Habitat Fragmentation Edge Effects: When Having an Edge is Not a Good Thing

August 6, 2018 By Mark Aspelin

The following is a longer version of an article that was published on GreenBiz on 8/13/18: https://www.greenbiz.com/article/when-it-comes-habitat-having-edge-not-good-thing


We usually think it’s great when we have an edge, but that’s certainly not the case when we’re talking about habitat fragmentation edge effects and their impact on biodiversity and wildlife.  In this post we’ll explore the topic of edge effects and how it relates to business and biology.

Habitat destruction is the #1 issue that impacts wildlife and biodiversity today.  This fact shouldn’t come as much of a surprise.  When we think of all the roads, power lines, buildings, clearcutting, and other development activities taking place all over the world, we can quickly get a sense of the widespread reality of this issue.

The World Wildlife Fund estimates that forests cover about 31% of the land area on Earth and, for a variety of reasons, we’re losing about 46,000 to 58,000 square miles of forest each year – roughly equivalent to losing 48 football fields every minute.  In the Amazon alone, we’ve lost about 17% of the forest over the past 50 years, mostly due to forest conversion for cattle ranching.  Habitat destruction is clearly a big issue, and it won’t be going away anytime soon.

The term “habitat destruction” can refer to the complete destruction of a habitat or, more commonly, habitat fragmentation, where a large, continuous area of a habitat is divided into two or more fragments.  The primary culprit behind habitat loss, degradation, and fragmentation is a change in land use, usually in the form of agriculture, logging, mining, and urban or residential development.  

There are three important conditions that characterize habitat fragmentation: smaller habitat, increased edge effects, and increased isolation.  Today, we’ll focus on the second characteristic – edge effects, which refers to the effect of an abrupt transition between two different, adjoining ecological communities.

We can see examples of edge effects occurring naturally all over the place.  These natural edges, such as the forest and meadow pictured below, can lead to greater biodiversity in the area.

However, the edge effects that I’m focusing on in this post are man-made edges that are created in the middle of an existing natural habitat.  From a business perspective, habitats are commonly fragmented by the construction of roads, power lines, and buildings, or the clearing of land for agriculture and forestry.

In the context of habitat fragmentation, edge effects increase the proportion of habitat edges in relation to the total area.  In other words, any given point within the fragment of land is, on average, closer to an edge.  Why does that matter?  Edges matter because they create changes in the species composition for a given chunk of land.  These species-composition changes found at edges are caused by the following conditions:

  • Edges of a forest have microclimatic changes that impact the types of vegetation that can grow there.  These microclimatic changes include more direct sunlight, higher soil temperatures, differences in humidity and depth of humus, and increased wind exposure and snow loads compared with the interior of a forest.  The seeds of some plant species are sensitive to drying out with increased sun and wind, leading to significant differences in the types of vegetation found at a forest edge compared with the forest interior.  To make matters worse, these species alterations extend into the forest interior.  In some tropical rain forests, vegetation changes have been detected as far as nearly 1,500 feet from the edge.  In the scenario where we have a small fragment of a natural habitat or a narrow corridor of land, the microclimatic changes associated with the edges can permeate throughout the entire piece of a habitat.  The result may be a decrease in the presence of rare and sensitive species, while weedy species and generalist predators may thrive.
  • Edges are suitable for some species but unsuitable for others.  If we build a road through a forest, some plant species will thrive with the extra sunlight, and some bird species will enjoy perches next to these open areas where they can pounce on exposed prey.  “Edge species” such as deer and elk like forest edges because they can find food in open areas and take cover in the forest.  Other species of animals will actively shy away from areas of increased sunlight and exposure, moving further into the interior habitat where the characteristics of land remain unchanged.  For example, spotted owls (pictured below) prefer old-growth, mature forests with a lot of canopy and few edges.  When we push these species into the now-smaller interior habitat, we are likely to see increased competition for limited resources.
  • Edge-tolerant species are often generalist predators and exotic species that outcompete native species and habitat specialists.  Examples of edge-loving species include brown-headed cowbirds, crows, raccoons, and opossums.  These species thrive in an edge habitat and act as nest predators and cavity competitors of interior species, which can decrease the populations of forest songbirds, ground-nesting birds, reptiles, and amphibians in the remaining habitat fragments.
  • Edges become areas with increased noise, light, pollution, human recreation, and roadkill.  The increased noise, light, and human activity may cause some species to move further inland, away from habitat edges. Traffic on adjacent roads can cause pollution in the form of nitrogen deposition, and the increase in noise and light can deter or disorient animals.  Roadkill continues to be a significant source of wildlife mortality with several million collisions per year reported worldwide.  In one study in Saguaro National Park on the United States–Mexico border, an estimated 30,000 animals were killed by vehicles annually.  This included a variety of reptiles, amphibians, birds, and mammals, such as the mountain lion pictured below at Saguaro National Park.

Business Strategies for Managing Edge Effects

To address the issue of edge effects, corporations typically use one or more of the following four strategies:

Avoidance: The first—and best—strategy that companies can adopt to address edge effects is a simple one: Avoid the construction of buildings, roads, trails, power lines, pipelines, etc. in areas with high-quality habitat for species that are classified as endangered, threatened, or vulnerable to extinction.  This avoidance strategy may also be extended to a high-quality habitat for species that are classified as “species of concern,” depending on the health of the populations of those species as well as the degree and types of potential impacts.  To identify these “avoidance zones,” you’ll need to conduct a biodiversity assessment to collect data about the species that are in the areas where you hope to develop or operate.  

Minimization: For land that is not categorized as an avoidance zone, corporations shift their attention towards minimization strategies that reduce the duration, intensity, and extent of their impacts for biodiversity and wildlife.  For example, some oil and gas corporations take steps to reduce the width of land cleared for the construction of a pipeline or road.  In another example, the State Grid Corporation of China implemented an “Electricity Caravan” concept to minimize environmental impacts in a fragile plateau environment in the area of Sanjiangyuan National Nature Reserve (pictured below), known as “the water tower of China”.  This project between Golog and the main grid of Qinghai needed to adhere to strict environmental and water protection requirements.  To do this, workers from SGCC Qinghai Electric Power Company didn’t build any roads or bridges, but used horse caravans known as “Electricity Caravans” to transport the material and facilities needed for the project.  This alternate mode for transporting materials also served to reduce edge effects compared with the normal practice of building a road or bridge.

Rehabilitation and Restoration: In situations where avoidance and minimization are not practical or feasible, companies may turn to a third strategy: rehabilitation and restoration.  With this strategy, a company attempts to rehabilitate degraded ecosystems or restore cleared ecosystems in areas that have previously been cleared, developed, or neglected.  In another example from China, The China National Petroleum Corporation (CNPC) pursued an ecological restoration effort as part of its Western Pipeline project.  As soon as the new pipes were laid down and buried, CNPC planted vegetation in an attempt to restore the original landscape.  In addition, CNPC adopted a higher design grade, increased the pipeline burial depth, enhanced the anti-corrosion grade of the pipes, and installed cut-off valves to prevent oil leakage in the event of any accidents.  Since the project was launched in 2004, CNPC has followed up with monitoring and remediation measures on an annual basis to ensure that the restoration effort is a success.

Biodiversity Offsets and Voluntary Compensatory Actions: If avoidance, minimization, and restoration strategies aren’t a viable option, then companies may turn to a fourth strategy: biodiversity offsets and voluntary compensatory actions.  The concept of a biodiversity offset is relatively simple. A company has a proposed project that will result in negative impacts to biodiversity at the target site.  To offset that loss, the company enters an agreement to protect biodiversity at another site.  The result is no net loss of biodiversity or, preferably, a net gain of biodiversity from the perspective of species composition, habitat structure, ecosystem function, and cultural values of biodiversity.  Biodiversity offsets differ from philanthropic donations and other compensatory actions by linking the offset to the biodiversity impacts of a specific project.  With voluntary compensatory actions, there is no formal link between the actual biodiversity impacts of the company’s development activities and the biodiversity gains from purchasing land for conservation.

Are these strategies “profitable conservation” strategies?

The short answer is, it depends.  From a business perspective, the business case is not always attractive.  In some industries, businesses are encouraged, and sometimes required, to implement these strategies in order to obtain permission to operate in certain areas.  The permission to operate in these areas can lead to huge financial gains.  In other cases, these approaches have fewer tangible benefits to the bottom line, but they can be effective risk-management strategies that are well received by regulators, customers, employees, and the local community.

From a biodiversity and wildlife perspective, anything that we can do to minimize impacts to the habitat they depend upon is a good thing.  However, the reality is that the cumulative impact of development projects is taking a toll on the health of wildlife populations throughout the world.

Parting words and coming attractions

Well there you have it!  I hope this post gives you a better idea about the topic of edge effects, why it matters from a biodiversity perspective, and the steps that businesses can take to minimize edge effects during planning and construction activities.

Next week, we’re off to The Netherlands, where we’ll be looking at oil and gas giant, Royal Dutch Shell, and it’s profitable conservation strategies that are good for business, biodiversity, and wildlife.

Thanks for reading!


Author: Mark Aspelin

Mark Aspelin is a freelance nature, health, and travel writer who helps people become more engaged in biodiversity conservation and live a lifestyle that optimizes physical and mental health. Mark has worked as a conservation biologist, healthcare project manager, certified personal trainer, and is the author of numerous articles, the New Mexico & Beyond Travel Blog (www.nmbeyond.com), and two highly rated books: “Profitable Conservation: Business Strategies That Boost Your Bottom Line, Protect Wildlife, and Conserve Biodiversity” and “How to Fail at Life: Lessons for the Next Generation”. He has a B.S. in Biology from the University of Notre Dame, M.S. in Biology from Creighton University, and MBA from the University of Texas at Austin. Mark has worked with a wide variety of organizations such as The Nature Conservancy, The Coca-Cola Company, Intel Corporation, Molina Healthcare, United HealthGroup, and The International Crane Foundation, and his articles and interviews have been featured by GreenBiz, Inside EPA, Perceptive Travel, and the E.O. Wilson Biodiversity Foundation’s Half-Earth Project. Mark is also an avid traveler who has visited over 100 countries and all 50 U.S. States and he lives in the mountains outside of Albuquerque, New Mexico.

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