500 Naturwissenschaften
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Soil seed banks have a high potential for vegetation re-establishment in restoration projects. We studied the soil seed bank in an oxbow system of a disconnected floodplain of the Danube River in Southern Germany. The aim of the study was to analyze if floodplain target species were still present in the seed bank after more than 150 years of embankment and disconnection from fluvial dynamics. In this context we investigated seed density, seed bank species richness and species composition in four broad habitat types with and without water-level fluctuations during the time of embankment (permanent water, fluctuating water, reed bed, hardwood floodplain forest). In addition, the similarity between seed bank and above-ground vegetation in these habitat types was studied in order to predict the success of future restoration measures. In total, 124 vascular plant species were determined in the seed bank samples. More than 50 % (66 species) were target species typical for floodplain habitats and 26 of these target species were lost or very rare in the above-ground vegetation. The four habitat types differed significantly in mean seed density and mean species richness. Mean species richness and the number of target species in the seed bank as well as the mean seed density were greatest in the habitats with fluctuating water level whereas mean seed density was much lower in the parts with more or less stable conditions like permanently standing water and hardwood floodplain forest. Sørensen similarity between seed bank and above-ground vegetation was very low in habitats with more or less stable water levels and desirable floodplain target species were very rare or completely absent. Our results indicate that the soil seed bank can be an important seed reservoir for the ecological restoration of floodplain plant communities especially for habitats with unstable environmental conditions during the period of disconnection. Restoration of water level dynamics is important to maintain the seed bank of populations of floodplain target species.
Restoring depleted soil organic carbon (SOC) stocks of arable land to remove carbon from the atmosphere and offset fossil fuel emissions is a promising strategy for the mitigation of climate change. In agroecosystems conservational tillage practices and the abandonment of formerly plowed fields (ex-arable land) are shown to have the highest potential to sequester SOC. Nevertheless reported sequestration rates vary and the effects of environmental site conditions remain poorly understood. Our results are based on a meta-analysis of 273 paired SOC estimates from 65 publications which included only mineral soils from the temperate zone. SOC stocks of ex-arable grasslands with an average of 14 years since abandonment were 18% larger compared to the SOC of arable land. Likewise, SOC stocks of never-plowed grassland plots were 11% larger than the SOC stocks of abandoned fields. The average sequestration rate was 0.72 t C ha− 1 yr− 1. Semi-arid and sub-humid climate as well as low initial SOC stocks positively affected proportional SOC gains suggesting that the recovery of carbon stocks is not limited by low primary production. Therefore, the northward shift of cultivation areas in the temperate zone will lead to the abandonment of soils with high SOC recovery potential. However, if native soils are opened up elsewhere to compensate for yield losses due to abandonment the surplus of SOC in ex-arable land can easily be overcompensated by cultivation losses.
Despite the high significance of the Western Siberian grain belt for crop production in Russia, its weed communities are largely unknown. In this region spring wheat is grown on fertile Chernozem soils with large field sizes but land-use intensity per area is low compared to Central Europe. By usin a randomized sampling design we studied arable weed assemblages in the northern forest-steppe zone of Tyumen region on 99 within-field sampling plots of 100 m² size. Surprisingly, with average of 9.8 ± 3.8 species 100 m-2 species richness was low when compared with low-input farming in Central Europe and did not differ between areas of different land-use intensity. Against expectations species composition was not predominantly controlled by soil characteristics and climate, most likely due to short natural gradients. Instead, management factors such as fertilization and tillage intensity seemed to be important factors. Except for two species the Tyumen weed flora consisted mainly of species that are widespread throughout the temperate zone. We found only 10 species with an origin or core area in North Asia or Eastern Europe. The species pool was generally small and with 26% the proportion of non-native spe cies (archaeophytes) was low, when compared to Central European weed communities. Given that weed communities with higher species richness are described from neighboring Bashkiria, we conclude that arable land-use intensity in Tyumen region is high enough to reduce community species richness within arable fields estimated by a randomized sampling design. Since measured soil nutrient values did not affect species richness, herbicide use is most likely the crucial management factor. Furthermore, species-richness was vitally restricted by the small species pool. The low proportion of thermophilous arable weed species that originate from the Mediterranean or Middle-Eastern area and contribute signif icantly to the Central European weed diversity indicate that climatic dispersal limitations may be re sponsible for the small number of weed species in the Tyumen flora. An additional constraint was the short history of arable farming in Western Siberia, where considerable arable land use was started only by the end of the 17th century.
Between Ekaterinburg and Nowosibirsk, in the Western Siberian grain belt, spring wheat is grown on fertileChernozem soils. Field and farm sizes are large but the land-use intensity per area is low compared to CentralEurope. Fertilizers and pesticides are applied only in low to moderate quantities and yields range between 10and 20 dt ha-1 . We studied the arable weed flora in the northern forest steppe zone of Tyumen region using arandomized sampling design. Surprisingly, the species richness was only moderate, on average 9.8 ± 3.8species per 100 m². Compared to weed communities of Bashkiria (Southern Ural) and less intensively usedarable land of Central Europe these numbers are rather low. Moreover, most of the recorded species werecosmopolitans or widely distributed throughout the temperate zone. We suggest that the land use intensitywas high enough to reduce the density of a number of weed species in a way that they were not registered byour random sampling design. The limited conservational value of the weed vegetation of large grain fields inTyumen leads to the conclusion that if intensification of land use is unavoidable, it should be directed to arableland and not to ex-arable land or ancient grassland, which is of higher conservation value.
Wasser- und Ufervegetation
(2016)
Osnabrück’s so called “Green Fingers” – eleven landscape corridors reaching from the inner city into the region – structure the regional metropolis’ urban pattern. They supply the city centre with fresh air, serve as recreational destinations for the city’s inhabitants and provide space for close to the city agriculture and forestry. First defined in 1926, the Green Fingers have since been part of various planning documents and programs. However, these open spaces have been diminished bit by bit over time. The city’s growing need for land to build on had its impact just like the development of major traffic routes. On the one hand a lively debate has emerged: the Green Finger’s qualities, their ecological, aesthetical and cultural significance become increasingly important. Yet on the other hand decision makers still tend to put greenfield building activity first. A lot of efforts in striving for inner development are undermined by the ever growing demand for space. The urban sprawl continues, although various kinds of sanctuaries have been added to the urban and landscape planners’ equipment. The growing urban framework with its semidetached and single family houses does not come to a halt.