Berlin's
Peatlands and
Climate Change

The natural restoration ability of the native vegetation depends on a number of factors. Residues from native vegetation promote their restoration, as these are seeds of expansion in terms of re-vegetation and the spreading of diaspores. Furthermore, residues of the original vegetation signal a weaker, only partly complete change in site-specific factors. In parts, the light as well as trophic conditions may still represent the original conditions.

The availability of diaspores in the soil is significant for the restoration, if removal of topsoil is part of the process (Hölzel & Otte 2003, Urban 2004, Reid et al. 2009). Long lost or very rare species may reappear. Nonetheless, the comparison with historical sources in the case of a heathland pond in Lower Saxony showed „…that approx. half of the formerly existing species in the area did not reappear“ (Urban 2004). Topsoil removal can effectively be used to do away with unwanted vegetation and eutrophic horizons. Sod removal is considered more beneficial for the preservation of the diaspore bank than the removal of the top peat layer. In a peatland in the Upper Rhine valley, where 30 cm of topsoil were removed, 20–40 % of diaspores were preserved; when 50 cm were removed, the diaspore bank was completely destroyed (Hölzel & Otte 2003). The less soil has to be removed, the better. The question arises, where greater depths are concerned, how the degraded peat can be disposed off and whether removing it is a reasonable decision (cost-benefit analysis).

Buried fen soils may host good diaspore banks and consequently have a high regeneration potential for (eutrophic) wetland forests and meadows as well as species diversity of rewetted wetland forests and meadows. „The results suggest that the targeted use of soil seed banks can be a suitable method to initiate a repopulation with native plants relatively quickly“ (experimental project Brögberner Teiche/Lower Saxony, University Oldenburg 2001).

In the case of species-rich wetland meadows, diaspore banks are qualitatively and quantitatively usually unsatisfactory. The main reason is previous intensive utilization resulting in degraded soils (soil compaction, mineralization, eutrophication, and other consequences) (Roth et al. 2001). If the restoration of the target area is hampered by isolation and an exchange of diaspores is not happening, there is a risk that it becomes a long-term area of low ecological value (Roth et al. 2001). „Additional to abiotic conditions, the diaspore availability in the soil as well as the germination and growth conditions of the individual species is important for success (Urban 2004).

„Succession is not a deterministic process“ (Urban 2004). Nonetheless, there are typical development stages after rewetting that occur in dependence on the site. And the success of restoration needs to be considered in dependence of the nature target.

Eutrophic peatlands (eutrophic fens) develop independently and dynamically. The only prerequisite criterion is a rising annual median water level. Common competitive plants establishing as stocks are markers of the succession stages of the open sites. Through peat formation, a polytrophic ecosystem may transition to a semi-natural, or undisturbed eutrophic state. Temporary, polytrophic stages are parts of quasi-natural restoration processes („self-healing powers of nature“) and, therefore, must be accepted temporarily.

Drained, eutrophic or polytrophic alder swamp forests may also transition indenpendently and dynamically towards wetter variants. In Berlin, for example, the margins of the peatland Grosser Rohrpfuhl have changed from a drained alder forest to become a water violet and black alder forest.

From rewetting of nutrient-high areas with flat overflow (< 40 cm), stocks of broadleaf cattail begin to establish (Typha latifolia) and the „formation of gyttja soil“ (according to KA 5 Sapropel from detritus gyttja) begins. After a few years, peat-forming reeds (Phragmites australis) and large sedge-reeds (Carex paniculata, C. elata, C. pseudocyperus) (Succow & Runze 2001, S. 505) enter into it. Historical examples from semi-natural or undisturbed vegetation with similar nature targets cannot be recommended, as their former soil characteristics were irreversibly altered by intensive utilization (Succow & Koska 2001, p. 479). Seasonal or temporary shallow water sites often become dominated by communities of Phalaris arundinacea and Glyceria maxima (Lietzengrabenniederung). Stocks of these communities may establish themselves long-term (Succow & Runze 2001). Carex species (C. riparia, C. acutiformis) and Salix species (S. alba, S. cinerea) could immigrate under certain circumstances.

Brown moss peatlands (mesotrophic-subneutral or -calcareous mires) are fens which are well provided with bases or lime, but as a consequence of a lack of nitrogen are characterised by a specialised mesotraphent vegetation beyond that of sphagnum bogs. As these sites that are also called „brown moss peatlands“ are highly sensitive to nutrient contamination, they are extremely rare today and very valuable. Restoration is very complex, and, in addition, it would be difficult to assess the outcome of a successful restoration. Therefore, long-term maintenance care should be part of the planning process where this nature target is concerned. Eutrophic variants of the „brown moss peatlands“ are the low-growing Barbilophozia-Carex reed as well as tall-growing Barbilophozia-Carex reed peatlands, which can be found on the protected nature reserves of Berlin (NSG Bäkewiese, Müggelheimer Wiesen, NSG Pfaueninsel, NSG Tegeler Fließ). In all of these cases, the lands are regularly mowed meadows or pastures on which water buffalo graze. The removal of the straw produces a successive depletion of nutrients, and near-surface light conditions promote the growth of moss.

Sphagnum bogs predominantly show the characteristics of kettle-hole or terrestrialisation mires in Berlin-Brandenburg. As their vegetation includes plants typical of both raised bog and fen vegetation, they can be classified as transition mires. Sphagnum bogs have a good capacity for regeneration. Removal of the top peat layer, for example, can rapidly lead to a regeneration of native plant life (Bernrieder 2003). Jeschke & Paulson (2001) also state that oligo- or mesotraphent vegetation may start to regrow in the case of overflow after only 3–5 years. Accordingly, the example of the peatland Kleine Pelzlaake showed a rapid recolonization with typical vegetation on open peatland already in the first vegetation period after woody plants and moor-grass hummocks had been removed (Stiftung Naturschutz Berlin 2013).

Coniferous forests consume more water than deciduous forests (Grüne Liga e.V. 2008). As opposed to deciduous trees, evergreen pine-tree communities transpire also during the cold season and thus contribute to a reduction in the rebuilding of groundwater, which has a very high value (potential) in the cold season. At a raspberry-wavy hair-grass pine forest near Finow, between 0 to 29 % of the annual rainfall of 620 mm is lost to seepage over the course of the year depending on age group, while the values for a may-lily beech forest at the same site are down at 21 to 43 % (Anders et al. 1999). A thick beech forest at the margins of a peatland thus reduces the radiation balance of the marginal area, limiting the evaporation and saves the water reserves of the peatland (Edom 2001). So deciduous or hardwood stocks in the catchment area have a positive impact on the regional groundwater table and the peatland water level as well as the dissipation budget overall, and thus a positive influence on the local climate (Luthardt et al. 2010).

Undisturbed fens possess a large pore volume (85 %) and a small substance matter volume (15 %) (Zeitz 2014). Drainage is followed by the physical process of subsidence, which causes the natural deposition of peats to be changed through compression, large pores being lost along the way. The deeper a mire, the larger the potential subsidence (or sagging) and the fewer the irreversible changes to the ground. Further, the capacity for re-swelling when the peatland water level rises is increased. As the peatland surface more or less goes where the water level goes, the peat is minimally decomposed and the trophic and hydrologic status of the native plant communities persists to be stable.

The analysis of the absolute degree of decomposition (depth) of 397 soil horizons, or profiles of Berlin's peatlands showed that the part deep soil decomposition decreases from a depth of approx. 4.50 m on down. The number of profiles that showed (initial) peat growth increased steadily proportionate to the increase in peatland thickness (see graphic).

With 12.6 or 13 m each, the permanently wood-free central areas of, for example, the peatland Kleine Pelzlaake or the Teufelsseemoor in Koepenick possess the greatest thicknesses of all. Here, there was no evidence in the soil indicating that longer periods of dry weather had left their mark on them. At the Teufelsseemoor, oscillation at the peatland surface has been recorded and documented since the 1970s. The amount of subsidence (or sagging) had been approx. 90 cm and the subsequent raising back up of the surface amount to approx. 30 cm (Scheffler et al. 2013).

Clay and silt as well as loam with higher contents of fine substance have a much lower water conductivity than gravel or sands (Schlichting et al. 1996). Peatlands within sand dominated geolocial formations, like in the glacial valley “Berliner Urstromtal„ or the “Nauener Platte“ in the Grunewald area, are therefore hydro-geolocically at a disadvantage with regard to their water retention potential in dry periods. Here, it must be reckoned with a significantly higher loss through seepage in the catchment area than in the marly loam containing ground-moraine plates of areas Barnim and Teltow. Nonetheless, some peatlands with a sandy catchment area may well be able to retain water effectively. These peatlands contain water retention enhancing organo-mineral gyttja (clay, silt or calcareous gyttja). In Berlin, the peatland Langes Luch in Koepenick hydrologically benefits from silt gyttja that seals its basin. So the floating peat mat of the Barssee, too, is supported by binding organo-mineral gyttja, which in this case is critical to the preservation of its ecosystem, as the groundwater table in the Grunewald area has sunk significantly as a consequence of drinking-water extraction and is probably now at a depth several metres below the peatland water level.

Pure medium sand usually has Kp values that are significantly > 100 cm/d. By contrast, the Kp values of the calcareous gyttja of the Tegeler Fließ and of the nature reserve NSG Mittelbruch according to Waniek (2014) are at approx. 3 cm/d, and with that can be grouped with the silty and clayey substrates as having the same poor water conductivity.

According to a comparative study of peatlands in terminal moraines and peatlands in sandy ground moraines both in Northeast Brandenburg, the sphagnum bogs of the terminal moraines, which are embedded in signfificantly better binding substrates, are the mire-hydrological preferred option and are in a significantly better state of preservation (Luthardt et al. 2010).

Peatlands or mires with kettle-hole or trough-shape basins naturally possess a ability to protect against dissipation through shading, which is owed to geomorphology of the closely adjoining catchment area (Edom 2001). Furthermore, the shape and situation is accompanied by a critically lower air-mass exchange as is the case in catchment areas with a lower relief. The formation of real kettle-hole mires with self-sufficient water levels only becomes possible through this advantage from local climate, and is additionally fostered by the subsurface runoff from the above-ground catchment area (Succow 1988, Hasch 1994).