By Delaney Farwell, Community Forestry Member, Mississippi Park Connection

Living near the Mississippi River means you’ve probably seen it through its various cycles. I’m not originally from the Twin Cities, but I went to college on the Mississippi and remember 2023 being a huge flooding year. I was presenting at the Mississippi River Research Consortium in La Crosse, Wisconsin and we were all so interested in the flooding across Illinois, Iowa, Wisconsin, and Minnesota. It made the news for months and I was amazed to see the effects it had on my college town: new permanent and temporary infrastructure had to be built, small businesses had to temporarily close and lose a chunk of profit, people’s livelihoods were deeply affected. I distinctly remember my favorite park being 10-12 feet underwater for months, leaving me down and out for a particular beloved reading and writing spot.

These experiences made me reflect upon how societies have historically been drawn to and created around rivers, even at the risk of disruptions like floods. Rivers provide food, water, power, transportation, sanitation, and recreation. Rivers are the link between nature, life, and civilization, yet they come with a risk of extreme disturbances for those living in the floodplain.

Before moving on to how floods and droughts impact the floodplain, it is necessary to understand the specific ecosystem we have here in the Mississippi National River and Recreation area. We live in a floodplain forest, which is a forest dominated by various deciduous hardwood trees that grow on alluvial soil, basically meaning that they tolerate semi-frequent inundation. These areas are usually well-drained throughout most of the year, but in seasons of frequent precipitation like rain or snow-melt, the river floods and the areas next to it become an overflow zone for the water that’s looking for somewhere to go. Mature trees are paramount in the floodplain because they help to anchor the soil and prevent excessive erosion as the floodwaters deposit sediment and wash away aspects of the surface of the floodplain.

Floodplain forests are extremely beneficial to wildlife as they provide a large variety of habitats for aquatic and terrestrial animals. The Mississippi River is a migratory corridor for birds; bald eagles love to nest alongside the river, and many other fish, amphibians, and reptiles call these areas home. Floodplains help recharge groundwater supply and create fertile ground for vegetation, which is a large reason why many agricultural societies settled around rivers. The earliest Native Americans lived in floodplains due to the wealth of food and ease of access to travel.

For centuries, humans have deeply altered the floodplain ecosystem as well as rivers themselves. This idea can be good or bad and many management techniques have their own unique advantages and disadvantages. A common management practice for rivers is to straighten the channel to make transportation or acquisition of hydropower easier, even though when left to its own devices, a river will become more and more S-shaped over time. The straightening of the river leads to higher and faster flooding since there are less natural breaks for the motion. Locks and dams are other forms of human intervention in rivers and can prohibit fish migration and have historically destroyed Native American wild rice harvesting processes, but can also help with flood control and water supply for domestic, industrial, and agricultural systems.

Another way that humans have interfered with the floodplain’s ecosystem is by pouring carbon and other warming gases into the atmosphere. Climate change has altered and will continue to alter our precipitation patterns over time. In general, climate change is going to make significant weather events more severe and more frequent for longer periods of time. In Minnesota, this will look like more frequent floods, more days with temperatures above 95°F, and more intense storm events. We can begin to see the effects now as our plant hardiness zone recently changed from Zone 4 to Zone 5, which means there has been an upward trend in winter warming throughout the years.

Habitat Restoration Event February 2024. Photo: Edwige Moses / NPS

The way a river flows (also known as flow regime) has a huge impact on local ecosystem functions. For example, since we’ve gotten so little snow this winter the river has been pretty low. If the river is flowing a relatively small amount, leading to a drought, organic material and nutrients are able to accumulate on the surfaces of the floodplain forest so that when a flood does come, there are more resources available than under a normal flooding season (“Floods and Droughts Impact Ecosystems”). On the other hand, floods can also cause significant erosion which can cause streambanks to collapse. As floodwaters carry parts of the eroded bank material, water quality can decrease which may lead to algae blooms along the corridor. Contamination may also be carried down the stream during a flood which further disrupts some more sensitive ecosystems (“The Many Effects of Flooding”).

In our floodplain, droughts, climate change, and human alteration all come together to affect some of our key species. Cottonwoods are an iconic part of the floodplain forest. They tower above the rest of the canopy and have massive trucks with deeply ridged bark. They also rely on disturbance regimes like floods to regenerate. Cottonwood seedlings thrive on the sandy part of the river at the point of each turn, known as the point bar. The point bar floods regularly, and as the floodwaters recede, this sandy part will hold onto water like a sponge and allow cottonwood seeds to germinate. As long as there is no large flood the next year, the cottonwoods will anchor themselves down with roots. Where the stream is straight to accommodate something like a road and thus lacking point bars, young cottonwoods do not regenerate. Similarly, they will not regenerate if there are large floods multiple years in a row since the saplings will be quite vulnerable for the first few years (“Cottonwoods: Born from the Floods”).

If our weather systems keep changing significantly and we get more floods or droughts, the cottonwood’s regeneration schedule will be deeply affected. After a winter like the one we just had, cottonwoods might struggle to anchor down at all, which is something we’ve been seeing happen pretty regularly. We have very few young cottonwoods naturally regenerating in our forests right now. With our permanently altered ecosystems comes altered flood timing, and if floods don’t line up with when cottonwoods drop their seeds, they may not be able to find their preferred habitat in time to germinate.

Disturbance regimes like droughts and floods are an integral part of many ecosystems, and whether we alter our rivers intentionally or unintentionally, there will be various consequences for us here in the river corridor. Ecosystems adapt to change, but we need to do what we can to better understand these changes and the repercussions they will have on all the other critters in the forest. This notion is especially important as we are faced with significant climatic change; we have a lot of decisions to make in the upcoming seasons. Perhaps now that we know more about how floods, droughts, and river maintenance affect our landscape, we can “begin [to think] like a river if we are to leave a legacy of beauty and life for future generations,” as David Brower once so astutely said.

Balancing Act: Exploring the Impacts of Disturbance Regimes on Floodplain Forests