Beautiful to both humans and bees, Japanese knotweed is a severe threat to ecosystems, quickly forming thick, spreading mono-culture areas, displacing native habitats. Photo: Maja Dumat, iNaturalist
Invasion of the Biodiversity Snatchers, Non-Native Species
By Kevin McKeon, Maine Master Naturalist
Distinguishing between native and non-native species often raises the question: What’s the difference?
If the species now exists here, and perpetuates itself, why isn’t it deemed a native? How long does the species need to live here to earn native status? And what does attaching the term invasive mean?
Native species have evolved to become a part of diverse, regional ecosystems made up of other native species. All these species have become interwoven into a complex, living community in which all natives support each other in some way through a continuous cycle of reproduction, life, death, and recycling. The short story: The sun’s energy is captured by plants; things eat those plants; other things eat the plant-eaters; still other things eat the plant-eater eaters. Sometimes some of those species die from injury or disease and will get eaten by carrion eaters or decomposer species — but everything gets eaten. The sun’s energy gets moved around through all these actions, never being destroyed — always being transferred.
All this is what’s being bandied about, increasingly, as biodiversity — all life interactively sharing a place. All the eating is called the food web, and as is glaringly obvious, it begins with plants making their food from the sun’s captured energy – photosynthesis. A plant will do this until it dies; then it will regenerate itself through seeds, root sprouts, or spores. Other times, another plant moves in to displace it and begins its own life cycle. This new plant then may end up getting eaten by a different species than the previous plant did, with the species that eats that species also moving in. As these displacements happen throughout a healthy, biodiverse landscape, many different species are constantly moving around toward food sources that are constantly being displaced by other food sources.
Then, maybe a fire burns down the forest, or a hurricane blows everything down — or even a single tree dies. Grasses and wildflowers emerge in the space thus created to form a meadow, supporting a biodiverse meadowland with all its creatures. The meadow gets displaced by shrubs and pioneering, short-lived trees, outcompeting the shorter grasses and flowers by shading out their life-giving sunlight. We now have a young forest and all of its resident creatures, with some species different than the meadow creatures, having evolved to exist there with these new food sources. Squirrels and blue jays, hiding their acorns and pinecones for their winter food, offer the landscape seed sources from which emerge our famous and valuable pine and oak forests, which in turn support a different assortment of critters than the meadow, shrub-land, or young forest.
This all happens throughout time in various areas within landscapes and regions, but all the various types of landscapes tend to exist within the region, holding and supporting the various food sources and life forms. But here comes a bird that was recently feasting on colorful seeds from a plant that the big box store or unscrupulous nursery says will look healthy in our house’s landscaping at all times because our bugs won’t eat it. “And this plant will turn green sooner and stay greener longer,” they say. What they don’t say is that this plant won’t support any part of a landscape’s biodiversity — ecologically, it’s a concrete statue! So, the bird drops the seed with some attached “fertilizer,” and poof! — another plant that doesn’t support biodiversity pops up, its leaves remain uneaten, offering seeds to other birds and the wind to spread.
Wait! “The birds eat the seeds, so it must be good for them!” What the bird doesn’t quite understand — yet — is that those seeds, for which the bird has not yet evolved an effective digestion system, often cause diarrhea, weakening it, lowering its chances for survival.
So, our non-native plant is now spreading throughout the landscape. It greens up sooner and longer so can photosynthesize earlier and longer than our native plants, thus outcompeting our native plants for growing space. It has successfully “invaded” our biodiverse landscape, becoming more invasive as it spreads, causing a substantial loss of food sources within its growing territories, disrupting the natural food chain, thereby greatly decreasing our landscape’s ability to maintain a healthy, native biodiverse ecosystem.
Back to the native vs. non-native vs. invasive descriptive terms, and what a non-native invasive is.
Audubon defines some terms for us. “Native plant species are species that have existed historically in that area.” It further defines historically as “prior to European colonization,” and area as “North America.” Non-native is defined as “species that have not existed historically in one area but have been introduced due to human activities.”
Many other folks also split the definition of North America area as being on either side of the Rocky Mountains, where human intervention was deemed necessary for plants to make that particular mountain range crossing. So, for instance, some folks consider sequoia trees as native to North America, while others say they are native to North America’s West Coast and non-native to other North American areas.
Not all non-native species are necessarily evil, but most haven’t evolved the helpful biological factors or compositions to support the landscapes which they now occupy, like the natives have. Non-native plants don’t necessarily pose a threat to native plants, but as mentioned before, many non-native plants do not support a biodiverse food web as well as native plants do.
The term invasive has been anointed a much more attention-grabbing distinction by the National Invasive Species Information Center, an organization overseen by the United States Department of Agriculture: Invasive Species are “plants, animals, or pathogens that are non-native (or alien) to the ecosystem under consideration, and whose introduction causes or is likely to cause harm.” The center established an advisory committee charged to more precisely define invasive species, which it did with this 2006 seven-page white paper. The short summary is worth a read.
As awareness of the need to control invasive species rises in importance to us humans, the methods involved have also birthed debates regarding manual, mechanical, biological, and chemical controls; a future column will offer some current thinkings of experts.
National Invasive Species Information Center: https://www.invasivespeciesinfo.gov/
White paper: https://www.doi.gov/sites/default/files/uploads/isac_definitions_white_paper_rev.pdf
The post Out in the Woods appeared first on Sanford Springvale News.
