Ecological succession in areas degraded by bauxite mining indicates successful use of topsoil

Brazilian ironstone outcrops (cangas) are nutrient‐poor stressful habitat dominated by slow‐growing woody species with high biodiversity and unique evolutionary history. Mining has produced great impacts on this ecosystem. Spontaneous regeneration of abandoned canga mined areas has not been observed. One of the active methods most widely used for ecological restoration in environments where soil has been lost or severely degraded is topsoil transposition due to the physical, chemical, and microbiological improvement of the substrate, in addition to the seed bank. Thus, plant succession was monitored for 40 months after topsoil transposition in a canga area degraded by aluminum mining, without any other type of management. A completely randomized design with 70 permanent plots (1 × 1 m) was used. Annual phytosociological surveys were carried out and floristic and vegetational spectra were constructed with the life‐forms proposed by Raunkiaer. Floristic composition was compared with a reference site. Overall, 105 species were identified. Both flora and vegetation changed over time, increasing resemblance to the reference areas. The floristic and vegetational spectra after 4 years of topsoil deposition are similar to pristine ones. The vegetation spectrum showed an increase in the dominance of phanerophytes and hemicryptophytes, while therophytes reduced their proportion. The early successional stage is dominated by weeds, like in other canga restoration studies, but did not impede the native species regeneration. Cangas's species recruited well from transposed topsoil. Unlike other studies with fertilized topsoil, our findings show the efficiency of topsoil transposition to provide initial conditions for the ecological restoration of this ecosystem.     

Assigning plant communities to a successional phase: Time trends in abandoned limestone quarries

We investigated spontaneous vegetation succession and the relationship between time and vegetation patterns in several abandoned quarries of the Botticino extraction basin (Lombardy, Italy) and then assigned plant assemblages to a predetermined theoretical successional phase using an original procedure. To recognise and validate the gradient due to time, an ordination approach of vegetation plots linked to constant variables and time since last mining Canonical Correspondence Analysis was conducted first. Then, to determine the durations of the vegetation succession phases and trends between the colonisers and late successional species, we used an original six-step procedure based primarily on the regression curve of the percent relative abundance of life forms (RALFs) over time. The results demonstrated that time is the primary factor that significantly affects life form turnover during succession. Vegetation establishment and development in the “pioneer phase” (0–6 years) were affected by abiotic filters, which determined the dominance of a few ruderal and annual/alien species, mostly therophytes. The successive phases were characterised by an increasing presence of perennial species (mostly phanerophytes) with a consequent influence of biotic filters. The RALF procedure may be applied to other environments to investigate the time trends of plant communities during successions.     

An experimental study of old-field succession in relation to different environmental factors

From 1984 to 1986, old-field succession on sterilized sand and loam was studied under different water- and nutrient regimes. Within one month, moss and phanerogam species appeared on all experimental plots but further succession was rather varied. Salix species established quickly on loam and formed within 3 years a shrub layer up to 3 m in height. On sand, woody plant species were observed only at a high ground-water level. On loam, the well-known old-field succession from short-living therophytes to long-living phanerophytes of clearings and woodlands proceeded very quickly. In contrast, on sand, therophytes, hemicryptophytes and herbaceous chamaephytes of ruderal- and grassland communities were still dominant after three years. A high ground-water level as well as mineral fertilization had sometimes positive, sometimes negative effects on this succession. Periodic estimates of cover, made during the succession were supplemented at the end of the experiment by the measurements of phytomass and bioelement storage. The highest amount of biomass was measured on the three loamy soils where shrub layers were well developed. In comparison with data published elsewhere, the above-ground biomass of 2.2–2.8 kg dry matter m^-2 and the below-ground biomass up to 7.2 kg dry matter m^-2 were both extraordinarily high. Over the three years, the vegetation on sandy soils accumulated between 1.2 and 5.1 g N m^-2 yr^-1 and on loamy soils between 17.1 and 24.7 g N m^-2 yr^-1.     

The age of Calluna stands moderates post‐fire regeneration rate and trends in northern Calluna heathlands

Questions: Does stand age influence the direction and rate of post‐fire successional dynamics in coastal Calluna heaths and can old degraded heath vegetation be restored through reintroduction of fire? Location: Coastal heaths in the Tarva archipelago, central Norway. Methods: We investigated revegetation dynamics after experimental fires set in young (8 years since last fire) and old (>50 years since last fire) grazed heath stands. A repeated measures design was used, with floristic data recorded in permanent plots in the post‐fire successions (n=12) over a 7‐year period. The data were analysed using multivariate ordination techniques (PCA, RDA and PRC) and mixed effects models. Results: The age of Calluna stands strongly influenced post‐fire succession, different trends due to age explained 10.4% of variation in floristic data. Young heath showed faster succession towards pre‐fire community composition than old heath, and this could partially be explained by succession‐related factors: young heath had lower cover of mosses and lichens in the pre‐burned vegetation, and lower cover of litter early in succession. Young heath had a less pronounced overall community response to fire than old heath. Vegetative regeneration of C. vulgaris was absent in both old and young heath, but Calluna still re‐established as the dominant species within 5–7 years in both young and old stands. Regeneration dynamics were also affected by habitat conditions, different trends due to habitat explained 6% of variation. Conclusions: Our study demonstrates that old stands do develop characteristic heathland vegetation and structure after fire, and while potential invasives into the system such as trees and rhizomatous species are present, they do not impair Calluna regeneration or vegetation development towards the target heathland community composition and structure. Further, as our young stands are only in their second fire rotation after restoration, we suggest that characteristic dynamics of managed heathlands can re‐establish relatively rapidly, even in severely degenerated sites (>50 years since last fire). Site‐specific factors also need to be considered. We conclude that there is restoration potential in old heaths, despite slow dynamics in the first rotation.     

Secondary dune succession on Inhaca Island,Mozambique

Old field succession was studied on coastal dunes supporting tropical evergreen forest on Inhaca Island, Mozambique. Plots of 10×10 m were sited in three early successional stages and in relatively undisturbed forest. Woody species increased in number during succession; leptophylls were most frequent in younger vegetation, whereas microphylls and mesophylls were most frequent in forest. Grasses, shrubs and forbs dominated initially following abandonment, and shrubs persisted as dominants in the three early successional stages. The initial floristic composition model was generally supported by the pattern of species sequences, with many forest species entering early in the succession. Of the few species conforming to the relay floristic model, many were grasses and forbs of the forest understorey. Similarity between plots of equivalent vegetation age indicated that, at least in early succession, there was linearity in the successional pathway; there was no evidence for divergence or multiple pathways. In early succession, no accumulation was detected in either soil organic matter or extractable nutrients, thus providing little support for the facilitation model of succession. It is stressed that the findings are probably scale-dependent.     

The relationship between soil seed bank,above‐ground vegetation and disturbance intensity on old‐field successional permanent plots

Questions: How does disturbance and successional age influence richness, size and composition of the soil seed bank? What is the potential contribution of the soil seed bank to the plant community composition on sites differing in their successional age or disturbance intensity? Location: Experimental Botanical Garden of Göttingen University, central Germany. Methods: Above‐ground vegetation and soil seed bank were studied on formerly arable fields in a 36‐year‐old permanent plot study with five disturbance intensities, ranging from yearly ploughing via mowing to long‐term uninterrupted succession. We compared species compositions, seed densities and functional features of the seed bank and above‐ground vegetation by using several methods in parallel. Results: The seed bank was mainly composed of early successional species typical of strongly disturbed habitats. The difference between seed bank composition and above‐ground vegetation decreased with increasing disturbance intensity. The species of greatest quantitative importance in the seed bank was the non‐native forb Solidago canadensis. Conclusions: The ability of a plant community to regenerate from the soil seed bank dramatically decreases with increasing time since abandonment (successional age) and with decreasing disturbance intensity. The present study underlines that plant species typical of grasslands and woodlands are limited by dispersal capacity, owing to low capacity for accumulation of seeds in the soil and the fact that most species do not build up persistent seed banks. Rare and target species were almost absent from the seed bank and will, after local elimination, depend on reintroduction for continuation of their presence.     

Changes in Mediterranean plant succession: old-fields revisited

Abstract. Old-field plots used for a study of succession in Mediterranean France were revisited after 12–14 yr. Our aims were: (1) to verify if predicted patterns of species richness, turnover and composition are confirmed; (2) to compare the development in disturbed plots with that in undisturbed ones; (3) to discuss the impact of management changes. In undisturbed plots species richness and turnover decreased with successional age. Floristic composition changed in a way consistent with the predicted successional development in most plots. Therophytes decreased and phanerophytes increased; anemochorous species decreased and endozoochorous species increased, as expected. In plots disturbed since the first analysis richness decreased with successional age, but generally remained higher than in undisturbed plots. Floristic composition, species turnover and an increase in therophytes indicated changes towards younger successional stages. Thus, disturbance changed succession but not much. This is probably linked with the regeneration abilities typical of mediterranean species, e.g. resprouting. At the landscape scale, richness did not change and species turnover was low. The plots studied were situated in two distinct locations. One had not been disturbed between the two observation periods, while the other is a mosaic of undisturbed and disturbed sites. Observations fitted predictions much more closely at the undisturbed location. We conclude that permanent plot studies are powerful in identifying successional trends and can also provide additional insights into the effects of disturbance some of the mechanisms underlying the dynamics of diversity.     

Role of plant functional traits in determining vegetation composition of abandoned grazing land in north‐eastern Victoria,Australia

Question: In the Northern Hemisphere, species with dispersal limitations are typically absent from secondary forests. In Australia, little is known about dispersal mechanisms and other traits that drive species composition within post‐agricultural, secondary forest. We asked whether mode of seed dispersal, nutrient uptake strategy, fire response, and life form in extant vegetation differ according to land‐use history. We also asked whether functional traits of Australian species that confer tolerance to grazing and re‐colonisation potential differ from those in the Northern Hemisphere. Location: Delatite Peninsula, NE Victoria, Australia. Methods: The vegetation of primary and secondary forests was surveyed using a paired‐plot design. Eight traits were measured for all species recorded. ANOSIM tests and Non‐metric Multi‐dimensional Scaling were used to test differences in the abundance of plant attributes between land‐use types. Results: Land‐use history had a significant effect on vegetation composition. Specific leaf area (SLA) proved to be the best predictor of response to land‐use change. Primary forest species were typically myrmecochorous phanerophytes with low SLA. In the secondary forest, species were typically therophytes with epizoochorous dispersal and high SLA. Conclusions: The attributes of species in secondary forests provide tolerance to grazing suggesting that disturbance caused by past grazing activity determined the composition of these forests. Myrmecochores were rare in secondary forests, suggesting that species had failed to re‐colonise due to dispersal limitations. Functional traits that resulted in species loss through disturbance and prevented re‐colonisation were different to those in the Northern Hemisphere and were attributable to the sclerophyllous nature of the primary forest.     

Some factors affecting successional change on uranium mine wastes: Insights for ecological restoration

Question: Are growth form and dispersal-mode replacement during vegetation succession in semi-arid Mediterranean conditions affected by the starting quality of the substrate and by site aspect? Location: Central-western Spain. Methods: We monitored successions on three waste materials left after uranium mining: unbroken waste, broken waste and wastes amended with a sandy material (Arkoses); both north and south aspects were also studied on each substrate. Results: The substrate starting quality had the greatest influence on spontaneous succession, separating the poorer quality substrates (broken and unbroken wastes) from the better ones (Arkoses) and two reference communities (Topsoil and Dehesa). The importance of aspect was confirmed then within each substrate type. Most species with a short life span (mostly annuals and a few biennials), together with some woody species on Arkoses, showed no response to age (years following the deposition of new soil). Others short-lived species declined over time on the poorer wastes but not on the better Arkoses. There was a tendency for life form replacement (from thero-phytes to hemicryptophytes) during succession only on the poorer-quality substrates. No dispersal-mode replacement sequence was found. Conclusion: Improving the abiotic conditions of the substrate had a great effect on vegetation succession, but this effect was modified by aspect. Aspect took longer to induce differences in floristic composition on the poorer substrates, where succession was slower. Some trends in species responses to successional change were found by considering species traits, particularly life-form.     

Changes in life history trait composition during undisturbed old-field succession

This paper describes the patterns of vegetation change by spontaneous succession on former agricultural land. In 1968, initiated by Heinz Ellenberg, an experimental study site was set up on an arable field in the new botanical garden of Göttingen University (Germany). The undisturbed successions on four plots of a long sere (since 1968/69) and on four additional plots of a shorter sere (since 1982) were evaluated. The seres were classified into stages by cluster analysis, which yield to four subsequent stages for the long sere and to three subsequent stages for the short sere. The early succession is characterized by a high proportion of species invasion, whereas with developing time species extinction increased. On all study plots undisturbed succession directed to the development of pioneer forests. Altogether 247 vascular plant species were recorded. The total species richness shows a fluctuating course during the successional seres, with significantly increased numbers shortly after succession has started and a decline in the pioneer-forest stage, when stands age and close down. The primary aim was to compare the characteristics (particular traits) of species occurring at different stages of succession. The majority of the traits concerned exhibited some clear trends in the course of succession. Exclusive reproduction by seeds decreased and the ability for additional vegetative reproduction increased. Anemochorous dispersal significantly decreased, whereas the importance of dispersal by animals, especially endochorous, dominates in the pioneer-forest stage. The mean seed weight significantly increased. During early succession, plant species staying green over winter dominated, but are of none relevance in the pioneer-forest stage, where summergreen plant species dominate. The change in strategy type features a significant increase of competitive species. The mean indicator value for light in the herb layer decreased significantly in the pioneer-forest stage.     

Temporal trends in species composition and plant traits in natural grasslands of Uruguay

Abstract. We report the successional trends of the major life‐forms (graminoids and forbs) in natural grasslands of Uruguay over a 9‐yr period after the removal of domestic herbivores. For the whole community, species richness and diversity decreased over the successional period. In graminoids we observed clear temporal trajectories in floristic composition; the rate of floristic change decreased with time and was associated with a shift in plant traits. The exclusion of large herbivores promoted erect and tall grasses with narrow leaves and greater seed length, vegetative growth constrained to the cool season and increased frequency of annual species. Forbs did not show a clear temporal trend in species composition, but there was, nevertheless, a plot‐specific species turnover of this functional group that was reflected in their attributes. Species spreading by means of rhizomes, with vegetative growth restricted to the warm season. Species with larger seeds increased under grazing exclusion, as did annual and nitrogen‐fixing forbs. The floristic changes induced by cattle exclusion occurred early in the succession. This early high rate of change has practical implications for management and conservation programs of the natural grasslands of Uruguay. Additionally, the shift in plant traits may be helpful in devising simple indicators of grazing impact.     

Soil seed bank and driftline composition along a successional gradient on a temperate salt marsh

Abstract. This study focuses on the relationship between vegetation succession and soil seed bank composition on the Schiermonnikoog (The Netherlands) salt marsh over 100 yr. The importance of driftline material in seed dispersal and the relationship with succession is also investigated. The results indicate that the majority of species have a transient or short‐term seed persistent bank. Seeds of most species are able to float over the salt marsh and become concentrated in the driftline higher up the marsh. After plants have established a seed bank forms, which disappears when vegetation is replaced by later‐successional species. Exceptions are Spergularia mar‐itima, which is still present in the seed bank of late successional stages, and Juncus gerardi and Glaux maritima, which appear in the seed bank of early successional stages, but are absent in the vegetation. Based on the results of this study constraints and possibilities for salt‐marsh restoration by de‐embankment are discussed.     

Colonization and early succession on anthropogenic soils

Abstract. This paper reports on vegetation development on permanent experimental plots during five years of succession. Nine (1 m²) plots were filled with three typical substrates from man-made habitats of urban and industrial areas in the region of Berlin. The three substrates (a commercial ‘topsoil’, a ruderal ‘landfill’ soil and a sandy soil), differ in organic matter and nutrient contents. Relevés of species composition and percent cover of each species present were made monthly during the growing season from the start of vegetation development. This paper describes the different successional pathways on topsoil and ruderal soil and the colonization process on sandy soil. On topsoil, ruderal annuals are dominant in the first year and are replaced by short-lived perennials from the second year. Those species were replaced by long-lived perennial herbs (Ballota nigra or Urtica dioica) from the third year of succession onwards. On the ruderal land-fill soil the early successional stages are less sharp and the perennial Solidago canadensis is able to dominate within one year after the succession was initiated. On sandy soil there is still an ongoing colonization process, where pioneer tree species like Betula pendula and Populus nigra play a main role. The importance of ‘initial floristic composition’, the role of substrate for community structure and the peculiarities of successional sequences on anthropogenic soils in the context of primary and secondary successions are discussed.     

Woodland regeneration on grazed former arable land: A question of tolerance,defence or protection?

Ecological restoration of native woodlands and wooded pastures on former agricultural land is an important topic in modern conservation practice. The introduction of large herbivores is increasingly used to achieve these aims. We investigated how grazing, resistance traits of plants (concerning herbivory) and associational resistance interact and affect the establishment pattern of woody species on abandoned arable land (N-Belgium, W-Europe). In these early successional tree assemblages, we tested whether grazing increased or decreased spatial heterogeneity, which is supposed to be a crucial factor for biodiversity.With repeated measurements, 2-3 and 5-7 years after the cessation of agricultural use, we sampled 87 grazed and 56 ungrazed plots (314 m²) in 14 sampling areas (former arable land) on nutrient rich, (sandy) loam soils. We recorded established tree frequencies, related to grazing, time, resistance traits and unpalatable/spiny vegetation cover in the herb and low shrub layer. We investigated horizontal and vertical heterogeneity using variances in establishment frequencies and variances in frequencies of trees that were able to grow beyond the browse line, respectively.We found massive colonisation of grazing tolerant and resistant woody species in early successional stages. Grazing decreased frequencies and height of the most abundant tolerant species (mainly Salix caprea L.). After 5-7 years, frequencies of defensive and tolerant species were equal, but the former (mainly Betula pendula Roth) were able to grow beyond the browse line. When the cover of unpalatable/spiny vegetation was high enough (>60% of plot size), it also provided suitable nurse sites for tolerant species to grow out. In early assemblages, grazing increased horizontal and vertical heterogeneity, resulting in intermediate successional stages. In the long-term, the mechanism of associational resistance will also allow non-resistant and tolerant species to grow beyond the browse line and promote forest succession and the order of species establishment and replacement.     

Long‐term changes in the vegetation after the cessation of livestock grazing in Eucalyptus marginata (jarrah) woodland remnants

This paper documents changes in the floristic composition of Eucalyptus marginata Donn (jarrah) woodlands over 7 years of recovery from continual, intensive livestock grazing. In remnants of native woodland left after agricultural clearing, which have been subjected to livestock grazing, comparisons were made between the floristics of fenced exclosure plots and open plots that continued to be grazed. The vegetation in nearby remnants, which had not been subjected to livestock grazing, was also surveyed. An initial increase in annual exotic pasture species after grazing relief was only temporary and highly influenced by fluctuations in annual climatic patterns, particularly rainfall distribution and abundance. Subsequent years saw a decrease in exotic annuals in exclosure plots and an increase in native perennials, in a trend towards becoming more floristically similar to the ungrazed sites. Germination of overstorey species was observed in the exclosure plots, however, development of seedlings and saplings was sparse. Results indicate that for jarrah woodland in southwestern Australia, natural regeneration is possible after the removal of livestock, with the return (within 6 years) of native species richness to levels similar to those found in ungrazed vegetation. Re‐establishment of cover, however, appears to take longer. The floristic dynamics are described in terms of a nonequilibrium model. Two vegetation states exist, degraded remnants with an understorey dominated by annual species, and ungrazed vegetation with an understorey dominated by perennial shrubs and herbs. The former state is maintained by continual heavy grazing by livestock. Upon relief from grazing, the vegetation undergoes a transition towards floristic similarity to ungrazed vegetation. After 6 years, vegetation change in the exclosure plots appears to be continuing and therefore it is still in transition.     

Vegetation changes on formerly overgrazed hill slopes in semi-arid central Tanzania

Abstract. Composition of hill slope vegetation was studied in a semi-arid part of upland Tanzania where all grazing had been banned for 12 yr. The hills had been severely overgrazed previously and suffered from heavy gully and sheet erosion. Eight vegetation types are described. Floristic gradients revealed by numerical ordination techniques were found to be related mainly to degree of erosion, soil type and succession. The more or less bare soil that prevailed after grazing had ceased is now covered by grassland, woodland and immature secondary forest. The grasslands are still characterized by early successional species and they will probably remain open grassland as long as frequent burning continues. Brachystegia woodlands may have developed during earlier periods when the field layer was sparse due to grazing. The grazing had reduced the frequency of fire which in turn promoted the establishment of Brachystegia spp. Secondary forests are believed to have developed mainly where fires were not frequent, particularly at higher altitudes.     

Quantifying patterns and controls of mire vegetation succession in a southern boreal bog in Finland using partial ordinations

Question: How do we distinguish between concurrent allogenic and autogenic forcings behind changing patterns in plant community structures during mire development? Location: Lakkasuo raised bog, southern Finland. Methods: Two radiometrically dated peat profiles were studied using high resolution plant macrofossil analysis. A combination of partial direct and indirect gradient analyses (CCA and DCA) was applied to quantify the role of different drivers of vegetation changes. Results: Autogenic hydroseral succession explained 16% of the compositional variation in the vegetation. Disturbance successions initiated by fire explained 15% of the variation in the hummock, but only 9% in the wetter lawn. The early post‐disturbance successional stages were characterized by Eriophorum vaginatum. After partialling out the effects of peat depth and time since fire, a moisture gradient explained 29% of variation in the hummock core and 26% in the lawn. The analyses also indicated alternation between species with a similar niche. This interaction gradient explained 26% and 31% of the compositional variation in the hummock and lawn, respectively. The similar order of species replacement from both cores supported the existence of general directional succession in mire vegetation, both during the mire development and after fire events. The autogenic succession was slow and gradual while the disturbance successions were episodic and fast. Conclusion: Our results support the paradigm of the complex nature of mire vegetation dynamics where several interlinked agents have simultaneous effects. The approach of combining partial ordinations developed here appeared to be a useful tool to assess the role of different environmental factors in controlling the vegetation succession.     

Succession during the re‐creation of a flood‐meadow 1985‐1999

Abstract. The study site, Somerford Mead, is located on the river Thames floodplain and was a species‐rich flood‐meadow in the 1950s. In the 1960s and 1970s it was subjected to intensive grassland management with regular NPK additions and occasional herbicide treatment. In 1981 Somerford Mead was ploughed for the first time and converted to arable land. Seeds of an Alopecuruspratensis‐Sanguisorba officinalis flood‐meadow community (MG4; Rodwell 1992) were sown onto prepared soil in the autumn of 1986, and botanical records were made from 1985 to 1999. From 1989 to 1999, three replicates of three treatments: cow‐grazing, sheep‐grazing and no‐grazing were introduced after hay‐cutting. Analysis successfully separated the establishment phase from the experimental phase and showed a significant difference between the grazed and ungrazed treatments. Abiotic and biotic factors which might contribute to successional trends are discussed. A convoluted pattern for each treatment could be attributed in part to intrinsic‘cycles’of perennial hemicryptophytes behaving as short‐lived species and in part to the percentage frequency of many species which was reduced in 1990 and 1995/1996, years of drought. After the initial inoculation of MG4 seed and the disappearance of arable therophytes, recruitment of new species was very slow. Coefficients for Somerford Mead matched against MG4 (Rodwell 1992) produced an equilibrium within three years. It subsequently fluctuated over a 10‐yr period well below the level of Oxey Mead, the donor site. Land managers should ensure that their proposed site has the right soils and hydrology for MG4 grassland and that traditional management of hay‐cutting and aftermath grazing is practised. Only one cut a year in July could lead to a reduction in percentage frequency of most species except Arrhenatherum elatius.     

Implications from the Buell‐Small Succession Study for vegetation restoration

Abstract. Succession is relevant to restoration because managers have to prevent, enhance or replace natural vegetation dynamics. Features of a permanent plot study of post‐agricultural succession in central New Jersey, USA, illustrate important implications of vegetation dynamics for restoration. In the past, such implications had to be drawn from chronosequences and coarse resolution studies, neither of which exposes the local contingencies relevant to site specific restoration. However, the fine scale and continuous nature of the current study reveal that succession is highly contingent on historical and local spatial heterogeneity. For example, the absence of one generally expected dominant stage, the demise of shrubs without replacement by later successional tree species, and the long and multimodal persistence of individual species suggest that neither the relay floristic or initial floristic models of succession is adequate to guide restoration. At the local scale, volleys of species appear through the succession, and reflect spatial contingencies such as neighboring vegetation and edge relationships, and patchy behavior of different functional groups. The role of introduced species and of plant consumers are additional sources of local contingency. These local and time‐specific behaviors in the vegetation are the patterns that restorationists must understand either to choose appropriate reference states, to prevent unexpected local dynamics, or to design interventions that are appropriate to the specific site of interests.     

Weed vegetation of arable land in Central Europe: Gradients of diversity and species composition

Question: What are the main broad‐scale spatial and temporal gradients in species composition of arable weed communities and what are their underlying environmental variables? Location: Czech Republic and Slovakia. Methods: A selection of 2653 geographically stratified relevés sampled between 1954–2003 was analysed with direct and indirect ordination, regression analysis and analysis of beta diversity. Results: Major changes in weed species composition were associated with a complex gradient of increasing altitude and precipitation and decreasing temperature and base status of the soils. The proportion of hemicryptophytes increased, therophytes and alien species decreased, species richness increased and beta diversity decreased with increasing altitude. The second most important gradient of weed species composition was associated with seasonal changes, resulting in striking differences between weed communities developed in spring and summer. In summer, weed communities tended to have more neophytes, higher species richness and higher beta diversity. The third gradient reflected long‐term changes in weed vegetation over past decades. The proportion of hemicryptophytes and neophytes increased, while therophytes and archaeophytes decreased, as did species richness over time. The fourth gradient was due to crop plants. Cultures whose management involves less disturbances, such as cereals, harboured less geophytes and neophytes, and had higher species richness but lower beta diversity than frequently disturbed cultures, such as root crops. Conclusions: Species composition of Central European weed vegetation is mainly influenced by broad‐scale climatic and edaphic factors, but its variations due to seasonal dynamics and long‐term changes in agricultural management are also striking. Crop plants and crop‐specific management affect it to a lesser, but still significant extent.