The day Tropical Storm Irene blasted through Vermont and the Middlebury River flowed down East Main Street seems far in the distant past, but Irene's effects are still visible on the landscape. There are still roads with patchwork paving on them (even more so than usual), piles of sediment pushed off of roads and driveways, crumbling eroding riverbanks left by the flood, and smoldering arguments about how to repair damage and prepare for the next flood without sacrificing the Vermont way of life or damaging our rivers. In the longer term, there is also an invader that has been spread by the flood - Japanese knotweed.
Japanese knotweed is an odd plant. It thrives along rivers and streams. In the spring, it sprouts from the ground, as seen above, in succulent shoots that look a bit like giant asparagus. They are apparently edible at this life stage, but be warned: don't eat knotweed in an area where people have tried to kill it with pesticides. As the stems grow a bit larger, they sometimes grow to resemble bamboo, though they are not very closely related. Then the plant sprouts huge leaves.
Eventually, the plants bear big white flowers, and then when fall comes the plant dies back to its rhizomes. In the winter only dead stalks remain.
So what's wrong with Japanese knotweed? It's edible, funny looking, has flowers, we should be glad to see it along our streams, right? Well... maybe we would be, except that it is outcompeting the other plants that grow along rivers, such as willows and cottonwoods. It also has shallower roots, meaning it doesn't hold the banks up as well. If all of our rivers become lined with knotweed, it may be one more factor leading to increased flooding.
Above: Knotweed along the Mad River.
In Vermont, Japanese knotweed is an invasive species. Invasive species are one of the most confusing, controversial, and difficult to deal with issues in ecology and land management today. It's not entirely understood why a species becomes invasive, but many features come into play including a lack of predators and pathogens compared to the species they are outcompeting; human disturbance favoring the spread and survival of disturbance-loving species; fragmentation of habitat; changes in the climate; and perhaps even a form of 'cheating' - not connecting to and adding to the symbiotic fungal mycorrhizal network that is present in intact ecosystems. Some focus on the fact that most invasive species are non native (have been introduced to an ecosystem by humans), but most non-native species introduced to an area do not become invasive, and sometimes native species do become invasive when conditions change. As with other threats facing our ecosystems today, the magnatude and number of invasive species has created a problem much more severe than might occur naturally. Certainly species sometimes naturally invaded new habitats and crowded out other species, but never before this period in our planets history have so many species been moved around all at once.
The real answer to why invasive species occur and how we could manage them may be found in the emerging field of complex systems. This field addresses how small 'units' following relatively simple rules can result in incredibly complex phenomena as they interact. Examples are found in natural ecosystems, within computer simulations, in our economy, and within our own bodies. In all of these cases, incredible complexity and beauty can develop in surprisingly diverse ways. Also in all of those cases, complexity can result in equilibrium and surprisingly resilient systems, but a small change, if in the wrong place, can cause the entire system to crash. Diversity and complexity are lost and the system is dropped to a much less diverse and more unstable state. We see this when our computer systems crash, when economies collapse and when a few companies dominate everything, and even in our own bodies when diseases invade our bodies. In some ways cancer also acts in this way, and the fact that it originates with our own cells makes it no less horrifying and heartbreaking. As with cases where native species become invasive, cancer can be set off by disturbances in our body such as carcinogenic toxins - but of course there are times when we have no idea why it occurs.
I've lost too many people I love to cancer, and have watched others fight it off at the cost of years of painful battle. My point here is not to say that knotweed along the river is as 'bad' as cancer, but simply that there is a unity in how complex systems work. Perhaps studying and understanding why knotweed and other invasives outcompete native organisms will also help us understand more about how cancer works and how we can fight it. Science is an amazing thing and our natural world is full of complex connections we don't yet understand. Any increase in our understanding of the world around us will lead to new discoveries ahead.