A powerful force

  • Fog rises off of the Suncook River in Chichester near fields off of of Route 28 on Friday, March 15, 2019. GEOFF FORESTER

  • Caleb Danjon of Boscawen casts near the dam runoff of the Soucook River in Loudon as he and friend tried fishing on Saturday, April 20, 2019. The pair decided the river was running too fast to be good for fishing and went downstream. GEOFF FORESTER

  • Heavy runoff goes over the spillway on the Soucook River in late April. GEOFF FORESTER / Monitor staff

For the Monitor
Published: 5/4/2019 8:00:26 PM

In my recent travels, it’s been hard not to notice the high water in local rivers and streams. The mighty Merrimack River is up to the brink of its banks as it surges through Concord. Smaller rivers and streams are gushing and cascading over rocks and around bends. It’s an exciting time as snow melt from the North Country mixes with seemingly endless rain to create the floods or near floods of this spring.

Moving water is a powerful force. It is loaded with minerals, sand, silt and floating debris from the landscape. Some of what it carries and deposits in new places can be beneficial. When the open flood plains dry out, current farmers will carry on a centuries-old tradition of growing crops in the soil that is rich with organic matter and silt left behind when the water recedes. Other parts of the river channels will have been scoured and eroded by the moving water, leaving a barren sand bar or cobble beach devoid of vegetation.

Whether an area receives deposits or is stripped of its riches depends a great deal on its location, and the intensity, duration and timing of the flow of water. In turn, these areas vary widely in the types of vegetation and communities that they can support. The actual channel that carries water supports fewer trees than the flood plains that spread out from the banks. Instead, they will have flexible shrubs and herbaceous plants that can bend and flow with moving water and tolerate longer periods of being inundated. In contrast, the flood plains have more trees, vines and robust plants that grow fast, tolerate moderate periods of inundation and thrive with the greater amount of nutrients deposited in the soil. But because of their unique adaptations and specific habitat types, some of the river-loving plants are among our rarer species.

According to Dan Sperduto and Ben Kimball, authors of The Nature of New Hampshire: “More than a third of New Hampshire’s vascular plant species occur in riparian natural communities, including 93 rare species.”

The rarity is based partly on their ability to tolerate river conditions and thus out-compete plants that are not well adapted to the transitional nature of the river. Trees such as silver maple, eastern cottonwood and box elder are so well designed for this type of habitat that it is the only place in New Hampshire where they are found.

In our area, silver maples, sometimes called river maples, are the most widespread of these trees. They arch out over the river creating a distinctive and magical canopy that is a pleasure to walk under (after the water recedes) or paddle past (when it slows down a bit). Flakey gray bark and deeply cut five-lobed leaves distinguish them from other maples, as does their location along river banks. No other maple can survive being in saturated soil for the majority of the growing season. Adventitious roots which sprout above the soil surface to aid with oxygen uptake is one thing that makes this possible. Another adaptation is their ability to tolerate extreme acidicy, such as is found in river muck. Rapid growth and early reproduction help them out-compete other species. Silver maples may begin to reproduce as young as 11 years old. They produce large seed crops and the seeds germinate quickly in moist mineral soil.

It only takes a slight variation in elevation to cause a change in the plant community. The silver maples are replaced by red maples in areas that are slightly higher and flooded less often.

These changes can also be seen with herbaceous plants. Wetland species with strong root systems that help anchor them to the soil survive better in the frequently inundated zones. Thus ostrich ferns are found in the lower, wetter zones, replaced by sensitive ferns in the less wet areas and northern lady fern as you get further from the river.

The subtle variations in the riparian plant communities are worth exploring once the water recedes. Pay attention to where the water is now and when things dry out a bit, go for a walk along a river and look for the wide diversity of plants that can withstand various levels of being waterlogged.

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