Posted September 22, 2015 by Rachel Smith
Invasive species are increasingly becoming one of the greatest threats to healthy working ecosystems.According to the International Union for Conservation of Nature (IUCN), invasive species “represent the second most significant cause of species extinction, after habitat destruction, and in islands, they are undisputedly first.” To a biologist, conservation worker, or someone who spends most of their life in the forest or other protected habitats, this statement speaks for itself. But what does that really mean for the rest of us? What effect does a biodiversity threat in the forest have on our lives?
Economy, human health, and valuable natural resources are all impacted by invasive species in the forest. One of the chief adverse impacts of invasive species is erosion. Invasive plants and animals alike can cause significant damage in the forest and trigger immense landslides and soil loss. Erosion is a natural process, but too much can be detrimental to soil and water health. Geological erosion occurs from natural processes such as gravity, water, ice or wind. Accelerated erosion happens as a result of introduced species, wildfires, drought, or human influence. Invasive species in the forest can adversely affect our lives geographically from high elevation to sea level.
Feral pigs are making waves across the nation. Without natural predators to make a significant impact on their population numbers, pigs run rampant throughout forests across the US, including the forests in Hawaii. Pigs and feral goats alike, dig up, rut up, and eat up copious amounts of vegetation in forests or mountains. Because their populations are so high, they consume the forest floor flora at such a fast rate that the forest cannot replenish itself with new growth. When a rain comes, without a healthy forest understory growth, large amounts of sediment, soil, and feral animal excrements rush into our waterways. Feral animal feces can contain extremely dangerous bacteria and disease. Toxoplasmosis, leptospirosis, Ringworm, E. coli, and other intestinal parasites are just some of the health risks associated with erosion and run-off from feral animal infested forests.
Invasive plants make an even larger negative impact in forests. Many invasive plants are extremely aggressive and out compete native plant species. The benefits of having a native species forest are numerous, but in the case of erosion, natives offer the benefit of having intricate, deep, and healthy root systems. A native tree often will grow over the course of decades; slowly pushing it’s elaborate root system through the forest floor. Often, invasive plants grow rapidly with weak, shallow, or tap roots, all of which increase erosion run-off.
Another effect invasive plants have on native forests is that they have to ability to crowd out anything in its path. This can often cause a monocrop, where literally nothing grows except for one plant. This is the case in Tahiti with what happens to be KISC’s #1 target species, Miconia. Over 75% of Tahiti’s forests are nothing but a monotypic stand of 50 foot tall Miconia trees. Miconia tree leaves can grow up to 3ft long. So, if you can imagine standing on a forest floor with a 50 foot canopy of trees that have leaves the size of couch cushions…not much light would be touching you or the forest floor. A Miconia stand shades out the understory, so almost nothing can grow underneath. Here, we face the same issue with feral animals consuming the forest understory. No plants = no roots = nothing to hold the soil together.
As more invasives dominate the forests, the faster erosion occurs. Erosion from invasive species change water health, quality, and turbidity. They impact ocean temperatures and cause flooding. Bacteria and diseased run-off do not only cause harm to people swimming in infected waters, but also to our drinking water, and the aquatic species that live in the waters we use for fishing.
Invasive species are not just causing erosion from high elevation forests, but in coastal areas and riverbeds as well. As invasive aquatic plants invade marshlands, wetlands, and tidal zones, they voraciously consume all the available space, crowding out all the native species that are there to collect sediment from erosion. Wetlands are like the liver of watersheds. Everything that flows into a healthy wetland ecosystem is collected, filtered and released. A properly working tidal marsh will filter out most of the turbid waters and bacteria, before releasing the water into the ocean. But, if a wetland or tidal zone is threatened by aggressive invasives, ocean health is at risk. Everything in in the wetland system works together, so even if just one invasive species invades, and causes one piece of the ecosystem to become extinct, the entire system can be disrupted. With one piece missing, the system cannot work symbiotically, causing the run-off filtering organisms to not be able to do their job. Wetlands also act like a sponge so that when there is a large storm surge to heavy rains, a wetland will hold large amounts of water, preventing our roads from being flooded. Keeping both high elevations and low elevations clear of invasive species is imperative to protecting ourselves from worsening natural disasters as well as disease outbreaks.
So now the question is, not what effect does the forest have on our lives, but what effect can we have on the forest? An applicable motto here is: What goes around comes around. What we plant in our backyards and the environmental legislation we support, ultimately affects forest and wildlife health, which in turn, affects our quality of life. We are dependent on a healthy forest and ecosystems. If we can minimize the spread of invasive species by not planting them in our backyard, or paying more attention to what we bring into the islands, we can help to protect the forest. Kauai is threatened by invasives from each of the other islands, as well as the rest of the world. We have the power to protect ourselves as well as the forest, we just have to make the effort.