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Summary1. Atmospheric nitrogen (N) deposition is expected to change forest understorey plant community composition and diversity, but results of experimental addition studies and observational studies are not yet conclusive. A shortcoming of observational studies, which are generally based on resurveys or sampling along large deposition gradients, is the occurrence of temporal or spatial confounding factors. 2. We were able to assess the contribution of N deposition versus other ecological drivers on forest understorey plant communities by combining a temporal and spatial approach. Data from 1205 (semi-)permanent vegetation plots taken from 23 rigorously selected understorey resurvey studies along a large deposition gradient across deciduous temperate forest in Europe were compiled and related to various local and regional driving factors, including the rate of atmospheric N deposition, the change in large herbivore densities and the change in canopy cover and composition. 3. Although no directional change in species richness occurred, there was considerable floristic turnover in the understorey plant community and a shift in species composition towards more shade-tolerant and nutrient-demanding species. However, atmospheric N deposition was not important in explaining the observed eutrophication signal. This signal seemed mainly related to a *Correspondence author. E-mail: kris.verheyen@ugent.be Ó 2011 The Authors. Journal of Ecology Ó 2011 British Ecological Society Journal of Ecology 2012Ecology , 100, 352-365 doi: 10.1111Ecology /j.1365Ecology -2745Ecology .2011 shift towards a denser canopy cover and a changed canopy species composition with a higher share of species with more easily decomposed litter. 4. Synthesis. Our multi-site approach clearly demonstrates that one should be cautious when drawing conclusions about the impact of atmospheric N deposition based on the interpretation of plant community shifts in single sites or regions due to other, concurrent, ecological changes. Even though the effects of chronically increased N deposition on the forest plant communities are apparently obscured by the effects of canopy changes, the accumulated N might still have a significant impact. However, more research is needed to assess whether this N time bomb will indeed explode when canopies will open up again.

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The present investigation was part of a fen restoration project, which deals with the rehabilitation of a deeply drained peat land used for intensive agriculture for more than 200 years. Consequently, the conditions for restoration are unfavorable. The hay of well‐developed fen meadows from nature reserves in the region appeared to contain enough viable seeds to act as a source for the development of target communities when spread out on bare peat after topsoil removal. Repeated vegetation analysis showed that a combination of topsoil removal and hay transfer resulted in the establishment of new populations in the target area for 70% of the species of the donor area. Germination conditions of fen species were investigated to determine the optimal combination for stimulating germination rates. Most fen species were found to be dormant, and it was shown that dormancy could be broken with fluctuating light and temperature cycles and stratification pre‐treatment.

Question: How does fire influence species richness and diversity in subtropical grassland in southern Brazil? Location: Recurrently burned grassland in Porto Alegre, Brazil (30°03′S, 51°07’W; max. altitude 311 m a.s.l.) and abandoned grassland near São Francisco de Paula, Brazil (29°47′S, 50°22’W; ca. 900 m a.s.l.). Methods: In the burned grassland, between‐year changes in community composition and single‐plot diversity, species number and vegetation structure were analysed in two consecutive years for plots with different time since last fire. Responses to fire of individual species were analysed. At the abandoned site, diversity, species number and vegetation structure were examined. Results: Species number and small‐scale species turnover were highest ca. one year after the burn, and decreased as caespitose grasses increased in cover with time since fire until reaching a stable, but less diverse state three to four years after a fire. The abandoned grassland showed higher dominance of caespitose grasses and lower richness and diversity. Conclusions: Fire clearly leads to a short‐term increase in species richness and diversity at the plot scale, as competitive interactions are being reduced and recruitment possibilities are high in early post‐fire vegetation development. Overall community composition does not change after a fire. While small herbs seem to be slightly favoured in the early post‐fire environment, no clear group of fire following species (absent in vegetation unburned for longer) was observed. The results indicate that the community is adapted to the current fire regime and is being maintained under the influence of fire.

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Questions What are the main short‐term changes in vegetation structure after fire and mowing in Campos grasslands? Are there differences in functional vegetation group responses between sites with diverse fire histories and different treatments (fire and mowing)? Location Subtropical grasslands in Porto Alegre, Brazil, 30 °03′ S, 51 °07′ W. Methods In two sites with different fire histories: FB – frequently burned grasslands and E – exclusion of fire for 6 yr, seven pairs of plots were examined. In each pair, fire and mowing treatments were established. Bare soil and litter cover were estimated. Vegetation relevés were conducted, plants identified, their cover estimated and stems counted (except for graminoids). Later, plants were grouped according to their functional group (graminoids, forbs and shrubs) for statistical analyses. Observations were conducted 30, 90 and 360 d after treatments. Results Burned plots always showed a higher percentage of bare soil, whilst mowed plots had higher litter cover. Fire enhanced graminoid and forb cover, but did not affect shrubs. Species turnover was very high, mainly in burned plots in site FB and in mowed plots in site E. Species diversity in burned plots was the same in sites FB and E 1 yr after treatments, contrary to our hypothesis. However, in mowed plots, the number of species tended to decrease 1 yr after treatments for both sites FB and E. Conclusions The most important short‐term effect was the removal of litter and consequent opening of gaps, mostly by fire. This stimulated vegetation regeneration and provided microsites for the establishment of new species. However, fire did not enhance plant diversity, as we had hypothesized. Moreover, the disturbance history of sites should be considered, since vegetation in these sites responded differently to fire and mowing.

Question: How does fire influence species richness and diversity in subtropical grassland in southern Brazil? Location: Recurrently burned grassland in Porto Alegre, Brazil (30°03′S, 51°07’W; max. altitude 311 m a.s.l.) and abandoned grassland near São Francisco de Paula, Brazil (29°47′S, 50°22’W; ca. 900 m a.s.l.). Methods: In the burned grassland, between‐year changes in community composition and single‐plot diversity, species number and vegetation structure were analysed in two consecutive years for plots with different time since last fire. Responses to fire of individual species were analysed. At the abandoned site, diversity, species number and vegetation structure were examined. Results: Species number and small‐scale species turnover were highest ca. one year after the burn, and decreased as caespitose grasses increased in cover with time since fire until reaching a stable, but less diverse state three to four years after a fire. The abandoned grassland showed higher dominance of caespitose grasses and lower richness and diversity. Conclusions: Fire clearly leads to a short‐term increase in species richness and diversity at the plot scale, as competitive interactions are being reduced and recruitment possibilities are high in early post‐fire vegetation development. Overall community composition does not change after a fire. While small herbs seem to be slightly favoured in the early post‐fire environment, no clear group of fire following species (absent in vegetation unburned for longer) was observed. The results indicate that the community is adapted to the current fire regime and is being maintained under the influence of fire.