Productivity of reed (Phragmites australis Trin. ex Steud.) in continental-arid NW China in relation to soil, groundwater, and land-use

Reed (Phragmites australis Trin. ex Steud.) is a cosmopolitan plant species which can build up large stands in wetlands, floodplains, and on sites where groundwater is available. Phragmites australis provides many ecosystem services, such as the production of raw material (e.g. house construction or organic fuel). In the desert regions of Central Asia, reed occurs along river, e.g. the Tarim, Syr Darya, Amu Darya, and serves as fodder plant and raw material for construction and paper production. In those arid regions, reed occurs on submerged sites as well as non-flooded sites in a wide variety of phenotypes, ranging from so-called „giant reed“ (2-4 m high) to dwarf-like thorny reed not exceeding 40 cm stem length. We investigated the net primary production of the different phenotypes and their distribution with regard to soil and groundwater salt content and regarding grazing. The phenotypes were characterized through stem length, stem diameter, number of leaves per stem length, leaf weight ratio, leaf length, and leaf width. The net primary production reached 6,004 kg/ha·a on a non-grazed site, which is submerged for one month in late summer. The depth of the closed capillary fringe before onset of the flood was 2.2 m. The electric conductivity at the closed capillary fringe (determined from a water saturated soil extract) was 2 mS/cm. Stem length and stem diameter did not decrease with increasing soil and groundwater salt content, as expected. Conversely, stem length and stem diameter decreased and leaf weight ratio increased with increasing grazing intensity. Thus, grazing turned reed into dwarf-like thorny phenotypes. Non-grazed reed stands are the most productive ecosystems of the riparian vegetation at the Tarim and have a high potential to be used as raw material plant. We conclude that biomass harvesting could be an alternative to grazing with regard to sustainable land use

Species trait shifts in vegetation and soil seed bank during fen degradation

Fens in Central Europe are characterised by waterlogged organic substrate and low productivity. Human-induced changes due to drainage and mowing lead to changes in plant species composition from natural fen communities to fen meadows and later to over-drained, degraded meadows. Moderate drainage leads to increased vegetation productivity, and severe drainage results in frequent soil disturbances and less plant growth. In the present article, we analyse changes in plant trait combinations in the vegetation and the soil seed bank as well as changes in the seed bank types along gradient of drainage intensity. We hypothesize that an increase in productivity enhances traits related to persistence and that frequent disturbance selects for regeneration traits. We use multivariate statistics to analyse data from three disturbance levels: undisturbed fen, slightly drained fen meadow and severely drained degraded meadow. We found that the abundance of plants regenerating from seeds and accumulating persistent seed banks was increasing with degradation level, while plants reproducing vegetatively were gradually eliminated along the same trajectory. Plants with strong resprouting abilities increased during degradation. We also found that shifts in trait combinations were similar in the aboveground vegetation and in soil seed banks. We found that the density of short-term persistent seeds in the soil is highest in fen meadows and the density of long-term persistent seeds is highest in degraded meadows. The increase in abundance of species with strong regeneration traits at the cost of species with persistence-related traits has negative consequences for the restoration prospects of severely degraded sites

Hydro-ecological analysis of the fen system Lieper Posse, eastern Germany

The Lieper Posse is a calcareous, ground water-fed fen system, situated in the end-moraine area of northeastern Germany. Nowadays the fen is partly drained and the vegetation adversely affected; hence regeneration measures are considered. Here we report a pilot survey of the actual vegetation cover in relation to the hydrological conditions of the system. The vegetation in the central part of the fen system can be assigned to the Caricetum lasiocarpae, with small areas of Eleocharitetum quinqueflorae. The southern part of the system includes a Ledo-Pinetum sylvestris bog. Along the edges eutrophic forest types are present. Peat analysis revealed that the system started as an open lake and subsequently changed into a rheophilous mire, ‘percolating mire’. The southern bog has only recently come into being. Hydrological investigations showed that the original mineral-rich ground water had to a large extent been replaced by acid rainwater; this is likely due to the construction of a ditch before 1850. The effects of this drainage on hydrological conditions and some aspects of soil fertility are discussed. Possible consequences for the restoration of calciphilous vegetation types are being considered. It is concluded that the vegetation development is predictable only to a limited extent, which is mainly due to a lack of knowledge on hysteresis effects in both vegetation and soil.