Habitat Fragmentation Edge Effects: When Having an Edge is Not a Good Thing (Part 1 of 2)

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. Note that I originally published a shorter version of this article on Greenbiz.

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.

http://www.profitableconservation.com/wp-content/uploads/2018/07/Forest-and-meadow-smaller-475x300.jpeg

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.

Well that was a depressing note to close on for this week, but hopefully this gives you a better understanding of edge effects and how they can impact biodiversity and wildlife. Next week we’ll switch gears and look at some strategies that businesses can implement to help manage edge effects.

Thanks for reading!

Mark

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Mark Aspelin is the Founder of Corporations for Biodiversity and author of the highly rated book “Profitable Conservation: Business Strategies That Boost Your Bottom Line, Protect Wildlife, and Conserve Biodiversity.”

Cisco Systems and Biodiversity Conservation (Part 1 of 2): Small-Scale, Local Solutions

“We see massive opportunities for our innovation, expertise, and culture to play a role in finding solutions to some of society’s biggest challenges.”
—Chuck Robbins, Chairman and CEO of Cisco

Cisco Systems (#64 on the Fortune 500 list) is a technology conglomerate that is known for its networking hardware, software, and telecommunication equipment. For those of you who work for large organizations, you may be all all too familiar with Cisco subsidiaries such as Webex and Jabber. And for those of you who don’t, you’ve probably heard of a thing called the internet … and it just so happens that 80 percent of the world’s web traffic currently travels securely across Cisco connections. In other words, Cisco Systems, and it’s 75,000 employees, plays a role in the day-to-day life for many of us and we may not even know it.

Another thing that we might not know about Cisco Systems is that the company consistently lands towards the top of the list in the various corporate sustainability rankings. Given the high marks that the company consistently receives from the sustainability community, I thought it would be worth checking out what Cisco is up to in the world of biodiversity conservation.

Like many sustainability leaders, Cisco is doing a lot of work to reduce greenhouse gases, leverage renewable energy sources, and adopt responsible sourcing and manufacturing practices. However, Cisco is also engaged in some interesting (at least to me!) small-scale efforts that have a positive impact on biodiversity and wildlife. In this week’s post, I’ll share two simple strategies that any company or homeowner can embrace. Next week, I’ll share a third biodiversity / wildlife conservation strategy that requires a bit more technology, something that Cisco has in spades.

Minimize impacts to local wildlife during breeding season

Many companies take steps to avoid certain types of operations or construction activities during the breeding season for birds and other animals in the area. This precaution helps prevent the destruction of active nests and reduces noise that can scare away or stress animals during the breeding season. In the case of Cisco Systems, several of the buildings at its San Jose, California headquarters are located near a protected area for American cliff swallows. To help protect American cliff swallow habitat during nesting season, Cisco closes its balconies on those buildings and doesn’t remove the mud nests until nesting season is over.

A pair of Cliff swallows (Petrochelidon pyrrhonota) building a nest on a wooden ledge, in the spring time, San Francisco bay area, California.

Easy right? Yes, this might be a small gesture, but it’s an indicator of the company’s desire to be a good corporate citizen. In the words of famed basketball player and coach John Wooden, “It’s the little details that are vital. Little things make big things happen.”

Wildlife Corridors

Wildlife corridors are often viewed as a useful tool to help maintain and restore biodiversity and wildlife populations on private and public land. A “wildlife corridor” is defined as any space that facilitates the movement of animals between core habitat fragments. The goal of a corridor is to maintain or improve the number and health of species in an area. This assumes that improving the connectivity of separate patches of a suitable habitat will allow isolated populations of animals to interbreed. Corridors may also help alleviate climate-change impacts on animal populations by enabling animals to move to a more suitable habitat as conditions change. From a human perspective, well-designed corridors help us avoid collisions that kill or injure wildlife and cause property damage and injury to humans.

The importance of wildlife corridors is perhaps best illustrated with an example of large carnivores, such as bears or mountain lions, which require large home ranges for food, den sites, and other needs. To maintain a sustainable population of 50 to 70 mountain lions, we need a minimum of 3,120 square miles; to maintain a sustainable population of 200 black bears, we need at least 780 square miles.

These large habitat requirements are significantly larger than most protected areas in the United States, and that’s where corridors can help. Corridors can link large patches of habitat and enable these large carnivores to move from one patch of habitat to another and support a sustainable population of these animals. We could also consider the option of having a smaller population of mountain lions or bears in a certain area, but such small populations of either species are unlikely to be sustainable in the long term.

Corridors come in a wide variety of shapes and sizes. Some corridors take the form of linear patches of land that directly connect two patches of habitat. Other corridors are irregular-shaped stepping stones of land that enable species to move from one patch of habitat to another, even when these stepping stones are not directly connected to the core patches of habitat. Corridors may be man-made, such as underpass tunnels or overpass bridges across a roadway, or they may take the form of natural corridors, such as rivers and mountain ranges.

Some corridors are designed with a regional scale in mind, such as a corridor that facilitates bird and butterfly migration from Canada to Mexico. Other corridors are designed at a local level, perhaps connecting local wetlands to help sustain populations of reptile or amphibian species. That’s where our second Cisco Systems example comes in. Cisco created three turtle tunnels under the highway at its Boxborough, Massachusetts location to provide safe passage for the migration of Blanding’s turtles and eastern box turtles, listed as International Union for Conservation of Nature and Natural Resources (IUCN) Endangered Species and IUCN Vulnerable Species, respectively. Cisco also installed curbing around the site to prevent migrating turtles from entering the roadway and parking areas.

The endangered Blanding’s turtle (Emys blandingii or Emydoidea blandingii) is a semi-aquatic turtle named in honor of American naturalist Dr. William Blanding (1773–1857).

We can design corridors that are intended to be used for brief periods to support seasonal migrations or the dispersal of young animals, or we can design corridors that are intended to be used on a permanent basis. Some species of plants, reptiles, and insects may even spend their entire lives in the corridor habitat.

This brings us to an important point. We’ve all heard the saying, “Beauty is in the eye of the beholder”, not to be confused with a similar truth that some of us might have “heard” in college: “Beauty is in the eye of the beer holder”. But I digress. This beauty perception concept also applies to corridors. A corridor that is attractive to one species may be a barrier to another (e.g., a corridor that is appealing to a coyote may not be appealing to a bear, amphibian, otter, or butterfly). It’s important to be clear on the target species that the corridor is intended to help before choosing a corridor design. Cisco focused on creating a corridor that was specific for Blanding’s turtles and eastern box turtles. Similarly, you might think of ways to support specific species in your area to help them move between core habitat fragments.

Next week, we’ll continue this discussion as we look at a third strategy that Cisco uses to protect wildlife and biodiversity. Hope to see you then!

Thanks for reading,

Mark

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Mark Aspelin is the Founder of Corporations for Biodiversity and author of the highly rated book “Profitable Conservation: Business Strategies That Boost Your Bottom Line, Protect Wildlife, and Conserve Biodiversity.”