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I have a long history of interaction with plants, through time spent in the garden and exploring the piedmont, the Rivanna River, and the foothills and mountains. I have spent many hours seeking out wild edibles and bringing them home, from oyster mushrooms growing on fallen logs to chickweed growing in the shade of a building.
Through this I have learned to recognize the health of the ecosystem housing the plants. In a healthy ecosystem, there is a diversity of living and dead organisms. These make up an elaborate system of checks and balances where no creature is in complete control. A healthy ecosystem is like a healthy representative democracy. A healthy ecosystem also has abiotic factors that are consistent with the organisms' needs. This means having clean water, clean air, and appropriate temperatures and sunlight for the ecosystem. When these natural balances and resources are disrupted, the vitality of the ecosystem is too. An arctic ecosystem cannot flourish in warming temperatures. A rainforest cannot flourish without the trees. Without the trees, the howler monkey has nowhere to live and nothing to eat, the birds have nowhere to raise their young, tree frogs have nowhere to lay their eggs, the plants that take refuge high in the trees have nowhere to live and lack the nutrients provided by the tree, and so on. By taking away any essential factor in an ecosystem, the careful balance collapses.
Native virginia bluebells on the undisturbed side of the Rivanna River.
This is the balance that is shattered when invasive plants are introduced to an ecosystem that has evolved separately from them for millions of years. When organisms inhabit a place together for millions of years, their interactions and the process of natural selection lead to a careful system of checks and balances ensuring survival of the fittest. The wolves catch the slowest deer, so the deer from the survivors are faster. The wolves that catch these deer must be faster, so those wolves survive and pass on their genes. When introduced to a new place, invasive species often do not have organisms from their original ecosystem that keep them in check. This allows them to spread fast and outcompete native species that have evolved to be part of an ecosystem where no single species is dominant. Thus the careful balance of the ecosystem is broken as one or more species become dominant.
Native species often develop beneficial relationships with each other, but invasive species mainly choke out natives. Perhaps it is true that left alone for many thousands of years, the ecosystem would adapt to the invasive species. But it is also important to remember that invasive species thrive in disturbed areas. In places with established native ecosystems, invasive species often have less of a foothold and are more naturalized than in places that have been disturbed and cleared by humans.
This was illustrated to me clearly one day when I was canoeing with my family along the Rivanna River. On one side of the river, there were train tracks, and the area on that side was covered in invasive vines. I got out of the boat to examine the flora on the other side more closely. There were no signs of human disturbance, and only few invasive species were there. The invasive species on that side were in no way dominant. Instead, many species of native plants were thriving.
However, when established invasive species are removed, native vegetation is often quick to regain hold of the area. But for this to happen, the invasive species must be kept from taking hold again. For example, in our creekside area, the jewelweed returned the spring following the removal of invasive species. This comeback is also reliant on having at least some native vegetation in the area to provide seeds or runners.
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