding-season usage by farmland birds. Methods We measured bird usage of winter-sown cereal fields across a gradient of inorganic fertilizer inputs and tested for influences of management intensity and availability of semi-natural habitat on species richness and abundance of farmland birds. Results Avian species richness and bird abundance were unrelated to fertilizer inputs, and declined at higher levels of total vegetation cover. Sky Lark abundance increased, while Yellow Wagtail counts declined with the extent of semi-natural habitat. Sky Lark abundance increased with vegetation cover and peaked at an intermediate level of weed species richness. Yellow Wagtail counts peaked at intermediate levels of fertilizer inputs. Conclusions Compared with much of western Europe, cereal production in central Hungary is characterized by modest fertilizer inputs and large areas of semi-natural habitat. There was little evidence that increased applications of fertilizer are likely to have negative impacts on farmland birds, although increased application might reduce habitat suitability for Yellow Wagtails. Loss of semi-natural habitat is likely to have negative impacts on Sky Larks.

Landscape and land-use effects on weed flora in Mediterranean cereal fields

Land-use intensity and landscape complexity could potentially affect weed flora of agroecosystems, by means of changes in species richness and composition. However, previous results indicate diverging patterns. This paper evaluates the relative importance of both factors on weed species richness and weed community composition within cereal fields in Catalonia (NE Spain). The percentage of arable land plus that occupied by human settlements within a circular sector of 1 km radius was used as a surrogate for landscape complexity and the amount of nitrogen inputs for land-use intensity. The seedbank, which could reflect the long-term effects of the agricultural intensification, and the emerged vegetation with and without weed control were surveyed to obtain comparable assessments of the weed flora, taking into account differences caused by weed control effectiveness. Intensive management induced changes in the emerged weed flora and caused a decline in species richness. Moreover, in the long-term (seedbank), it has also led to a certain level of weed loss. Conversely, landscape complexity had little effect on the seedbanks and emerged flora of cereal fields. Consequently, weed conservation policies in Mediterranean cereal fields should focus on farming practices and need not take account of the surrounding landscape.

A novel index of land use intensity for organic and conventional farming of Mediterranean cereal fields

The conservation of biodiversity in agro-ecosystems is closely related to land use. Intensive land use is considered to be a major cause of biodiversity loss. Most studies addressing the effect of land use intensity on biodiversity have compared organic and conventional systems. However, little is known about the heterogeneity of the management intensity within each farming system. We hypothesise that there is a gradient of land use between and within the farming systems and that an index of management intensity is more useful than the farming system for evaluating the effects of the management practices on weed flora. In this study, 18 pairs of organic and conventional cereal fields were selected in northeastern Spain. The farmers were interviewed to gather information on the management practices performed. We selected the five following variables from these interviews: nitrogen inputs, crop diversity, weed control, seed origin and cereal ratio. We used principal components analysis to create a new management index. Weed species richness was recorded in 10 field pairs before crop harvest. Our results showed that the index values displayed huge variation within each farming system. Index values of conventional fields varied between −0.01 and 1.00, whereas within organic ones the values ranged from −1.19 to 0.18. The index better explained weed species richness than did the farming system. The index values demonstrate the existence of a land use intensity gradient, which indicates that it is an over-simplification to always equate organic farming with low intensity management. Here, we also prove that this new index is more appropriate for evaluating the effects of management practices on weed species richness than the classical organic-conventional dichotomy.

Exploring the potential for sustainable weed control with integrated rice−fish culture for smallholder irrigated rice agriculture in the Maranhão Lowlands of Amazonia

AbstractCombining existing traditions of rice and of fish in an integrated rice−fish (IRF) culture is a promising strategy for sustainably increasing land productivity and diminishing the need for external inputs in smallholder agriculture of Amazonia. This study evaluates the potential of IRF for weed control in irrigated rice production. It was conducted from August 18 to December 5, 2008 in the Maranhão lowlands in the eastern periphery of Amazonia. We compared weed communities in four 3-year-old IRF and four adjacent ‘conventional’ irrigated rice (CIR) fields at 20 and 40 days after transplanting (DAT), at the mid-vegetative stage and at the onset of flowering, which served as an indicator of potential grain yield. Rice–fish fields contained differing mixtures of herbivore and omnivore fish species totaling 4000 fish per ha or 1.7 fish per m3. Total weed density was reduced in the IRF system, particularly early in the season, the most critical stage for rice development. The integration of fish into irrigated rice cultivation affected weed species composition, with fish-weeding preferentially reducing monocotyledonous Cyperaceae, one of the more aggressive and problematic weed families in this region. Monocot weed density was negatively correlated with rice aboveground biomass at 40 DAT rice. Although floristic similarity between IRF and CIR fields was low, the impacts of IRF on weed species diversity and weed species richness were not significant. Thus, IRF was not associated with a simplification of the weed community. We conclude that fish-weeding may substitute for manual or chemical weeding in irrigated rice agriculture, an important consideration for resource-poor smallholder agriculture in environmentally sensitive riverine or delta areas of eastern Amazonia.

Does soil biota benefit from organic farming in complex vs. simple landscapes?

Organic farming can counteract detrimental effects of agricultural intensification on farmland biodiversity. Enhancing biodiversity with agri-environmental schemes is hypothesized to be more efficient in simple than complex landscapes, a pattern confirmed for many aboveground taxa. Although belowground biodiversity is an important part of the agroecosystem, studies on the interacting effects of local and landscape intensification on the belowground detritivore community, including bacteria, fungi, collembolans and earthworms are lacking. We sampled diversity and abundance of arable weeds, earthworms and collembolans, soil respiration rate and microbial biomass in 12 pairs of organically and conventionally managed fields in landscapes differing in structural complexity. Organic farming significantly enhanced species richness of arable weeds, while conventional farming enhanced soil respiration and abundance of Collembola with furca. This research shows that the landscape context plays a significant role in shaping effects of organic vs. conventional farming on soil biota. Earthworm species richness in simple landscapes, where predation pressure is reduced, was enhanced by organic farming, whereas in complex landscapes, conventional farming, which often causes reduced predation, fostered earthworm species richness. As the same pattern was found for microbial carbon biomass, earthworms may have enhanced microbial biomass. In contrast to earthworm and microbial diversity, aboveground biodiversity benefits most from organic farming in simple landscapes. In general, organic farming appears to be more efficient in conserving aboveground than belowground diversity.

Remarkable changes of weed species in Spanish cereal fields from 1976 to 2007

Management practices, geographical gradients and climatic factors are factors explaining weed species composition and richness in cereal fields from Northern and Central Europe. In the Mediterranean area, the precise factors responsible for weed distribution are less known due to the lack of data and surveys. The existence of weed survey data of year 1976 in the Zaragoza province of the Aragon region, Spain, offered us the opportunity to compare present weed species with weed species growing 30 years ago. No detailed comparison of changes in weed species composition in cereal fields in that period of time has been conducted in the Mediterranean area. Here a survey was conducted in the Aragon region from 2005 to 2007. Weeds were surveyed in 138 winter cereal fields in ten survey areas where winter cereals are the main crops, using the same methodology applied 30 years ago. In the Zaragoza province, 36 fields were chosen in the same municipalities than in the previous survey. Several management, geographic and climatic variables of each field were recorded and related to weed species with multivariate analysis. Diversity index were calculated and related to survey area and altitude. Our results show that out of the 175 species only 26 species were found in more than 10% of the surveyed fields. The main species were Papaver rhoeas, Lolium rigidum, Avena sterilis and Convolvulus arvensis found in more than half of the surveyed fields. L. rigidum was related to dryland, while the other species were found overall. Furthermore, we found that management, geographical and climatic factors were significantly related to weed species distribution. In particular altitude, survey areas, irrigation and herbicide use in post-emergence were the most driving factors explaining weed species distribution. Species richness was higher in survey areas with extensive management practices and increased with altitude excepting a very productive area with intensive management practices at high altitude where richness was as low as in the irrigated lowlands. The main differences found between the 1976 and the 2005–2007 surveys were (1) the striking increase of grass weeds, (2) the high decrease of mean weed species number found in each field declining from 9 to 3 and (3) the frequency decrease of many weed species probably caused by agriculture intensification in that period of time. The growing importance of other weed species is probably related to their adaptation to minimum tillage, which is a widespread technique nowadays.

Farmers’ fears and agro-economic evaluation of sown grass strips in France

Since 2005, French farmers must set up sown grass strips along rivers in order to decrease pesticide levels and soil erosion. Farmers have thus parcelled out their fields, set aside 3% of their farm size and managed grass without herbicide. Consequently, this environmental policy may cause farmers’ fears due to economic losses and weed infestations of their field margins. Here, we studied farmers’ perception of sown grass strips. First, we interviewed 29 farmers in two French regions. Second, we evaluated the economic loss of gross margin when replacing crop by grass. Third, we evaluated the weed risk using flora surveys in sown grass strips. Our results showed that two thirds of interviewed farmers thought that sown grass strips affected their farm revenue and represented a weed risk. Concerning economy, we found that farmers loose from 358 to 853€/ha the year of installation and from 126 to 641€/ha next years. This economic loss is mainly due to the loss of crop production, with a minor impact of grass management cost. At the farm level, 3% of sown grass strips decreased the farm revenue by 7%. Concerning the weed risk, the farmers’ perception was linked with the presence of some competitive perennial weeds, e.g. Cirsium arvense, and wind-dispersing weeds, e.g. Asteraceae. Sown grass strips with high weed species richness of 26 species on average, or with dominance of non-sown species (16.7% of sown grass strips) did not affect the farmers’ perception. In our study, the economic loss was weak and acceptable at the farm level.

Species richness and evenness as a function of biomass in arable plant communities

Poggio SL & Ghersa CM (2011). Species richness and evenness as a function of biomass in arable plant communities. Weed Research51, 241–249.SummaryWe evaluated the hypothesis that competitive dominants change the species richness and evenness of arable plant communities. Three field experiments including cool‐season crops and unsown short fallows were carried out in Buenos Aires, Argentina. Ground cover, biomass and species richness of crops and weeds were assessed. Evenness was calculated by using species biomass data. Richness and evenness were correlated with total community biomass, and with the biomass of either weeds or the dominant species in the community. Crops, through growth and shading effects, affected the species richness and evenness of arable plant communities. Conversely, the dominant weed in fallows was not as suppressive as crops. Species richness and evenness were constrained by community biomass. Species richness of understory weeds decreased as crops suppressed weed growth. Evenness also decreased as the dominant species became increasingly productive, regardless of their identity (weeds or crops). Our findings provide valuable models to characterise the trajectories that species richness and evenness may follow in different farming scenarios. Community biomass is a major constraint on the maximum diversity of local communities and, consequently, of substantial ecological importance for both biodiversity conservation and weed management purposes.

Effects of cultivation regimes on weed community structures in newly reclaimed sandy farmlands

The varieties, quantities, coverage rates and heights of farmland weeds were surveyed and species diversity and richness analyzed in a newly reclaimed sandy farmland located in the margin oasis of the middle reaches of Heihe River Basin, Northwest China. The aim of the study was to evaluate the effects of cultivation regimes on weed community structure characteristics in the basin. A total of 16 weed species from 10 families were identified and recorded. The most common species of weed communities in newly reclaimed sandy farmlands are Chenopodium album, Eleusine indica, Setaria viridis and Amaranthus retroflexus. Weed community compositions are largely influenced by cultivation regimes. Weed species richness, Shannon-Wiener index and Simpson in-dex are lower in conventional cultivation regimes (film mulching, autumn plowing and continuous maize planting). Those could, however, be improved under straw mulching, zero-autumn plowing and maize-soybean rotation treatments. Compared with film mulching, E. indica has a higher dominance ratio while C. album and A. retroflexus have lower dominance ration under straw mulching treatments. Compared with autumn plowing, S. viridis, A. reteroflexus, Silene conoidea and C. glaucum have a higher dominance ratio whereas E. indica has a lower dominance ratio under zero-autumn plowing treatments. Also compared with con-tinuous maize planting, S. conoidea exhibits a higher dominance ratio under maize-soybean rotation regimes. There exist random rare weed species distribution in the field, which are not significantly effected by cultivation regimes. Results further show that weed species is few and weed communities composition is single in a newly reclaimed sandy farmland, and cultivation regimes obviously influence weed species diversity and community structure in reclaimed sandy farmlands. It is recommended to conduct additional research for a non-subjective interpretation of the effects of cultivation regimes on weed growth in order to guide weed control in newly reclaimed sandy farmlands.

Influence of field margin type on weed species richness and abundance in conventional crop fields

AbstractNatural vegetation occurring on farms in field margins, fallow fields, ditch systems and neighboring forests, provides increased biodiversity, structural diversity, habitat for wildlife and beneficial insects, and can act as a protective buffer against agrochemical drift. Nevertheless, farmers frequently view these areas as non-productive and as potential sources of weeds, insect pests and diseases. Weed species richness and abundance were examined in crop fields in 2002–2003 at the Center for Environmental Farming Systems near Goldsboro, NC to determine if crop field weed infestation was associated with field margin management (managed versus unmanaged). Weed species abundance and richness were measured over two growing seasons on four occasions in crop fields along permanent transects that extended from the field edge toward the center of the field. The presence/absence of data for all plant species in the field margin was also recorded. For both margin types, managed and unmanaged, more weeds were found near the field edge than in the center of the field. Weed species richness was slightly higher in cropland bordering managed margins than in cropland along unmanaged margins. Several significant interactions led to an examination of nine dominant weed species in each field margin type and their distribution in crop fields. When all sampling dates were pooled, only 42 (40%) of 105 species identified in the field margins were observed in the crop field. Managed margins had lower species richness than unmanaged field margins—less than half the mean number of species (15 versus 6 species, respectively). Contingency table analysis did not reveal any association between plant species occurring in the margin and those found in the crop field. Furthermore, margin type and weed presence in the field margin were not effective predictors of weed occurrence in the crop field as determined by logistic regression.

Using selective herbicides to manage beneficial and rare weed species in winter wheat

Weed species within arable farming systems act as a source of food and provide habitat for various taxa at higher trophic levels. Using field experiments in winter wheat, we investigated whether selective herbicides can be used as a potential tool for sustaining beneficial, less competitive weed species and rare species of high conservation value while controlling highly competitive weed species. We tested three selective herbicides with different active ingredients (amidosulfuron + iodosulfuron, fluroxypyr, mecoprop-P) at two application rates. We analysed cover of selected focal species (Centaurea cyanus and Papaver rhoeas) as well as weed species richness, winter wheat yield and weed community composition as influenced by herbicide treatments. Herbicide treatments involving fluroxypyr generally allowed for the selective retention of the regionally threatened weed species C. cyanus and P. rhoeas as a beneficial species of high value for associated trophic level and provided considerable control of the competitive species G. aparine. Herbicide treatments significantly affected weed species composition. The PRC method clearly showed the time-dependent herbicide treatment effects on weed community composition and allowed an estimate of the variance in species composition that is explained by the herbicide treatments. Our results indicated that applying selective herbicides can provide a feasible option for in-crop management of weed diversity by retention of beneficial or rare weed species occurring at moderate densities and control of highly-competitive weeds. However, weed control strategies must be tailored to site-specific conditions to account for increased abundance of competitive species.

Impact of climate and land use type on the distribution of Finnish casual arable weeds in Europe

Hyvönen T, Glemnitz M, Radics L & Hoffmann J (2011). Impact of climate and land use type on the distribution of Finnish casual arable weeds in Europe. Weed Research51, 201–208.SummaryThe aim of the study was to explore the impact of climate and land use type on species richness and abundance of arable weeds found as casual aliens in Finland. We used an empirical data set collected along a European climate gradient, from which 163 plants were selected for the analyses. Using generalised linear modelling (GLMM) and redundancy analysis (RDA), we compared species richness and abundance of all species and three functional groups (dicotyledons and grasses, C3 and C4 species, alien and native species to Europe), as well as occurrence of the 13 most common individual species between three land use types (fallow, low‐input and conventionally cultivated) and six regions. In general, fallowing and low‐input cultivation, as well as warmer climate, supported greater weed species richness and abundance. Temperature was found to be a more important factor for weed abundance than land use. The only exception was C4 species richness, which did not respond to either factor. The impact of land use was independent of climate for all variables, except C4 species abundance. Non‐cultivated fallows had more weeds than cultivated fields, in most cases. No difference was found in the species richness and abundance of grasses or in the occurrence of individual species between low‐input and conventionally cultivated fields. It was evident that climate and land use affect the distribution of arable weed species currently found as casual aliens in Finland. This suggests that climate warming will increase the risk of the population establishment of new weed species in northern regions.

FITOSSOCIOLOGIA DE PLANTAS DANINHAS DE PASTAGENS CULTIVADAS SOB DOIS NÍVEIS DE DEGRADAÇÃO EM CERRADO, NO MATO GROSSO DO SUL

Cultivated pastures, in general, go through a decline process, associated with the occurrence of weeds, whose successful management begins with the survey of species and their biology. This study aimed to carry out phytosociological surveys, during the rainy and dry seasons, in two pastures cultivated with Brachiaria ( Urochloa ) spp., with cattle (AI) and without cattle (AII), in Cerrado (Brazilian savanna) areas of the Mato Grosso do Sul State, Brazil. The occurrence of 104 weedy herbaceous and subshrubby Phanerogams species was recorded. The families with the highest number of species were Fabaceae (23 species), Poaceae (16), and Asteraceae (15). Hemicryptophytes predominate with 41% of the species. The species with the highest importance value and relative coverage are B. decumbens and Sida rhombifolia , in AI, and B. brizantha and Desmodium incanum , in AII, plus Paspalum notatum , in both pastures. The Shannon diversity index was 4.19 and 4.43 nats, for AI and AII, respectively, indicating considerable weed species richness. The floristic dissimilarity index between AI and AII, obtained from the Euclidian distance, is 0.7468, indicating just a few species in common (44%). In the dry season, the number of species in AI decreased 10% while in AII it increased 4%. KEY-WORDS: Agroecosystem; Brachiaria ; flora; plant ecology; Urochloa .

Weed species richness in winter wheat increases with landscape heterogeneity

There is empirical evidence that landscape composition and structure can affect the distribution and long-term dynamics of the organisms that live in it. Weeds are no exception and in this paper, we investigated how weed richness and diversity in 123 winter wheat fields within a small agricultural region were affected by the landscape surrounding each field (radii ranging from 100 to 1000 m) and the field properties such as its size and the preceding crop. Landscape was described by its proportion (cover of spring crops, winter crops, woodland, grassland, set-aside) and its structure (number of fields, number of land use types). Akaïke criterion-based models indicated that variations in weeds were best explained at the 200 m radius. At that scale, hierarchical partitioning shows that the independent contributions of field level and landscape level variables were significant for two variables. Weed richness and weed diversity increased significantly as field size decreased and as the number of fields within 200 m increased. This suggests that weed richness and diversity are higher in landscapes that have a finer grain, probably because these landscapes offer more habitat heterogeneity within cultivated areas and contain more crop edges that can shelter many weed species.

Glyphosate management strategies, weed diversity and soybean yield in Argentina

From their introduction in 1996, glyphosate resistant (GR) soybean cultivars have been rapidly adopted by farmers in Argentina and in other countries in the world. The high rate of adoption of this technology seems to be based on the simplicity of use provided by a single herbicide (glyphosate), its high efficacy to control many weeds and, the low costs of the technology relative to that used in conventional crops. During 2001–2002, 2002–2003 and 2003–2004 soybean growing seasons, field surveys and field experiments were performed with the aim of studying the effect of different glyphosate management strategies on the diversity of soybean weed communities, weed control, individual survival, fecundity and crop yield. In addition, the emergence pattern of three important weeds, Digitaria sanguinalis, Cyperus rotundus and Anoda cristata, was also studied. Both field surveys and field experiments were carried out on no-till soybean crops sown immediately after wheat or barley harvest (double cropped system). Experiments were set up in commercial soybean crops and consisted of different times of a single glyphosate application, two glyphosate applications and also the application of glyphosate plus a residual herbicide imazethapyr. A. cristata, D. sanguinalis, Stellaria media, Chenopodium album and Cyperus sp. were the most prevalent weeds recorded at pre-harvest of the soybean crops, showing regional constancy higher than 80% in both years. In three out of four field experiments, crop yield was not increased when glyphosate was applied twice compared with a single application of the herbicide. In addition there was a lower negative effect on weed species richness when glyphosate was applied once during the crop cycle than with two applications of glyphosate or glyphosate plus imazethapyr. D. sanguinalis escaped the glyphosate early treatment because of the long weed emergence period, while A. cristata and C. rotundus survived treatments due to their high individual tolerance. The results suggest that it is possible to manage glyphosate application to get high crop yield with a low impact on weed diversity, depending on the weed species and their abundance.

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.

Early vegetation development after grassland restoration by sowing low-diversity seed mixtures in former sunflower and cereal fields

We studied the early vegetation dynamics in former croplands (sunflower and cereal fields) sown with a low-diversity seed mixture (composed of 2 native grass species) in Egyek-Pusztakócs, Hortobágy National Park, East-Hungary. The percentage cover of vascular plants was recorded in 4 permanent plots per field on 7 restored fields between 2006 and 2009. Ten aboveground biomass samples per field were also collected in June in each year. We addressed two questions: (i) How do seed sowing and annual mowing affect the species richness, biomass and cover of weeds? (ii) How fast does the cover of sown grasses develop after seed sowing? Weedy species were characteristic in the first year after sowing. In the second and third year their cover and species richness decreased. From the second year onwards the cover of perennial grasses increased. Spontaneously immigrating species characteristic to the reference grasslands were also detected with low cover scores. Short-lived weeds were suppressed as their cover and biomass significantly decreased during the study. The amount of litter and sown grass biomass increased progressively. However, perennial weed cover, especially the cover of Cirsium arvense increased substantially. Our results suggest that grassland vegetation can be recovered by sowing low diversity mixtures followed up by yearly mowing. Suppression of perennial weed cover needs more frequent mowing (multiple times a year) or grazing.

Responses in plant and carabid communities to farming practises in boreal landscapes

The effect of organic farming compared to conventional mixed and cereal farming on arable weeds and carabid beetles in boreal landscapes was studied by comparing the distribution of ecological traits, diversity partitions, species richness and abundance. Organic farming increased both insect-pollinated as well as overall weed species richness, whereas the proportion of insect-pollinated weed species of the total species richness was unaffected by farming practises. Carabid species richness was mainly unaffected by farming practises although a higher alpha diversity of large and intermediate carabid species in organic and conventional mixed farms was marginally significant. Activity-densities of carabids were highest on conventional mixed farms. Landscape variables did not affect weed diversity but carabid beta diversity increased with increasing landscape heterogeneity. Local richness of large and intermediate carabid species showed a marginally significant decrease with increasing field cover. It is concluded that arable weed diversity is affected by organic farming to a higher extent than carabids.