Conservation Evidence: Wildlife Corridors
Habitat fragmentation greatly threatens global biodiversity, by limiting population sizes of species, and restricting gene flow between populations (Kirchner et al., 2003). This results in a reduction in genetic diversity in populations, and increases their susceptibility to local extirpation.
Corridor creation is a direct and popular method for mitigating the negative effects of habitat fragmentation, and restoring habitat connectivity (Haddad et al., 2014) and (Evans et al., 2012). Corridors are expected to increase the likelihood of a species’ survival within fragmented landscapes, by increasing gene flow between populations (Kirchner et al., 2003).
However, the science of creating wildlife corridors is relatively new. As a result, it’s important to evaluate projects based on metrics that demonstrate success. Equally important is understanding opportunities for improvement.
As a result, Saving Nature has partnered with undergraduate students at Duke University to review the literature on building wildlife corridors to understand what has been achieved and how we can build from here. Our goal is to build a model that allows us maximize the return on conservation investments.
In the End, it's results that count. that's why evaluating project results matters.
Wildlife Corridors: Observational Evidence
One of the core principles of wildlife corridors is enabling isolated populations of species to disperse. Movement of species through wildlife corridors is fundamental to species rebounding through genetic enrichment and population growth. Evidence that they are doing so is critical to ensuring project success. Conversely, evidence that species are not dispersing signals that corrective action is required.
There are many considerations that go into designing an effective corridor. For example, evidence of how the characteristics of the corridor, such as size and habitat quality, influence its utilization by different species informs corridor design. Also, how the dynamics of seed dispersal and pollination enrich recovering habitat inform what plant species are needed to promote corridor utilization and species recolonization.
Below we summarize insights from a collection of papers with conservation evidence based on observing species movement through corridors.
by Ren Cao, Duke University
The destruction of native landscape and fragmentation of continuous vegetation is evident through a series of human activities (Bennet & Saunders, 2010). The demand for land resources for conversion into agricultural and residential purpose drives habitat loss and isolation for species across the globe (Collinge, 1996).
Existing studies have found that human infrastructure construction and agricultural production can lead the lack of connectivity and result in the shrinking range for vulnerable species (Vos & Chardon, 1998).
Key Findings
A total of six studies examined animal movements in natural habitat corridors. Collectively, the studies illuminate preferred characteristics of habitat corridors and how the reactions of species may differ as a result of the changes in characteristics.
One stream of literature has assessed potential pathways to reconnect divided habitat patches using a narrow linear landscape called corridor. The narrow linear strip connecting to two patches of habitat in a matrix can facilitate animal movements between patches (Beier & Noss, 1998). This role of the strip of landscape characterizes the fundamental function of a habitat corridor. Corridors can be replanted trees or the remains of native landscapes that are not disturbed.
One study in Australia found that corridors facilitate both one-way and two-way movements and subsequent residency in patches connected to corridors of small mammals in narrow remnant strips.
One replicated study in Germany found that corridor width affect voles’ movements in corridors, and voles’ personality, or exploration scores, do not affect movements in the same corridor.
One study in North Dakota found that birds traveled and occurred more frequently in patches connected by habitat corridors in a riparian remnant landscape within farmland.
Another study in Australia found that arboreal mammals preferred floristically diverse remnants.
Conclusions and Recommendations
Overall, depending on different species, preferred corridors have moderate width, internal complexity, rich vegetation diversity, and connectivity to habitat patches.
Also, the connected patches can have an impact on the use of corridors, since species movements through corridors may not occur if the quality of patches and matrix is not optimal.
A potential gap in the reviewed literature is that most research projects are observational and lack a control group. For example, the authors in the first study on different types of movements of small mammals in natural corridors in Australia acknowledged that there is no comparison group in a landscape with either no natural corridor or planted corridor. To fill this gap in research, future studies can focus on a comparison between the effectiveness of different types of corridors on species movements.
Click here to read the full analysis.
by Courtney Horn , Duke University
Few studies have examined the effects of corridors on plants, largely because of the difficulties inherent in studying the effects of corridors on sedentary organisms (Evans et al., 2012) and (Tikka et al., 2001).
Out of the studies which have been conducted, several have demonstrated that corridors may benefit plants by increasing pollen and seed dispersal (Evans et al., 2012). However, corridors may also fail to benefit dispersal and populations (Tikka et al., 2001).
In addition, corridor creation could have negative effects on plant populations. For example, studies have reported invasions of exotic species through corridors (Tikka et al., 2001).
The effect of corridors on plant dispersal is important to understand, because the persistence of existing plant populations, and the recolonization of plants to disturbed areas within fragmented landscapes, is largely determined by gene flow through pollen and seed dispersal (Tewksbury et al., 2002). Therefore, plant dispersal is important recovery of fragmented habitat.
Key Findings
Studies analyzing the effect of corridors on plant dispersal were used for this paper.
A study by Kirchner et al. found that flooded natural corridors have been shown to increase seed dispersal and gene flow between plant populations, and connection among habitats.
A study by Kormann et al. found that tropical forest corridors likely increase hummingbird mediated pollen dispersal.
A study by Tewksbury et al. in the Savannah River site found that corridors facilitate animal mediated pollen and seed dispersal, and this effect may be widespread among plant species. A study by Damschen et al. in the Savannah River site found that corridors have been found to increase diversity of native plants, and not increase diversity or number of exotic species. A study by Townsend and Levey in the same site found that corridors increase insect (butterfly, bee, and wasp) mediated pollen transfer.
Conclusions and Recommendations
There was a consensus among the research papers reviewed that corridor existence benefits plant dispersal. In addition, the papers did not find evidence supporting any of the predicted negative effects of corridor creation.
Although the research papers covered a limited set of species, the predicted and determined mechanisms through which corridors benefit the analyzed plant species seem as though they would hold true for most species.
For example, increased animal movement as a result of corridor creation would likely increase dispersal of most animal dispersed plants. As a result, corridor creation should benefit the dispersal and population persistence of most plant species. In addition, corridor creation does not appear to pose a risk of negative effects.
Click here to read the full analysis.
by James Robinson , Duke University
While more attention has been payed towards the movement of larger mammalian species, the impacts of wildlife corridors on endemic plants are of critical importance. Plants come in numerous forms and their means of dispersing are numerous. Some plants disperse through wind. Other plants rely on birds and mutualistic relationships. Thus, plant dispersal is both site and species dependent.
Key Findings
In most cases, the creation of corridors helps facilitate the dispersal of plants, creating benefits above and beyond that which would be experienced by simply adding the same amount of land.
In certain scenarios, building connected corridors did not benefit plant dispersal, suggesting
that plant dispersal benefits can be site and species specific, depending on both plant and
mutualistic animal (i.e. birds) that spread seeds.
In cases where benefits of a corridor were not found, the creation of a “step ladder” was found to be more effective.
Conclusions and Recommendations
The creation of habitat corridors has been largely effective in promoting the dispersal of native plants. That being said, conservation is locally dependent, and critical adjustments to corridor design must be made depending on targeted species and forest type.
When designing corridors with plants that live in open landscapes, it is beneficial to attempt to align corridors with prevailing wind patterns in order to facilitate wind-dispersal. When designing corridors that are meant to benefit plants, whose seeds are dispersed by birds, it is critical to remain cognizant of edge effects.
The dispersal of plants is dependent on the health of butterflies, bees, and birds and, as such, cannot be studied or pursued in isolation.
Click here to read the full analysis.
by Siqi Liang, Duke University
This analysis focused on quantifying the impacts of corridors on species richness and abundance were summarized.
A total of six studies from across the world were summarized in this document. One of them is based on urban gardens, one of them was based on indoor moss micro-ecosystem, and the rest four were based on natural corridors.
Key Findings
All the six studies provide empirical support that creating corridors or maintain existing corridors have positive influence on maintaining species richness or abundance. The three studies done in Brazil Amazon also provide insights about the impacts of corridors on different taxa and what factors influence the effect of corridors. The two main influence factors mentioned are the width of corridor and the vegetation quality of the corridors.
Corridors can help habitat patches contain relatively higher species richness, abundance, and slow down the rate of local extinction.
The width and the vegetation composition of the corridors are important to the communication function of the corridors.
In a long corridor, the end near to the “mainland” has more “mainland” species and high abundance than the far end.
The response of different species taxa to the same corridors can be different.
All the six studies provide empirical support that creating corridors or maintain existing corridors have positive influence on maintaining species richness or abundance.
The three studies done in Brazil Amazon also provide insights about the impacts of corridors on different taxa and what factors influence the effect of corridors. The two main influence factors mentioned are the width of corridor and the vegetation quality of the corridors.
Corridors can help habitat patches contain relatively higher species richness, abundance, and slow down the rate of local extinction.
The width and the vegetation composition of the corridors are important to the communication function of the corridors.
In a long corridor, the end near to the “mainland” has more “mainland” species and high abundance than the far end.
The response of different species taxa to the same corridors can be different.
Conclusions and Recommendations
The species richness and abundance of the ‘near mainland’ sites seem higher than the “far mainland” sites, and this effect seem different with different taxa. Though fragmented habitats are everywhere, few scientists have done relevant empirical studies about corridors, which makes each relevant study very valuable.
Click here to read the full analysis.
by Jen Marsh, Duke University
This section consists of an in depth look at the effects of corridors on population abundance, which refers to the representation of a species within a certain ecosystem (Farmer 2011). Recent studies show that introduction of corridors to fragmented habitats has a significantly positive effect on population structure. Corridors can be effective for terrestrial species both on the ground and those with flight, as well as marine species.
Key Findings
Ten studies evaluated the effects of implementing green corridors on the biodiversity and abundance of species.
Five studies evaluated major motorways and highways where species are found to have very high mortality rates.
6 studies evaluated dry grassland or forested areas. Many studies are successful in these areas as it is easier to track and observe species using the corridors.
1 study evaluated a marine environment. Marine environments are particularly difficult for measuring progress as well as making determinations to design and built corridors.
Conclusions and Recommendations
Overall, using corridors is a successful method to increase population abundance in mammals, amphibians, reptiles, and birds. Corridors do not affect all species equally, for example, frog mortality was not significantly decreased when corridors were placed underneath a highway.
However, small and large mammals see a positive effect from corridors, as well as butterflies. Based on these studies it is difficult to determine which type of habitat is most successful, but certain methods of implementation proved more successful than others.
Measures which found success were often those with careful construction of corridors that were well fit to the specific species under observation.
Additionally, maintaining vegetation well suited for the certain species is crucial for success of the animals moving through the corridor. A more difficult area to study is marine environments, as many factors are at play there; understanding high priority and cohesiveness of marine animals and environments is crucial to making corridors underwater.
Additionally, land use in urban areas presented a different problem than did more open, agricultural areas. Urban green space is very limited, so it is important to have a good grasp on where to make linkages between them. One study suggested that using vacant land and network connectivity in high priority areas was most successful.
Human infrastructure should be considered in conservation planning for wildlife. Corridor creation can be prohibitively expensive but, when done strategically, significant gains can be made for wildlife in a cost efficient manner (Machtans et al, 1996; Poplar Jeffers et al, 2009).
When examining whether or not a corridor is successful one could use the 6-step checklist, as well as methods of measuring minimum permeability to see where corridors are needed most in an area of migration.
The main takeaway from this analysis of various studies is that corridors do help improve species abundance, richness, gene diversity and population density, if design and implementation measures are done thoughtfully for each species.
Click here to read the full analysis.
by Longyi Yang, Duke University
The isolation problem has become a serious topic as the human activity increases in wildlife habitats, and corridor can conserve the connected and viable populations of species (Schultz 1998, Schultz and Crone 2005), thus the effectiveness of planted corridor is a crucial concern.
Yet many corridor researches are lack of collaborative movement dataof animals (Rosenberg et al. 1997), the difficulty of collecting movement data also lead to an absence of corridor effectiveness evaluation (Tewksbury et al. 2002).This summary collectssome researches on planted corridors in different areas, and focuses on the results of corridor construction.
Conclusions and Recommendations
Overall, planted corridors have a positive effect on increasing the connectivity between habitats, as given researches indicated. The proportion of studied subject’s movements within corridor increases(Jerimiah et al. 2004, Shepherd et al. 2006).
The effect of planted corridors diminishes as the body size of mammal increases, (Paetkau et al. 2009, Saura et al. 2013). The predator ‘s presence will have significant negative effect on corridor’s connectivity for a specific specie (Brinkerhoffet al. 2005), while the targeted specie’s prey’s abundance will have positive effects on the connectivity (Shepherd et al. 2006).
The elevation also has significant effect on the effectiveness of corridor (Shepherd et al. 2006, Wang et al. 2014), the slope of correlation depends on the target specie’s and its prey’s preference.
The planted corridor’s effectiveness is commonly more obvious after corridor is built (Shepherd et al. 2006,Paetkauet al. 2009), and decreases as the corridor is colonized (Paetkau et al. 2009).
The human activity has significant negative effect on planted corridor, as the connectivity drops when there is road or human residence nearby (Shepherd et al. 2006, Wang et al. 2014).
The recommendation for selecting potential planted corridor is to choose corridor at appropriate elevation and slope for target species and preys, with relatively low predator density, far from human residence and roads, and close to alternative wildlife crossing structures.
The biodiversity of corridor plants is also need to be consider, all the studied corridors used various native plant species to ensure the quality of corridors.
Click here to read the full analysis.
Wildlife Corridors: Empirical Evidence
An unavoidable consequence of a small population is that it becomes inbred. Inbred populations quickly show horrific problems, physical abnormalities, and increasing infertility.
Therefore, one important question is: do corridors allow for previously isolated populations to interbreed?
Although species can be seen moving through a wildlife corridor, they may not necessarily interbreed. Therefore, verifying that corridors are effective at genetic rescues requires DNA analysis.
Another important question is: do wildlife corridors help populations rebound?
The answer to this question may complex – while some species may rebound, other may not. Finding correlations between population abundance and habitat quality through controlled experiments can provide a framework for designing effective corridors.
Here, we share insights into these questions from published literature on genetic analysis and controlled experiments.
by Victoria Grant, Duke University
To ensure successful conservation practices, genetic diversity must be protected in wild populations. Genetic techniques can be used as a potential tool to monitor wildlife corridors to ensure genetic diversity is being maintained.
Additionally, genetic tools can be applied to assist with monitoring the effectiveness of the corridor. Genetic analysis gives insight into information that cannot be gathered through standard observation methods, like what individuals are crossing and what is their reproductive success, which can be important information when studying the success of a corridor or when considering where to develop new corridors (Frankham, 2015).
Key Findings
Genetic technologies allow for more non-invasive comprehensive analysis of corridors effectiveness.
Genetic analysis provides conservationists with empirical data of wildlife using corridors while providing census information on the individuals crossing, reproductive success, and genetic admixture.
Corridors facilitate reproductive success by increasing males’ access to females.
With genetic information, conservationists can better target areas in need of corridors to prevent inbreeding depression. Furthermore, genetics information reveals the change in genetic diversity of wildlife before corridors and after their introduction to monitor the effectiveness of the corridor.
Conclusions and Recommendations
Corridors play a crucial role in reducing the harm caused by human created barriers on wildlife fragmentation and inbreeding depression by permitting movement of animals to allow gene flow (Corlatti, 2009). To obtain a holistic view of how wildlife is interacting with corridors or how corridors reducing population decline, genetic tools should be applied to monitoring techniques.
Genetic analysis gives more comprehensive information about the effectiveness of corridors that can not be obtained with other monitoring methods. With the use of genetic technologies, conservationists can determine the effect of corridors on sex dispersal, reproductive success, and genetic diversity of populations surround the corridor.
Click here to read the full analysis.
Six of the ten studies found that corridors increase gene flow and genetic variation between fragmented populations.
Key Findings
Ten studies assessed the impacts of man-made habitat corridors on genetic variation.
Two of the ten studies found that corridors are effective for maintaining gene flow between fragmented populations and preventing genetic isolation.
Two of the ten studies found that genetic analysis is not a sufficient way to assess corridor effectiveness because of a lack of data and excess of confounding factors.
Four of the ten studies followed before-and-after designs and three of the four concluded that corridors increase gene flow and genetic variation between fragmented populations.
Conclusions and Recommendations
Conclusions from the above papers overwhelmingly suggest that habitat corridors are an effective means of maintaining or increasing gene flow and genetic variation between fragmented populations.
While two studies concluded that genetic analysis is not an effective means of assessing corridor success overall, they were hindered by inadequate population sizes to provide statistical significance or an abundance of confounding factors.
However, three controlled before-and-after studies showed that corridors caused a statistically significant increase in gene flow and genetic variation. These before-and-after studies were supported by three others indicating that corridors increase genetic variation and two others indicating that corridors effectively maintain gene flow and genetic variation. All but one of the studies supporting the use of corridors analyzed their use by mammals, suggesting that corridors may be most useful in facilitating gene flow for mammalian species.
Overall, this review indicates that the use of man-made habitat corridors is effective for maintaining or increasing gene flow and genetic variation between fragmented populations.
Click here to read the full analysis.
Ecology studies conducted at large, landscape scale generally supported this theory by identifying positive correlation between habitat connectivity and population abundance (Beier & Noss, 1998; Pardini et al., 2005).
The effects of specific corridors on the population of specific species, however, deserves a closer examination, since corridors’ effects on population may be mediated by factors like edge effect, habitat quality, and species-specific behavioral traits (La Polla & Barrett, 1993; De Lima & Gascon, 1999; Weldon, 2006).
These topics have been studied by ecologists over a wide range of taxa both through controlling “corridor treatments” on experimental sites and by monitoring outcomes of restored or remnant corridors in real world landscapes.
Key Findings
Positive effects of corridor connection on population abundance have been observed through controlled studies on experimental landscapes.
Researchers believe that corridors can increase population abundance by increasing dispersal rates, reducing inbreeding, increasing home range available, and directing species movements.
On real world landscapes, the effects of corridors in providing connectivity are less clear than their effects in providing extra habitat areas.
Corridors can have a negative effect on species survival by increasing edge effect and risk of predation.
Conclusions and Recommendations
Evidence from the case studies showed that the effects of corridors on wildlife abundance can be more complicated than suggested by theories.
The real-world cases showed that positive effects of corridors on wildlife abundance were mainly associated with increased habitats created by the corridors themselves, as the increases were mostly observed inside the corridor rather than on the ends (De Lima & Gascon, 1999; Harrison et al., 2003; Jansen, 2005).
In the Williams et al. (2012) study, corridors were found to have no effect on the colonization of the patches they connect. From those studies, the effects of corridors in improving connectivity could not be easily distinguished from the effects in increasing habitat area (Fahrig, 1997).
Another possible reason for the lack of evidence for the effects of connectivity might be that population abundance changes in real landscapes can take longer time to manifest and require harder efforts to monitor. The Weldon (2006) study found the population of Indigo Bunting to be negatively affected by corridors due to increased nest predation.
This finding warns us that the effects of corridors in improving the chance of survival for species cannot be taken as granted. By changing the spatial configuration of the landscape, corridors will interact with the species behaviors and inter-specific interactions to create complicated and unexpected outcomes for different species.
Click here to read the full analysis.
by Alex Bennett , Duke University
The determination of connectivity impacts on species richness have fundamental importance to basic landscape ecology research, applied conservation, landscape-level planning and management, as well as resource allocation to best preserve biodiversity (Brudvig, 2016).The below supporting evidence provides studies which experimentally test, document through observation and presence-absence surveys, or model the consequences of habitat corridors on species richness.
Key Findings
One field-experiment study in the United Kingdom found microecosystems with connected corridors lost an average of 24.5% less species richness then microecosystems with disconnected islands.
One population viability modeling study in Australia found the expected minimum population size of endangered Mountain Pygmy-possum of a reconnected population remained 15% lower than that of a comparable undivided population, displaying the negative impact of habitat fragmentation on species richness.
Three remote camera trap studies in Canada, the United States, and China found small, medium, and large-sized terrestrial mammals utilized anthropogenic corridors and enhanced overall species richness, particularly for predator species in California.
One study in Australia examined patterns of activity and species richness of microbat assemblages using a highway overpass and found that the overpass may facilitate permeability of a major road, suggesting potential for enhancing habitat connectivity and species richness.
Three studies in Australia found avian species utilized vegetated corridors to cross roads and connect rainforest patches, which lead to statistically significant differences in species richness
One study in France found metacommunities of staphylinids display greater species richness in domestic gardens connected by green corridors than in disconnected gardens.
Conclusions and Recommendations
Based on the above literature review, there is evidence that constructed wildlife corridors in fragmented habitats maintain greater species richness than in disconnected fragmented habitats and may slow the process of extinction following fragmentation. However, the corridors do not appear to benefit all species equally.
Microecosystems of moss and certain arthropods experience less species loss with constructed corridors to connect habitat fragments. Many terrestrial mammal populations appear to experience increased species richness when they utilize anthropogenic corridors. Interestingly, the benefits of habitat connectivity through corridors extends to flying mammals (bats) as well as avian species. This literature review captures studies from across the globe; there is no clear relationship between location and species richness impacts due to corridors.
Although the literature supports the theoretical benefits of corridors on species richness, these studies were all conducted on a relatively small spatial scale. Although some studies spanned years, they largely focused on one ecosystem or even a single wildlife corridor. Further research is needed on the effects of habitat corridors on a larger spatial scale and the effects of competing ecological processes.
Additionally, the effects of corridors must be verified on the population-scale in order to fully comprehend the impacts on population extinction and viability. Further, many of the studies conduct analysis based on presence-absence surveys so the detection probabilities of fauna must be considered. Further research is also needed on the utilization of wildlife corridors based on habitat availability and fragmentation differences. Lastly, the construction of anthropogenic corridors are resource-intensive and can also be disruptive to both humans and wildlife.
In order to best rescue species from extinction, maintaining species richness is key. Therefore, establishing short, vegetated corridors may provide the best results in maintaining and increasing species richness. Vegetated and replanted corridors showed clear use by both terrestrial and avian species. However, potential corridors must be evaluated systematically to determine if they will have a net positive effective on species richness.
Click here to read the full analysis.
Wildlife Corridors: Potential Risks
Not every species dispersing through a wildlife corridor may be intended. In addition to species targeted for rescue, invasive species, predators, and even diseases can also move through corridors.
Awareness of these unintended consequences is an important part of corridor design. Anticipating the conditions under which threats to ecosystems can spread through corridors, or predators can opportunistically forage informs effective corridor design.
Here we share useful insights into some of these considerations to avoid corridors becoming ecological traps or pathological pathways.
Despite their popularity, corridors may have potential costs, both ecological and economic (Simberloff & Cox, 1987). Simberloff (1992) noted the weak theoretical and empirical basis for many corridors, and his previous papers identified the failings of the current literature in considering the potential negative consequences of biological corridors (Simberloff & Cox, 1987).
While empirical data on corridors tends to be lacking, relying more heavily on observational data, the empirical studies that do exist have either been conducted on a small scale or ignored confounding effects (Tewksbury et al., 2002). One major potential consequence of corridors is their possible role in increasing the dispersal rates of invasive species.
Key Findings
Two studies at the Savannah River Site Corridor in South Carolina and literature review including 17 papers that were located at the same study site, six of which focused on invasion, found that the benefits of biological corridors outweigh the potential negative effect of increasing invasion by exotic species.
A literature review assessing the various negative effects of corridors as well as an empirical study conducted at the Savannah River Site found that edge effects, not invasion, are of more concern when building corridors.
A study on invasive cane toads in Australia found that a simple way to prevent corridors being used for invasion is to leave areas more vegetated.
Additionally, a study focusing on hedgerows as possible modes for invasion found that they instead have the potential to block invasion if constructed properly.
Conclusions and Recommendations
While the literature surrounding the effect of corridors on invasive species is lacking, the few studies that do exist tend to share the same view that the benefits of corridors for conservation largely outweigh the potential negative effects of invasion.
Although corridors may slightly increase the level of invasion for certain species, it is not enough to be considered a major concern as these species have the potential to invade with or without the presence of a corridor.
Instead, the greater and more supported concern over negative corridor effects lies in the creation of edges and their accompanying effects. It is critical to use our substantial knowledge of the behavior of potentially invasive species when building corridors as the dispersal behavior of some species may be better-suited to invasion than others.
Additionally, this knowledge can help the construction of corridor elements, like fences and hedgerows, that can mitigate potential invasions. Going forward, more empirical and large-scale studies are required in order to more completely support the statement that corridors do not support the spread of non-native species.
Click here to read the full analysis.
by Ashley Marko, Duke University
Fragmented ecosystems benefit from connectivity, but connectivity helps facilitate the spread of all wildlife, including invasive alien species. The supporting evidence highlights the detrimental ecosystem effects of invasive species and how corridors can contribute to this conservation issue, leading some researchers to question if conservation corridors have as much ecological value as previously thought, or if it’s simply a stab in the dark at protecting our vulnerable ecosystems (Mann, 1995).
Key Findings
These studies highlighted that roads and highways are often pre-existing corridors for many species, and since invasive species thrive in unstable environments along the edges of habitat patches, they are typically going to be found at the entrances of conservation corridors as well as along roads.
Studies that looked at untraditional corridors (roads, drainage, dams etc.) aimed to shed light on the ability for invasive populations to spread quickly in many environments, and that urban areas were not necessarily barriers for their dispersal. .
Studies that took into account “prey traps” were utilized to stress that the social structure of ecosystems are extremely important before constructing a corridor. Many invasive predators were able to utilize the corridors as a feeding hub, which decreased the native usage of the corridors.
Two studies were done at the same location at Savannah River Site in South Carolina, and had conflicting results. Where one study found species richness lowered in the connected habitats and the corridors appeared to facilitate the spread of invasive fire ants, another found no increase of invasive species in the connected habitats.
Conclusions and Recommendations
Conservation corridors have many benefits, but the cost should not be ignored. The two leading threats to biodiversity are habitat fragmentation and invasive species, and their solutions are contradictory.
Invasive species by nature reproduce and grow quickly, as well as thrive in a variety of environments, making it easy for their populations to spread. Knowing this, it is easy to understand that invasive species will typically spread over conservation corridors much faster than their native counterparts, meaning that the solution to habitat fragmentation is just the opposite for invasive species.
Invasive predators have also been found to utilize conservation corridors to their advantage, by funneling (typically) native prey into their mouths. This does not mean that conservation corridors should not be implemented, but more thought should be given to them and they are not a band-aid to conservation issues, as many people treat them.
The social behavior of species and the social structure of a habitat should be considered before building a conservation corridor. Vegetation should be installed throughout the corridor to give native prey shelter and security. Non-native invasive plant species should be removed from entrances to corridors, and this should be maintained.
Non-native invasive plant species should be removed from entrances to corridors, and this should be maintained. Non-native animal species should also be monitored in and around corridors and perhaps completely removed. When considering underpasses, corridors should be varying sizes in order for a variety of different fauna can cross effectively and comfortably.
More research should be put into these considerations, as well as, what some articles mentioned, if the scent of a predator near a corridor could influence a prey’s behavior towards the corridor.
Click here to read the full analysis.
by Elle Xu, Duke University
The effectiveness of corridors and the interaction between wildlife and corridors has been evaluated on multiple aspects, and the species interaction and community dynamic in fragmented landscapes with corridors are crucial to understand the conservation impacts of corridors. The effects of corridors to promote movement and to alter population genetics have been evaluated rigorously in recent years.
Other than animal dispersal, we look at other animal behaviors in response to conservation corridors in a fragmented landscape, such as foraging and roosting. A study in a fragmented urban area northwest of Los Angeles, California found that bobcats and coyotes used natural corridors and linear fragmented areas of vegetation, as habitat and, less often, for travels (Tigas, Van Vuren, and Sauvajot, 2002).
Key Findings
Two before–and–after replicated studies in South Carolina found that foraging of invertebrates was inhibited by corridors, while foraging of rodents and birds was enhanced by corridors, and Old–field mice and Cotton mice increased foraging activities on connected patches, which was also significantly positively correlated with predator presence.
A replicate site comparison study in South Carolina found that Indigo Bunting nest success was reduced on connected patches because corridors encourage predator foraging.
Two replicated, site comparison studies in South California found that Seminole bats and evening bats roost in forested corridors more than logged stands, or mature forests.
Conclusions and Recommendations
From the reviewed evidence, corridors demonstrate significant influence on foraging and roosting behavior of many species including invertebrates, small mammals, avians, and other predators. Corridors affect foraging behaviors in different ways within a given trophic level.
The foraging behavior of invertebrates were mitigated with forested corridors, while predators of edge-specialists, small mammals such as rodents, and birds were found to be more active in foraging along corridors.
Corridors not only support traveling between isolated patches, but also provide habitats for small mammals like bats, and avians like the Indigo Bunting to roost or nest, especially on edges. Corridor edges may encourage small mammal activity and occupancy rates, and also appear to be an important component for commuting and foraging and should be maintained across the landscape. Thus, features associated with edges can be enhanced; for instance, increasing effective overstory height to provide better habitat services.
Also, wide corridors with smaller edge-area ratio are preferred for stabilizing ecosystem dynamics. Corridors may also function as ecological traps for some birds as edge effects can be magnified on predator abundance and efficiency by not only providing more suitable habitats but also connectivity between foraging habitats for predators (Bider, 1968). Thus, thorough evaluation of the impact of corridors on species interaction is essential for using corridors as a conservation tactic.
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Wildlife Corridors: Road Underpasses and Overpasses
With new roads and highways comes new challenges for conservation. Infrastructure creates physical barriers to wildlife movement, isolating populations and possibly leading to their extirpation. In addition, vehicle collisions increase wildlife injuries and fatalities. There are a small, but an increasing number of examples where managers are now creating corridors across roads.
The question is: are road underpasses and overpasses effective at mitigating negative impacts on wildlife?
Here we share insights into highway design considerations as they relate to wildlife movement and protection.
by Ethan Ready, Duke University
Road border fences prevent animal mortality, but can disrupt habitat connectivity especially without adequate overpasses or underpasses. In fact, a barrier wall-culvert system can reduce animal mortality by up to 93%.
In addition, overpass/underpass corridors can mitigate the population disturbance of building new roads. Furthermore, driver-oriented measures like speed reduction and warning signs can reduce animal mortality impacts of roads.
Key Findings
One before-and-after study in Florida found that a barrier wall-culvert system on a road reduced total animal mortality by 65% and by 93.5% for animal mortality excluding tree frogs.
Another before-and-after Florida study found that a drift fence installation in conjunction with an existing culvert reduced turtle mortality from 11.9/km/day to 0.09/km/day.
One study in California showed that barrier fences along roads can reduce desert tortoise mortality, but can increase fragmentation if the animals fail to use culverts or other means of connectivity.
One study in Australia found that construction of a corridor leading to two tunnels allowed male pygmy possums to disperse to female breeding areas, after which the population structure and survival rate changed to match that of the undisturbed study area.
One 24 year study in the Netherlands showed tunnels mitigated the fragmentation and mortality from roads, as badger risk of mortality stayed the same despite increased road construction and road use.
One study in Tasmania suggested that road improvement led to extirpation of local quoll population and reduction by 50% of local Tasmanian devil population. Mitigation measures such as slowing driver speeds, increased driver awareness, wildlife reflectors, and pipes and ramps to encourage escape allowed the quoll population to rebound to 50% of former levels and allowed Tasmanian devil population to increase.
Conclusions and Recommendations
If a road is built, or road traffic is increased, through an area with wildlife, there will be negative effects on population abundance through mortality and habitat fragmentation.
Culverts and overpasses can be used to allow safe animal passage across a road, and barrier walls or fences can be used to prevent dangerous animal road crossings, mitigating the effects of roads. Barrier fences without adequate corridors, however, will result in population fragmentation. In addition, driver-oriented measures to slow driver speed and increase awareness can prevent wildlife mortality.
While construction of roads generally have negative effects on population abundance, they can be mitigated through culverts, overpasses, barrier fences, and reducing driver speeds.
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by Lannette Rangel, Duke University
Key Findings
Wildlife corridors appear to direct animal movements, and wildlife species move more between connected than unconnected habitat patches.
Wildlife crossings appear effective at assisting animal dispersal, as target species are largely recorded using crossings. It may be that they’re assisting the most with aiding the movement of species that are already the most abundant in study regions.
Forest birds use corridors to move more frequently than clear cuts, and corridors allow birds to maintain their movements at rates similar to those observed in undisturbed areas.
Ringlet butterflies move between woodland clearings via grassy tracks, as they act as conduits between habitat patches. Connectivity would be significantly lower without grassy tracks.
Culverts in mountainous regions pose a significant barrier to movement and passage of local fish species. The most common, cost effective solution to fish passability problems
in steep terrain will be building bridges or open bottom arch crossings in strategically selected locations.
Lemur species use overpass “lemur bridge” crossings in areas of significant habitat disturbance, although it takes some time for them to fully utilize the crossings.
Mammalian nest predators are more abundant in greenways with wider trails and narrow forest corridors surrounded by mature, streamside forests.
Small mammals use wildlife crossings at ski resorts, and they’re likely to aid their movement. These crossings can even become part of mammals’ home range with time.
Constructing tunnels for cars may be the most effective infrastructure to aid the movement of Giant Pandas in central China.
The best possible locations for wildlife corridors to aid animal dispersal across highways are far from other existing crossing structures and between large forested areas.
Conclusions and Recommendations
A corridor that aids one species may even impede another’s movement. Thus, corridors may need to be designed to target specific species. (Sutcliffe & Thomas, 1996). Furthermore, target species may take up to several years to start using new crossing structures (Mass et al, 2011). Seemingly simple solutions, such as limiting high density development near greenways, without further habitat management may have little effect on the movement of wildlife species.
Overall, wildlife corridors appear effective at assisting with animal dispersal, and they can direct animal movements. However, wildlife corridors do not affect all wildlife species in the same ways, and wildlife response to corridors is likely to be species specific.
Ultimately, natural resource managers must aim to balance habitats to promote multiple wildlife management objectives. Threatened small mammal species found in disturbed alpine environments make use of wildlife crossings.
However, without additional conservation measures, species are not likely to persist (Sato and Schroder 2017). Ultimately, creating wildlife corridors is not enough. Multiple, complementary strategies must be employed together to offset development disturbances to wildlife.
Human infrastructure should be considered in conservation planning for wildlife. Corridor creation can be prohibitively expensive but, when done strategically, significant gains can be made for wildlife in a cost efficient manner (Machtans et al, 1996; Poplar Jeffers et al, 2009).
For instance, integrating corridor creation into timber harvesting or road development plans can significantly reduce costs and planning time. But, if corridor planning is not based on sound, quantitative information about species-environment relationships, there is little practical value in it (Wang et al 2014). Since funding for wildlife conservation is limited, it’s essential to establish the relative contribution each proposed corridor will have on aiding animal dispersal and maintaining habitat connectivity.
A number of future studies could further our knowledge on the effectiveness of wildlife corridors in facilitating animal dispersal. For one, there’s a need for more studies that monitor the presence of targeted species before and after wildlife crossings are built to account for pre-disturbance populations, and to see if population changes and dispersal patterns are in fact due the new infrastructure, or other factors. In this era of unprecedented climate change, more research needs to be done on how crossings can aid animal dispersal as species migrate into new environments. Studies that examine the nuances of crossing design could prove useful to see which structural elements are the most beneficial to wildlife.
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by Kaitlin Saxton, Duke University
As urbanization and human expansion increases, wildlife are facing habitat destruction and fragmentation. Roads cutting through the landscape decrease habitat connectivity, creating a barrier effect that restricts animal movement resulting in isolated populations that are less stable and more vulnerable to extinction (Forman and Alexander, 1998).
Additionally, roads are a cause of mortality for many species, particularly those that are large, rare, or who regularly come into contact with them which can be detrimental to their conservation status (Bennett, 1991).
One solution to this issue is to perforate the barrier by constructing underpasses that provide safe passage for animals without disrupting traffic, but the degree to which these successfully mitigate car related deaths and facilitate animal movement/dispersal depends largely on location and design.
Key Findings
Underpasses have the potential to significantly decrease wildlife mortality and thereby extend animal movement/dispersal if designed correctly.
Proximity to human activity may be a key deterrent in underpass usage by wildlife.
Strategic placement of natural habitat elements may encourage underpass use.
Underpasses may accommodate many species of different sizes and types of movement.
While there may be a target species, other species who are likely to also use the underpass should be taken into account.
Underpasses must be strategically designed to bar accessibility to dangerous alternative crossing options.
Underpasses require regular maintenance to make them a viable long-term solution.
Wildlife usage may not be immediate.
Conclusions and Recommendations
It is important to design a corridor with the target species in mind by considering things like habitat preference, movement style, and behavior to create an underpass that they are willing to use.
However, it is also necessary to take into account that what appeals to one species may discourage another and could result in an uneven distribution of species across the landscape and potentially lead to a cascade of problematic ecological effects.
Attention should also be given to additional measures such as fencing and other exclusion tools to discourage accessibility to unsafe alternative routes and encourage wildlife to seek and utilize the underpass. Once an underpass has been established, regular monitoring and upkeep is necessary to understand how it is being used and where it could be improved to be more effective.
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by Cameron Hawkins , Duke University
Five studies looked at underpasses use by a variety of animal species. Overall, most species used the underpass, but some species like bobcats, coyotes, and deer were seen to use them most often.
Key Findings
The impact on wildlife usage of underpasses, overpasses and culverts in areas with high human population depends on the animal.
One study showed deer to more successfully cross overpasses.
Arboreal and land-bridge overpasses were studied in two articles and are successful in connecting arboreal species to fragmented pieces of land while also protecting them from predators.
Conclusions and Recommendations
The implantation of underpasses, overpasses, culverts, and glide poles do not treat all species equally and these are not overnight solutions.
When continuing to study these methods of connection, it is important to work enough time into the study to allow for the wildlife to warm up to the new crossing structures.
The study that looked at glide poles concluded that vegetation on the land-bridge should be installed along with the glide poles, but a clear path must be ensured. Moving forward, it is recommended to look at other species of gliding mammals besides small petaurid marsupial gliders (Taylor & Goldingay, 2011).
When considering culverts, it is important to understand the animals that will be using the connector to ensure the dimensions are large enough to accommodate the targeted species. These dimensions were seen to significantly impact the use by deer. It is also recommended to install animal proof fencing to encourage passage of these wildlife species (Ng, Dole, Sauvajot, Riley, & Valone, 2004).
Overall, these structures have been proven to be successful in facilitating wildlife attempting to cross roads and are important in regional conservation strategies. A recommendation moving forward is to consider alternate designs of these crossing structures to see if they are more effective than the existing designs.
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by Sam Lee, Duke University
As the world continues to develop, more roads and highways are constructed to facilitate easy access to developing areas. While roads are essential to economic development and infrastructure expansion (Malkoc 2019), they can pose detrimental consequences to the wildlife that inhabit the area in which it is built.
Governmental agencies, road authorities, and environmental advocates have recently become interested in designing and constructing various structures that will allow the safe passage of animals under or over roads. These structures are usually fauna underpasses and overpasses and have increasingly been incorporated into plans to build new roads or upgrade old roads (Mata et al. 2008).
Key Findings
While flying animals have previously been overlooked in overpass effectiveness studies, one study focusing on bats and two studies focusing on birds have revealed that species richness of bats and birds differ between overpasses and surrounding forests. Some species were not observed crossing the open road and only crossed using the overpass.
One study focusing on birds found that larger birds (mean weight of 110 grams) more commonly crossed the open road, but smaller birds (mean weight 15 grams) were more likely to cross using the overpass. Species that are known to inhibit the forest interior were also detected using the overpass.
One study in Australia found that rope bridges effectively act as overpasses for strictly arboreal species. However, when the use of the rope overpasses was compared to the use of a nearby natural canopy crossing, it was determined that the natural canopy was preferred to the man-made overpass.
In Queensland, Australia, a one-lane road was upgraded into a two-lane road with four underpasses. A study found that the overall roadkill declined, but a greater number of rainforest bird species were killed on the road in the year following the upgrade.
Two studies, one located in Poland and one in Australia, have found that invasive and non-native species are often the first to use an overpass or underpass and are commonly found on the crossing structure thereafter. These species included the European hare Lepus europaeus, the house dog Canis lupus familiaris, and the house cat Felis catus.
One study in Banff National Park determined that structural attributes of overpasses and underpasses were correlated with the use by different species. Grizzly bears, wolves, and elk favored tall, wide, and short crossing structures, while black bears and pumas preferred more constricted structures.
Conclusions and Recommendations
Overall, overpasses and underpasses appear to be effectively used by a large proportion of the species present in a habitat fragmented by a road. The inclusion of rope bridges should be considered when designing a new crossing structure, as this allows arboreal species that would not cross over the ground surface of the overpass or underpass to cross the road (Goosem et al. 2005).
Before a new crossing structure is constructed, extensive studies should be done on the species composition of the surrounding forests, so that any changes in species richness caused by the implementation of the crossing structure can be calculated.
When evaluating the effectiveness of an overpass or underpass, it is important not to exclude flying species such as birds and bats, as their tendency to cross a road can be impacted by a crossing structure (Pell 2016, McGregor et al. 2017).
Invasive and non-native species make use of the crossing structures, so these species need to be closely monitored when a new overpass or underpass is constructed (Krauze-Gryz & Gryz 2016, Abson et al. 2003).
If multiple crossing structures are being built for a road, then varying the structural attributes of each overpass or underpass would allow for a greater number of species to cross the road, as species have different preferences for the structure of the overpass or underpass (Clevenger & Waltho 2004).
However, if only one crossing structure is being constructed, then an overpass should be constructed if financially feasible because a greater number of species were observed crossing an overpass than an underpass on the same road (McGregor 2016).
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10 studies investigating the impact of human-constructed habitat corridors on wildlife are summarized: 5 include underpasses, 3 include overpasses, and 3 include planted stands and reforested segments.
Key Findings
Each study focuses primarily on 1-3 target species, including large-medium sized mammals, small mammals, and birds.
4 studies included before and after construction comparisons
Studies span the globe, with 3 in Canada, 2 in North America, 2 in Europe, 2 in South America, and 1 in Australia
9 studies clearly found some improvement in habitat connectivity and/or positive influence on movement patterns for target species
Conclusions and Recommendations
These studies provide a wide breadth of information on how various types of corridors, including underpasses, overpasses, and reforested areas, can serve as effective and useful wildlife passages for a range of species.
The relative efficacy of corridor measures depends heavily on
the target species and primary aim, but several general recommendations can be made concerning optimal corridor solutions.
Underpass construction has potential to be effective in maintaining connectivity and reducing vehicle collisions, and should focus on abundance and variation in size, shape, and environmental conditions to account for the widest variety of species.
Overpasses are overall a less effective measure in maintaining population movement and should be considered secondarily to other corridors, but may provide some use after a specified habituation period. Planted and reforested passages at targeted, high priority locations are useful as travel corridors and may increase habitat and population connectivity for some species.
Overall, more studies must be conducted, especially those comparing wildlife movement and connectivity before and after construction of corridors, to truly understand the relative capacity and success of various corridor types.
Future monitoring should include a combination of camera traps, infrared sensors, track pads, snow tracking, animal trapping, genetic analyses, and computer modelling depending on the goal of the study or surveillance program.
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Wildlife Corridors and Local Communities
The impact of conservation practices on local communities is a critical area of study. It illuminates both challenges and opportunities that must be taken into consideration in order to ensure long-term efficacy of proposed solutions.
by Chiara Klein, Duke University
The articles analyzed below highlight some of the most likely drawbacks and challenges of wildlife corridors as they affect local communities.
These include increased potential for human-wildlife conflict, the inherent tension of outside conservation organizations working in local areas, and community livelihoods being negatively impacted by conservation-based restrictions.
Key Findings
Five studies assessed the impacts of ecological corridors on local communities.
Two of five studies found that when communities are involved from the initial stages, corridor projects are more likely to be successful.
All five studies determined that corridor and conservation projects must have some tangible economic benefit to the surrounding communities in order to garner local support.
Four of the five studies actively involve local communities in corridor establishment or restoration in a way that supports community members having autonomy in resource management and use.
Conclusions and Recommendations
Based on analysis of the above studies, I offer several recommendations:
1.) Local communities should be involved at the ground level when planning a wildlife corridor. The human impacts of a corridor will be far-reaching and community buy-in is best achieved when the decision-making process is participatory and transparent.
2.) Corridors must have some positive economic benefit to the local community. Informed effort should be put into understanding the needs and strengths of all potentially impacted communities, in order to assess how community members can be involved, and how the corridor project can serve to sustain or even elevate their quality of life.
3.) Similarly, communities can be integral to maintaining corridor projects, if the benefit to them is clear and outweighs any potential costs. Involving community members in everything from corridor planning, to construction, to maintenance, to monitoring can not only be cost-effective, but can serve to strengthen the impact of the project, as local communities will be more likely to support current and future conservation efforts in the area if they are active participants in the process.
To summarize, wildlife corridor projects are best implemented when the community is involved early on and throughout the duration of the corridor project in ways that directly benefit them. The benefits that have been shown to generate the most motivation are poverty alleviation and increased economic opportunity. An important component of effective involvement of communities in corridor projects is management through outside governance and strong inter-institutional partnerships.
These practices are generally best conducted by conservation organizations or governmental institutions which create partnerships with local communities to establish autonomy within the community. The goal of outside governance should always be to create community self-sufficiency and move towards local ownership of the corridor project. Best practices for establishing autonomy include providing training and workshops, conducting stakeholder meetings, and establishing governing boards on which community interests are well-represented.
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by Monisha Eadala, Duke University
All the studies below focus on benefits of constructed and restored corridors, and each of them note positive effects of the corridors not only on the environment but also on the key communities at stake. In all the studies the community is noted to have benefited from the construction of corridors.
Key Findings
Three individual studies investigated effects of restored and planted corridors across the Terai Arc Landscape of Nepal and India. The monitoring periods differ from one study to the other, making our inferences about TAL corridors more robust. All the three studies reported significant number of animals (especially tigers) using the corridors.
Two studies investigate the effects of corridors constructed over and under highways. Both the studies report appropriate usage of the underpasses/overpasses and overall mitigation in road accidents.
Two studies are based in Queensland, Australia. They mainly investigate the effects of constructed corridors on species such as the kangaroos along with few other incidental species.
One study relies extensively on qualitative data to understand the effects of constructed corridors and their better management.
One study uses only flora (different species of plants and trees) as a measure for success of the corridor project based in Madagascar, while using the same data to understand its long-term potential benefits.
One study assesses canopy bridges installed to facilitate monkey movement across forests in Brazil.
Conclusions and Recommendations
While the three Terai Arc Landscape studies focus on mitigation of human-wildlife conflict, two studies talk about enhancing highway safety and mitigating road–kills. The study based in Madagascar talks in depth about community benefits from gaining basic needs from the ecosystems restored. It also indicates the importance of flora as much as fauna while restoring corridors.
All other studies talk about enhanced environmental awareness and communities’ willingness to participate as they realize their benefits from corridor constructions and management. In two studies, communities are even handed over the projects and take ownership.
Overall, we do see that strategic and well-planned corridors bring community benefits such as better harmony with nature, ecosystem services, social capital, sustainable lifestyles, safety, security and social and environmental awareness. However, as some of the above studies note, there is scope for better management of communities during restorative or any environmental initiatives.
Often, communities are given temporary incentives to help the advancement of projects in the short run. However, these incentives are not sustainable, and the communities’ usually relapse into their old habits and lifestyles. Therefore, it is important to monitor and help communities sustain the transformation that took place post building of such structures.
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by Meksem, Duke University
While there exists a wide body of literature discussing and confirming corridors’ positive effects on biodiversity, species richness, edge effects, and much more, there is a certain lack of information on their effects on ecosystem services that these fragmented habitats provide. Thus, it is important to discuss existing studies, as well as potential for future insights.
There exist large review articles about both the positive and negative effects of wildlife corridors on the ecosystems they are created in. For example, Haddad, et al. (2004) found that wildlife corridors have very limited negative effects from a list of potential harms, and found that of only one potential harm, increased fire intensity, even this one was beneficial in the many ecosystems that rely on fire (Brudvig, et al. 2014). Several other studies have shown that wildlife corridors have a net positive effect, with potential negatives being very limited.
Studies by both Poffenberger (2015) and Paiva, et al. (2014) have shown that wildlife corridors in both India and Brazil are very attractive investments due to their lower cost and high amount of benefits. Because of this, they have been very popular as destinations for carbon offsets. Further, wildlife corridors, by their very nature, must be created. This creation leads to many benefits in and of itself because of the capital that is required for creating them.
Overall, the benefits to ecosystem services seem quite apparent, as wildlife corridors provide such a large amount of benefits to the ecosystems they connect, it is safe to say that the benefits these ecosystems will provide to people will be impacted positively as well. Stronger ecosystems means their services will be protected for a longer amount of time while benefits to species themselves can allow them to perform more services. The rest of this summary will look into specific studies on interventions and some of their benefits, as well as recommendations for future projects.
Key Findings
Carbon markets can be great sources of not only money to help fight deforestation, climate change, and more, but also provide important services in more resilient landscapes, more valuable forests, and job creation in both reforestation efforts and consequent stewardship.
Corridors are especially attractive carbon market options because of their low cost to impact ratio compared to more expensive or less efficient programs.
Corridors can impact the spread of intended and unintended organisms and ecological disturbances. In one case, fires can be spread easier due to both more understory vegetation and connected larger forest fragments.
Riparian buffers are fantastic corridor options because they prevent erosion and runoff, absorb fertilizers and pesticides, and provide aesthetic beauty in monotonous agricultural land.
In some cases, however, fires can be beneficial to the ecosystem rather than detrimental, such as in longleaf pine or shrubland fragments.
Concerns of invasive species spreading easier are also unfounded because they would already be able to proliferate while rarer, less dispersive species are helped much more, preventing native lands from being overrun.
Pollinators being able to move easier through corridors is a fantastic ecosystem service that these projects improve because it allows seeds to be dispersed more widely and also allows more genetic diversity within the plant species.
Riparian buffers are fantastic corridor options because they prevent erosion and runoff, absorb fertilizers and pesticides, and provide aesthetic beauty in monotonous agricultural land.
Planning of these wildlife corridors must take into account the regional impact of their construction in order to have the largest net positive impact.
With respect to monetary services, landscape corridors in urban areas can provide massive amounts of value for undeveloped land, which must be considered when creating urban plans.
Conclusions and Recommendations
Wildlife corridors seem to have a very positive benefit on ecosystem services in many cases. However, it has been shown that some types of corridors offer more, or higher value benefits to humans than other types. While certain projects such as riparian buffers and wetland restoration increase the value of land, save land from erosion, and create more agriculture, others benefit species themselves more directly. Still, it is important to consider that corridors play a vital role in helping to keep ecosystems from disappearing regardless, meaning corridors protect the cultural, spiritual, and medicinal values of all types of ecosystems.
While corridors are generally thought of as being positive, they do have some potentially negative effects, namely on fire or pest connectivity. While pest connectivity is unavoidable typically because of the ease by which many spread, fire connectivity due to increased vegetation and corridors by which to spread is not necessarily an evil. Many ecosystems such as longleaf pine rely heavily on fires and isolated forest patches might not burn enough, leading to catastrophic large scale fires, or might burn out completely due to edge effects. Thus, it is important to consider fire depending on the type of ecosystem one is working with.
Finally, all of these factors must be taken into consideration for planning purposes. Wildlife corridors are one of the most effective conservation practices and thus receive much funding, but that funding must be managed well in order to protect the ecosystems and provide truly sustainable development for adjacent communities. Plans must be able to work on a regional scale and be cost effective, particularly when applied to land or urban planning. A wider body of literature into the actual economic and monetary effects of corridors should be done, considering the value of benefits such as agricultural land protection, cleaner water, and carbon offsets, among others. This can help create better plans to incorporate corridors into existing ecosystems and account for them in future development plans.
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by Alessandria Greco, Duke University
Key Findings
Studies incorporatingreducing emissions from deforestation and forest degradation(REDD+)aim to uplift poverty-stricken communities by repurposingand protecting local land to create corridors, forested areas, riparian zones, etc.thathelpto reduce carbon emissions. The money generated from investors in these projects is reinvested into community projectsthat helpto provide services, resources, educational experiences,and employment opportunitiesto community members. These corridors increase biodiversity, improve natural resources, and help to sequester carbon.
Bodies of water often provide community services including aquaculture, transportation avenues, watersportsetc.,but often suffer from the negative consequences of human impact. Studies conducted on corridors within bodies of water display that restorative structuresimplementedfor marineorganismsimprove marine environments,water quality,and biodiversitywhile stillallowingcommunity servicesand recreational activites.
Experimental studiesconducted in Savannah River Site, South Carolina,demonstrate that corridorspromote interpatch movement and pollination, promoteprescribedunderstory fires that restore woodlands, and do not increase disease spread/prevalence between patches.
Planning of these wildlife corridors must take into account the regional impact of their construction in order to have the largest net positive impact.
With respect to monetary services, landscape corridors in urban areas can provide massive amounts of value for undeveloped land, which must be considered when creating urban plans.
Conclusions and Recommendations
These studies have displayed that corridors positively impact ecosystem services. All four services (community services, regulating services, supporting services, provisioning services)have been provided by human made corridors. Corridors have increased biodiversity, increased carbon sequestration, increased gene flow, increased pollen movement, decreased land erosion, maintained key mutualisms between plants and animals, improved natural resources, improved environmental conditions, etc.
They have also provided jobs, educational experiences, resources, recreational potential, governmental organization, and revenue to local communities. governments should implement corridors to help their local ecosystem and provide services to their people.
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