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.     

Variation in species composition and vegetation structure of succulent scrub on Tenerife in relation to environmental variation

Abstract. On Tenerife, the occurrence of environmental gradients over short distances provides a unique opportunity to investigate the relationship between vegetation and environmental factors. In the semi‐arid coastal region of Tenerife, floristic composition, species richness and vegetation structure of perennial plants have been studied in 67 locations covering the existing precipitation gradient. On the island as a whole, variation in species composition could be best explained by mean annual precipitation; at coastal sites, substrate age and soil characteristics also played a significant role. On the other hand, substrate chemistry and the type of eruptive material explained little of the floristic variation. Stand biomass was strongly correlated with mean annual precipitation and was, on the youngest lava flows studied, also affected by substrate age. The native stem succulent species made up the bulk of total biomass along the whole precipitation gradient. Disturbed and undisturbed sites differed significantly in stand biomass and cover. Species richness was correlated with precipitation and substrate age. Distribution of plant functional types was also related to the precipitation gradient. The relative abundance of hemicryptophytes and shrubs with non‐hairy leaves increased with increasing precipitation whereas the ratio of shrubs with hairy/non‐hairy leaves and succulent plants decreased. Some alien plants were quite frequent at disturbed sites but, on the whole, they contributed little to the species spectrum and to the stand biomass. Undisturbed sites remained almost free of introduced species not considering annuals.     

The relative importance of local, regional and historical factors determining the distribution of plants in fragmented riverine forests: an emergent group approach

Aim To investigate how local, regional and historical factors shape the herbaceous plant communities in fragmented riverine forests, and how the community composition and species richness of these fragments is related to the interplay between the environmental factors and specific plant life‐trait combinations. Location Riverine forest fragments in the Grand‐duché de Luxembourg. Methods Forest fragments were surveyed for their abundance in herbaceous plant species. All plant species where clustered into Emergent Groups (EG) by means of a formal classification based on 14 life‐history traits. Within each EG, the local, regional and historical factors were related to the community composition using partial Canonical Correspondence Analyses (pCCA) and to the species richness using Generalized Linear Models (GLMs). The EG colonization ability was characterized by means of logistic regressions. Results We defined and characterized seven EGs, among which three consisted of forest specialist species (barochorous perennials, short geophytes and zoochorous perennials), which exhibited specific life‐trait combinations: large and short‐lived seeds and/or vernal phenology. Differences in EG composition between forest fragments were mainly explained by local environmental factors such as soil productivity and pH. The richness of barochorous perennials and short geophytes was well predicted by the historical and regional factors. The colonization ability appeared very low for barochorous perennials and short geophytes. Main conclusions Local environmental conditions appear to drive the differentiation of the riverine forest plant communities owing to the specific habitat requirements of many forest species. Spatial and temporal forest discontinuities affect the richness of forest specialist species, due to dispersal and/or recruitment limitations. The emergent group approach enhances the understanding of the relative influence of local, regional and historical factors by distinguishing between forest specialists from generalists or ‘matrix’ species, which have a masking effect.     

Biodiversity of semi‐arid Mediterranean grasslands: Impact of grazing and afforestation

Question: What is the impact of grazing and/or afforestation on grassland diversity, species composition and cover parameters? Location: Semi‐arid Mediterranean grasslands of Jordan. Methods: Vegetation, litter, bare soil and rock cover were compared among four management types – free grazing and protected from grazing with three levels of tree cover. Species composition, plant cover, species richness and evenness were used to evaluate differences in vegetation among management types. Species composition differences among management types were also investigated. Results: Semi‐arid Mediterranean grasslands harbour appreciable levels of plant biodiversity. Grazing did not affect plant diversity, indicating the high resilience against and adaptation to grazing; however,grazing affected species composition and cover parameters. Afforestation seems to protect soil through higher litter cover but its impact on plant biodiversity was negative and markedly affected species composition. Conclusions: Neither protection from grazing or massive afforestation alone are sufficient for conserving biodiversity in this system. A management model is suggested where the landscape should be maintained as a mosaic of four management types: complete protection from grazing, grazing rotation, planting sparse trees in eroded areas and revegetating degraded areas using native, herbaceous and grazing tolerant species.     

Environmental drivers of the bryophyte propagule bank and its comparison with forest-floor assemblage in Central European temperate mixed forests

Species richness, composition and abundance of the bryophyte diaspore bank of Central European temperate mixed forests were compared with the forest-floor bryophyte assemblage. The impact of environmental variables and anthropogenic disturbances, including tree species composition, stand structure, microclimate, light conditions, soil and litter properties, management history, and landscape properties, potentially influencing bryophyte diaspore bank assemblages were explored. Thirty-four, 70–100 years old mixed stands with differing tree species composition were examined in the ?rség National Park, Western Hungary. The diaspore bank was studied by soil collection and cultivation, and data were analysed by multivariate methods. Contrary to the forest-floor bryophyte assemblage, where substrate availability, tree species composition and stand structure were the most influential environmental variables, the composition and abundance of the diaspore bank was mainly affected by site conditions (microclimate, litter and soil properties). Species richness of the bryophyte diaspore bank was lower than that of the forest-floor bryophyte assemblage. Short-lived mosses (colonists, short-lived shuttles) were dominant in the diaspore bank, as opposed to the forest-floor bryophyte community, where perennial mosses dominated. In the studied forests, the importance of the bryophyte diaspore bank was relatively low in the regeneration and maintenance of the forest-floor bryophyte vegetation.     

Patterns of diversity in the strata of boreal montane forest in British Columbia

Abstract. Patterns of diversity were analyzed in a boreal coniferous forest and its strata (tree, shrub, herb and bryophyte layers): number of species per community — α-diversity, total species richness — γ-diversity, mean similarity — β-diversity, and mosaic diversity, a measure of complexity. These four measures of diversity consistently decreased from lower to upper vegetation layers. To study the effect of juveniles of larger life forms on diversity of lower layers, they were removed from the data and the measures of diversity reanalyzed. Number of species per community and mosaic diversity decreased substantially, but β-diversity did not change. So, the effect of juveniles on γ-diversity is due to the greater number of species per community. Multiple regression models revealed that the relationships between α-diversity and the environmental variables were the same for the whole forest and for the herb layer. Elevation and soil pH were the major variables explaining α-diversity in the whole community. Climate was the only environmental gradient related to species richness in all individual strata. Tree and herb richness values were negatively related to soil drainage and acidity, respectively. Species richness of the plant community was affected by environmental variability mostly through the herb layer. Various explanations of the observed diversity patterns included: environmental constraints, resource competition, generation time, and colonization processes.     

Floristic composition and floral phenology of the Mediterranean batha of Ariel,Samaria

Field observations over a three-year period were used to document the floristic composition, flowering and fruiting sequences of the Sarcopoterium spinosa Mediterranean batha of Ariel. This plant community was found to be species-rich, with high percentages of annuals, bushes and geophytes, low percentages of herbaceous plants, climbers and trees, and ten species considered rare in Israel. Typical Mediterranean characteristics were observed in the S. spinosa batha: spring flowering reaching a peak in April, small between-year variation in flowering and fruiting, most species having Mediterranean distribution, and partial resistance to fire.     

Changes in species composition of European acid grasslands observed along a gradient of nitrogen deposition

Question: Which environmental variables affect floristic species composition of acid grasslands in the Atlantic biogeographic region of Europe along a gradient of atmospheric N deposition? Location: Transect across the Atlantic biogeographic region of Europe including Ireland, Great Britain, Isle of Man, France, Belgium, The Netherlands, Germany, Norway, Denmark and Sweden. Materials and Methods: In 153 acid grasslands we assessed plant and bryophyte species composition, soil chemistry (pH, base cations, metals, nitrate and ammonium concentrations, total C and N, and Olsen plant available phosphorus), climatic variables, N deposition and S deposition. Ordination and variation partitioning were used to determine the relative importance of different drivers on the species composition of the studied grasslands. Results: Climate, soil and deposition variables explained 24% of the total variation in species composition. Variance partitioning showed that soil variables explained the most variation in the data set and that climate and geographic variables accounted for slightly less variation. Deposition variables (N and S deposition) explained 9.8% of the variation in the ordination. Species positively associated with N deposition included Holcus mollis and Leontodon hispidus. Species negatively associated with N deposition included Agrostis curtisii, Leontodon autumnalis, Campanula rotundifolia and Hylocomium splendens. Conclusion: Although secondary to climate gradients and soil biogeochemistry, and not as strong as for species richness, the impact of N and S deposition on species composition can be detected in acid grasslands, influencing community composition both directly and indirectly, presumably through soil‐mediated effects.     

库姆塔格沙漠南缘植物物种丰富度格局及主要影响因素

通过对库姆塔格沙漠南缘植被进行实地调查,对该地区植物物种丰富度及其群落组成进行研究,并选取11个影响物种丰富度的气候因子和地形因子,利用PCA分析、方差分解等方法探讨气候、地形因子对物种丰富度的影响。结果显示：该区共有植物15科32属38种,植物群落种类匮乏,物种组成单一,植物生活型主要以灌木、多年生草本为主,占所有物种的80%以上;植物物种丰富度与植物群落组成明显受到水热条件的制约。回归分析结果表明,该区物种丰富度与能量因子呈显著负相关（P<0.05）,而与水分因子呈显著正相关（P<0.05）。方差分解结果表明,水分、能量共同制约了该地区的物种丰富度,二者的共同解释率为44.3%。此外,地形因子对研究区物种丰富度也存在一定影响,能进一步提高环境因子对物种丰富度的解释率。总之,库姆塔格南缘物种组成单一、物种丰富度格局受到水热条件的共同制约,同时地形的变化也有重要影响。     

Landscape patterns of understory composition and richness across a moisture and nitrogen mineralization gradient in Ohio (U.S.A.) Quercus forests

This study quantified relationships of understory vascular plant species composition and richness along environmental gradients over a broad spatial scale in second-growth oak forests in eastern North America. Species frequencies were recorded in 108 25 × 25 m plots in four study sites extending over 70 km in southern Ohio, U.S.A.. The plots were stratified into three long-term soil moisture classes with a GIS-derived integrated moisture index (IMI). In addition to the IMI, the environmental data matrix included eight soil and three overstory variables. Canonical correspondence analysis (CCA) indicated that variations in understory species composition were most strongly related to topographic variations in predicted moisture (IMI), N mineralization rate, nitrification rate, and soil pH. In addition, floristic variation at the regional scale was correlated with variations in soil texture, nitrification, pH, and PO₄ ^–, resulting from differences in the soil parent material complexes among sites. Species richness averaged 65 species/plot, and increased with moisture and fertility. Stepwise regression indicated that richness was positively correlated with N mineralization rate and nitrification rate, and inversely correlated with tree basal area. Greater richness on fertile plots was the largely the result of increasing forb richness. Forb richness per quadrat (2 m²) was most strongly and positively related to N mineralization rate. Conversely, richness of understory individuals of tree species was greatest on xeric, less-fertile plots. Our results describe general, broad-scale species-environment relationships that occurred at both the topographic scale (long-term moisture status and fertility) and the regional scale (geomorphological differences among the sites). Strong species richness-N mineralization correlations indicate an important link between below-ground processes and above-ground biodiversity. Because N availability was a strong correlate to vegetation patterns at a broad-scale, our results suggest that the increasing rates of atmospheric N deposition in the region could have a major impact on understory vegetation dynamics.     

Eurosiberian meadows at their southern edge: patterns and phytogeography in the NW Tien Shan

Question: What are the community types, underlying gradients and phytogeographical affinities of montane meadows in the western Tien Shan? Location: Aksu‐Jabagly Nature Reserve, South Kazakhstan, Middle Asia. Methods: Species composition, structural and environmental variables were studied in 98 plots. Species composition was classified by cluster analysis and gradients explored using NMDS. Relationships between species richness, environmental and structural variables were investigated with regression analysis. Phytogeographic patterns were assessed by examining species distribution types. Results: Seven community types were distinguished by cluster analysis. Three axes of the NMDS explained 77% of the variation, showing different overlap of communities with environmental and structural properties. Species richness showed linear relationships with pH, altitude, heat load, soil skeletal content and structural variables. Middle Asian and Eurosiberian species constituted the majority of the species pool and cover. Conclusion: The studied communities represent a unique mixture of Middle Asian and Eurosiberian species that exhibit structural and environmental similarities to Eurosiberian meadows. The Tien Shan mountain meadows can thus be considered an endemic‐rich southern outlier of the broader Eurosiberian meadow formation. Shifts in land‐use patterns pose a potential threat that deserves more attention from conservationists.     

Determining the important environmental variables controlling plant species community composition in mesotrophic grasslands in Great Britain

Question: What is the relative importance of local site effects and selected important environmental variables in determining plant species composition? How do species respond to these environmental variables? Location: Ten mesotrophic grassland sites of high conservation value in southern England. Methods: Species cover was assessed in between 10 and 25 randomly selected 1‐m² quadrats at each site. At each quadrat degree of waterlogging (W), soil Olsen extractable phosphorus (P) and soil pH were measured. Variation partitioning was used to separate site and soil effects, and HOF (Huisman, Olff & Fresco) modelling was used to produce response curves for the major species on soil gradients, based on coenoclines derived from partial canonical correspondence analysis (pCCA). Results: Variation partitioning identified Site as the most important environmental variable (34.6%). Only 18.7% was accounted for by the three soil variables together; W (degree of waterlogging), P and pH accounted for 11.1%, 5.7% and 4.3%, respectively in raw form with 2.4% shared. However, when Site and the other soil variables were removed the variation explained reduced to 2.3% for W, 1.1% for P and 1.0% for pH. The species responses to each of these soil environmental factors could be separated into four types on each gradient. Most species were abundant at low W, low soil P and intermediate pH. Conclusions: Site‐based factors were more important than the three soil variables, which were assumed to be directly or indirectly associated with productivity. This implies that each site has unique properties that are more important than the soil variables. The three soil factors were, however, significant and the groups of the most common species, based on significant response curves, can be used as a first approximation of indicators of environmental conditions in British mesotrophic grasslands for conservation. However, W accounted for most variation, and the current reliance on soil available P and soil pH for assessing conservation/restoration potential should be viewed with caution.     

Does invasion by an alien plant species affect the soil seed bank?

Questions: How does invasion affect old‐field seed bank species richness, composition and density? How consistent are these effects across sites? Does the soil seed bank match vegetation structure in old‐fields? Location: Menorca, Balearic Islands, Spain, western Mediterranean basin. Methods: We monitored seed germination in soils from old‐fields that were both uninvaded and invaded (legacy effect) by the annual geophyte Oxalis pes‐caprae. We also added O. pes‐caprae bulbs to uninvaded soils to test O. pes‐caprae interference with seedling emergence (competitive effect). We compared species composition in the seed bank with that of the vegetation. Results: Species richness in the seed bank and in the vegetation was not significantly different between invaded and uninvaded areas. Uninvaded areas did not have larger seed banks than invaded areas. More seedlings, especially of geophytes, emerged when O. pes‐caprae bulbs were added to the soil. Species similarity between invaded and uninvaded areas was higher in the seed bank (74%) than in the vegetation (49%). Differences in species composition were as important as differences among sites. The degree of species similarity between the seed bank and the vegetation was very low (17%). Conclusions: Despite invasion by O. pes‐caprae not affecting species richness, the variation in the seed bank species composition in invaded and uninvaded areas, and the differences between the seed bank and the mature vegetation, highlights that even if the invader could be eradicated the vegetation could not be restored back to the exact composition as found in uninvaded areas.     

Analysis of the endophytic lifestyle and plant growth promotion of Burkholderia terricola ZR2-12

Nitrogen (N) enrichment has been pinpointed as a main driver for biodiversity change. Most of our knowledge of effects of increased N availability on ecosystems comes from northern Europe and America. Most other ecosystem types have been neglected. In contribution to filling this gap, our study examined the short-term effects of N enrichment in a N-manipulation (doses and forms) field study of a severely nutrient-limited Mediterranean ecosystem located in a Natura 2000 site in Portugal. Our aims were to (a) understand the effects of N enrichment on plant diversity, and to (b) link N-driven plant community changes with changes in soil inorganic N availability. In general, the standing plant community responded to short-term N enrichment with increased richness and evenness. Changes in the plant community occurred through changes in species composition and cover, and were correlated with soil N, and N and phosphorus availability. Fertilization with 80 kg NH₄NO₃ ha^?1 y^?1 was the treatment which changed plant composition the most, while geophytes, hemicryptophytes and therophytes were the biological types more responsive to N enrichment. Dittrichia viscosa was the only species that responded significantly to increased N, i.e., its cover decreased in control plots, but increased in fertilized plots, suggesting that it could be used as an indicator of N enrichment in Mediterranean maquis. Changes in plant richness and evenness were correlated with the mean and/or the variation (standard deviation) of soil inorganic N parameters (e.g. nitrate concentration in the soil solution and the soil??s ratio of bioavailable N and phosphorus) measured along the time between the two plant community assessments. However, short- and long-term effects can be quite distinct, thus highlighting the need for further studies.     

Determinants of bryophyte species composition and diversity on the Great Alvar of Öland,Sweden

Factors driving the species richness and distribution of bryophytes are poorly studied and not well understood, particularly in grasslands. We analysed the occurrence of bryophyte species and variation in species richness across 674 plots (0.5?m?×?0.5?m) in alvar vegetation (grassland on limestone pavement with thin or no soil) on Öland (Sweden) in relation to substrate characteristics and chemistry, inundation frequency, grazing pressure and geographical variables. We found 148 taxa, including 11 nationally red-listed ones. Species richness per plot was significantly associated with substrate type, positively associated with pH and grazing intensity, but negatively associated with soil depth. However, richness of species typical of, or restricted to, alvar habitats responded differently to richness of species more common in other habitats. Typical alvar species were favoured by high pH, shallow soil and low phosphate availability, while generalists preferred relatively low pH, higher phosphate availability and organic or mull soil types. Distance from the alvar margin had only weak effects. Concerning the effects on individual species and community composition, inundation frequency and pH were found to have the largest effects, although other factors (substrate type, soil depth, bare soil, bare stone, phosphate availability and grazing pressure) were more important for some individual species, stressing the importance of microsite variability and variability in management for regional species richness. From a conservation perspective, it is concluded that grazing is generally positive whilst factors increasing phosphate availability may disadvantage the typical alvar species, and proximity to the alvar margin is not a major problem.     

The effects of stand structure on ground-floor bryophyte assemblages in temperate mixed forests

The effect of tree species composition, stand structure characteristics and substrate availability on ground-floor bryophyte assemblages was studied in mixed deciduous forests of Western Hungary. Species composition, species richness and cover of bryophytes occurring on the soil and logs were analysed as dependent variables. The whole assemblage and functional groups defined on the basis of substrate preference were investigated separately. Substrate availability (open soil, logs) was the most prominent factor in determining species composition, cover and diversity positively, while the litter of deciduous trees had a negative effect on the occurrence of forest floor bryophytes. Besides, bryophyte species richness increased with tree species and stand structural diversity, and for specialist epiphytic and epixylic species log volume was essential. Sapling density and light heterogeneity were influential on bryophyte cover, especially for the dominant terricolous species. Many variables of the forest floor bryophyte community can be estimated efficiently by examining stand structure in the studied region. Selective cutting increasing tree species diversity, stand structural heterogeneity and dead wood volume can maintain higher bryophyte diversity in this region than the shelter-wood system producing even-aged, monodominant, structurally homogenous stands.     

Factors determining plant species richness in Alaskan arctic tundra

Abstract. We studied the relationship between plant N:P ratio, soil characteristics and species richness in wet sedge and tussock tundra in northern Alaska at seven sites. We also collected data on soil characteristics, above‐ground biomass, species richness and composition. The N:P ratio of the vegetation did not show any relationship with species richness. The N:P ratio of the soil was related with species richness for both vegetation types. Species richness in the tussock tundra was most strongly correlated with soil calcium content and soil pH, with a strong correlation between these two factors. N:P ratio of the soil was also correlated with soil pH. Other factors correlated with species richness were soil moisture and Sphagnum cover. Organic matter content was the factor most strongly correlated with species richness in the wet sedge vegetation. N:P ratio of the soil was strongly correlated with organic matter content. We conclude that N:P ratio in the vegetation is not an important factor determining species richness in arctic tundra and that species richness in arctic tundra is mainly determined by pH and flooding. In tussock tundra the pH, declining with soil age, in combination with Sphagnum growth strongly decreases species richness, while in wet sedge communities flooding over long periods of time creates less favourable conditions for species richness.     

How gradients of climate and soil determine Mediterranean annual-rich dryland vegetation

Questions

Dryland annual plant communities constitute the most species-rich small-scale vegetation in the Mediterranean. Nevertheless, the composition and diversity of these units and the factors controlling their variation are still insufficiently understood. Therefore, we investigated species composition and richness patterns in relation to important environmental gradients provided by climate and soil.

Location

Central Crete, Greece.

Methods

The study is based on 82 plots of 4 m² sampled at altitudes between 11 and 1400 m a.s.l. We conducted vegetation relevés and soil analyses. We used generalised additive models to model species richness and community characteristics along the studied gradients. We then performed distance-based redundancy analysis to determine the main environmental factors influencing species composition. To determine species of diagnostic value for bedrock types, we applied an indicator species analysis. Correlation tests were used to test the performance of the South Aegean Plant Indicator Values on our dataset.

Results

We recorded 347 taxa (species and subspecies) of 43 plant families, and mean species numbers of 47.2 ± 12.5 per plot. While overall species richness varied only slightly along the analysed environmental gradients, significant changes were observed for relative proportions of species from different life forms and families. Soil pH and elevation had the highest influence on the variation in species composition (23.3% explained). We found 22 species indicative of calcareous rock and 24 species indicative of lime-deficient rock types. The South Aegean Plant Indicator Values were relatively strongly correlated with environmental variables.

Conclusions

Results indicate considerable species turnover both along climatic (elevation) and soil gradients, highlighting the special importance of soil pH. The data provided by our study are expected to supply relevant ecological background information for a pending classification of East Mediterranean annual-rich vegetation.     

Plant diversity in a calcareous wooded meadow – The significance of management continuity

Questions: What is the contribution of management continuity during the last 30–40 years to variation in species diversity and composition of a calcareous wooded meadow plant community? Is tree cover related to species diversity and composition of the herbaceous layer? What are the effects of local soil gradients on species diversity? Location: Laelatu calcareous wooded meadow, Western Estonian coastal zone. Methods: Plant community composition was assessed in 150 1 m × 1 m plots, located at 30 sites with known management history within Laelatu meadow (7 ha). Light and soil conditions and relative altitude were measured at each plot. DCA was used to analyse variation in species composition and general linear mixed models to analyse the effects of management and environmental parameters on diversity. Results: Management continuity was the primary determinant of plant community composition, followed by light conditions and soil parameters. Species richness, diversity and evenness are positively dependent on management continuity. Spatial autocorrelation is important as well. Diversity started to decline under the tree canopy where 50% or less irradiation reached the level of the herbaceous layer. We did not find significant effects of soil conditions on small‐scale diversity. Conclusions: Management continuity, together with the cover of the tree layer, are the most important determinants of diversity. Despite grassland stands with different management history are located side by side, the regeneration of diversity and composition of plant communities after restoring regular management practices is a slow process.     

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.