Introduction

Habitat fragmentation is widely acknowledged as a major threat to biodiversity worldwide [1–3], but see [4]. It encompasses at least four interacting processes: (i) pure habitat loss, which usually directly destroys sessile organisms (e.g. plants) and constrains mobile organisms (e.g. birds and mammals) that retreat into remnant patches of habitat; (ii) reduction of fragment size, which reduces species richness and population sizes, increasing the risk of local extinction [5]; (iii) increase in edge:interior ratio, which can promote the colonisation of habitat generalists and species from neighbouring habitats to the detriment of habitat specialists that have retreated to remnants [6]; and (iv) increase in spatial isolation of remnant habitat patches, which reduces the movements of individuals between populations [7] and disrupts metapopulation and meta-community functioning [8, 9]. In Europe, forest has a long history of fragmentation and land use/cover change [10–12]. The clearance of forests for agriculture and their recovery on abandoned lands resulted in patchy forest cover with patches of different quality, age, size and isolation embedded in a more or less intensively managed agricultural matrix. Ecologically, these forest patches often exhibit homogenized stand structure, either because they are intensively managed or originate from plantations or afforestation of former farmlands [13–15], or management can be neglected [16].

The increasing demand for food and the promotion of bioenergy crops in the context of a bio-based energy transition have led to an increasing demand for new agricultural areas worldwide and increased crop production to the detriment of semi-natural habitats, including forests [17]. Therefore, landscape change in the forms of clearance of existing forest patches and afforestation of abandoned lands are still ongoing processes in European lowlands [18•]. In general and at the same time, forests are of major importance to human society, delivering several crucial ecosystem services [19••], but also some disservices (e.g. diseases [20]). There is growing evidence that biodiversity is vital to ecosystem functioning [21–23, 24•, 25, 26]. By decreasing biodiversity, fragmentation may thus impact ecosystem processes such as nutrient cycling and energy flows and ultimately affect flows of ecosystem service [27, 28••]. Ecosystem services (ES) are often categorized as provisioning, regulating, cultural and supporting services [29]. Costanza [30] proposed an alternative classification based on the spatial characteristics of ES, using five categories: in situ, local-proximal, directional flow related, global and user movement related.

Compared to large forest ecosystems, e.g. [19••, 31], little is known about the role of biodiversity of small forest patches (SFP, from less than 1 to 50 ha; [32]) in delivering ES to society [33•, 34••] in agricultural landscapes, which cover 40 % of the Earth’s surface [35]. The research effort has indeed mostly focused on how forest fragmentation actually alters the delivering of ES. Furthermore, these SFP are potentially threatened by urbanisation, expanding croplands and agricultural intensification despite their potential to maintain biodiversity and contribute to the “ecological intensification” of agro-ecosystems [36] and human well-being. Thus, there is an urgent need to increase our understanding of the relationship between biodiversity and ES delivered by SFP embedded in an agricultural landscape matrix (Fig. 1). We here review the literature on the topic, with a special focus on temperate European landscapes and make profit from still unpublished results of the smallFOREST BiodivERsA project into which all co-authors of this paper were involved. Following Costanza’s classification [30], we successively review in situ ES (i.e. that are delivered locally, within the ecosystem), local-proximal ES (i.e. that depends on the spatial proximity of the focal ecosystem), directional flow-related ES (i.e. from the ecosystem to the point of use), global ES (i.e. independent from ecosystem location) and user movement-related ES (i.e. involving a movement of people towards the ecosystem) (Table 1).

Fig. 1
figure 1

Various aspects of small forest patches in European agricultural landscapes. Small deciduous forests look like isolated patches within intensively cultivated open fields (a) or more or less connected by hedgerows within grasslands (b); even sometimes as small islets in a coniferous-dominated landscape (c). These small forest patches are often hotspots of biodiversity within agricultural landscapes, with a species-rich herb layer (d) and a mixture of deciduous tree species (e). These patches are sometimes managed for wood production (f) but are often unmanaged (g). They potentially deliver a wide range of ecosystem services to neighbouring crop lands (h) and pastures (i), such as pest biocontrol and shelter for grazing animals, respectively. a Open fields in North-West Germany (A. Kolb); b bocage of Thiérache (A. Jamoneau), North France; c agricultural landscape in Central Sweden (G. Decocq); d understory in an alder stand in North-East Germany (M. Wulf); e understory of Flanders in Belgium (E. Brosens); f fuel wood harvest in North France (J. Lenoir); g unmanaged woodlot in North France (G. Decocq); h forest edge in an open field landscape of North France (G. Decocq); i forest edge in an open field landscape of North France (G. Decocq)

Full size image
Table 1 Ecosystem services delivered by small forest patches embedded in agricultural landscapes that are assessed in this review (right part), grouped in five classes according to their spatial characteristics (left part), after [30]
Full size table

In Situ Services

Biodiversity

Most contemporary SFP are young, in an early secondary-successional stage, homogeneous in their structure, and, as a consequence, host only a few forest-specialist species [37–40]. The sensitivity of biodiversity components to remnant habitat size and habitat structural quality varies significantly [41–43]. Sessile and less mobile organisms are more threatened by habitat degradation [40, 44–46] in comparison to species with good dispersal or mobility [47, 48•]. The effect of fragmentation on species richness and community composition in forests is mediated by four main groups of variables: (1) forest patch quality in terms of soil variables, notably pH, nutrient availability and light [11, 49]; (2) patch heterogeneity, i.e. the variability of environmental drivers and stand diversity [50, 51]; (3) habitat configuration in terms of forest patch size and isolation [49, 52]; and (4) the history of the patch, especially whether it has been continuously forested for centuries (ancient forest) or afforested on agricultural land (recent forest) [52, 53]. Generally, the number of species in SFP increases with increasing patch area, decreasing isolation, increasing heterogeneity and temporal continuity, while the effects of patch quality are more complex and often species specific. Edge effects may have negative impacts on forest specialists due to altered microclimate (e.g. [54, 55] for fungus species diversity). Forest management and the creation of novel forest habitats such as parks do not always have a negative effect on forest biodiversity, as the optimization of stand structure can result in SFP that support a high diversity of vascular plants [56, 57], insects [58, 59] and bats [60, 61]. The positive effect of management on biodiversity, however, is generally driven by the increase of habitat generalists or open habitat species [43, 62]. As a result, the positive species–area relationship underlying the patch size effect in some cases has been weak or absent (e.g. [63] for plants; [64] for arbuscular mycorrhizal fungi), meaning that even SFP may comprise a high number of species [65]. Moreover, irrespective of the variation in the environment, a dense network of SFP can contribute to counteracting the disruption of the meta-population functioning of the landscape with respect to new colonization events [9], depending on the species dispersal ability [43, 66]. On the other hand, many long-lived organisms, such as some vascular plant species, may persist over many decades even under non-favourable conditions. This “extinction debt” of species in SFP offers an opportunity to halt biodiversity loss by taking conservation action in time [67•].

Wood Production

SFP may be important for local timber and firewood production as a provisioning ES. In Western Europe, a heavily fragmented region with a mean forest cover of c. 26 %, 93 % of all forests were available for wood supply [68]. In total, 172 million cubic metres of wood were harvested in this region in 2010. Nevertheless, the mean patch size of private forests, for instance, in Belgium, the UK and Germany is only 2, 13 and 10 ha, respectively [69]. Wood production in these forests is faced with management challenges like a high number of forest owners and a patchy occurrence of the wood resource, which—nevertheless—could partly be resolved by a specific local organization [70]. Close-to-nature management systems such as continuous cover, retention forestry or selective logging of single trees can often be a good option for wood production in SFP because they most likely sustain the continued delivery of other ES [71, 72•]. Given that the demand for fuel wood is expected to continuously increase in the near future, the pressure on SFP to provide local inhabitants with wood in densely populated areas is expected to increase over the next few decades [73].

Wild Food Production

Wild food provision, of which the most iconic components are game hunting and mushroom picking, is hardly accounted for in any mapping of ES in Europe. A key aspect that regulates the availability of wild food (including hunting) is a heterogeneous landscape that is threatened by agricultural intensification [30, 74, 75]. SFP can provide a wide range of edible plant products (e.g. wild berries and nuts) and mushrooms, which are commonly used by local populations and/or marketed. A recent study revealed that 11 wild plant species were still used as food in Sweden but none as medicinal plants, whilst in the economically less developed rural areas of Ukraine, 26 and 60 species are used as food and herbal, respectively, suggesting that the consumption of wild food and medicine is influenced by the socioeconomic situation in a country [76]. In western Europe, a considerable number of forest plant species have been used in the past (22.2 and 13.6 % for food and medicinal applications, respectively, out of a total species pool of 1024 species; smallFOREST project, unpublished data). Thus, gathering of wild food may be considered more of a cultural service in Europe and part of people’s identity [77], with the potential for increasing demand in response to industrialization [78].

SFP can also act as a refuge for game animals (e.g. roe deer, wild boar, hare, rabbit and pheasant). Mammals such as hares and roe deer are generalist herbivores that move and forage freely across agricultural landscapes and can use SFP as a source of food and as shelter during periods of agricultural activity in neighbouring croplands [79, 80]. Their value as hunting reservoirs is often one of the main reasons that have prevented these SFP from being converted into agricultural land [81].

Biological Invasion Risk

Habitat loss and fragmentation are thought to promote the spread of invasive species. An increased risk of biological invasion can be seen as a disservice provided by SFP, and it may alter some of the beneficial ES and thus have huge costs to society [82]. In some countries, exotic tree species have been widely used for reforestation [83]. However, the assumption that SFP are more exposed to invasion mainly comes from percolation-based model simulations [84], and empirical evidence is still scarce. It has also been suggested that fragmentation may slow down invasion spread, at least for species that are not dispersal-limited [84], and therefore, SFP might also provide a beneficial ES in this sense. A negative relationship between patch size and exotic species richness has been repeatedly found [85–87], but other landscape factors (e.g. landscape composition and configuration, management intensity and proximity from seed sources) interact with patch invasibility. Although forest ecosystems are usually considered as resistant to biological invasion but see [88], fragmentation creates more edge, which offers a more suitable habitat than the forest interior for many exotic species that are not dispersal-limited and able to move through the landscape matrix [89]. It is likely that the (dis-)services associated to invasive species do not fundamentally differ between SFP and other forest ecosystems. For example, the Asian shrub Lonicera maackii, one of the most widespread invaders of US woods, has been shown to reduce the survival, growth and fecundity of native herbs and tree seedlings [90], hence, to negatively impact local biodiversity. A recent meta-analysis found that pollinator communities of bees and bumblebees were negatively impacted by the combined effect of fragmentation and biological invasions via the disruption of plant–pollinator networks [91]. Another potential disservice is seed dispersal from small forests into adjacent cropland, but this has been shown to be limited, so that the forest edge cannot be regarded as an important source of weed infestation of crop fields [92].

Local-Proximal Services

Disturbance Regulation

Flooding, storm, wildfire or fast spread of pests and pathogens are disturbances that strongly affect human activities and have heavy financial consequences. Their frequency or their consequences are influenced by landscape characteristics, such as connectivity, that may contribute to the expansion of these disturbances. SFP may play a key role in this process and then provide a regulation ecosystem service. However, the low frequency of these events renders the study of how SFP may reduce their consequences challenging yet crucial since the occurrence and magnitude of such extreme events are predicted to increase with global warming [93]. Lindner et al. [93] reviewed the impacts of climate change on European forests with a special focus on the risks of greater disturbances, but without taking into account the spatial patterns of forest fragmentation. The analysis of past disturbance in European forests during the nineteenth and twentieth centuries did not address spatial patterns either [94] and as such little is known. SFP may, depending on their location in relation to farmland or housing, act as windbreaks and protect land against erosion, although there is a little research on this topic. It is generally admitted that several SFP scattered across agricultural and flat landscapes might be better than a one single large forest stand at reducing, breaking up and dissipating wind storms, but empirical results [95] do not always fit with this assumption, underlying the need for more detailed studies.

Habitat/Refuge

Of around 220 forest plants in northwest and central Europe (list in prep. by the FLEUR network, http://www.fleur.ugent.be/), two-thirds have been found in SFP along a latitudinal gradient from southern France to central Sweden [96••]. Small forest fragments are therefore important habitats for these habitat specialists. Moreover, it has been demonstrated that several habitat specialists can persist for many decades or even longer in SFP [67•, 97]. In general, SFP may serve as transitional habitats or stepping stones in a network of isolated forest habitats [59, 98•]. On the other hand, SFP can act as “lifeboat” habitats for species, particularly in landscapes with a high degree of fragmentation [99]. These fragments could ultimately act as climate refugia in the current context of climate change [100], as long as surface area is large enough to sustain a viable population and species are not bounded by matrix habitat and therefore unable to migrate due to climate change. However, obviously, microhabitat conditions within SFP offer short-term (e.g. minutes to days for wildlife inhabiting agricultural landscapes) protection from anthropogenic disturbances dominating in the surrounding matrix and thus act as “transit shelters” or “refuges” for biotas [101] (cf. disturbance regulation). Less obvious, the cooler and more stable conditions generated by forest canopy closure in SFP compared with the highly disturbed agricultural matrix (cf. vegetation-cover effect in [100]) may be partly responsible for the buffering effect on warming-induced community composition changes that have been reported in lowland forests [102, 103]. Coherently, it has been demonstrated through a manipulative experiment that light accelerates warming-induced changes in understory plant communities [104]. Given these recent findings, we argue that SFP have a strong potential to provide climatic refugia (cf. involving longer time scales than refuges), as a local-proximal ES. This is especially important in lowland agricultural landscapes [100], which are heavily disturbed by humans and where both habitat fragmentation and long distances between isotherms hinder species range shifts that are lagging behind climate change [105]. Noteworthy, the identification of climate refugia, such as SFP, within anthropogenic-disturbed lowland ecosystems and the assessment of their capacity for conservation planning under contemporary and future climate change has recently been highlighted as a daunting but timely endeavour [106].

Biological Pest Control

Biotic interactions associated with biodiversity can provide important local-proximal, regulating ES, particularly in terms of pest control in crop fields through natural enemy diversity from proximal non-crop habitats [107]. As a rough estimate, the value of pest control attributed to insect predators and parasitoids, which are primarily responsible for natural control in 33 % of cultivated systems [108], has been estimated at $4.5 billion per year [109].

SFP host a broad spectrum of natural pest-predators, from microbial pathogens to small mammals. Edges of forest fragments generate wider boundary areas, which operate as a source for biocontrol agents dispersing into adjacent matrix habitats just before pest outbreak [48•, 110–112]. Since SFP are often the last semi-natural habitat scattered across a matrix of agricultural landscapes [62, 113, 114], they have the potential to offer environmental (reduced need of chemical pesticides) and economic benefits (reduced yield loss free of charge) to crop production [61, 115–119]. Although it is likely that smaller forest fragments provide fewer natural enemies than larger fragments, both in terms of richness and abundance, several SFP might be more efficient in providing a sufficient pressure of natural enemies on crop pests across an entire agricultural landscape than just a single large forest [120, 121], simply by providing more edge habitat. Mitchell et al. [34••] found that insect herbivory regulation in soybean fields in Canada was maximized adjacent to forest fragments and decreased with distance from the forest fragment edge. Thompson and Hoffmann [122] showed that species of parasitoids and predators strongly aggregate close to SFP. Shackelford et al. [123] found a positive effect of the compositional complexity of agro-ecosystems (proximity to, diversity of or proportion of natural or non-crop habitats) on the abundance and richness of natural enemies, although this trend was mainly driven by spiders. Spiders are very mobile and generalist predators and have therefore a large potential in contributing to the natural pest control [124]. This confirmed former findings from Bianchi et al. [125] who showed that natural enemy populations were greater and pest pressure lower in heterogeneous landscapes containing a good mixture of crop fields and non-crop habitats (including SFP).

Pollination

Almost 90 % of the world’s Angiosperm plant species and about 75 % of the most important global food crops depend, at least partly, on animal pollination [126, 127]. Pollinators thereby play a critical role in the maintenance of biodiversity and provide an essential intermediate ES to society. Habitat loss and fragmentation may influence pollination processes by affecting plant densities, pollinator densities and pollinator behaviour, all of which in turn may affect plant pollination success [91, 128–131]. Effects are often negative, for example, plants in fragmented populations may receive fewer flower visits, smaller pollen loads or pollen of poorer quality, thereby suffering pollen limitation and reductions in reproductive success [132–135], which may lower population viability and increase local population extinction risk.

However, SFP within agricultural landscapes are also habitats for insect species that provide pollination services in adjacent fields. The compositional complexity of agro-ecosystems has been shown to increase the abundance and species richness of crop pollinators, an effect which was even greater than the positive effect on natural enemies [123]. This further highlights the importance of non-crop habitats such as SFP in delivering local-proximal ES [136]. Indeed, crop pollination declines with the distance from natural or semi-natural habitats, with patterns being stronger in tropical than in temperate regions [137]. Moreover, Garibaldi et al. [138] found that temporal and spatial stability of pollination services also decrease with isolation from natural areas such as forest.

Infectious Diseases

SFP might also have a negative impact on human society through the provision of what has been called ecological disservices [139]. Among the most important disservices is the prevalence of ectoparasites like ticks (mainly Ixodes ricinus) that can transmit a variety of viruses, bacteria or parasites and thereby play an important role in providing infectious diseases to a wide range of animal hosts, including humans [140]. Lyme Borreliosis, which has Borrelia burgdorferi sensu lato as causative agent, is the most common infectious disease transmitted by ticks and seems most prevalent in central European countries [141]. Other tick-borne diseases include tick-borne encephalitis with ever increasing case numbers all over Europe (see [142] for a comprehensive study on all known tick-borne diseases occurring in Central Europe). In North America, landscape fragmentation seems to play a crucial role in explaining patterns of tick abundance and Lyme Borreliosis prevalence mediated by ungulate and small mammal dynamics [143]. The influence of the landscape context is not yet completely understood in Europe, but there are indications that landscape fragmentation is responsible for patterns of tick-borne encephalitis in European agricultural landscapes [144] and the prevalence of B. burgdorferi in forests and pastures [145]. This is presumably due to the greater amount of edges in fragmented landscapes where small vertebrates, ungulates and medium-sized mammals act as reservoir hosts. An important concept, the dilution effect, is based on higher diversity of potential tick-host species. Higher species richness results in fewer interactions between ticks and those host species known to be infective to ticks. A loss of biodiversity associated to landscape fragmentation might thus conversely increase the prevalence of pathogens in fragmented landscapes [146, 147].

Among emerging diseases, the African swine fever (ASF) might have an increasing socioeconomic impact (OIE-CIC Joint Meeting on ASF 2014). A close link between wild boar (Sus scrofa) ecology and the spread of ASF can be assumed, since both wild boar and domesticated pigs are vulnerable to ASF [148] and are suspected to infect each other [149]. Wild boar are known to show generalist life-history traits and while other medium to large mammals occur less frequently in fragmented landscapes, wild boar is less sensitive to fragmentation [150]. However, the response of infectious diseases less relevant to humans directly, and in particular diseases of domestic animals, to landscape fragmentation is still largely unknown.

Directional Flow Related

Water Regulation

Water quality is not only important for drinking supply but also to other hydrologic services, including recreation and freshwater biodiversity. Forests have important regulatory functions on the water cycle by fixing soils, modifying soil structure and producing litter. Due to their capacity for restricting or delaying water flow, forests regulate water flows in the ground, streams and rivers [151, 152], providing substantial economic values to human societies and activities downstream. As high-water-retention ecosystems, forests decrease both flood peaks and low flows [153], but the intensity of this effect varies with plant water use throughout the year, which depends upon interactions between seasonal growth patterns and local climate. Riparian forests promote the infiltration of surface water to groundwater, which reduces flood peaks while increasing base flow, thus increasing the predictability of water availability [154].

Since agriculture is widely acknowledged as a major source of water pollution, the water quality regulation ES provided by neighbouring SFP is of great interest. Trees are indeed able to capture, transform and store a wide range of chemicals, pathogens, excess nutrients, salts and sediments from surface and groundwater [155].

Water Supply

Water supply is crucial to a number of domestic, agricultural, commercial, industrial and electric power uses but also to the freshwater life. According to FAO, agriculture represents about 70 % of the water use on Earth, of which 80 % comes from rainfall stored in soils [156]. Water storage in soil depends upon plant cover, organic matter content and the biotic community [118]. Forests might increase infiltration while decreasing the total water volume due to transpiration [155]. The hydrologic effects of forests have been extensively debated, but in general the volume of surface and groundwater available from forested watersheds is lower than that from watersheds dominated with other land cover types [157].

In agricultural landscapes, water is a key factor to be managed to enhance the agricultural production. In rain-fed farming systems, maximizing soil infiltration of rainfall water and soil water holding capacity ensures good growth of crops. Land cover type and cycling through soils are hidden parts of the water cycle albeit crucial. It has been suggested that improving rainfall water retention by soils is a more suitable strategy than irrigation to increase crop productivity [156].

Erosion Control

The negative effects of soil erosion encompass water pollution and siltation, crop yield depression, organic matter loss and reduction in water storage capacity [158]. Forest ecosystems provide the most effective vegetation for preventing soil erosion, thereby contributing to soil protection [159, 160]. Soil loss is generally more than an order of magnitude lower in forests than on arable land [160]. In managed forests, heavy forestry vehicles and mechanical operations associated with logging, as well as clearcutting practises cause important disturbances of the upper soil layers and ground vegetation, thus expose these areas to water run-off and soil erosion [161]. Since SFP are usually less intensively managed, the terrain they cover would be less prone to soil loss and run-off.

Global Services

The northern hemisphere is currently acting as a net terrestrial carbon (C) sink which has mainly been attributed to C sequestration in forests [162], of which a significant part is in boreal forests [163]. Current increases in the C stock of forest biomass have been estimated to range from 50 to 100 Tg C year−1 for Europe [164–167]. Most of the annual changes in the forest C stock are influenced by forest management, such as clearcutting and replanting, whereas smaller changes are due to natural disturbances [69, 167, 168]. In the wake of climate change, C sequestration and storage play an important role across all ecosystems [169]. The forest C stock is influenced by anthropogenic drivers such as climate change and nitrogen (N) deposition [170]. The magnitude of the C pools in forest soils depends on soil properties, particularly temperature and humidity [171] and dominant tree species [172, 173].

Forest fragmentation has the potential to affect C and nutrient cycling, through decreased area, increased isolation and greater exposure in forest edges [174, 175]. Fragmentation leads to drier and warmer edges with altered light availability and wind microclimate [176–178]. Advection and inflow of air cause forest edges to trap and concentrate wind-borne dry deposition of soil nutrients and pollutants from adjacent agricultural or industrial areas [179]. The large spatial variation in nutrient deposition fluxes in forest edges [180–184] generally points to the deposition of N being up to four times higher in the edge of the forest (0–200 m) than in the forest interior.

In temperate forests, the total C accumulated in biomass is generally limited by the availability of N since the cycling of C and N is closely linked [185]. Increased supplies of plant available N from deposition may stimulate tree growth and litter fall and result in increased biomass production and, consequently, additional C sequestration [186–188] as, for example, in a fragmented landscape with a higher forest edge density. This elevated forest productivity has been hypothesized to increase soil organic C stocks by increasing the C input to the soil and by reducing the decomposition of soil organic matter. There is evidence from respiration and litter decomposition studies that the effect of added N on the soil organic matter decomposition rate is negative [189–191] and that it might be responsible for up to a 10 % increase in soil organic C stocks [162]. Remy et al. [unpublished data] recently showed that both C and N soil stocks were increased by approximately 30 % at the forest edges compared to the forest interiors. Other unpublished data (Ginzburg, personal communication) found no edge effect on soil C stocks. In sum, the impact of forest fragmentation on C cycling and storage is still uncharted territory and should be the focus of future research.

User Movement Related Services

User-movement ES from SFP are represented by the recreational and aesthetic values they provide. The recreational potential of a forest is determined by access rights and customary traditions and, more specifically, by a series of factors such as population density, substitutive or complementary character of forests [192, 193], and proximity and accessibility to the forest patch [194–196]. Actual recreational values that people derive from forest stands can also depend on the activities they carry out in the forest [197]. Still some general trends have been ascertained such that the recreational preference for a forest increases with increasing tree size and stage of stand development [198, 199], including provision of view as an important factor [200].

In the case of SFP, the assessment of these values may be even more challenging since their contribution is highly determined by the agricultural matrices in which they are embedded. In general, more heterogeneous landscapes are appreciated [201–203] and SFP contribute substantially to heterogeneity in the agricultural landscapes. Assessing social values of the cultural services provided by these SFP may be more related to the assessment of the landscape values [204] rather than their role as forests per se [203, 205, 206]. The preference for a given type of landscape increases with the number of SFP and their size [202], although our perception of the landscape and its beauty varies depending on our background and knowledge [198–200, 207]. Analyses of social preferences for changes in forest area and forest structure of SFP in Picardy (northern France) and Flanders (northern Belgium) (Varela et al. submitted) found that social preferences varied depending on the intensity of disturbance of the agricultural landscape where citizens lived. It was hypothesized that this variation may be linked to the character of the population in these areas, as people living in landscapes with intensive agriculture had a more urban character, while people living in areas with less intense disturbance were more rural. These two regions showed a proportion of forest close to 6 % in the agricultural landscapes and the surveyed respondents were willing to increase the area covered by SFP. The preferences of people with a more urban-like profile were determined by forest structure and also by biodiversity aspects; in contrast, the population in rural areas was mostly concerned about features related to the forest structure.

The recreational and aesthetic experience people derive from SFP may differ greatly from that in large forests, where the focus is placed on the stand features: recreationists mainly enjoy the forest-interior; in contrast, SFP embedded in agricultural matrices may be also valued as part of the agricultural landscape where they are situated, being likely to be considered as relicts of wilderness or naturalness [202]. This landscape-based appreciation depends on their size and shape. In landscapes of north France and north Belgium economic valuation surveys have shown that patches are enjoyed from both outside and inside the landscape (Varela et al. submitted). Hence, these in-out recreational components did make a difference in the way forest features are valued. People enjoying the forest-interior were more concerned than the average population to enhance biodiversity (e.g. paying for measures that will increase the number of bird or butterfly species), while people enjoying the patches from outside were more willing than the average population to increase the area of these patches (Varela et al. submitted). Forest interior and forested landscapes have also long been a source of inspiration for painters (e.g. “Birch forest” from Gustav Klimt, 1903 or “Dans la forêt” from Paul Cezanne, 1898–1899). Their works probably contributed to the positive perception of forest structure and forest patches by the society.

SFP may also contribute to the construction of community identity [208••], since a community forest can be an element for local legends [209] signifying sanctuaries, social events. When dealing with private forests, some locations may be of personal significance for the forest owners and their families [210]. It has been observed that a share of the farmers owning land in the analysed landscapes of north France and north Belgium was reluctant to enhance the structural properties of these SFP to promote higher biodiversity levels. This may be related to their forest use, linked to hunting or wood extraction that may be to some extent hindered by (lack of) management measures aimed at increasing such structural diversity.

Conclusion and Perspectives

SFP influence their surroundings through ecological processes, mediated by patch characteristics such as their species composition, age, size and shape. Some of these processes are the basis for ES that benefit (or harm, in the case of disservices) different human activities. Mitchell et al. [28••] recently proposed a general and comprehensive framework for analysing the consequences of forest fragmentation on several ES (carbon storage, crop production, decomposition, pest regulation, soil fertility and water quality regulation). According to their work, forest fragmentation reduces the provision of most of the ES, mostly due to the negative consequences of fragmentation on biodiversity, but this could be counterbalanced by the fact that fragmentation, at a certain level, can increase the flow of ES to more beneficiaries (e.g. food foraging, hunting, and walking) through an easier accessibility. Hence, SFP produce fewer services than larger forests, but more people can potentially benefit from them. The spatial patterns of fragmentation (patch isolation, size and edge:interior ratio) are among the key drivers of the supply of many of the local and proximal ES, but there is still a strong need for more research to link given patterns to levels of services.

Moreover, new ES may emerge from fragmentation or existing ES may increase in intensity. For example, many local-proximal ES are strongly associated to the so-called “edge effect”. Since a primary effect of forest fragmentation is the increased edge:interior ratio, one can expect that those local-proximal ES will increase as well. The spatial arrangement of forest patches in agricultural landscapes also matters: for a same total area and number, forest patches evenly distributed throughout the landscape are more effective in delivering local-proximal ESs, such as, e.g. pest biocontrol, than clumped patches [136]. For some ES, such as soil protection and water regulation, the localisation of forest patches within the landscape is likely of utmost importance. For instance, steep slopes are more exposed to soil erosion and water run-off than flat areas; a forest patch will thus be more efficient with respect to soil protection on the former. Similarly, it is obvious that forest patches located along streams are more efficient at regulating water flow and quality than distant patches.

Agriculture intensification threatens biodiversity in many rural areas and can jeopardize the delivery of multiple ES [211]. How to meet the rising demand for agricultural land and crop production without compromising biodiversity and associated ES is thus a critical challenge for the twenty-first century in lowland agricultural landscapes. Only recently attention has been paid to ES and many unresolved issues still remain, especially in the context of fragmented ecosystems such as SFP embedded in agricultural landscapes. ES delivered by SFP have the potential to mitigate the disservices provided by agriculture, including loss of biodiversity, agrochemical contamination of the environment, soil erosion, emission of greenhouse gas and other pollutants [212]. However, there is still an urgent need to document individual and combined (synergistic and antagonistic) ES flows and their impacts on agriculture and agricultural landscapes and to analyse whether so-called intrinsic and functional biodiversity values of these SFP can go hand in hand. Other research challenges include the determination of the spatial and temporal scales at which ES significantly contribute to agricultural productivity and thus, at which spatial and temporal scales management should be implemented to increase their efficiency; and how to design incentives to promote the provision of ES in agricultural landscapes and, ultimately to green agriculture and increase their biodiversity and scenic beauty.