![Schematic overview of this thesis. Chapter numbers in black frames: [2] Functional diversity of small forest patches, [3] Contrasting microclimates among hedgerows and forests, [4] Plant diversity in hedgerows and road verges, [5] Forest herb performance in hedgerows vs forests, [6] Experimental warming of forest herbs in hedgerows vs forests.](https://www.researchgate.net/profile/Thomas-Vanneste/publication/348694257/figure/fig5/AS:983034677436419@1611385139708/Schematic-overview-of-this-thesis-Chapter-numbers-in-black-frames-2-Functional_Q320.jpg)
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Linear landscape elements as ecological corridors for plant species under a changing climate
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Linear landscape elements such as hedgerows and road verges can connect isolated fragments of natural and semi-natural habitats, thereby facilitating the movements of species across fragmented landscapes. This could be particularly important as the need for species to move is predicted to increase substantially with climate change. However, so far, we know little about the efficiency of these linear structures to act as habitats or movement corridors for plant species with limited dispersal capacity and specific habitat requirements. Moreover, we do not know whether linear landscape elements will continue to deliver this function under a changing climate.
In this research, we show that hedgerows and road verges across Europe can support diverse plant communities, including also species that are usually associated with large and stable habitats such as oldgrowth forests and species-rich, semi-natural grasslands. Furthermore, these linear structures may also serve as a dispersal route for some, but certainly not all, plant species. Factors such as time and spatiotemporal connectivity played an important role here (i.e. ancient corridors with long-term connection to a source population in a larger habitat patch are generally more effective), but also other habitat-specific features including soil properties, microclimate and management.
We conclude that hedgerows and road verges may contribute to species persistence and increase functional connectivity in fragmented agricultural landscapes. Further research is needed to elucidate how climate change will alter plant community dynamics in linear elements and influence their future efficiency as ecological corridors. Finally, we emphasize the importance to integrate efficient strategies for preservation, creation and management of linear landscape elements in policies and management plans, both at national (e.g. agri-environment schemes) and international level (e.g. European Common Agricultural Policy).
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Hedge density, structure, and function vary with primary production and slope gradient and are subject to other diverse factors. Hedgerows are emerging ecosystems with both above- and belowground components. Functions of hedges can be categorized as provisioning, regulating, cultural, and supporting ecosystem services; these functions include food production, noncrop food and wood production, firewood production, pollination, pest control, soil conservation and quality improvement, mitigation of water flux and availability, carbon sequestration, landscape connectivity and character maintenance, and contributions to biodiversity. Urban hedges provide a relatively equitable microclimate and critical connections between green spaces and enhance human health and well-being through contact with biodiversity. Soil and water conservation are well researched in tropical hedges but less is known about their contribution to pollination, pest control, and biodiversity. Establishing a minimum hedge width and longer intervals between cutting of temperate hedges would enhance biosecurity and promote carbon sequestration and biodiversity. Hedges have a global role in mitigating biodiversity loss and climate change, which restoration should maximize, notwithstanding regional character.
Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 51 is November 2, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
1. This account presents information on all aspects of the biology of Poa nemoralis L. (Wood Meadow-grass) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, and conservation.
2. The grass Poa nemoralis is widespread and frequent to locally common across the British Isles, except for western and central Ireland, and northern Scotland. In both its native Eurasian range and introduced ranges in, for example, the Americas, its main habitat comprises temperate (mixed) deciduous woodland. The species finds important secondary habitats in hedgerows, as well as in non-woodland vegetation such as on cliffs, screes and walls or sporadically in grassland and heathland. Although not always taxonomically or morphologically distinct units, the species is suspected to comprise many cytological races and hybrid polyploid populations with variable morphology. Morphological variation among P. nemoralis populations may also be a sign of local environmental adaptation or a result of introgressive hybridization with other, morphologically variable members of Poa section
Stenopoa such as P. glauca, P. compressa or P. pratensis.
3. Poa nemoralis is a small-statured, loosely caespitose grass, with populations ranging from a few individual tufts to those visually defining the aspect of the herbaceous understorey. The species tolerates moderate to deep shade on the forest floor, yet it tends to forage for available light, occurring more and growing taller in canopy gaps, forest edges and hedgerows. The amount of light is central to its survival and reproductive ecology, being important for flower induction, seed production and seed germination. The species produces large quantities of small, light seeds which facilitate spatial and temporal dispersal.
4. The species occupies a wide range of soil pH (3–7) and nutrient conditions (C/N ratio ranges between 10 and 25), though it clearly prefers moderately acid and somewhat drier soils with limited litter thickness, avoiding soils with mor humus types. Poa nemoralis displays distinct small-scale acidifuge responses, being absent in areas of low soil pH (<3).
5. Poa nemoralis is a moderately strong indicator of ancient woodland: it can quickly colonize recently established wooded areas adjacent to ancient woodland when it is not hindered by dispersal limitation and elevated nutrient levels. Nonetheless, dispersal limitation impedes rapid colonization of isolated, recently established woodlands, in spite of ample records of zoochorous seed dispersal. While currently frequent to locally common, the species is at risk if ancient woodlands continue to decline in its native Eurasian range. Across N.W. Europe, it is already in moderate decline in temperate deciduous ancient woodlands because of acidification, eutrophication and darkening of the forest understorey. In its introduced ranges, it is considered invasive.
Protected areas (PAs) are essential to biodiversity conservation, but their static boundaries may undermine their potential for protecting species under climate change. We assessed how the climatic conditions within global terrestrial PAs may change over time. By 2070, protection is expected to decline in cold and warm climates and increase in cool and hot climates over a wide range of precipitation. Most countries are expected to fail to protect >90% of their available climate at current levels. The evenness of climatic representation under protection—not the amount of area protected—positively influenced the retention of climatic conditions under protection. On average, protection retention would increase by ~118% if countries doubled their climatic representativeness under protection or by ~102% if countries collectively reduced emissions in accordance with global targets. Therefore, alongside adoption of mitigation policies, adaptation policies that improve the complementarity of climatic conditions within PAs will help countries safeguard biodiversity.
In summer 2018, central and northern Europe were stricken by extreme drought and heat (DH2018). The DH2018 differed from previous events in being preceded by extreme spring warming and brightening, but moderate rainfall deficits, yet registering the fastest transition between wet winter conditions and extreme summer drought. Using 11 vegetation models, we show that spring conditions promoted increased vegetation growth, which, in turn, contributed to fast soil moisture depletion, amplifying the summer drought. We find regional asymmetries in summer ecosystem carbon fluxes: increased (reduced) sink in the northern (southern) areas affected by drought. These asymmetries can be explained by distinct legacy effects of spring growth and of water-use efficiency dynamics mediated by vegetation composition, rather than by distinct ecosystem responses to summer heat/drought. The asymmetries in carbon and water exchanges during spring and summer 2018 suggest that future land-management strategies could influence patterns of summer heat waves and droughts under long-term warming.
There is mounting evidence of species redistribution as climate warms. Yet, our knowledge of the coupling between species range shifts and isotherm shifts remains limited. Here, we introduce BioShifts—a global geo-database of 30,534 range shifts. Despite a spatial imbalance towards the most developed regions of the Northern Hemisphere and a taxonomic bias towards the most charismatic animals and plants of the planet, data show that marine species are better at tracking isotherm shifts, and move towards the pole six times faster than terrestrial species. More specifically, we find that marine species closely track shifting isotherms in warm and relatively undisturbed waters (for example, the Central Pacific Basin) or in cold waters subject to high human pressures (for example, the North Sea). On land, human activities impede the capacity of terrestrial species to track isotherm shifts in latitude, with some species shifting in the opposite direction to isotherms. Along elevational gradients, species follow the direction of isotherm shifts but at a pace that is much slower than expected, especially in areas with warm climates. Our results suggest that terrestrial species are lagging behind shifting isotherms more than marine species, which is probably related to the interplay between the wider thermal safety margin of terrestrial versus marine species and the more constrained physical environment for dispersal in terrestrial versus marine habitats. Compiling a global geo-database of >30,000 range shifts, the authors show that marine species closely track shifting isotherms, whereas terrestrial species lag behind, probably due to wider thermal safety margins and movement constraints imposed by human activities.
Applying an invasive framework to native species that are shifting their ranges in response to climate change adopts an adversarial, local and static paradigm that is often at odds with protecting global biodiversity.
The effectiveness of hedgerows as functional corridors in the face of climate warming has been little researched. Here we investigated the effects of warming temperatures on plant performance and population growth of Geum urbanum in forests versus hedgerows in two European temperate regions. Adult individuals were transplanted in three forest–hedgerow pairs in each of two different latitudes, and an experimental warming treatment using open‐top chambers was used in a full factorial design. Plant performance was analysed using mixed models and population performance was analysed using Integral Projection Models and elasticity analyses. Temperature increases due to open‐top chamber installation were higher in forests than in hedgerows. In forests, the warming treatment had a significant negative effect on the population growth rate of G. urbanum. In contrast, no significant effect of the warming treatment on population dynamics was detected in hedgerows. Overall, the highest population growth rates were found in the forest control sites, which was driven by a higher fecundity rather than a higher survival probability. Effects of warming treatments on G. urbanum population growth rates differed between forests and hedgerows. In forests, warming treatments negatively affected population growth, but not in hedgerows. This could be a consequence of the overall lower warming achieved in hedgerows. We conclude that maintenance of cooler forest microclimates coul, at least temporarily, moderate the species response to climate warming. Warming treatment on Geum urbanum negatively affects population growth in forests but not in hedgerows.
Local factors restrain forest warming
Microclimates are key to understanding how organisms and ecosystems respond to macroclimate change, yet they are frequently neglected when studying biotic responses to global change. Zellweger et al. provide a long-term, continental-scale assessment of the effects of micro- and macroclimate on the community composition of European forests (see the Perspective by Lembrechts and Nijs). They show that changes in forest canopy cover are fundamentally important for driving community responses to climate change. Closed canopies buffer against the effects of macroclimatic change through their cooling effect, slowing shifts in community composition, whereas open canopies tend to accelerate community change through local heating effects.
Science , this issue p. 772 ; see also p. 711