A test of naturalness indicator values to evaluate success in grassland restoration

Restoration of lowland meadows in Austria: A comparison of five techniques

Summary1. Highly disturbed areas such as surface‐mined land provide a great challenge for ecological restoration. The goal is to identify appropriate restoration approaches in a continuum between technical reclamation and spontaneous succession. In particular, on slopes endangered by erosion, appropriate methods are needed that quickly establish vegetation cover but also take into account the natural potentials of the site.2. In the mined area Roßbach (Saxony‐Anhalt, Germany), we evaluated the effects of spontaneous succession and assisted site recovery (species introduction through hay transfer and sowing) during a 9‐year experiment. We asked how rates and pathways of vegetation development differ between treatments and whether species composition converges over time owing to species exchange.3. The application of green hay as well as the sowing of regional seed mixtures clearly accelerated vegetation development and led to the rapid establishment of species‐rich grasslands. Hay transfer was most successful owing to the high amount of transferable target species. Moreover, both treatments facilitated the establishment of cryptogams and provided effective erosion control. Also, hay transfer and sowing clearly affected the pathway of succession.Calamagrostis epigejosmigrated from nearby source populations and became increasingly dominant at sites with spontaneous succession. In contrast, the species‐rich grasslands established after hay transfer and sowing were highly resistant to invasion ofCalamagrostisand other ruderals.4. Species exchange between treatments led to increasing similarity in vegetation composition over time. Nine years after implementation of the experiment, we did not find any significant differences between treatments in terms of total vegetation cover, species richness and the number of target species. However, the dominance ratio between target and nontarget species differed significantly. Species introduction through hay transfer and sowing led to a permanently higher abundance of grassland species and a lower coverage of ruderals compared with spontaneously developed sites. Hence, our results highlight the importance of initial floristic composition and the order of species arrivals for long‐term vegetation development.5. Synthesis and applications. Hay transfer and sowing of regional seed mixtures are appropriate restoration tools to achieve rapid revegetation when no potential seed sources of target species are available nearby or there are undesirable species that need to be suppressed. Our results show that introduced grassland species are able to grow under postmining site conditions and can migrate into adjacent spontaneously developing sites. A combination of spontaneous and assisted site recovery can promote the development of species‐rich grasslands in postmining landscapes.

Can ecological engineering restore Mediterranean rangeland after intensive cultivation? A large-scale experiment in southern France

Summary Species‐rich grasslands are highly endangered habitats in Central Europe. To halt their ongoing loss, many sites have become subjects of restoration efforts. Traditionally, restoration success is measured using target species or by comparing similarity in species composition. Here, we suggest to additionally use functional community composition to assess restoration success as functional traits might offer mechanistic insights into restoration processes. In a 5‐year restoration experiment, we annually evaluated the responses of (i) floristic composition and species diversity, (ii) number and cover of target species, (iii) functional identity and (iv) functional diversity to four different methods of assisted recolonization through species introduction: hay transfer and application of threshing material from a local provenance, combined with and without addition of regional seed mixtures of target species, as well as to a control treatment. Across all treatments, floristic composition, species diversity, and number and cover of target species approached the values of reference sites. In the last observation year, Shannon diversity was still lower in all treatment plots than in the reference plots, while the number of target forb species had reached or exceeded the reference levels. We demonstrated that the community was also restored functionally in many aspects, but not in all studied traits. Calculated community‐weighted means (CWMs), specific leaf area (SLA) and leaf dry matter content (LDMC) in experimental plots did not differ significantly from the reference plots, thereby indicating that productivity of restored sites had reached target values. In contrast, CWMs of strategy types and pollination modes revealed significant differences, showing that biotic interactions among plant species and with other trophic levels have not yet been fully restored. However, almost all CWMs showed a trajectory towards the reference, thus giving a positive prospect for the future development. With respect to functional diversity (FD), we found steadily increasing FD values for almost all traits analysed. Synthesis and applications. We demonstrated that all applied restoration measures were appropriate to achieve the restoration aim in terms of species composition of a given community and the establishment of target species. With respect to many functional traits, the restored meadows were already as functional as communities from the reference sites. Hence, including functional criteria did not only corroborate traditional criteria of restoration success but also allowed identifying those floodplain meadow's functions that can be quickly and less quickly restored.

Assessments of restoration are usually made through vegetation community surveys, leaving much of the ecosystem underexamined. Invertebrates, and ants in particular, are good candidates for restoration evaluation because they are sensitive to environmental change and are particularly important in ecosystem functioning. The considerable resources currently employed in restoring calcareous grassland on ex-arable land mean that it is important to gather as much information as possible on how ecosystems change through restoration. We compared ant communities from 40 ex-arable sites where some form of restoration work had been implemented between 2 and 60 years previously, with 40 paired reference sites of good quality calcareous grassland with no history of improvement or cultivation. A total of 11 ant species were found, but only two of these were found to be significantly different in abundance between restoration and reference sites: Myrmica sabuleti was more likely to be present in reference sites, whereas Lasius niger was more likely to be found in restoration sites. Myrmica sabuleti abundance was significantly positively correlated with age of restoration sites. The potential number of ant species found in temperate grasslands is small, limiting the information their assemblages can provide about ecosystem change. However, M. sabuleti is a good indicator species for calcareous grassland restoration success and, alongside information from the plant community, could increase the confidence with which restoration success is judged. We found the survey to be quick and simple to carry out and recommend its use.

Restoration of grasslands on ex-arable land using regional and commercial seed mixtures and spontaneous succession: Successional trajectories and changes in species richness

Summary We do not know which aspects of community structure and ecosystem processes are restorable for most ecosystems, yet this information is crucial for achieving successful restoration. We quantified three success criteria for 8–10‐year‐old grassland plantings in large‐scale tallgrass prairie restoration (reconstruction) sites relative to three nearby prairie remnant sites. The restoration sites included management of native ungulates and fire, important regulators of diversity and patchiness in intact grasslands. These have not been incorporated simultaneously into previous studies of restoration success. We used the additive partitioning model of diversity, where α is neighbourhood (quadrat) scale diversity, β is accumulation of species diversity across neighbourhoods, and γ is total diversity. We decomposed α into richness and evenness to determine if both were equally restored. The proportion of exotic biomass was similar between the restoration and remnant sites, but the proportion of exotic species and above‐ground net primary productivity remained between two and four times higher in the restoration sites. Alpha diversity (Simpson's 1/D) and richness (S) values were exceptionally high in remnant sites, and approximately twice those of the restoration sites. Alpha evenness was similar between the restoration and remnant sites. Distance per se between quadrats was not related to diversity after accumulated quadrat area was taken into account. Therefore, we may be able to use the additive partitioning model of diversity in areas that differ in size, at least at the scale of this study. Contrary to our original predictions, the proportion of β diversity (1 − D) was approximately twice as high in the restoration sites than in remnant sites, possibly because patches of individual species were larger in the restoration. Synthesis and applications. We have shown that current restoration methods are unable to restore plant diversity in tallgrass prairie. Grassland restoration will be improved if the number of species that co‐exist can be increased. New, local‐scale restoration techniques are needed to replicate the high levels of diversity observed in tallgrass prairie remnant sites.

Functional diversity analysis helps to identify filters affecting community assembly after fen restoration by top-soil removal and hay transfer

Holzel, N. (corresponding author, nhoelzel@uni-muenster.de): Institute of Landscape Ecology, University of Munster, Robert-Koch-Str. 28, 48149, Munster, Germany Buisson, E. (elise.buisson@univ-avignon.fr) & Dutoit, T. (thierry.dutoit@univ-avignon.fr): Institut Mediterraneen d’Ecologie et de Paleoecologie (UMR CNRS/IRD), IUT, Universite d’Avignon et des Pays de Vaucluse, site Agroparc BP 61207, 84 911, Avignon Cedex 09, France

Enhancing success in grassland restoration by adding regionally propagated target species

In 1993, experiments on the restoration of calcareous grasslands on ex‐arable fields were started in order to provide new habitats for species of a small nature reserve with ancient grasslands north of Munich (Germany). The effects of diaspore transfer by the application of seed‐containing hay on vegetation establishment were studied on restoration fields with and without topsoil removal for 5 years. The aim of the study was to assess plant diversity for the evaluation of restoration success by different methods including determination of species with viable seeds in the hay by germination tests, phenological investigations on hay‐transfer source sites at the time of harvest, and vegetation analyses on the restoration sites. Total seed content of the hay and the number and composition of plant species with viable seeds were affected by the time of harvesting and differed between a site which had been used as arable field until 1959 and ancient grassland sites. Nevertheless, the number of established hay‐transfer species showed only few differences between restoration fields. The proportion of species transferred to restoration fields in relation to the number of species with viable seeds in the hay was between 69 and 89%. Five years after the hay transfer, the proportion of the established species was still between 58 and 76%. Up to now, topsoil removal had no significant effect on the number of established hay‐transfer species. After triple hay application the absolute number of transferred grassland species was higher than on sites with single hay application, but restoration efficiency was lower because many of the species with viable seeds in the hay did not establish. In general, our results showed that the transfer of autochthonous hay is a successful method to overcome dispersal limitation in restoration projects.

The steering role of plant-soil interactions in natural community dynamics and nature restoration

Hay transfer is a promising method to restore temperate and subtropical grasslands, but its efficiency may depend on the harvesting timing and amount of hay used. We evaluated effects of harvest date (mid‐spring/November, early summer/December, and mid‐summer/February) and hay quantity (500 and 1000 g/m2) on vegetation cover, species richness, and species composition in an experimental study in subtropical southern Brazil for a period of 2 years. We transfer undried hay from a well‐conserved reference area onto a former grassland site degraded by pine plantations. Hay harvested during mid‐spring and early summer led to higher soil cover and species richness compared to the mid‐summer hay treatment in the first year of the experiment. A drought spell decreased vegetation cover in the second year following the hay transfer, with the mid‐spring hay treatment being the least affected. C3 grasses were more effectively introduced by mid‐spring and early summer hay, in contrast to C4 grasses that were better introduced by mid‐summer hay. Lower quantities of hay tended to lead to higher cover and species richness for all harvest dates. Freshly cut undried hay can be an effective way to reintroduce native species in degraded subtropical grasslands. We conclude that timing of hay collection and the amount of hay used influence vegetation cover and species composition at the restoration site and that multiple harvest dates increase restoration success. The drought in the second year of the experiment illustrates the need to consider the possibility of adverse climatic conditions in restoration planning.

1 A great deal of money is being invested in calcareous grassland restoration on arable land within agri-environment schemes in the European Union. There is, however, little evidence that the target ecosystem can be obtained from the restoration techniques and management practices currently used. We evaluated these techniques using a multi-site approach in order to improve the success of future restoration efforts. 2 We compared 40 restoration sites with 40 paired reference sites and addressed the following specific hypotheses: (i) Are plant communities of restoration sites becoming more like those of mature calcareous grassland? (ii) How long does the restoration process take? (iii) Are there any environmental filters that hinder the process? (iv) Is there a difference in plant attributes between restored and ancient grassland communities, and between restored communities of different ages? 3 We used a multivariate approach to assess the similarity of sites and found that there was little overlap between restored and ancient grassland communities even after 60 years. Successful restoration of calcareous grasslands is achievable but the process is slow. 4 Different plant attributes were present at different frequencies in restored and reference sites, and the frequency of some attributes became more like those of reference sites with increasing age of restored site (e.g. perenniality and ruderality). 5 Seeding restoration sites with a low diversity mix appeared detrimental to restoration. Sites that regenerated naturally moved towards the target over time, although success was limited by proximity to ancient grassland vegetation. High soil phosphorus concentration was detrimental to restoration. 6 Synthesis and applications. We recommend selecting restoration sites with low phosphorous concentrations that adjoin patches of ancient calcareous grassland. Seed mixes should be devised carefully to prevent the assembly of low-value, competitive, stable communities dominated by grasses; natural regeneration may avoid this, but will only be effective close to sources of propagules. Other methods of restoration or habitat management would undoubtedly benefit from similar multi-site evaluation.

Recovery of physical conditions and processes is increasingly emphasized in ecosystem restoration. We examined a restoration project aimed at recovery of groundwater levels and base flows on an undammed desert river. We sampled streamside plant communities and hydrology annually (2003–2008) at six restoration sites at two farms (Three Links Farm and H&E Farm) after groundwater pumping was curtailed for restoration purposes, and at six reference sites. Vascular plant cover was recorded, and species were classified into functional groups based on water needs and life history. Synthetic vegetation metrics and community composition were compared between restoration sites and perennial‐flow reference sites representing target conditions. Perennial sites had higher cover, species richness, relative cover of hydric perennials and hydric annuals, and lower wetland indicator scores than non‐perennial sites, but did not differ in relative cover of non‐native species. Perennial sites had distinct species composition and high species constancy among years. Streamside vegetation was similar at Three Links Farm and perennial reference sites, indicating restoration success; streamside vegetation at H&E Farm differed from target conditions according to most measures. Hydrology is a key factor shaping desert streamside plant communities. However, single river sites may respond differently to hydrologic restoration. Contrasts in site response were likely due to differences in hydrogeomorphic context, exacerbated by drought. Understanding the constraints on restoration response is critical for setting realistic restoration goals and anticipating time frames of ecosystem change. Copyright © 2009 John Wiley & Sons, Ltd.