Urban greenspace has gained considerable attention during the last decades because of its relevance to wildlife conservation, human welfare, and climate change adaptation. Biodiversity loss and ...ecosystem degradation worldwide require the formation of new concepts of ecological restoration and rehabilitation aimed at improving ecosystem functions, services, and biodiversity conservation in cities. Although relict sites of natural and semi-natural ecosystems can be found in urban areas, environmental conditions and species composition of most urban ecosystems are highly modified, inducing the development of novel and hybrid ecosystems. A consequence of this ecological novelty is the lack of (semi-) natural reference systems available for defining restoration targets and assessing restoration success in urban areas. This hampers the implementation of ecological restoration in cities. In consideration of these challenges, we present a new conceptual framework that provides guidance and support for urban ecological restoration and rehabilitation by formulating restoration targets for different levels of ecological novelty (i.e., historic, hybrid, and novel ecosystems). To facilitate the restoration and rehabilitation of novel urban ecosystems, we recommend using established species-rich and well-functioning urban ecosystems as reference. Such urban reference systems are likely to be present in many cities. Highlighting their value in comparison to degraded ecosystems can stimulate and guide restoration initiatives. As urban restoration approaches must consider local history and site conditions, as well as citizens’ needs, it may also be advisable to focus the restoration of strongly altered urban ecosystems on selected ecosystem functions, services and/or biodiversity values. Ecosystem restoration and rehabilitation in cities can be either relatively inexpensive or costly, but even expensive measures can pay off when they effectively improve ecosystem services such as climate change mitigation or recreation. Successful re‐shaping and re-thinking of urban greenspace by involving citizens and other stakeholders will help to make our cities more sustainable in the future.
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•Global restoration initiatives face strong trade-offs among single objectives.•The choice of suitable indicators is a key aspect for restoration success.•Grassland ecosystems ...highlight potential restoration pitfalls.•To avoid pitfalls, restoration projects must integrate holistic assessments.•This requires an ambitious indicator system including socio-ecological outcomes.
Restoring degraded ecosystems is crucial for human wellbeing and biodiversity conservation. Nowadays, ecological restoration goes far beyond recovering a degraded ecosystem according to a historic reference. Instead, more specific restoration goals are set, following global environmental strategies that are individually highly important, but often conflicting. Furthermore, various pitfalls exist regarding the evaluation of ecosystem degradation and, directly related to this, the question what is the most desirable ecological state of an ecosystem. Ignoring such issues can lead to a failure of restoration projects and do more ecological (and social) harm than good. A crucial aspect in tackling conflicting goals and circumnavigating restoration pitfalls is the considerate choice of the indicators to assess ecosystem degradation and restoration capacity.
In this Perspective, grasslands and rangelands are used exemplarily for ecosystems with globally high restoration demand. I discuss potential restoration pitfalls related to enhancing carbon sequestration, soil fertility, and ecosystem service multifunctionality. For all three goals, strong trade-offs and unwanted side effects exist. For example, while increasing carbon storage and restoring soil fertility are widely acknowledged environmental goals, both can compromise other restoration targets such as grassland biodiversity and further ecosystem services, depending on the specific context. Thus, there are no universally applicable indicators for ecosystem degradation and restoration. Instead, indicator systems have to account not only for strong trade-offs among restoration goals but also for a number of environmental and socio-ecological misconceptions, such as presented for the case of grassland ecosystems.
I argue that one-sided goal setting and an imprudent choice of indicators can misguide the science-policy dialogue and related restoration efforts. To avoid this, restoration programs must integrate holistic assessments of their objectives across spatial scales and with all stakeholders concerned. The associated ecological indicator system for restoration success and program performance must therefore also be based on multidisciplinary and participatory approaches. Restoration and degradation indicators have to further ensure the target ecosystem is correctly and comprehensively identified, and the manifold conflicting land management objectives associated with heterogeneous human societies are taken into account. Researchers can assist this process by by-default considering the socio-ecological context of a restoration target and by identifying trade-offs arising from potential solutions, before these are suggested to the public. Only when all these aspects are considered, restoration projects at the local to global scale will result in long-term sustainable outcomes.
Urbanization is one of the most severe threats to biodiversity, so why should not we use green space in cities to counteract the biodiversity loss as much as possible? Urban grasslands provide a ...large number of social, financial, recreational, and environmental ecosystem services but can also support high biodiversity. In this article, I describe the importance of urban grasslands for (local) biodiversity and recommend strengthening restoration ecological research and efforts to optimize these novel ecosystems for conservation purposes. The management intensity of a high proportion of urban grasslands decreased over the last decades. However, species richness of these grasslands is still low, although there is now a great potential for higher plant, but also animal diversity. While communal authorities are interested in cost‐efficient but at the same time biodiversity‐friendly management of urban grasslands, a well‐founded scientific basis for the restoration of urban grassland is still missing. I argue that besides all challenges associated with the restoration of urban habitats we should urgently proceed in the development of appropriate and effective restoration approaches and communicate knowledge gained to urban planners and stakeholders. Widening the scope of restoration ecological research to novel ecosystems such as urban grasslands is one of the most important recent challenges for biodiversity restoration and it gives urban habitats the significance they deserve.
Abstract
Globally, we face a dramatic biodiversity loss in agricultural systems as well as severe ecosystem degradation. In grasslands, higher biodiversity in terms of plant diversity was shown to ...increase the diversity of higher trophic levels and provide benefits for farmers such as higher and more stable yields. However, we lack a systematic overview of costs for more diverse seed mixtures, which are an essential tool in maintaining and increasing plant diversity in grasslands. We here investigated the prices and characteristics of 262 commercially available seed mixtures from six German or Swiss online shops and quantified the relationships between seed mixture prices and plant diversity. The most frequent seed mixtures contained 1–10 species and were designed for rather intensive grassland management. On the contrary, a smaller set of seed mixtures with particularly high plant diversity (>30 species), usually of native ecotypes, were offered for restoration purposes. More diverse seed mixtures were also more expensive. For example, a seed mixture with 10 or 30 species was on average +63% or +387% more expensive, respectively, than a product containing only one species. The relationship between plant diversity and seed mixture prices per ha was related to other seed mixture characteristics, of which plant provenance (i.e. native ecotypes vs. cultivars) was particularly important for the price. Seed mixtures containing only native ecotypes had considerably higher prices per ha (⩾+75%) than those including cultivars. In conclusion, increasing biodiversity in grasslands can be costly. These costs need to be considered when making recommendations to farmers and other stakeholders. Measures to reduce such costs for maintaining and/or increasing plant diversity could promote establishment of grasslands with higher plant diversity, facilitate the restoration of semi-natural grasslands, and contribute to solving the biodiversity crisis in agroecosystems.
Both climate change and agricultural intensification are drivers of global nutrient cycles and biodiversity loss. A potentially great environmental threat can arise when these two drivers interact, ...for example, when farmers try to compensate reduced soil nutrient availability due to drought by the application of liquid organic fertiliser. As dry soils don't hold back nutrients very well, this approach can lead to nitrate leaching and potentially also to the pollution of drinking water. However, little is known about leaching from dry but fertilised grassland soil, and how this is affected by land use intensity and plant diversity.
In this mesocosm study, we transferred 60 grassland sods differing in past land use intensity to a greenhouse and treated them with severe drought, fertilisation and both together. Drought was induced by almost entirely stopping irrigation for seven weeks. Fertilisation was done by three applications of slurry summing up to 168 kg total nitrogen per hectare (111 kg NH4-N). We assessed nutrient leaching risk with ion-exchange resin (IER) bags installed in the soil of all mesocosms. IER bags were retrieved after drought and extracts were analysed for concentrations of nitrate, ammonium, phosphate and potassium.
Fertilisation partially buffered drought-induced losses in yield. However, the interaction of fertilisation and drought resulted in a drastic increase in nitrate leaching risk when soils are rewetted (>300%), while neither drought nor fertilisation alone were significant. Ammonium concentrations followed the same trend as nitrate, but less pronounced. Phosphate and potassium concentrations were not affected by the treatments. Past land use was hardly related to soil nutrient concentrations, rather was plant diversity. However, results indicate that plant diversity was not driving nitrate and ammonium concentrations under drought and/or fertilisation. This study reveals grassland fertilisation during drought to be a severe environmental problem due to significantly increased nitrate leaching risk.
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•Grassland fertilisation during drought buffers yield losses, but depicts a severe threat to groundwater safety.•Fertilisation or drought alone did not affect nutrient leaching from clay-rich soils.•However, their interaction lead to a drastic increase in nitrate leaching risk.•Plant diversity was much closer related to soil nutrient concentrations than past land use intensity.•Interactions among climate change and land-use intensification might put clean drinking water at risk.
Human land use may detrimentally affect biodiversity, yet long-term stability of species communities is vital for maintaining ecosystem functioning. Community stability can be achieved by higher ...species diversity (portfolio effect), higher asynchrony across species (insurance hypothesis) and higher abundance of populations. However, the relative importance of these stabilizing pathways and whether they interact with land use in real-world ecosystems is unknown. We monitored inter-annual fluctuations of 2,671 plant, arthropod, bird and bat species in 300 sites from three regions. Arthropods show 2.0-fold and birds 3.7-fold higher community fluctuations in grasslands than in forests, suggesting a negative impact of forest conversion. Land-use intensity in forests has a negative net impact on stability of bats and in grasslands on birds. Our findings demonstrate that asynchrony across species--much more than species diversity alone--is the main driver of variation in stability across sites and requires more attention in sustainable management.
Abstract
Experimental evidence shows that grassland plant diversity enhances ecosystem functioning. Yet, the transfer of results from controlled biodiversity experiments to naturally assembled ‘real ...world’ ecosystems remains challenging due to environmental variation
among sites
, confounding biodiversity ecosystem functioning relations in observational studies. To bridge the gap between classical biodiversity‐ecosystem functioning experiments and observational studies of naturally assembled and managed ecosystems, we created regionally replicated,
within‐site
gradients of species richness by seeding across agricultural grasslands differing in land‐use intensity (LUI) and abiotic site conditions.
Within each of 73 grassland sites, we established a full‐factorial experiment with high‐diversity seeding and topsoil disturbance and measured 12 ecosystem functions related to productivity, and carbon and nutrient cycling after 4 years. We then analysed the effects of plant diversity (seeded richness as well as realized richness), functional community composition, land use and abiotic conditions on the ecosystem functions within (local scale) as well as among grassland sites (landscape scale).
Despite the successful creation of a
within‐site
gradient in plant diversity (average increase in species richness in seeding treatments by 10%–35%), we found that only one to two of the 12 ecosystem functions responded to realized species richness, resulting in more closed nitrogen cycles in more diverse plant communities. Similar results were found when analysing the effect of the seeding treatment instead of realized species richness.
Among sites
, ecosystem functioning was mostly driven by environmental conditions and LUI. Also here, the only functions related to plant species richness were those associated with a more closed nitrogen cycle under increased diversity.
The minor effects of species enrichment we found suggest that the functionally‐relevant niche space is largely saturated in naturally assembled grasslands, and that competitive, high‐functioning species are already present.
Synthesis
: While nature conservation and cultural ecosystem services can certainly benefit from plant species enrichment, our study indicates that restoration of plant diversity in naturally assembled communities may deliver only relatively weak increases in ecosystem functioning, such as a more closed nitrogen cycle, within the extensively to moderate intensively managed agricultural grasslands of our study.
Land-use intensification can increase provisioning ecosystem services, such as food and timber production, but it also drives changes in ecosystem functioning and biodiversity loss, which may ...ultimately compromise human wellbeing. To understand how changes in landuse intensity affect the relationships between biodiversity, ecosystem functions, and services, we built networks from correlations between the species richness of 16 trophic groups, 10 ecosystem functions, and 15 ecosystem services. We evaluated how the properties of these networks varied across land-use intensity gradients for 150 forests and 150 grasslands. Land-use intensity significantly affected network structure in both habitats. Changes in connectance were larger in forests, while changes in modularity and evenness were more evident in grasslands. Our results show that increasing land-use intensity leads to more homogeneous networks with less integration within modules in both habitats, driven by the belowground compartment in grasslands, while forest responses to land management were more complex. Land-use intensity strongly altered hub identity and module composition in both habitats, showing that the positive correlations of provisioning services with biodiversity and ecosystem functions found at low land-use intensity levels, decline at higher intensity levels. Our approach provides a comprehensive view of the relationships between multiple components of biodiversity, ecosystem functions, and ecosystem services and how they respond to land use. This can be used to identify overall changes in the ecosystem, to derive mechanistic hypotheses, and it can be readily applied to further global change drivers.
Land‐use intensification drives changes in microbial communities and the soil functions they regulate, but the mechanisms underlying these changes are poorly understood as land use can affect soil ...communities both directly (e.g. via changes in soil fertility) and indirectly (e.g. via changes in plant inputs).
The speed of microbial responses is also poorly understood. For instance, whether it is long‐term legacies or short‐term changes in land‐use intensity that drive changes in microbial communities.
To address these topics, we measured multiple microbial functions, bacterial and fungal biomass and abiotic soil properties at two time intervals 3 years apart. This was performed in 150 grassland sites differing greatly in management intensity across three German regions.
Observed changes in microbial soil properties were related to both long‐term means and short‐term changes in: abiotic soil properties, land‐use intensity, community abundance‐weighted means of plant functional traits and plant biomass properties in regression and structural equation models. Plant traits, particularly leaf phosphorus, and soil pH were the best predictors of change in soil microbial function, as well as fungal and bacterial biomass, while land‐use intensity showed weaker effects.
Indirect legacy effects, in which microbial change was explained by the effects of long‐term land‐use intensity on plant traits, were important, thus indicating a time lag between plant community and microbial change. Whenever the effects of short‐term changes in land‐use intensity were present, they acted directly on soil microorganisms.
Synthesis. The results provide new evidence that soil communities and their functioning respond to short‐term changes in land‐use intensity, but that both rapid and longer time‐scale responses to changes in plant functional traits are at least of equal importance. This suggests that management which shapes plant communities may be an effective means of managing soil communities and the functions and services they provide.
Kurzauszug
Die Intensivierung der Landnutzung bedingt Veränderungen in mikrobiellen Gemeinschaften und den Bodenfunktionen, die diese regulieren. Jedoch sind die Mechanismen, die diesen Veränderungen zu Grunde liegen, bisher kaum geklärt, da sich die Landnutzung sowohl direkt (z.B. über Änderungen der Bodenfruchtbarkeit) als auch indirekt (z.B. über Änderungen der Pflanzeneinträge) auf die Gemeinschaften der Bodenmikroorganismen auswirken können. Die Geschwindigkeit, mit der Bodenmikroorganismen auf Umweltveränderungen reagieren, ist ebenfalls kaum erforscht. Dazu zählt die Frage, ob Veränderungen in den bodenmikrobiellen Eigenschaften stärker von den über lange Zeiträume wirkenden „Legacy“‐Effekten, oder von kurzfristigen Veränderungen der Landnutzungsintensität bestimmt werden.
Um die beschriebenen Wissenslücken zu schließen, haben wir eine Reihe an mikrobiellen Funktionen, die bakterielle und pilzliche Biomasse sowie abiotischen Bodeneigenschaften an zwei Zeitpunkten im Abstand von drei Jahren untersucht. Dies geschah auf 150 Grünlandflächen mit sehr unterschiedlicher Nutzungsintensität in drei Regionen Deutschlands.
Die beobachteten Veränderungen der mikrobiellen Bodeneigenschaften zeigten sowohl einen Zusammenhang mit langfristigen Mittelwerten, als auch mit kurzfristigen Veränderungen von abiotischen Bodeneigenschaften, der Landnutzungsintensität, den funktionellen Pflanzeneigenschaften (berechnet als gewichtete Mittelwerte der Speziesabundanzen der Pflanzengesellschaften) und den Eigenschaften der Pflanzenbiomasse in Regressionsanalysen und Strukturgleichungsmodellen. Funktionelle Pflanzeneigenschaften, im Speziellen der Phosphorgehalt der Blätter, und der pH‐Wert des Bodens stellten sich als die besten Prädiktoren für Veränderungen in den bodenmikrobiellen Funktionen sowie der pilzlichen und bakteriellen Biomasse heraus, während die Landnutzungsintensität geringere Einflüsse zeigte.
Indirekte Legacy‐Effekte, bei denen mikrobielle Veränderungen durch Einflüsse der langfristigen Landnutzung auf funktionelle Pflanzeneigenschaften erklärt wurden, stellten sich als wichtig heraus und deuten auf eine Zeitverschiebung zwischen Veränderungen der Pflanzengemeinschaft und der mikrobiellen Gemeinschaft hin. Wenn kurzfristige Effekte der Veränderung der Landnutzungsintensität auftraten, wirkten sich diese direkt auf die Bodenmikroorganismen aus.
Synthese. Die Ergebnisse geben neue Hinweise darauf, das bodenmikrobielle Gemeinschaften und ihre Funktionen auf kurzfristige Veränderungen in der Landnutzungsintensität reagieren, aber das sowohl schnelle als auch über längere Zeiträume auftretende Reaktionen auf Veränderungen der funktionellen Pflanzeneigenschaften mindestens ebenso wichtig sind. Dies deutet darauf hin, dass eine Landnutzung, die die Pflanzengesellschaften steuert, eine effektive Möglichkeit darstellt, um bodenmikrobielle Gemeinschaften sowie ihre Funktionen und Dienstleistungen zu beeinflussen.
Using hierarchical regression and structural equation modelling, relationships between short‐term changes in land‐use intensity, plant functional traits, plant biomass and abiotic soil properties as well as concurrent changes in soil microbial properties were investigated in 150 grassland sites in three German regions. In addition, legacy effects of land‐use intensity and plant functional traits on changes in soil microorganisms were assessed.
Extreme events such as drought and heatwaves are among the biggest challenges to agricultural production and food security. However, the effects of cropping systems on drought resistance of arable ...crops via their hydraulic behaviour remain unclear. We investigated how hydraulic traits of a field‐grown pea‐barley (Pisum sativum L. and Hordeum vulgare L.) mixture were affected by different cropping systems, that is, organic and conventional farming with intensive or conservation tillage. Xylem vulnerability to cavitation of both species was estimated by measuring the pressure inducing 50% loss of hydraulic conductivity (P50), while the water stress plants experienced in the field were assessed using native percentage loss of hydraulic conductivity (nPLC). Pea and barley showed contrasting hydraulic behaviours: pea was less vulnerable to xylem cavitation and less stressed than barley; cropping systems affected the xylem vulnerability of barley, but not of pea. Barley grown under conventional farming with no tillage was more vulnerable and stressed than under organic farming with intensive tillage. nPLC proved to be a valuable indicator for plant water stress. Our results highlight the impact of cropping systems on crop xylem vulnerability and drought resistance, thus plant hydraulic traits, for protecting food security under future climate.
Effects of cropping systems on drought resistance of arable crops were investigated for a field‐grown Pisum sativum/Hordeum vulgare mixture. Pea was less vulnerable to xylem cavitation and less stressed than barley. Cropping systems only affected xylem vulnerability of barley, but not of pea.
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