No abstract

Succession is one of the most studied processes in ecology and succession theory provides strong predictability. However, few attempts have been made to influence the course of succession thereby testing the hypothesis that passing through one stage is essential before entering the next one. At each stage of succession ecosystem processes may be affected by the diversity of species present, but there is little empirical evidence showing that plant species diversity may affect succession. On ex-arable land, a major constraint of vegetation succession is the dominance of perennial early-successional (arable weed) species. Our aim was to change the initial vegetation succession by the direct sowing of later-successional plant species. The hypothesis was tested that a diverse plant species mixture would be more successful in weed suppression than species-poor mixtures. In order to provide a robust test including a wide range of environmental conditions and plant species, experiments were carried out at five sites across Europe. At each site, an identical experiment was set up, albeit that the plant species composition of the sown mixtures differed from site to site. Results of the 2-year study showed that diverse plant species mixtures were more effective at reducing the number of natural colonisers (mainly weeds from the seed bank) than the average low-diversity treatment. However, the effect of the low-diversity treatment depended on the composition of the species mixture. Thus, the effect of enhanced species diversity strongly depended on the species composition of the low-diversity treatments used for comparison. The effects of high-diversity plant species mixtures on weed suppression differed between sites. Low-productivity sites gave the weakest response to the diversity treatments. These differences among sites did not change the general pattern. The present results have implications for understanding biological invasions. It has been hypothesised that alien species are more likely to invade species-poor communities than communities with high diversity. However, our results show that the identity of the local species matters. This may explain, at least partly, controversial results of studies on the relation between local diversity and the probability of being invaded by aliens.

Separating the chance effect from other diversity effects in the functioning of plant communitiesLeps, J; Brown, VK; Len, TAD; Gormsen, Dagmar; Hedlund, Katarina; Kailova, J; Korthals, GW; Mortimer, SR; Rodriguez-Barrueco, C; Roy, J; Regina, IS; van Dijk, C; van der Putten, WH Published in: Oikos DOI: 10.1034/j. 1600-0706.2001.920115.x 2001 Link to publication Citation for published version (APA): Leps, J., Brown, VK., Len, TAD., Gormsen, D., Hedlund, K., Kailova, J., ... van der Putten, WH. (2001). Separating the chance effect from other diversity effects in the functioning of plant communities. Oikos, 92(1), 123-134. https://doi.org/10.1034/j. 1600-0706.2001.920115.x General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. The effect of plant species diversity on productivity and competitive ability was studied in an experiment carried out simultaneously in five European countries: Czech Republic (CZ), the Netherlands (NL), Sweden (SE), Spain (SP), and United Kingdom (UK). The aim was to separate the 'chance' or 'sampling effect' (increasing the number of sown species increases the probability that a species able 'to do a job' will be included) from the complementarity effect (species-rich communities are better able to exploit resources and to take care of ecosystem functions than species-poor communities). In the experiment, low diversity (LD) and high diversity (HD) mixtures of grassland species were sown into fields taken out of arable cultivation. The HD mixture consisted of five grass species, five legumes and five other forbs. The LD mixtures consisted of two grasses, one legume and one other forb, with different plant species combinations in each replicate block. The design of the experiment was constructed in such a way that the total number of seeds of each species over all the replications was exactly the same in HD and LD treatments, and the total number of grass seeds, leguminous seeds and other forb seeds were the same in both LD and HD. The responses measured were the total above-ground biomass (as a measure of productivity) and the average number of naturally establishing species in a plot (as a measure of the competitive ability of the mixture), both measured in the third year of the experiment. The results show that, on average, the HD plots performed better (i...

Plant species diversity, plant biomass and responses of the soil community on abandoned land across Europe: idiosyncracy or above-belowground time lags

To study the origin of replant disease of Ammophila arenaria (L.) Link the growth and development in sand originating from the rhizosphere of a natural Ammophila vegetation was compared with the growth in sand from the sea-floor. In a greenhouse experiment, the growth of Ammophila seedlings in rhizosphere sand, when compared with that in sea sand, was significantly reduced. As sterilization by means of gamma-irradiation increased the biomass production of Ammophila seedlings significantly, it was concluded that the rhizosphere sand contained biotic factors that were harmful to Ammophila. In rhizosphere sand the roots of Ammophila were brown and poorly developed, and the specific uptake rates of N, P and K were reduced. The shoot weight proportion of the total plant dry matter was hardly influenced. In an outdoor experiment with Ammophila seedlings and cuttings, using both sands, the mortality was high and the plants were feeble in rhizosphere sand whereas plants in sea sand grew vigorously. It seems plausible that the plants in rhizophere sand were dessicated because the root system was shallow and badly developed. In the greenhouse experiments, Ammophila cuttings were less sensitive to the inhibiting factors in the rhizosphere than seedlings. This was confirmed in the outdoor experiment. Calammophila baltica (Fluegge ex Schrader) Brand, however, was hardly affected by the harmful biotic factors in the greenhouse. These results are discussed with reference to the ecology of Ammophila. It is assumed that the catching of fresh windblown sand provides Ammophila with a way to escape from harmful biotic soil factors, and it was concluded that degeneration of Ammophila is caused mainly by self-intolerance due to these biotic soil factors.