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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.
After foundation of the Wadden Sea National Park, grazing and artificial drainage was ceased or reduced on large areas of the salt marshes at the Schleswig-Holstein mainland coast (Northern Germany). The effect of grazing cessation versus intensive and moderate grazing on vegetation diversity was studied on small (plant species richness on plots between 0.01 and 100 m2) and large scale (vegetation type richness per hectare) over 18 to 20 years by analysing data from long-term monitoring programs. Plant species richness and vegetation type richness increased strongly over time in all management regimes, because grazing-sensitive species increased first in ungrazed marshes and later dispersed to and established in intensively grazed marshes. Dominance of the tall, late-successional grass Elymus athericus on 7% to 52% of all moderately and ungrazed (primarily high marsh) plots led to a decrease in species richness. After 18 to 20 years, species richness was highest in moderately and intensively grazed high marshes. Differences were significant only on small plots of up to 4 m2. On the large scale, vegetation type richness in the low marsh was higher without grazing, while no differences were found in the high marsh. Our results indicate that grazing effects differ between spatial scales and that different spatial scales have to be considered for monitoring and evaluation of vegetation diversity in salt marshes. To conserve vegetation diversity on all scales, a large-scale mosaic of different management regimes should be maintained.
Species dispersal, establishment, and assembly are crucial stages of the life history of plants, and clear understanding ofthe governing forces and rules that shape species composition in a particular community is vital for successful ecologicalrestoration. In this article, we focus on five aspects of seed dispersal and plant establishment, which should be consideredduring habitat restoration actions. In the first two sections, we discuss the success of spontaneous dispersal and establishmenton restoration based on either spatial dispersal or local seed banks. In the third section, we assess the possibilities ofspecies introduction and assisted dispersal. In the fourth section, we introduce some possibilities for the improvement ofestablishment success of spontaneously dispersed or introduced species. Finally, we highlight issues influencing long-termpersistence and sustainability of restored habitats, related to the alteration of management type and intensity, climate change,and spread of non-native species. With the present article, we introduce the special issue entitled “Seed dispersal and soil seedbanks – promising sources for ecological restoration” containing 15 papers by 62 authors from 10 countries arranged in theabovementioned five topics.
15 δ N signals in plant and soil material integrate over a number of biogeochemical processes
related to nitrogen (N) and therefore provide information on net effects of multiple
processes on N dynamics. In general little is known in many grassland restoration projects
on soil–plant N dynamics in relation to the restoration treatments. In particular, 15 δ N signals
may be a useful tool to assess whether abiotic restoration treatments have produced the
desired result. In this study we used the range of abiotic and biotic conditions provided
by a restoration experiment to assess to whether the restoration treatments and/or plant
functional identity and legume neighborhood affected plant 15 δ N signals. The restoration
treatments consisted of hay transfer and topsoil removal, thus representing increasing
restoration effort, from no restoration measures, through biotic manipulation to major
abiotic manipulation. We measured 15 δ N and %N in six different plant species (two nonlegumes and four legumes) across the restoration treatments. We found that restoration
treatments were clearly reflected in 15 δ N of the non-legume species, with very depleted
15 δ N associated with low soil N, and our results suggest this may be linked to uptake of
ammonium (rather than nitrate). The two non-legume species differed considerably in their
15 δ N signals, which may be related to the two species forming different kinds of mycorrhizal
symbioses. Plant 15 δ N signals could clearly separate legumes from non-legumes, but our
results did not allow for an assessment of legume neighborhood effects on non-legume
15 δ N signals. We discuss our results in the light of what the 15 δ N signals may be telling
us about plant–soil N dynamics and their potential value as an indicator for N dynamics in
restoration.
Are natural floods accelerators for streambank vegetationdevelopment in floodplain restoration?
(2021)
Riverbanks are very dynamic habitats for riparian vegetation strongly influenced byfluvial and geomorphic processes. This habitat type was severely reduced in the pastby river straightening and bank stabilisation. Restoration and establishment of newfloodplain streams promote this habitat, but a directed succession to later stages wasobserved many times. Our study aimed to analyse whether the often observeddirected succession of the streambank vegetation after restoration implementationcould be reversed by a natural flood along a newly created floodplain stream. Weinvestigated the effects of a natural flood in 2013 and different prerestorationconditions on species development in the riparian zone. Vegetation was studiedalong 12 transects in four different sections from 2011 to 2014. Species composi-tion differed strongly between the sections. Species richness was lowest in a newlydug steep section with high morphological dynamics and highest on wider flatstreambanks. Changes during the years reflecting different hydrological eventsvaried between sections. The high natural flood in 2013 reduced the cover of theherb layer and increased bare ground, which led in most sections to a loss of non-target species. Total target species richness did not change due to the natural flood,while target species showed a high turnover rate. In the following year, however,the flood‐induced development of species composition, in general, was reversed.Natural floods changed abiotic and biotic conditions along the streambank, but theydid not accelerate ecological restoration towards predefined target ecosystems.However, they were necessary to preserve the needed dynamic vegetation changesand species turnover to hinder the succession to later stages dominated by a fewspecies. Our study shows that riparian vegetation near the streambank can bemonitored most effectively in cross‐profile transects, both in the long‐term andevent‐related.
Reconnection of floodplains to rivers to enhance fluvial dynamics is a favored method of floodplain restoration in Europe. It is believed that the restoration of hydrological conditions of the floodplain facilitates natural dispersal of target species, and hence the reestablishment, of typical plant communities. The aim of our study was to investigate whether floodplain target species could reach restoration sites via hydrochorous dispersal. We analyzed seed inflow from the river and seed dispersal in different sectors of a new watercourse in the Danube floodplain. Seeds were captured using 27 seed traps during three sampling periods of 3 weeks each from summer 2011 to spring 2012. After germination seedlings were identified, we detected a total of almost 39,000 seeds of 176 species, including 80 target species of riparian habitats. We found significant differences between seasons (most seeds in autumn/winter) and between stream sectors. Fewer seeds came in from the Danube (2,800 seeds) than were transported within the floodplain. Several new floodplain target species were detected, which had not been found in the aboveground vegetation or soil seed bank before the start of the restoration. Seeds of nonnative species did not disperse further than approximately 1 km. Our results indicated that hydrochorous seed dispersal from upstream habitats along the new watercourse was important for the establishment of target species and hence for the success of floodplain restoration. Technical water diversion weirs must be traversable for seeds, and small donor sectors upstream might enhance the reestablishment of target vegetation along new sectors downstream.
Wasser- und Ufervegetation
(2016)
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.
Standard extensive green roofs (EGRs) with their shallow substrate layers represent extreme sites for plant growth and therefore are planted mostly with drought-resistant species, including non-native plant species. As standard EGR substrates often lack potentially mutualistic soil microorganisms, it has been stated that inoculation with arbuscular mycorrhizal fungi (AMF) might increase plant performance and drought resistance. Aiming to support native biodiversity on EGRs, we tested whether AMF inoculation into standard green roof substrate can enhance plant performance and drought resistance of regionally occurring native dry grassland species.
The results of a pot experiment with 11 native plant species growing with and without AMF inoculation showed considerable differences in fitness-relevant plant traits. Over 88 days of moderate drought conditions, inoculated plants produced 2.5 times more above-ground biomass than control plants. In addition, the number of inflorescences on inoculated plants was significantly higher in 5 out of 7 flowering species. Under severe drought stress created by stopping the water supply, however, inoculated plants wilted on average 2.38 days earlier than control plants.
Although the underlying mechanisms of the observed results remain unresolved, AMF inoculation might help to enhance an earlier and higher seed set, facilitating the establishment of a soil seed bank, which is necessary for a self-sustaining plant population in drought-governed habitats such as EGRs.
Ecological restoration of an urban demolition site through introduction of native forb species
(2020)
Urban brownfields can provide habitats for endangered native plant species but may also support invasive non native species. The aim of our study was to develop and test different measures for the ecological restoration of an urban brownfield. We aimed to enhance native plant species richness by seeding two native forb seed mix tures containing 25 (HD-mixture) and 13 species (LD-mixture), respectively, without affecting spontaneously colonizing plant species of nature conservation value. Additionally, we tested the effects of species introduction and mowing on the establishment of invasive non-native plant species, woody species development, and per ennial grass dominance.
With establishment rates of 84% (HD) and 92% (LD) in the first study year and about 60% for both seed mixtures in the fourth year, species introduction was successful and led to rapid re-vegetation of the formerly bare brownfield. Although seeding did not result in increased species richness using either seed mixture, the dominance of perennial grasses was significantly reduced by the establishment of forb species from the HD mixture. Overall, we observed the spontaneous establishment of ten plant species of conservation value; seeding affected these species only temporarily, in the second year. Seeding (with either seed mixture) and mowing both resulted in reduced cover of woody species and a lower frequency of the invasive non-native Robinia pseudoa cacia.
Our study demonstrated the high nature conservation value of dry and nutrient-poor urban brownfields for spontaneously occurring threatened plant species. Further studies have to evaluate if the reduced cover of grasses and woody species through introduction of site-specific native forb species might increase these sites’ aesthetic value and broader acceptance of brownfields by urban residents.
Extensive green roofs (EGRs) offer several beneficial ecosystem services for sustainable urban development. However, most standard green roofs have been designed with species-poor plant mixtures containing non-native species. Aiming to increase the nature conservation values of EGRs, we developed and tested a vascular plant seed mixture including regionally occurring native sandy dry grassland species in experimental miniature roofs in Northwestern Germany (temperate oceanic climate) over 4 years. We tested the mixture at two seed densities (1 and 2 g/m2). Additionally, we tested seeding at 1 g/m2 and introducing raked plant material collected from an ancient dry grassland. The total establishment rates of sown species reached 92–96% in the first year, but dropped to 40–60% in the last 2 years, with the highest values for the plots with raked material. Twenty-four additional species (11 vascular, 7 lichen, and 6 moss species, including 7 red-list species) typical of sandy dry grasslands were introduced through the raked material. Vascular plants reached 60–70% cover in the second year. Severe drought periods in the third and the fourth year led to a strong decline of vascular plant cover then. As this cover was higher in the plots with raked material, we assume facilitative effects through the well-developed cryptogam layer containing a mix of pleurocarpous and acrocarpous mosses and lichens. Spontaneously establishing acrocarpous mosses in sown plots did not seem to provide this same function. We conclude that EGRs designed with regionally occurring sandy dry grassland plant species and especially the application of raked plant material from ancient grassland is a fruitful approach to increase the value of green roofs for native phytodiversity.
Green roofs are known to mitigate the negative effects of urban consolidation by offering diverse ecosystem functions compared to non-vegetated roofs. However, the support for native biodiversity might be improved by using native plant species. In a mesocosm experiment, we studied the suitability of three commercial green-roof growth substrates for the establishment of 27 native plant species from dry sandy grasslands of northwestern Germany over the course of four years. The substrates were mineral-based, but differed in the layering of organic matter. Total establishment rates reached 44–59% in Year 4, indicating the general suitability of the substrates. During the first weeks after seeding, with light irrigation, the vascular plant cover was greater in the similar substrates Zincolit® Plus (Z) and Zincolit® Plus-Leicht (ZL) with their compost-based organic mulch layers than in the substrate Sedumteppich (ST) with its organic matter evenly admixed with the mineral aggregates. In Years 2 and 3, however, the vascular plant cover was greater in the ST substrate, likely due to the better availability of water and nutrients from the organic matter compared to the dry surface-mulch layer variants Z and ZL. After severe drought events, the decline in plant cover was more pronounced in the ST substrate, likely representing a trade-off between lush growth and a susceptibility to drought. An indicator-species analysis revealed differences in species composition between the ST and Z/ZL substrates. Annual plant species were indicators of the ST substrate. Perennials, such as Thymus pulegioides and Achillea millefolium, were typical of the Z and ZL substrates. In addition to the general suitability of the tested standard substrates for target species establishment, the study indicated that a combination of different layers of substrate components resulted in different vegetation patterns that may have a positive effect on green-roof biodiversity.
Within the frame of the EU Common Agricultural Policy, most countries subsidise the establishment and maintenance of perennial flower strips on arable land within Agri-Environmental Schemes to provide foraging habitats and refuges for wildlife.
In a replicated field experiment, we studied the effects of different types of seed mixtures on the establishment and maintenance of perennial flower strips on fertile arable land in the federal state of Saxony-Anhalt, Germany over seven years. The seed mixtures were commonly applied within recent Common Agricultural Policy funding periods: (1) a low-diversity cultivar standard seed mixture (CULTIVAR), (2) a high-diversity cultivar and native plant mixture (MIX), and (3) a high-diversity native plant mixture (WILDFLOWER). All plots were mulched every year in March and at the beginning of August.
The low success of CULTIVAR triggered the massive encroachment of spontaneously established perennial grasses. In MIX, too, cultivars have disappeared after the first year. Both wildflower variants were successful in maintaining a high cover of sown perennial native forbs and a high ratio of established sown species, even after seven years. WILDFLOWER always tended to show better values than MIX. Furthermore, spontaneously establishing species began to spread their cover in MIX in the fifth year, with a very strongly increasing tendency, whereas in WILDFLOWER cover of spontaneously immigrating species stayed satisfyingly low.
Using native wildflowers to establish perennial wildflower strips was very effective in maintaining high species diversity within the Agri-Environmental Schemes funding period of five years and beyond. WILDFLOWER was especially successful. On the other hand, CULTIVAR failed completely. On fertile soils in regions with rather low yearly precipitation, mulching twice a year supported the maintenance of perennial wildflower strips.
Farmland bird populations are in a deep crisis across Europe. Agri-environment schemes (AES) were implemented by the European Union to stop and reverse the general decline of biodiversity in agricultural landscapes. In Germany, flower strips are one of the most common AES. Establishing high-quality perennial wildflower strips (WFS) with species-rich native forb mixtures from regional seed propagation is a recent approach, for which the effectiveness for birds has not yet been sufficiently studied. We surveyed breeding birds and vegetation on 40 arable fields with WFS (20 with single and 20 with aggregated WFS) and 20 arable fields lacking WFS as controls across Saxony-Anhalt (Germany). Additionally, vegetation composition, WFS quantity and landscape structure (e.g. distance to nearest woody element) were considered in our analyses. All WFS were established with species-rich native seed mixtures (30 forbs) in agricultural practice as AES. Arable fields with WFS had a higher species richness and territory density of birds than controls, confirming the effectiveness of this AES. A forb-rich vegetation was the main driver promoting birds. Flower strip quantity at the landscape level had positive effects only on bird densities, but also single WFS achieved benefits. A short distance from WFS to woody elements increased total bird species richness. However, the density of farmland birds, which are target species of these AES, were negatively affected by the proximity and proportion of woody elements in the vicinity. The effect of the proportion of non-intensively used open habitats and overall habitat richness was unexpectedly low in the otherwise intensively farmed landscape. Species-rich perennial WFS significantly promoted breeding birds. Successful establishment of WFS, resulting in high-quality habitats, a high flower strip quantity as well as implementation in open landscapes were shown to maximise the effectiveness for restoring declining and AES target farmland birds.