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Renaturierungsökologie
(2019)
During recent decades, many studies have shown that the successful restoration of species-rich grasslands is often seed-limited because of depleted seed banks and limited seed dispersal in modern fragmented landscapes. In Europe, commercial seed mixtures, which are widely used for restoration measures, mostly consist of species and varieties of non-local provenance. The regional biodiversity of a given landscape, however, can be preserved only when seeds or plants of local provenance are used in restoration projects. Furthermore, the transfer of suitable target species of local provenance can strongly enhance restoration success.
We review and evaluate the success of currently used near-natural methods for the introduction of target plant species (e.g. seeding of site-specific seed mixtures, transfer of fresh seed-containing hay, vacuum harvesting, transfer of turves or seed-containing soil) on restoration sites, ranging from dry and mesic meadows to floodplain grasslands and fens. Own data combined with literature findings show species establishment rates during the initial phase as well as the persistence of target species during long-term vegetation development on restoration sites.
In conclusion, our review indicates that seed limitation can be overcome successfully by most of the reviewed measures for species introduction. The establishment of species-rich grasslands is most successful when seeds, seed-containing plant material or soil are spread on bare soil of ex-arable fields after tilling or topsoil removal, or on raw soils, e.g. in mined areas. In species-poor grasslands without soil disturbance and on older ex-arable fields with dense weed vegetation, final transfer rates were the lowest. For future restoration projects, suitable measures have to be chosen carefully from case to case as they differ considerably in costs and logistic effort. Long-term prospects for restored grassland are especially good when management can be incorporated in agricultural systems.
The break-up of the Soviet Union in 1991 triggered cropland abandonment on a continental scale, which in turn ledto carbon accumulation on abandoned land across Eurasia. Previous studies have estimated carbon accumulationrates across Russia based on large-scale modelling. Studies that assess carbon sequestration on abandoned land basedon robust field sampling are rare. We investigated soil organic carbon (SOC) stocks using a randomized samplingdesign along a climatic gradient from forest steppe to Sub-Taiga in Western Siberia (Tyumen Province). In total, SOCcontents were sampled on 470 plots across different soil and land-use types. The effect of land use on changes in SOCstock was evaluated, and carbon sequestration rates were calculated for different age stages of abandoned cropland.While land-use type had an effect on carbon accumulation in the topsoil (0–5 cm), no independent land-use effectswere found for deeper SOC stocks. Topsoil carbon stocks of grasslands and forests were significantly higher thanthose of soils managed for crops and under abandoned cropland. SOC increased significantly with time sinceabandonment. The average carbon sequestration rate for soils of abandoned cropland was 0.66 Mg C ha1yr1(1–20 years old, 0–5 cm soil depth), which is at the lower end of published estimates for Russia and Siberia. Therewas a tendency towards SOC saturation on abandoned land as sequestration rates were much higher for recentlyabandoned (1–10 years old, 1.04 Mg C ha1yr1) compared to earlier abandoned crop fields (11–20 years old,0.26 Mg C ha1yr1). Our study confirms the global significance of abandoned cropland in Russia for carbonsequestration. Our findings also suggest that robust regional surveys based on a large number of samples advancemodel-based continent-wide SOC prediction.
Following the collapse of the Soviet Union in 1991 around 45 million hectares
of arable land became abandoned across Russia. Our study focused on the recovery
potential and conservation value of grassland vegetation on ex-arable land in the Tyumen
region of the Western Siberian grain belt. We compared ex-arable grasslands of different
successional stages with ancient grasslands as reference for the final stage of succession
along a climatic gradient from the pre-taiga to the forest steppe zone. Plant community
composition and species richness of ex-arable land clearly developed towards reference
sites over time, but even after 24 years of abandonment, the grassland vegetation had not
totally recovered. The c-diversity of vascular plants was slightly higher on ex-arable land
than in ancient grasslands but the mean a-diversity was still moderately lower. A significant proportion of the vegetation of ex-arable land still consisted of ruderal and mesic
grassland species and the number and cover of meadow-steppe species was significantly
lower than in ancient grasslands. Grazing and time since abandonment positively affected
the reestablishment of target grassland species, whereas it was negatively affected by the
cover of grasses. In contrast to ex-arable land, the conservation value of arable land is only
modest. Therefore, future intensification of land use is most likely less harmful if directed
to existing arable land. Re-cultivation of ex-arable land and grassland improvement operations such as seeding of competitive grass species are major threats for the biodiversity of secondary grasslands on ex-arable land in the forest steppe zone of Western Siberia.
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.
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.
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.