Edge effects are changes in biodiversity that occur within the space surrounding the common edge of two or more distinct ecosystems. This biodiversity-rich transition zone is known as the ecotone; examples are between woods and plains, forests and mountains, and land and water. Informally known as the border, the ecotone affects the plants and animals that live there in unique ways compared to connecting habitats.
In larger habitats, there is a smaller percentage of area affected by the edge. This allows flora and fauna to thrive in the ecosystems and along the edge. But in smaller habitats, edge conditions are more likely to threaten the stability of individual biomes, making it difficult, if not impossible, for many plants and animals to survive. Here we review some examples of positive and negative side effects.
Did you know?
Regardless of the size of the ecosystem, the size of the edge remains constant. Unlike some habitats that thrive on expansion, the edge does not become more robust with increasing size, and the effects can be devastating if it expands beyond what the surrounding habitats can support.
Positive side effects
When two adjacent habitats have enough individual space to allow for a wide gradient edge, the ecotone is uniquely positioned to provide habitable conditions for certain plants and animals. Prosperous edges support the greatest variety of natural structures, ranging from small to large, and they often support populations of wildlife exceeding any bordering habitats.
Changes in the landscape, including geographic features, soil types, temperatures, and humidity levels, are called inherent edges.
What are inherent edges?
Inherent edges are natural changes that are generally considered wide; they provide sufficient space for species inside and outside the ecotone to thrive. If left untouched by humans, the inherent boundaries tend to remain stable in size and population over long periods of time.
Unlike the interiors of most ecosystems, edges receive more sunlight, experience less humidity, face more wind, and experience higher temperatures. These environmental differences allow for a more hospitable environment for very bright, drought-tolerant flora. Therefore, more insects, birds and other herbivorous animals can settle inside the ecotone.
Some animals, including rabbits, deer, and elk, require multiple environments and depend on the edge as a foraging and nesting space. (Or, in the case of the dung beetle, waste removal). Humans, as animals living in the natural world, benefit from the edge effect because a large, healthy ecotone physically separates humans from predators.
Negative side effects
When people encroach on the natural world, ecological boundaries sharpen and the biodiversity of the ecotone decreases. Human-induced narrow edges can increase the risk of infectious diseases, degrade soil quality and reduce moisture levels.
What are induced edges?
Induced edges are human-caused disturbances to the natural environment resulting in abrupt changes in habitat boundaries. These edges do not remain stable even for short periods of time and are described as narrow, not because they take up less width, but because the transition between environments is so sudden.
Urbanization, timber harvesting, and food cropping all lead to induced borders. They can also have biological or climatic origins: floods, fires, winds, disease and insect infestations can all create curbs. Once these negative edge effects have set in, the climate along the edge can spread deeper into the environment, threatening habitat destruction for a number of species that can only survive in the original biomes.
Consider how different an edge defined by commercial deforestation is compared to the smooth transition from forest to clearing. Stronger winds along these man-made edges often fuel and exacerbate wildfires, causing additional damage. Sufficient destruction of the forest edge can cause fragmentation, which creates more edges around smaller and smaller ecosystems.
Predators, pushed out of their habitats, venture into the edge and beyond, affecting bird and, by extension, insect populations. Since the size of the border remains constant, the already more abundant border plants and animals can grow in population, creating a later environmental problem: invasive species.
From a planetary perspective, humans dominate the landscape. Agriculture alone occupies nearly 40% of all land on the planet. The negative side effects associated with clearing fields for crop growth are not only significant because of deforestation issues. Additionally, herbicides, fertilizers, and other chemicals used in food and animal production can leak out of these tight confines and contaminate surrounding natural habitats.
As the human population continues to grow, experts believe global demand for dairy and meat products will drive future land use changes, requiring even more space to grow food for humans and animals. Without sustainable natural habitats within the edge, ranching can also force livestock to compete with native species for food supply.
Like agriculture, urbanization also threatens vital ecosystems around the world. More than half of humanity currently lives in an urban area, with over 70% of the world’s population expected to live in cities by 2050. Urbanization can also create competition for natural resources and introduce new predators like domestic cats that can wreak havoc on wild bird populations.
The current state of the Los Angeles River provides a clear example of how urbanization can destroy an ecotone and harm surrounding biological communities. What once provided a rich biome for plants, animals and one of the largest groups of Native Americans in North America is now a 51-mile-long concrete wash, with only 5% of its natural habitat intact. .
Not only have plants and animals disappeared from the river and along the man-made rim, but communities of color living nearby suffer from some of the highest levels of poverty and pollution in all of Southern California – the consequences of the environmental racism.
To create a just and sustainable future for all life on the planet, lawmakers must work with scientists to develop specific, practical techniques to restore threatened ecosystems and maintain thriving, biodiverse frontiers that connect humanity to nature.
Frequently Asked Questions
What is an example of a side effect?
Imagine a river and land on either side. The plants and animals inside the river are quite different from those on land, and between these two areas there is greater biodiversity than in either ecosystem. The unique geography of this transitional space between habitats allows many plant and animal species to thrive, displaying a positive side effect.
What causes a side effect?
The diversity of life within an ecotone is due to the additional sunlight and drier conditions, both of which allow more plants and animals to thrive along the edge. However, the edge effect can turn negative when agriculture or urbanization shrinks the connecting ecosystems, causing the edge to expand into wetter, more shady conditions and leading to habitat destruction.
How important are edge effects?
When ecosystems are healthy and sustainable, they can support thriving borders where an array of insects, birds, mammals and plants can thrive. Without appropriate space to support life in these connected communities, the habitats themselves will shrink as the edges move closer and closer to the center.