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Role of hedgerow systems for biodiversity and ecosystem services in agricultural landscapes

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Climate change and loss of biodiversity are causing important economic and societal problems that are among the greatest global challenges of our time. Despite being a significant contributor to climate change and biodiversity loss, agriculture also has the capacity to provide solutions in this challenge. Agricultural lands can be designed and managed to be multifunctional, i.e. providing not only food, but also supporting biodiversity and delivering a broad set of ecosystem services. Hedgerow systems can play an important role in the realisation of such multifunctional landscapes. In this study, we address some of the pressing knowledge gaps on the plant biodiversity supported by hedgerow systems, the level of wood production they provide, and the degree to which they contribute to carbon sequestration. The high proportion of plant species present in the hedgerow systems clearly emphasises their role as (surrogate) habitat in the open landscape. The observed increase in plant species richness over a period of 40 years in hedgerow systems – opposite to the trend in nearby forests – indicates their importance as refugia and source habitats for plant species of both the open and closed habitats. Hedgerow trees are exposed to substantial solar radiation and consequently develop heavy crowns, resulting in higher proportions of branch wood (logs with diameter < 7 cm) compared to forest trees. Tree densities in hedgerow systems are high and hedgerow trees show a continuous diameter growth with aging, resulting in high yearly wood increments and carbon sequestration rates in their above-ground biomass. In addition, also in the hedgerow soil, carbon is sequestered through decomposition processes resulting in significantly higher soil carbon stocks compared to grass margins. Our findings help to underpin the multifunctional value of hedgerow systems in agricultural lands. We argue that hedgerow conservation will benefit biodiversity at the landscape level. Also, it could be very interesting to include hedgerow systems in landscape biomass budgets, using hedgerow-specific allometries (wood increments, proportion branch wood). Moreover, hedgerow systems represent non-negligible carbon stocks in biomass and soil and should be included in national carbon budgets.
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Background and aims Hedgerows have been shown to improve forest connectivity, leading to an increased probability of species to track the shifting bioclimatic envelopes. However, it is still unknown how species in hedgerows respond to temperature changes, and whether effects differ compared to those in nearby forests. We aimed to elucidate how ongoing changes in the climate system will affect the efficiency of hedgerows to support forest plant persistence and migration in agricultural landscapes. Methods Here we report results from the first warming experiment in hedgerows. We combined reciprocal transplantation of plants along an 860-km latitudinal transect with experimental warming to assess the effects of temperature on vegetative growth and reproduction of two common forest herbs (Anemone nemorosa and Geum urbanum) in hedgerows vs forests. Key results Both species grew taller and produced more biomass in forests than in hedgerows, most likely due to a higher competition with ruderals and graminoids in hedgerows. Adult plant performance of both species generally benefitted from experimental warming, despite lower survival of A. nemorosa in heated plots. Transplantation affected the species differently: A. nemorosa plants grew taller, produced more biomass and showed higher survival when transplanted at their home site, indicating local adaptation, while individuals of G. urbanum showed larger height, biomass, reproductive output and survival when transplanted northwards, likely owing to the higher light availability associated with increasing photoperiod during the growing season. Conclusions These findings demonstrate that some forest herbs can show phenotypic plasticity to warming temperatures, potentially increasing their ability to benefit from hedgerows as ecological corridors. Our study thus provides novel insights into the impacts of climate change on understory plant community dynamics in hedgerows, and how rising temperature can influence the efficiency of these corridors to assist forest species’ persistence and colonization within and beyond their current distribution range.
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Questions How do contrasting environmental conditions among forests and hedgerows affect the vegetative and reproductive performance of understorey forest herbs in both habitats? Can hedgerows support reproductive source populations of forest herbs, thus potentially allowing progressive dispersal of successive generations along the linear habitats? Location Hedgerows and deciduous forest patches in agricultural landscapes across the European temperate biome. Methods First, we assessed differences in environmental conditions among forests and hedgerows. Next, we quantified plant performance based on a set of functional life‐history traits for four forest herbs (Anemone nemorosa , Ficaria verna , Geum urbanum, Poa nemoralis ) with contrasting flowering phenology and colonization capacity in paired combinations of forests and hedgerows, and compared these traits among both habitats. Finally, we assessed relationships between plant performance and environmental conditions in both habitats. Results All study species showed a higher aboveground biomass in hedgerows than in forests. For P. nemoralis and G. urbanum , we also found a higher reproductive output in hedgerows, which was mainly correlated to the higher sub‐canopy temperatures therein. The ‘ancient forest herb’ A. nemorosa , however, appeared to have a lower reproductive output in hedgerows than in forests, while for F. verna no reproductive differences were found between the two habitats. Conclusions This is the first study on such a broad geographical scale to provide evidence of reproductive source populations of forest herbs in hedgerows. Our findings provide key information on strategies by which forest plants grow, reproduce and disperse in hedgerow environments, which is imperative to better understand the dispersal corridor function of these wooded linear structures. Finally, we highlight the urgent need to develop guidelines for preserving, managing and establishing hedgerows in intensive agricultural landscapes, given their potential to contribute to the long‐term conservation and migration of forest herbs in the face of global environmental change.
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The significant contribution to the global carbon budget made by soil organic carbon (SOC) inspired the “4 per 1000” initiative. It promotes agricultural practices aimed at raising SOC stocks 0.4 % annually over 20 years. However, the response of topsoil and deep soil profiles to agroecosystem changes is largely unknown at present. Our work aims to quantify deep SOC accumulations in stabilized croplands and grasslands of northeast Italy and identify the best management practices to increase those stores. Soil profiles were collected to 70 and 90 cm depths from three well-established long-term experiments. A total of 1242 soil samples were analyzed for SOC concentrations as a function of soil type, soil management practice, and cropping system. SOC stocks were quantified using the equivalent soil mass method. Results show that SOC stocks averaged 23.2 Mg ha⁻¹ in sandy Arenosol, 59.3 Mg ha⁻¹ in silty loam Cambisol, 111.6 Mg ha⁻¹ in clay loam Gleysol, and 383.5 Mg ha⁻¹ in peaty Histosol. Substantial SOC stocks were found in the subsoil beneath the tilled layer, ranging between 59 % and 74 % in sandy and clay loam soils. Among the considered managements, the SOC accumulation rate of permanent meadow topsoil was higher than croplands (0.299 Mg ha⁻¹ yr⁻¹), which fell to 0.256 Mg ha⁻¹ yr⁻¹ when estimated along the full soil profile. In contrast, organic carbon added through manures and residues, coupled with minimum tillage practices, led to increased average SOC stock rates in the topsoil (0.205 Mg ha⁻¹ yr⁻¹) and throughout the full soil profile (0.386 Mg ha⁻¹ yr⁻¹), suggesting that some translocation dynamics occurred. The long-term adoption of permanent meadow, along with manure or residue addition under minimum tillage, made it possible to achieve “4 per 1000” goals to great depths in naturally poor-SOC sandy and silty loam soils. In SOC-rich soil, only in the topsoil layer achieved this.
Article
Linear landscape elements such as hedgerows and road verges have the potential to mitigate the adverse effects of habitat fragmentation and climate change on species, for instance, by serving as a refuge habitat or by improving functional connectivity across the landscape. However, so far this hypothesis has not been evaluated at large spatial scales, preventing us from making generalized conclusions about their efficacy and implementation in conservation policies. Here, we assessed plant diversity patterns in 336 vegetation plots distributed along hedgerows and road verges, spanning a macro‐environmental gradient across temperate Europe. We compared herb‐layer species richness and composition in these linear elements with the respective seed‐source (core) habitats, i.e. semi‐natural forests and grasslands. Next, we assessed how these differences related to several environmental drivers acting either locally, at the landscape level or along the studied macro‐ecological gradient. Across all regions, about 55% of the plant species were shared between forests and hedgerows, and 52% between grasslands and road verges. Habitat‐specialist richness was 11% lower in the linear habitats than in the core habitats, while generalist richness was 14% higher. The difference in floristic composition between both habitat types was mainly due to species turnover, and not nestedness. Most notably, forest‐specialist richness in hedgerows responded positively to tree cover, tree height and the proportion of forests in the surrounding landscape, while generalist richness was negatively affected by tree height and buffering effect of trees on sub‐canopy temperatures. Grassland and road verge diversity was mainly influenced by soil properties, with positive effects of basic cation levels on the number of specialists and of bio‐available soil phosphorus on generalist diversity. Synthesis and applications. We demonstrate that linear landscape elements provide a potential habitat for plant species across Europe, including slow‐colonizing specialists. Additionally, our results stress the possibility for land managers to modify local habitat features (e.g. canopy structure, sub‐canopy microclimate, soil properties, mowing regime) through management practices to enhance the colonization success of specialists in these linear habitats. These findings underpin the management needed to better conserve biodiversity of agricultural landscapes across broad geographical scales.