Biodiversity and ecosystem services in forests: management and restoration founded on ecological theory

Ecological systems, including the collection of inhabiting organisms (i.e. biodiversity) and the vital functions provided and the resultant benefits (i.e. ecosystem services), face increasing threats from the stresses of an expanding human population. Despite inconsistent trends in biodiversity change among studies, particularly at the local scale (Vellend et al. 2013; Dornelas et al. 2014; Newbold et al. 2015; Gonzalez et al. 2016), there is a firm consensus that humans have increasingly affected biodiversity globally (Rockström 2009; Rockström et al. 2009; Butchart et al. 2010; Pereira et al. 2013; Pimm et al. 2014; Tittensor et al. 2014; Steffen et al. 2015). Because diverse assemblages of organisms, including diversity in genes, species and other forms of biological traits, are often necessary to generate and support the fundamental functioning of ecological systems, human-induced loss of diversity could have serious consequences for ecological goods and services that are essential for human well-being (Cardinale et al. 2012). Among the various drivers of global change, biodiversity loss is likely to have one of the largest impacts on the functionality and sustainability of Earth's ecosystems (Hooper et al. 2012), and its consequences may become gradually more severe than the currently observed trends because of the debts of both biodiversity and the associated ecosystem processes (Isbell et al. 2015). In terrestrial systems, biodiversity has been threatened by human influences such as degradation, fragmentation and loss of habitats, climate change and pollution. Different forms of life are thus increasingly at risk and this is especially germane in forest ecosystems, in which biodiversity is often higher than in other terrestrial biomes (Schmitt et al. 2009). Deforestation is not only one of the major causes of modern environmental crises, but has influenced the course of human societies historically (Diamond 2005); management efforts to deal with deforestation were even reported before the industrial revolution, such as the successful adoption of silvicultural practices to restore Japanese forests in the 1600s (Totman 1989). As such, the loss of forests has long been a concern, most likely resulting from anxieties about potential poverty and loss of goods (e.g. foods, materials and energy sources) and services (e.g. water purification, erosion control and microclimate regulation) directly derived from forests (Thompson et al. 2011; Trumbore, Brando & Hartmann 2015). In the current context of climate change and its mitigation, forests have garnered special attention because of their major role in sequestering carbon from the atmosphere (Mori et al. 2013; Bellassen & Luyssaert 2014). Beyond consequences for the development and prosperity of human societies, the loss of species following deforestation and forest degradation is now gaining focus for the primary purpose of biological conservation (Gibson et al. 2011). Motivations to preserve nature may differ among people (Mace, Norris & Fitter 2012), and such perspectives on nature conservation also change over time (Mace 2014). For instance, although the majority of people may be primarily interested in maintaining forests because they are fundamental for their livelihoods, others may be more concerned about the vulnerability of species to the loss of forests. However, the reasons and objectives for maintaining forest integrity are not necessarily mutually exclusive among the various stakeholders. Currently, there is an increasing recognition that safeguarding organisms, and thus biodiversity, can also be, beyond the primary aim of protecting life, an effective and essential measure to ensure the provision of ecosystem services to human societies, a view that could be essentially utilitarian in its reasoning (Naeem, Duffy & Zavaleta 2012; Mace 2014). Many scholars, managers and policymakers now recognize such shared potential between biological conservation and the maintenance of ecosystem services (Balvanera et al. 2013), an issue that encompasses all ecosystems, not just forest ecosystems. However, there are many difficulties to be overcome. Forests harbour the vast majority of terrestrial species (CPF 2008; Schmitt et al. 2009). Even in situations where the actual number of species is still largely unknown (Caley, Fisher & Mengersen 2014), there is a strong need to conserve species including those that remain undiscovered. The provision of ecosystem services is spatially heterogeneous in forests, and some services can be synergetic or antagonistic with others, and there are often trade-offs between them (Gamfeldt et al. 2013). Understanding the trade-offs and synergies among different ecosystem services is crucial to inform policy and management (Bennett, Peterson & Gordon 2009). The actual flow of provisioning of goods and services to society from biodiversity preservation has much uncertainty (Balvanera et al. 2013), and this is especially the case in natural forests characterized by high structural complexity, spatiotemporal heterogeneity of resource distributions and the dominance of long-lived organisms (Mori, Lertzman & Gustafsson 2016). Furthermore, there may be a trade-off and a conflict between biodiversity conservation and some ecosystem services within a landscape (Naidoo et al. 2008; Nelson et al. 2009; Koh & Ghazoul 2010), because some ecosystem services of interest are often independent of the diversity measured or of interest (Thompson & Starzomski 2006; Balvanera et al. 2013). In addition, the increased provision of specific goods and services often requires land conversion and other forms of human intervention that inevitably result in negative impacts on biodiversity at multiple spatial, temporal and biological scales (Reyers et al. 2012). Accordingly, there is much to be done to gain a firm understanding of how human-induced environmental changes can affect multiple facets of forests including biodiversity per se, the functionality of ecosystems and possible linkages between biodiversity and ecosystem services. Humans and nature cannot be separated and are indeed coupled (Berkes, Colding & Folke 2003; Liu et al. 2007; Carpenter et al. 2009), and this has been evident for societies living in or near forested regions throughout history. Considering the numerous cases of past failures to tighten this link (some described in Busenberg 2004; Liu et al. 2007; Mori 2011), further consideration is needed regarding future forest use, conservation and restoration within the context of social-ecological systems. The papers in this Special Feature focus on the profound potential of research on forest biodiversity and ecosystem services by summarizing the present state of the art (Mori, Lertzman & Gustafsson 2016) and adopting modern analytical tools and approaches to quantify issues of concern (Barros et al. 2016; Chamagne et al. 2016; Fujii et al. 2016; Law et al. 2016; Thom et al. 2016; Triviño et al. 2016). The topics and study regions in this Special Feature are diverse. The original studies include field-based work from different forests (Chamagne et al. 2016; Fujii et al. 2016) and ecological modelling of tropical, temperate, boreal and high-elevation forest landscapes (Barros et al. 2016; Law et al. 2016; Thom et al. 2016; Triviño et al. 2016). Our hope is that societies around the world can benefit from the wealth of such observational, experimental and theoretical works in forest ecosystems to help realize sustainable forest management. The synthesis by Mori, Lertzman & Gustafsson (2016) argues that forest ecology needs further investigations to integrate knowledge on multiple facets of biodiversity, ecosystem services, and the links and conflicts between them into real-world challenges. The synthesis emphasizes the increasing opportunities as well as some lags in the field of forest ecology by shedding light on fundamental efforts by individual scholars on the ground, emphasizing important initiatives and platforms that are emerging, and lending theoretical and empirical support from related environmental science disciplines. Information for such challenges, advances and gaps has been presented in diverse venues. Therefore, the synthesis aims to compile them together and to provide a research agenda based on up-to-date information and tools that are helpful for facing current issues as well as unknown, unexplored and uncertain issues that require novel exploration. In addition to issues of biodiversity loss per se, this Special Feature has a focus on climate change and land-use change, two significant drivers of environmental change in terrestrial regions (Travis 2003; Mantyka-Pringle, Martin & Rhodes 2012; Mori et al. 2013). The focus is further expanded to the synergies between climate and land-use changes and associated ecological changes such as those in species distributions and forest disturbance regimes (Seidl, Schelhaas & Lexer 2011). Thom et al. (2016) report on spatiotemporal trajectories of biodiversity in temperate forests in response to changing climate and to the accompanying changes in forest disturbance regimes. Barros et al. (2016) analysed synergetic influences between climate change and land-use change on plant communities in timberline forest–grassland ecotones, with explicit considerations of different types of climate impacts including climate extremes. Both studies demonstrate that the disturbance effects are variable and complicated and often have substantial impacts on biodiversity, depending on possible changes in the frequency and severity of disturbance under the changing climate. Thus, there is a need for careful land-use planning that acknowledges such dynamic features of ecological systems. The benefits of nature to people and ecosystem services are modern terms that, in practice, require a new way of thinking, capacity building and further accumulation of knowledge to do so (Diaz et al. 2015), although the underlying concepts are fundamental to humanity and thus not necessarily new. Many perceptions of biodiversity and ecosystem services exist, including that: biodiversity is an ecosystem service, biodiversity and ecosystem services are the same, and biodiversity is a source of ecosystem services (Mace, Norris & Fitter 2012) – but these two terms are now being discussed in tandem (MA 2005). Reflecting an increasing need to frame and face local and global issues surrounding the conservation of biodiversity, ecosystem services and sustainable development for societies, the Intergovernmental Platform on Biodiversity and Ecosystem Services was recently established (Perrings et al. 2011; Diaz et al. 2015). One of the important topics of this policy–science interface is scenario generation and modelling (IPBES 2016). These scenarios and the associated models give multiple, alternative options for policymaking under great uncertainty. In this Special Feature, Law et al. (2016) and Triviño et al. (2016) discuss land-use and management options informed by scenarios to ensure multiple ecosystem services in tropical and boreal forest landscapes with simultaneous consideration of biodiversity conservation. A common concept of these two original studies is multifunctionality. Given humanity's diverse requirements, the provision of multiple rather than single ecosystem services – the vital notion of multifunctionality – is of practical importance (Isbell et al. 2011; Mori et al. 2016; Soliveres et al. 2016). Relating to this context, Law et al. (2016) and Triviño et al. (2016) aim to identify options that can help management to optimize multi-objective needs including biodiversity conservation and other requirements by stakeholders. As noted above, there are many trade-offs and conflicts in managing real-world ecosystems. To face such realistic complexity, both Law et al. (2016) and Triviño et al. (2016) emphasize the need for mixed policies that can benefit from different perspectives on land allocation for economic and conservation purposes (i.e. land sharing and land sparing; Fischer et al. 2014). Lastly, the theoretical foundations for the roles of biodiversity in generating and supporting ecosystem services largely come from a pile of fundamental research testing the positive effects of biodiversity (mainly species richness) on fundamental functions in ecosystems (e.g. primary productivity) (Cardinale et al. 2012). The majority of such evidence has come from experimental, manipulation studies in systems characterized by short-lived, fast-growing organisms (e.g. grasslands). To complement knowledge gaps for forest ecosystems dominated by trees as a slow-growing, long-lived organism, there has been a dramatic expansion of such research in forests (summarized in Mori, Lertzman & Gustafsson 2016). Unlike experimental grasslands, many complexities exist in forests, particularly in naturally regenerating forests. By lending theoretical support from a series of biodiversity–ecosystem functioning studies, Chamagne et al. (2016) and Fujii et al. (2016) found that positive diversity effects on fundamental functions (i.e. forest productivity and litter decomposition) were very likely in forest ecosystems. Because of the high complexity inherent in forests, the linkages were not straightforward. However, both studies report on the important implication including a potential and need to shift forest management from monoculture to mixture in order to enhance the vital functionality. The studies of Chamagne et al. (2016) and Fujii et al. (2016) were conducted in central Europe and Japan, respectively. Including these regions, it is increasingly necessary to reconsider forest policy and management of tree diversity in many parts of the world (Knoke et al. 2008). Some benefits of increasing diversity in forests remain unclear, and practices such as those aimed at mixing tree species may come with economic costs. In this regard, Chamagne et al. (2016) call for further studies that also consider the societal aspects of management practices in addition to the potential for increasing tree diversity. Fujii et al. (2016) further emphasize the large variability in the functional consequences following diversification of trees and the associated taxa at different trophic levels, noting both uncertainty and opportunities in the field of applied ecology. The studies in this Special Feature undoubtedly contribute to the issue of forest biodiversity and ecosystem services in each study region; however, they are not merely shining as a local jewel but have global implications for societies around the world. In addition, the novel theoretical and practical approaches described here are important for both scholars and practitioners. At the same time, the authors are also explicit about uncertainty, which requires further study efforts and points to specific research frontiers. There is now increasing recognition that ecosystem management and restoration need to be grounded in ecological theory (Laughlin 2014; Mouquet et al. 2015; Perring et al. 2015; Schultz, Crone & Lewis 2015; Bennetsen, Gobeyn & Goethals 2016; Mori, Lertzman & Gustafsson 2016), although knowledge is limited and thus is often heuristically applied to actual management and restoration (Sasaki et al. 2015). At this juncture, the issues covered in this Special Feature are, of course, not the full list necessary to build a theoretical foundation, and therefore call for further research. The issues surrounding forest biodiversity and ecosystem services are multifaceted, in terms of the spatial, temporal, biological and societal scales. It is difficult and often unrealistic to achieve confidence in real-world management, due to the complexity and hierarchical nature of the issues. ‘Learning by doing’ to cope with this uncertainty may seem almost never-ending, and the frontiers may still seem vast. However, our pioneering efforts in each direction will have lasting impact. The accumulation of fundamental and applied research will eventually yield better – if not the best – solutions to cope with the difficulty and uncertainty of managing biodiversity and ecosystem services. A.S.M. was supported by the Organisation for Economic Co-operation and Development's Co-operative Research Programme. I thank Marc Cadotte and Alice Plane for all their help with organizing this Special Feature. Data have not been archived because this article does not contain data.