By Gia Mora
Edge effects are the changes in biodiversity that occur inside the space surrounding the shared edge of two or more distinct ecosystems. This transitional zone rich in biodiversity is known as the ecotone; examples are between woodlands and plains, forests and mountains, and land and water. Informally known as the edge, the ecotone affects the plants and animals living there in a way that is unique from the connecting habitats.
In larger habitats, there is a smaller percentage of area affected by the edge. This allows flora and fauna to thrive in both ecosystems and along the edge. But in smaller habitats, it is more likely for conditions from the edge 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 edge effects.
Positive Edge Effects
When two adjacent habitats have enough individual space to allow for an ample gradient edge, the ecotone is uniquely positioned to provide habitable conditions for certain plants and animals. Thriving edges house the greatest variety of natural structures, ranging from small to tall, and they often boast wildlife populations exceeding any bordering habitats.
Negative Edge Effects
When people infringe upon the natural world, ecological edges sharpen, and the biodiversity of the ecotone diminishes. Narrow, human-induced edges can increase the risk for infectious diseases, degrade soil quality, and decrease humidity levels.
Urbanization, lumber harvesting, and food cultivation all result in induced edges. They can also have biological or climate origins: Floods, fires, winds, disease, and insect infestations can all create edges. Once these negative edge effects take hold, 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 looks compared to the gentle transition from woodland to clearing. Higher winds along these anthropogenic edges often feed and exacerbate wildfires, causing further damage. Sufficient destruction to the forest edge can cause fragmentation, which creates more edges around increasingly smaller ecosystems.
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