Introduction

Context: the importance of connectivity

Rapid, disruptive landscape change is one of the most consequential phenomena of the Anthropocene (Crutzen 2002; Millennium Ecosystem Assessment 2005). Processes such as urbanization, extractive land use, agriculture, and road building continue to increase rapidly alongside human population and development, with both intensive and extensive impacts on the landscape (DeFries et al. 2004). Indeed, the widespread loss and fragmentation of ecosystems is a major driver of species decline and extinction from the local to global scales (Pimm and Raven 2000; Millennium Ecosystem Assessment 2005; Cardinale et al. 2012; Zambrano et al. 2019). Fragmentation also disrupts geophysical processes, potentially worsening the impacts of natural disturbances, both abrupt (e.g. storms, floods, wildfires) and progressive (e.g. heat waves, droughts, sea-level rise) (Laurance and Williamson 2001; Li et al. 2017), and diminishes the renewable economic and cultural resources in the landscapes people inhabit (DeFries et al. 2004). All of these outcomes, furthermore, are unevenly distributed across demographics and geographies, generating or worsening the systemic inequities experienced by society’s most vulnerable and disadvantaged communities (Voelkel et al. 2018; Baró et al. 2019). This fragmentation can be understood, to a large extent, as the loss or degradation of functional connections among landscape elements–which suggests that restoring such connections may be able to mitigate its negative and inequitable consequences (Crooks and Sanjayan 2006; Hilty et al. 2006).

Sustainable landscape stewardship aimed at reducing and mitigating fragmentation requires a holistic approach, including biotic, abiotic, and human elements in management, along with an explicit spatial understanding of how these elements function and interact (Wu 2013). Maintaining connections for species, processes, and socio–ecological relationships is critical to preserve ecological function in landscapes where fragmentation is a given, such as within cities. However, connectivity is not always considered, or effectively implemented if included, in conservation planning in these landscapes (Neeson et al. 2015). Identifying how humans benefit directly and indirectly from ecological connectivity could help increase collaboration and support for efforts to enhance and preserve existing connectivity. Our literature search for these benefits found examples spanning many disciplines and geographies yet also revealed many inconsistencies and gaps in how connectivity and its benefits are understood, discussed, and valued, particularly in the area of social equity and environmental justice. This paper, a general theoretical synthesis illustrated with examples from literature in the natural, social, and applied sciences, is our effort to build a common framework to advance work in these fields.

Landscape ecology strives to be a transdisciplinary science (Bastian 2001; Opdam et al. 2013), which requires collaboration across sectors. Developing shared language and values empowers researchers, practitioners, and community advocates to restore and preserve ecological function and to bring the benefits of functioning habitats to all people. In this paper we seek to structure and further develop the array of concepts around connectivity in landscape ecology, to expand and clarify the related terminology, and to use the ecosystem services (ES) framework to identify the many interrelated, interacting benefits (and risks) associated with connectivity in the landscapes we inhabit. While broadly applicable, this paper is particularly relevant to urbanized landscapes where the intensity of fragmentation, the economic and societal benefits of maintaining multifunctional connectivity, and the opportunity costs of ecological conservation are greatest (McDonald et al. 2009; Kabisch et al. 2018). With this context in mind, many of our examples are from urban settings, particularly Portland, Oregon, USA.

Understanding connectivity

Connectivity has emerged as a key concept in landscape ecology in recent years, particularly as the discipline has increasingly turned its attention to the novel ecosystems, altered geographies, and disrupted human and environmental functions of complex socio–ecological landscapes such as cities and agricultural regions (Bennett 2003). However, there is disagreement over what is meant by connectivity, as well as how to measure it and its ecological functions and benefits. As Fischer and Lindenmayer (2007) point out, the word “connectivity” is used in different disciplines to refer to different phenomena, ranging from gene flows within a metapopulation to the contiguity of protected greenspaces. These phenomena are not always analogous and, in some situations, can even conflict with each other. The confusion has grown with the inconsistent use of associated adjectives such as “ecological”, “landscape”, and “habitat” (Fischer and Lindenmayer 2007).

In the broadest sense, we define “connectivity” as the coherency of landscape components and processes across three-dimensional space (Box 1). Connectivity spans spatial and hierarchical scales (Spanowicz and Jaeger 2019) and can also be dynamic over time, even periodically appearing and disappearing, as with ephemeral wetlands (Allen et al. 2020). It is both possible and, we argue, necessary to include human needs within the definition of connectivity. Indeed, landscape attributes and dynamics such as connectivity may be crucial to sustaining the benefits humans receive, and require, from functional environments (Wu 2013). A growing body of evidence supports the direct and indirect benefits of human connection to nature (Bratman et al. 2019; Shanahan et al. 2016; Van der Bosch and Bird 2018), and reveals significant inequities in how those benefits are distributed across socioeconomic and demographic dimensions (Shanahan et al. 2014; Rigolon 2016; Cole et al. 2017; Haeffner et al. 2017). Connectivity mitigates the disruptive effects of landscape change by maintaining important processes, ecological resilience, and adaptive capacity, particularly when integrated into multifunctional, landscape-scale networks (Mastrangelo et al. 2014; Beller et al. 2019). However, it can also facilitate unwanted processes or changes, such as biological invasions (Aronson et al. 2017). Perhaps surprisingly, then, relatively little research has been conducted into whether connectivity sustains the social and economic benefits of landscapes in the face of increasing fragmentation, climate change, and other disruptions (Mitchell et al. 2015).

Connectivity is not exactly the antonym of fragmentation, as some kinds of fragmentation (e.g., gaps, edge effects) cannot be properly described in terms of connections, while some processes that disrupt connectivity (e.g., river channelization, increased recreational activity) do not quite fit within the general concept of fragmentation. The term “fragmentation” typically applies to landscape patterns and biotic populations, while “connectivity” can also include abiotic and social processes, as well as teleconnections such as long-distance migrations. However, connectivity is mainly of interest in the context of anthropogenic landscape alteration, as is reflected in much of the theoretical literature discussing connectivity and fragmentation (e.g., Fischer and Lindenmayer 2007; Mitchell et al. 2015).

In their review of fragmentation and connectivity literature, Fischer and Lindenmayer (2007) described three distinct, though related and nonexclusive, categories of connectivity: habitat connectivity, ecological connectivity, and landscape connectivity. Because these categories do not capture the integral place of humans in the landscape and the many social purposes of landscape sustainability, we propose a fourth, complementary category: eco-social connectivity. Although we generally embrace maintaining established terminology, we propose replacing the name “ecological connectivity” with the more precise term “geophysical connectivity” given that habitat, geophysical, and eco-social connectivity are all, in some sense, “ecological”.

Ecosystem services as a framework

For our discussion of the benefits people derive from connectivity, we examined the four categories of ecosystem services (ES) developed and popularized by the United Nations’ Millennium Ecosystem Assessment (2005): Provisioning, Regulating, Cultural, and Supporting Services. Provisioning Services include the material products obtained from ecosystems such as food, fiber, and usable water. Benefits from ecosystem processes such as climate or disease regulation or water purification are Regulating Services. Cultural Services capture non-material benefits from ecosystems such as inspirational or spiritual value, recreation, education, and cultural heritage. Underlying all those services are Supporting Services, such as soil formation, primary production, and nutrient cycling, which are necessary for these direct services to exist (Millennium Ecosystem Assessment 2005). Negative effects, or disservices, also exist for each of these categories, and need to be accounted for in any assessment (Lyytimaki and Sipila 2009).

While the ES framework is not without controversy (Vira and Adams 2009; Dempsey and Robertson 2012), it can make ecology more visible in decision-making, provide compelling arguments and incentives for environmental protection, and provide data to support efforts around environmental equity and justice (Goldman and Tallis 2009; Costanza et al. 2014; Everard 2017). In addition to multiple economic valuation methods for ES, it is possible to bring ecosystem function into the ES framework using societal values determined by stakeholders (e.g., Darvill and Lindo 2016). While useful in many cases, strictly economic valuation of environmental benefits can have numerous limitations and pitfalls (Vira and Adams 2009; Büscher et al. 2012; Olander et al. 2018), and is not accepted in many cultures. Therefore, we advocate for a focus on societal values determined by local communities. However quantified, ES implicitly depend on the functionality, integrity, and resilience of the ecosystems from which they arise. Many human activities can both directly and indirectly diminish the functional integrity of ecosystems, with a corresponding decline in ES from those ecosystems (Rapport et al. 1998). Nevertheless, many ES can still exist, to a surprisingly large extent, in novel ecosystems and highly altered landscapes such as cities (Evers et al. 2018).

The literature on ES tends to examine individual components of ecosystems and their associated services in isolation (but see Mastrangelo et al. 2014). Integrative socio–ecological processes (Liu et al. 2007), such as the spatial relationships of landscape elements, complicate our understanding of ES in important ways, particularly when considering multiple ES, heterogeneous landscapes, and/or large spatial extents (Field and Parrott 2017; Rieb and Bennett 2020). To address this issue, Termorshuizen and Opdam (2009) proposed the term “landscape services” as a more holistic, explicitly spatial alternative or complement. Landscape services are evaluated and categorized the same way as ES and the two are generally interchangeable in valuation and decision models (Bastian et al. 2014). While we embrace both terms, and emphasize spatial and integrative considerations, we use “ES” because it is more widely used in the global ecological literature, and because our focus is on conserving the natural components of socio–ecological landscapes.

Categories and services of connectivity

In this section, we define each of the four categories of connectivity, reviewing its theoretical foundations, representations on the landscape, applications, and relationships to ecosystem services.

Landscape connectivity

Landscape connectivity (sometimes referred to as “structural connectivity”) is the spatial contiguity or proximity of related landscape elements, which can include human-defined features, such as ownership parcels or management units, as well as natural features. It is inferred from spatial patterns without necessarily representing real-world ecological functions (Bélisle 2005; Önal et al. 2016). Its origins are in geographic information science (GIS), landscape architecture, and land-use planning, and it has become much more commonly used (and misused: see Kupfer 2012) as FRAGSTATS (McGarigal and Marks 1995), graph-theory (Urban and Keitt 2001) and circuit models (McRae 2008), and other GIS applications have facilitated complex spatial pattern analyses (Gustafson 1998). The term “landscape connectivity” is still sometimes used in the literature to refer to the various types of functional connectivity discussed below (e.g., VanAcker et al. 2019; Brodie et al. 2015; Allen et al. 2020), but we follow the lead of Fischer and Lindenmayer (2007) and recommend its exclusive use for connectivity inferred from landscape pattern.

Landscape connectivity is often deductive, assessed in the landscape using spatial statistical and modeling methods (Goodwin 2003), but also can be inductive, in the form of connectivity-oriented design, engineering, and planning criteria (Nassauer and Opdam 2008). The acquisition of adjacent greenspaces with the intent of building regional trails (Jim and Chen 2003), watershed-oriented conservation and restoration (Allan 2005), the conservation of corridor and/or stepping-stone landscape features for wildlife movement (Baum et al. 2004; Van Rossum and Triest 2012; Saura et al. 2014) (but see Stewart et al. 2019), and residential naturescaping initiatives (Rudd et al. 2002) are all applications of landscape connectivity, since they typically rely on spatial location and pattern rather than detailed measurement and analysis of biotic, abiotic, and/or social processes to drive decision-making.

As landscape connectivity is pattern- rather than process-based, it can only be linked indirectly, if at all, to the ES arising from functional types of connectivity (Forman 1991; Rieb et al. 2017). Landscape connectivity can provide a convenient representation when functional connectivity is difficult to measure, such as in the case of urbanized floodplains (Mason et al. 2007). On the other hand, landscape connectivity can miss cryptic processes, such as groundwater movement or stepping-stone habitats, or teleconnections, such as long-distance migrations (Bennett 2003). Alternatively, it may create an exaggerated impression of functional connectivity from map-apparent features with little actual ecological functionality (Kubeš 1996; Gippoliti and Battisti 2017; Laliberte and St-Laurent 2020). For landscape connectivity to be meaningful, there must be a known, scale-appropriate relationship between the observed landscape pattern and the expected process (Tischendorf and Fahrig 2000; Goodwin 2003; Lynch 2019) or ES outcome (Syrbe and Walz 2012; Duarte et al. 2019). A combination of clear goals, evidence-based strategies, rigorous research and monitoring, and adaptive management can strengthen the effective relationship between landscape and functional connectivity (Adams and Dove 1989; Tischendorf and Fahrig 2000; Kadoya 2009; Beller et al. 2019).

Habitat connectivity

Habitat connectivity is the ability of organisms and/or their genetic material to move among their populations and potential habitats. Originating in the disciplines of biogeography, natural history, and population ecology, habitat connectivity has long been understood intuitively but it was often not easily quantifiable until the development of techniques such as radiotelemetry, camera traps, and genetic analysis. The modern definition of habitat connectivity was coined by Merriam (1984).

Habitat connectivity is necessarily species-specific, as each species has its own habitat requirements and ability to disperse, although some studies seek to aggregate the habitat connectivities of guilds or even entire communities (Hilty et al. 2006). Habitat connectivity is either measured directly by tracking the movements of individual organisms or their propagules or inferred from the genetic similarity of potentially linked populations (Keogh et al. 2007). This form of connectivity is particularly important in metapopulation theory (Wiens 1997), and has led to several approaches to modeling how organisms move through heterogeneous landscapes (Kadoya 2009; Wey et al. 2008; Jeltsch et al. 2013), although research on the topic is still limited by taxonomic biases and methodological issues (Laliberte and St-Laurent 2020; LaPoint et al. 2015). Its applications include road crossings for wildlife (Clevenger and Waltho 2000; Bliss-Ketchum 2019), the geographical risk assessment and containment of biological invasions (Sharov et al. 2002; Epanchin-Niell and Wilen 2012), and land conservation efforts focused on enabling species and communities to shift their ranges in response to climate change (Heller and Zavaleta 2009; Keeley et al. 2018; Walsworth et al. 2019). It can be disrupted by the anthropogenic fragmentation or degradation of habitats, including the construction of barriers such as roads and dams, increased exposure to environmental hazards such as disease and predation, and wildlife avoidance of human activity (Bennett 2003; Hilty et al. 2006).

Habitat connectivity is most associated with biodiversity and the integrity of natural populations (Bennett 2003; Jeltsch et al. 2013; Damschen et al. 2019). While the extent to which biodiversity and ES are correlated is not entirely clear (Brondizio et al. 2019; Martínez-Jauregui et al. 2019), and probably subject to both great variation and great measurement subjectivity (Ricketts et al. 2016), habitat connectivity has a clear role in sustaining species, some of which provide measurable benefits to people and the landscapes they inhabit (Bennett 2003). Considering biodiversity and ES in tandem when making conservation decisions can optimize return on investment, as well (Watson et al. 2020). Examples of ecosystem services and disservices associated in the literature with habitat connectivity are listed in Table 1. In addition, the habitat connectivity of indicator species is sometimes used, with caveats, as a proxy for other connectivity processes (Simberloff and Cox 1987).

Table 1 Representative ecosystem services and disservices of different landscape features representing habitat connectivity
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Geophysical connectivity

Geophysical connectivity describes the permeability or resistance of the landscape to matter and energy flows; it is the connectivity of natural processes and the landscape features that regulate them. Its origins are in the geosciences and physical geography, particularly with hydrologic connectivity and the river continuum concept (Vannote et al. 1980) and, more recently, the integration of biogeochemical cycles (Pataki et al. 2011) and geomorphology (Brierly et al. 2006; Wainwright et al. 2011) with landscape ecology. However, it also encompasses energy fluxes, the movement of pollutants, disturbance processes such as wildfire, and atmospheric and ocean currents, among other features. It even includes connectivity of biota when viewed through a geophysical lens, as with the regulation of environmental processes provided by contiguous vegetation or biogeochemical transport via migratory animals. As with habitat connectivity, the permeability of the landscape to these flows can be greatly affected by land use change and the built environment, such as impermeable surfaces and above and below ground (Frazer 2005). They can also be altered by biological invasions (Donovan et al. 2013).

Geophysical connectivity is assessed by measuring matter and energy flows across space and time, using methods ranging from point monitoring to remote sensing analysis and computer modeling (Arnfield 2003; Mimikou et al. 2016). Its applications include such diverse practices as green stormwater infrastructure (Fahy 2018), wildfire management (Wei et al. 2019), and the use of tree canopy to mitigate the stresses of urban environments (Makido et al. 2019).

Geophysical connectivity underlies many regulating and supporting services, among others (Table 2).

Table 2 Representative ecosystem services and disservices of different landscape features representing geophysical connectivity
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Eco-social connectivity

Research on anthropogenic landscape change often focuses on impacts to biodiversity and natural systems (Fischer and Lindenmayer 2007), and frames management decisions through that lens (Newbold et al. 2015), overlooking the integral interrelationship of humans with the landscapes they use and inhabit. Eco-social connectivity [partially introduced as “social connectivity” in Kondolf and Pinto (2017)] captures how the spatial features and properties, both natural and built, of landscapes facilitate people’s access to nature and its benefits. While such access has been well-studied in numerous disciplines (e.g., ecopsychology, environmental sociology, environmental economics, environmental medicine, human geography, environmental education) (Thompson 2011), and although landscape sustainability science (Wu 2013) emphasizes the need to study access to nature in a geographical/landscape context (e.g., Weber and Sultana 2013), the literature rarely frames such access as a form of “connectivity” (Kondolf and Pinto 2017). Social connectivity has mostly been used for human-to-human connections, and has been defined as the communication and movement of people, goods, ideas, and culture (Kondolf and Pinto 2017). The study and modeling of social networks (Scott 1988) has made social connectivity, linking humans to humans, a widespread concept in the social sciences, but one not often explored in ecology. In addition, the concept of social connectivity does not fully capture the magnitude and importance of human access to nature’s benefits and the interrelationship between landscape and society. Thus, eco-social connectivity bridges the gap between ecological and social connectivity.

Eco-social connectivity overlaps with a number of other current ideas in landscape sustainability, such as inclusive (Imrie and Hall 2001) and biophilic (Beatley 2011) design philosophies, political ecology (Turner and Robbins 2008), nature-based learning (Jordan and Chawla 2019), and recreation ecology (Monz et al. 2010). As eco-social connectivity is fundamentally human-centered, it is best assessed by active stakeholder engagement, such as through surveys, interviews, workshops, and public participation/process equity in planning and implementation (Matsuoka and Kaplan 2008; Stringer et al. 2006; Rall et al. 2019). Passive measurements typically do not provide valuable data on eco-social connectivity, although some methods, such as trail counts, can (Reynolds et al. 2007). Eco-social connectivity is closely tied to environmental equity and justice. There is strong and growing evidence linking access to nature with human wellbeing (Van der Bosch and Bird 2018). In many landscapes, particularly urban areas where total greenspace is relatively scarce, profound disparities in this access reflect deeply embedded social inequities along lines such as race, ethnicity, ability, and socioeconomic class (Shanahan et al. 2014; Kowarik 2018; Nesbitt et al. 2019). Efforts to increase eco-social connectivity in disadvantaged communities can backfire, however, if increased access to natural amenities fuels gentrification, helping to displace the communities it is meant to serve (Dooling 2009; Cole et al. 2017). Planning for eco-social connectivity thus needs to occur alongside policies and practices to address the underlying causes of gentrification, and to integrate strong community input throughout the process (Wolch et al. 2014).

Eco-social connectivity can be disrupted by lack of natural resources integrated into communities, insufficient quantity and quality of reachable greenspace, inadequate accessibility infrastructure, and cultural barriers such as safety concerns and discrimination in parks (Gobster 2002; Williams et al. 2020). Discriminatory policies and practices such as red-lining have created enduring unequal access to quality natural resources and greenspace (Shanahan et al. 2014; Nesbitt et al. 2019). These policies have perpetuated localized disparities in green infrastructure benefits such as shade trees and stormwater management (Hoffman et al. 2020), and even have evolutionary and ecological implications (Schell et al. 2020). Applications of eco-social connectivity are diverse and widespread, ranging from biocultural restoration (Morishige et al. 2018) to inclusive design in outdoor recreational areas (Doick et al. 2013), community gardens (Glover et al. 2005), and tree-planting initiatives in under-resourced neighborhoods (Stone et al. 2015).

Eco-social connectivity is particularly associated with provisioning and cultural services (Table 3).

Table 3 Representative ecosystem services and disservices of different landscape features representing eco-social connectivity
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Discussion

Overlaps and interactions

The four types of connectivity are not mutually exclusive. Fully connected watersheds that allow stream passage for anadromous salmonids, for instance, represents habitat (the movement of organisms among feeding, transitional, and spawning waters), geophysical (the delivery of nutrient subsidies from the ocean to headwater streams), eco-social (access to fishing and associated cultural and economic activities), and landscape (planning and design practices to remove or mitigate barriers) connectivities (Smith 1994; Yeakley et al. 2014). Another example is extensive urban tree canopy, which makes the urban matrix more permeable to wildlife (habitat) (Baum et al. 2004); regulates stormwater, air quality, and local climate (geophysical) (Escobedo et al. 2011; Nyelele et al. 2019); increases the value and vibrancy of local communities (eco-social) (Bolitzer and Netusil 2000; Stone et al. 2015); and requires spatial analysis, modeling, and planning standards to be effective and equitable (landscape) (Gatrell and Jensen 2008; Ordonez and Duinker 2013).

Such overlaps frequently interact, resulting in both synergies and tradeoffs. These interactions can vary by location, time, and scale (Termorshuizen and Opdam 2009). The field of recreation ecology, for instance, is concerned with quantifying the many impacts human visitors have on natural areas and weighing them against the social benefits and conservation incentives of human access to nature (Monz et al. 2010). Here, the roads and trails that support eco-social connectivity can fragment habitats, deter wildlife, and impact watersheds, but at broader scales can justify and incentivize the protection of large, well-connected natural landscapes. Such overlaps and synergies, commonly termed “ecosystem multifunctionality” (Manning et al. 2018), provide opportunities to optimize landscape-scale conservation and planning efforts and maximize their return on investment (Conrad et al. 2012; Önal et al. 2016).

Using connectivity services in planning

We include Tables 1, 2, 3 with the intent that articulating the ES of these categories of ecological connectivity will help managers and communities gain support for connectivity projects. In Table 4 below, we illustrate the relationships between management actions, connectivity features, and socio–ecological outcomes. However, harnessing the synergies among the different connectivity categories and their services, and minimizing the disservices that also arise from connectivity, requires a decision framework that can integrate and leverage them together. The basic elements are those proposed by Termorshuizen and Opdam (2009): features linked to functions linked to values. While this suggests a simple, linear chain, real examples exist in a web of interrelated features, multiple function-value combinations, and even feedbacks from supporting ES. Connectivity may function differently at different scales of space, time, or systems organization, as well. Effective frameworks incorporate these complexities; we will propose such an approach in a future paper.

Table 4 Links between management actions, functional connectivity features, and outcomes providing ecosystem services and disservices
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Using this kind of assessment requires appropriate scope, effective goal-setting, accessible high-quality data (both baseline and monitoring), broad multi-sector collaboration both among and between decision-makers and community stakeholders, and the capacity to adapt to unexpected outcomes or changing circumstances (Rieb et al. 2017). Indeed, the complexity and situational uniqueness of socio–ecological landscapes demand an approach that is experimental, adaptive, scale-aware, and inclusive (Cumming et al. 2013). Naturally, it is generally simplest and least expensive to conserve existing connectivity first, and to take advantage of existing landscape elements to restore or enhance what has been diminished (Roni et al. 2002). The socio–ecological perspective is essential, as the conservation of ecological connectivity without regard to the social, economic, and political concerns of those living in its path can result in the displacement and fragmentation of human communities (Rantalla et al. 2013), in much the same way that the infrastructure of human connectivity can displace and fragment ecosystems.

Future directions

Several aspects of connectivity and ES are under-researched. The literature on habitat connectivity, for example, displays strong taxonomic biases towards charismatic organisms such as birds, pollinators, and megafauna (Mitchell et al. 2015). Though invasive species are frequently considered a risk in habitat connectivity, overall evidence for this risk is inconclusive, in many cases perhaps more related to edge vulnerability in narrow corridors (Haddad et al. 2014). Some invasive species, too, can have offsetting benefits such as food, timber, and erosion control (e.g., Dickie et al. 2014), and, in the absence of a specific invasion threat, the benefit of spreading desirable species generally appears to outweigh the risk of spreading undesirable species (Levey et al. 2005b). Geophysical connectivity of soils and the ecological features that regulate them seems to have been studied much less than other areas such as hydrology or biogeochemistry (Liu et al. 2020). Also, while there is much research on the air quality benefits of trees in a landscape context, these studies are often based on empirically limited modeling assumptions (Escobedo et al. 2011). Research on eco-social connectivity to date has been infrequent and, prior to Kondolf and Pinto (2017), we found no framework proposed to bring together ideas scattered across several disciplines; developing the concept of eco-social connectivity is a key motivation and contribution of our work.

We briefly review the translation of connectivity and ES into principles for environmental stewardship in Table 4. Nevertheless, there remains much work to be done in evaluating and improving modeling methodologies, planning strategies, design standards, and best management practices–i.e., bridging the gap between functional and landscape connectivity (Gippoliti and Battisti 2017). Progress here will require intentional collaboration at local to regional scales between researchers, practitioners, and community stakeholders in an iterative, adaptive-management approach, in which research, application, and equitable public inclusion each inform and support each other (Opdam et al. 2013).

Successful collaboration on connectivity and ES depends on having information which is plentiful, rigorous, diverse, and accessible. The long-term ecological research (LTER) framework (National Science Foundation 2018) provides a powerful, integrative approach to understanding landscapes across space and time, and has been applied to explicitly socio–ecological settings such as the Gwynns Falls Watershed in Baltimore, Maryland. Similarly, the “smart cities” movement, with its integrated networks of local and remote sensors collecting and sharing diverse types of data in built environments (Batty et al. 2012), has immense, if largely untapped, potential to support ecological research and natural resource valuation in inhabited landscapes (Gatrell and Jensen 2008; Colding and Barthel 2017). An equally necessary component is the cultural knowledge of communities, including traditional ecological knowledge (Berkes et al. 2000; Charnley et al. 2007), community science (Balazs and Morello-Frosch 2013), and public-participation mapping (Rall et al. 2019), which both challenges and complements quantitative scientific approaches. Local knowledge is crucial to bridging gaps between researchers, practitioners, and the public, and empowers responsive, equitable outcomes (Brondizio et al. 2009). The efficacy of these data, in turn, depends on having open access, open standards, and appropriate precautions or restrictions for sensitive information (Zuiderwijk and Janssen 2014). And, of course, landscape data can only attain their greatest value when effectively visualized and communicated, particularly to the public (Vervoort et al. 2012).

The final challenge is to develop innovative valuation and financing approaches to effectively prioritize and support connectivity conservation and to incorporate connectivity into conservation planning. We will discuss this in detail in a future paper.

Conclusions

Connectivity is the spatial glue that holds the elements of landscapes together, allowing them to interact, move, renew themselves, and adapt to changes over space and time. The ecosystem services concept provides a general framework for assigning values to the many benefits and costs of maintaining connectivity, including those of the greatest direct interest to the human communities within landscapes. These two concepts are typically viewed through separate lenses but are integrated, which presents a need to expand established definitions of ecological connectivity to include connectivity between people and their environment. Indeed, highlighting categories of connectivity, and the distinctions and relationships between them, can help broaden thinking about connectivity and remind ecologists and planners of the importance of including people as part of connectivity planning and research. Moreover, such approaches can help center equity and thus lead to more equitable outcomes. In identifying the four categories of connectivity we also aim to improve consistency of terminology for these different species-specific, process-specific, and pattern-specific concepts. Importantly, the many benefits of all categories of connectivity, highlighted by this discussion on ecosystem services, can be used to garner support for connectivity projects, identify synergies and tradeoffs among connectivity-related goals, and promote holistic thinking. With the shared language proposed in this paper, we aim to enable coordination and collaboration across goals, institutions, and communities. The ES framework creates an opportunity to incorporate connectivity of all kinds more effectively into planning, decision-making, and management of socio–ecological landscapes. Using ES to make connectivity-related decisions, however, requires effective, informed evaluation of landscape elements, connectivity goals, and their benefits and risks. A framework for such an evaluation process is the subject of a future paper.