Motivation and Aim
Many grasslands located in Natura 2000 areas have been assessed as having an unfavorable conservation status. Even after years of appropriate management and although optimal site conditions prevail, they often still lack the typical species composition and diversity of semi-natural grasslands of high nature conservation value. Species-rich grasslands are rare and often fragmented. Thus, the lack of appropriate seed sources combined with the low potential for long-distance dispersal of many target species are two of the main reasons that hamper effective re-colonization of species-poor grasslands. Furthermore, dense swards of dominant grasses can additionally hamper or almost inhibit the germination and establishment of newly arriving grassland species. In this project, different methods for the introduction of target species have been and are still being tested in species-poor grasslands within Natura 2000 sites. Species-rich grasslands were selected as donor sites for harvesting seeds, seed-rich green hay and threshing material. Using hay transfer and sowing of regional seed mixtures, we aim to restore the diversity and species composition of semi-natural grasslands within Natura 2000 sites.
Restoration sites in the district of Wittenberg. (Source: www.openstreetmap.org)
For all restoration sites, the implementation of measures takes place according to a standardized experimental design (block design, 4 variants, 6 repetitions). To create favorable, less competitive site conditions for germination and establishment of species, six 120 m long and 6 m wide strips are rotovated (10 cm depth) in the existing grassland. The loose soil is solidified by subsequent rolling. Seed-rich material is applied in four variants on each strip. First, the species-rich donor sites are mowed and the seed-rich green hay is immediately applied on the receptor site. Second, seed-rich material is directly harvested on donor sites via on-site threshing and the dried material is sown on prepared strips at the restoration site. Moreover, two variants are created, where in addition to the application of green hay and threshing material, target species are introduced via seed mixtures of local origin. Restoration measures were carried out in autumn of 2009 in the Natura 2000 areas “Küchenholzgraben near Zahna” and “Untere Schwarze Elster” near Hemsendorf, and in late autumn 2010 in the Natura 2000 area “Elbaue zwischen Griebo und Prettin“. In the Natura 2000 area "Dessau-Wörlitzer Elbauen" two restoration measures were implemented; in Oct. 2011 the "Cortenswiese" near Dessau and in Oct. 2014 a species poor grassland near Klieken. All restoration sites, as well as the associated donor sites, are located in the Wittenberg district of Saxony-Anhalt.
The success of the restoration measures is being scientifically evaluated in a monitoring program. We document the establishment of the species and compare rates between variants. For this purpose, vegetation surveys are carried out once a year using permanent plots (4 x 4 m) in any treatment as well as in adjacent undisturbed grassland. Furthermore, soil samples from both donor and receptor site are taken and analyzed for nutrients (C, N, P, K) and pH.
Vegetation development on restoration sites
The results of the 5 year long vegetation survey at our restoration sites „Küchenholzgraben“ und „Untere Schwarze Elster“ showed that all tested introduction methods are appropriate to increase biodiversity in species-poor grasslands. The number of target species of Category 1 (Red-listed species or species with population decline) and Category 2 (other characteristic species) continuously increased over the years and in the last year reaching up to 20 species per plot. Further, cumulative plant cover of these species showed positive trends. In the project area “Küchenholzgraben” target species of Cat.1 and Cat. 2 reached approx. 20% and cat 3 species 40 % cover after five years. In the case of restoration site “Untere Schwarze Elster” the corresponding values were comparable (approx. 15% for Cat. 1 and 2, and 35% for Cat. 3).In total, there were only slight differences concerning the establishment of target species between both introduction methods, thus, the transfer of hay and the use of threshing material have proofed to be similarly successful. Whereas, additional seeding of regional seed mixtures had a positive effect on restoration success: plots with additional seeding showed a significantly higher number and coverage of target species (Cat.1 and 2) than without seeding. We recommend seeding additionally or solely especially in cases, where species-rich donor sites are limited or not available. Furthermore, additional seeding can encourage establishment of early seed-shedding species, which are difficult to transfer via plant material harvested in September.
What are the next steps?
The experience so far shows that the applied methods were very effective in developing and enhancing the species composition and diversity of grasslands. The monitoring of vegetation development will be continued in all areas where restoration measures have already been implemented. Only in this way can it be shown whether or not target species will persist on the experimental strips. Moreover, it remains to be seen to what extend and how fast introduced species can migrate from strips into the surrounding grassland. Further research is needed for optimisation of methods. Especially the growing conditions within the first year (after restoration measures have been carried out) have a crucial impact on the establishment of the sensitive seedlings. For instance, we noticed on some plots several ruderal species and species emerged from soil seed bank as well as quickly regenerating grasses from the resident grassland, that can dominate and thereby hamper optimal establishment of target species. Both the intensification of sward disturbance (e.g. ploughing) and/or the adaptation of management actions may improve the conditions for establishing target species. Thus, it would be interesting to test the effect of different management regimes within the first year on the subsequent vegetation development. Furthermore, the experimental design could be extended by varying the amount of sward disturbance to clarify whether ploughing provides a more persistent suppression of the resident grassland vegetation than rotovating.
Funding: Europa-ELER, ELER-Sachsen-Anhalt, Landesverwaltungsamt Sachsen-Anhalt
Cooperation partner: UNB Wittenberg, UNB Jerichower Land , Biosphärenreservat "Mittelelbe", Georg Darmer - UBC Umweltvorhaben, Matthias Stolle Wildpflanzenvermehrung und –handel (Propagation of autochthonous seeds)