Quantifying establishment limitations during the ecological restoration of species‐rich Nardus grassland

Abstract

Aims Successful establishment of species‐rich Nardus grasslands on ex‐agricultural land requires identification and removal of barriers to effective seed germination and seedling survival. Therefore, we investigate how germination and early development are affected by soil conditions from different restoration phases and how this relates to their specific plant strategies. Location Grasslands and experiments in northern Belgium. Methods We selected three grassland restoration phases (Lolium perenne grasslands, grass–herb mix grasslands and species‐rich Nardus grasslands), which were characterized by a distinct plant community and soils with contrasting abiotic and biotic properties (respectively, eutrophic, mesotrophic and oligotrophic soils). In a first germination experiment we investigated the species‐specific responses (germination, lag time and emergence rate) of 70 grassland species (that typically occur along the restoration gradient) in each of the selected soils. Second, a mesocosm experiment was set‐up in which a mixture of 19 species (representative of the distinct grassland restoration phases) was grown together in the respective soils. Here, we analysed the intraspecific variation of plant growth, SLA and identified changes in community assembly. Results Irrespective of soil influences, Nardus grassland species had significantly lower germination potentials and longer germination lag times than L. perenne grassland species. Germination (and its lag time) of grass–herb mix grassland species were negatively affected by the oligotrophic soils. Soil factors determined early growth patterns during the emergence and establishment phase. L. perenne grassland species exhibited a more plastic growth response and were highly dependent on soil type. Nardus grassland species exhibited large intraspecific variation in SLA, which was found to be significantly lower in the oligotrophic soils. Even though the difference in bio‐available P between mesotrophic and oligotrophic soils was minor, Nardus grassland species were only able to compete in the oligotrophic soils (no significant difference in biomass between communities). Mesotrophic mesocosms exhibited the highest species richness after 200 d of growth. Conclusion Plant species from the three grassland restoration phases display distinct germination strategies, irrespective of soil type. Interactions between growth strategies and soil factors determine competitive asymmetry and therefore shape community assembly in the distinct grassland phases.

Extreme droughts in oligotrophic mountain grasslands cause substantial species abundance changes and amplify community filtering

“…Other species from more productive grasslands were not able to develop dominance after their short‐term increase in the following years. The competitive ability and regeneration of these species proved to be strongly constrained by consecutive droughts in oligotrophic systems (van Daele et al, 2017). Therefore, the observed changes in abundance of low‐productive and character species, together with the relative stability of species richness, indicate that community filters, which generate an altered set of alpha niches, may play an increased role in recovery of the community after droughts.…”

Are historical land‐use patterns and chemical soil characteristics complementary for assessing the restoration potential of Nardus grassland?

“…In the high‐priority zone, suitable for at least four Nardus grassland indicator species, additional soil analyses can increase the positive predictive value (from 61% up to 70.7%) and accuracy (from 74.7 up to 81.3%) of the model prediction. Furthermore, insight in the soil chemistry can help guide conservation and restoration measures and increase the chance of success (Ceulemans et al, 2014; Van Daele et al, 2017). When the Natura 2000 surface area and habitat quality objectives cannot be met within the high‐priority zone, soil samples in the lower‐priority zone (with a potential for up to three or four indicator species) are recommended to detect sites with a high potential, missed as a consequence of the low sensitivity of model 1.…”

“…However, this is essential to understand how land‐use legacies affect contemporary and potential natural vegetation (Perring et al, 2016). This is especially the case for species communities with a slow‐growth strategy which are sensitive to land‐use intensification due to competitive pressures, such as species‐rich Nardus grassland (syntaxonomic class Nardetea strictae ; Van Daele et al, 2017).…”

“…The habitat quality of acidic grasslands can be explained by chemical soil characteristics to a high degree (Janssens et al, 1998;Kleijn et al, 2008;Ceulemans et al, 2013). Increased availability of N, P and K, often as a result of fertilization, stimulates biomass production, alters the feedback between above-ground and belowground communities and reduces the species richness of grasslands through competitive exclusion (Wardle, 2004;Crawley et al, 2005;Leff et al, 2015;Van Daele et al, 2017). Furthermore, nitrogen deposition and the resulting acidification have been identified as important drivers of degradation (Bobbink et al, 2010;Duprè et al, 2010).…”

Win some, lose some: Mesocosm communities maintain community productivity despite lower phosphorus availability because of increased species diversity

“…In April 2016, each mesocosm received 111 seedlings of the same 19 grassland species. The planted species were selected from three pools of species (Van Daele et al, 2017): (a) seven Nardus grassland species, which are considered target species and are generally slow‐growing; (b) seven grass–herb mixed grassland species; and (c) five high‐productive grass‐dominated Lolium perenne grassland species, respectively called oligotrophic, mesotrophic and eutrophic grassland species from here on. The complete list of species can be found in Appendix .…”