Etablierung von Torfmoosen und Begleitvegetation bei Torfmooskultivierung auf geringmächtigem Schwarztorf

authored by
Amanda Grobe
supervised by
Michael Rode
Abstract

Given the decline of peatland habitats, climate change, and the associated need to reduce greenhouse gas emissions, it is essential to rewet drained peatlands. When agricultural peatlands are rewetted, conventional drainage-based land use is no longer possible. A solution to this is offered by the so-called paludiculture, which is defined as the sustainable, productive use of peatlands under wet and thus peat-preserving conditions. Peat mosses (Sphagnum spec.) can be grown on nutrient-poor bog soils, and their biomass can be used as a renewable peat substitute for substrate production or as donor material for the restoration of peatlands. If other plant species besides Sphagnum establish at Sphagnum cultivation sites (TKF), the areas could additionally provide substitute habitat for rare and endangered peatland species. Previous Sphagnum cultivation – also known as Sphagnum farming pilot projects have been implemented on thick layers of slightly decomposed peat and thus favourable conditions for rewetting. However, after peat extraction or many years of agricultural use, often only thin layers of highly decomposed black peat remain. Due to their low porosity and hydraulic conductivity, these present a challenge for maintaining a stable near-surface water table, which is essential for optimal growth of Sphagnum and thus for successful Sphagnum cultivation. The aim of this dissertation is to evaluate whether the establishment of TKF on rewetted peat extraction sites with shallow layers of highly decomposed black peat is possible and whether TKF are suitable as substitute habitat for bog-typical and threatened plant species. The results are used to derive recommendations for establishing TKF, improving their suitability as substitute habitat, and establishing Sphagnum by biomass introduction on shallow layers of highly decomposed black peat. The studies were conducted at two TKF with shallow layers of highly decomposed black peat in the district of Emsland (Lower Saxony). One site had already been rewetted for seven years at the time of establishment, while the second site was rewetted concurrently with the establishment of the TKF. At three different times from October 2015 to October 2016, the TKF were introduced with biomass of two peat moss species (S. papillosum, S. palustre) from a total of four near-natural donor sites. The biomass was manually spread with different application densities in separate sections on the bare peat that had previously been equipped with irrigation ditches. The Sphagnum was then covered with two different cover materials (straw, geotextile) for their protection during the initial phase. The data was collected from March 2017 to October 2018. The establishment of Sphagnum and associated vegetation was recorded at the TKF. The influence of abiotic factors (e.g. peat thickness, water table) and factors resulting from the establishment of the TKF (e.g. irrigation ditch distances, protective cover) was examined with statistical analyses. Plant species composition and vegetation structure were also recorded at the TKF, and additionally at three of the near-natural donor sites (NSF) as well as at three rewetted peat extraction sites without the introduction of Sphagnum biomass (WVF). These served as a reference for the suitability of the TKF as substitute habitat. The results show that the two Sphagnum species tested in the trial (S. papillosum, S. palustre) can establish successfully on shallow layers of highly decomposed black peat. However, the high productivity realised in Sphagnum cultivation projects on moderately decomposed white peat could not be achieved. This was primarily due to insufficient water supply at both TKF. This can be attributed to the drying out of the irrigation polders and summers with low precipitation. Especially under the given difficult peat conditions, an adequate water supply (stable, near-surface water table throughout the year) is essential. It promotes Sphagnum growth and can reduce vascular plant cover. Inundation and higher nutrient concentrations should be avoided because they damage the Sphagnum or promote the establishment of nutrient-tolerant species. In addition to Sphagnum, associated vegetation had established at the TKF. While most of the associated plant species had only a low cover, Eriophorum angustifolium was the dominant companion species. The cover of Sphagnum and associated vegetation was significantly higher at the TKF that had been rewetted seven years prior to the establishment compared to the site that was rewetted concurrently with the establishment of the TKF. However, the water table was more favourable at the site with the lower establishment success. This result and the significant difference between the sites demonstrated that the success of a TKF is influenced by a complex interaction of different factors. In addition to water availability, the most important factors that positively influenced Sphagnum cover were a close distance to an irrigation ditch, higher vascular plant cover, a protective straw cover, and a greater peat layer thickness. Vascular plants can reduce evaporation and provide a suitable microclimate. Similarly, a rewetted environment and beneficial site geometry contribute to a favourable microclimate and a reduced evaporation. To protect Sphagnum from evaporation in the initial phase, straw proved to be more suitable than geotextile. To avoid losses in the initial phase due to water deficits, when establishing a TKF, the irrigation systems should be set up to be fully functional before the Sphagnum is spread at the site. The spacing of irrigation systems should be designed based on the hydraulic conductivity of the peat for favourable distribution of irrigation water. With increasing distance and thus insufficient water supply, the cover of vascular plants has increased. If optimal Sphagnum growth is achieved at a TKF and homogeneous areas with an even water supply and closed Sphagnum carpet are established, a lower cover of vascular plants can be expected. This would reduce the need for active removal of associated vegetation, e.g. by mowing, if it becomes competition for the Sphagnum. In addition, a lower number of plant species (e.g. of drought-tolerant species) can be expected compared to TKF, where structural diversity results from an uneven establishment of Sphagnum. In addition to Sphagnum, bog-typical and threatened plant species have also established at the TKF (e.g. Drosera rotundifolia, Kurzia pauciflora, Vaccinium oxycoccos). Thus, the establishment of the TKF provided substitute habitats for these species. Many of the species were transferred from the near-natural donor sites, and a high similarity in species composition between the TKF and the associated donor site was found. The WVF without the introduction of Sphagnum biomass were species-poor compared to TKF and NSF. A higher application density of the donor material resulted in a better replication of species composition as well as limited immigration and therefore competitive pressure from other species from the surrounding area. The potential for colonisation from the surrounding area did significantly influence the cover of associated vegetation, species composition, and vegetation structure at the TKF. Whether the aim of cultivating Sphagnum and providing substitute habitats for bog-typical and threatened plants are compatible also likely depends on the management and the associated disturbance of the sites (e.g. harvesting of Sphagnum biomass, mowing of vascular plants). In this context, conservation-related enhancement through providing substitute habitat at TKF is likely more compatible with the cultivation of species-rich donor material for restoration measures than with the cultivation of pure Sphagnum biomass for substrate production. Currently, growing Sphagnum biomass on bog soils in paludiculture is not yet an economic alternative to conventional drainage-based agriculture. Given the importance of peatlands for climate change mitigation, Sphagnum cultivation and other types of paludiculture as well as peatland rewetting should continue to be a focus of research projects. For large-scale implementation, the political framework conditions in conjunction with funding for the management of rewetted peatlands must be directed accordingly and reliably established for the long term.

Organisation(s)
Nature Conservation and Landscape Ecology
Type
Doctoral thesis
No. of pages
82
Publication date
2023
Publication status
Published
Sustainable Development Goals
SDG 3 - Good Health and Well-being, SDG 7 - Affordable and Clean Energy, SDG 10 - Reduced Inequalities, SDG 13 - Climate Action, SDG 15 - Life on Land
Electronic version(s)
https://doi.org/10.15488/15684 (Access: Open)