My “ah-ha!” moment happened at a presentation I attended a few years ago. A slide on the screen showed two rows of fish: on the left, smaller fish from a river with an urbanized floodplain, and on the right, fish of the same species and same age from a river with a natural, functioning floodplain. The fish on the right were almost twice the size as the ones on the left.
Fish from rivers with healthy floodplains thrive, while those in rivers without a healthy floodplain merely survive.
The connection between thriving fish, healthy rivers, and functioning floodplains? Trees.
Forested watersheds have been shown much higher water quality than their urbanized counterparts. Trees provide a wide range of ecological services. Tree canopy lessens the erosive impact of rain and slows the velocity of stormwater flowing towards the river, as well as floodwaters spilling out onto the floodplain. Trees trap sediments that build the floodplain while the roots stabilize the riverbanks. Trees also provide shade for maintaining water temperature. Fallen leaves, limbs, and branches support the food web by providing food and habitat for the bugs that are in turn food for fish. Clean, cool water with more food equals bigger fish. Therefore, fish grow on trees.
The connection between fish and trees and rivers is now poised to emerge in our urban areas.
Many cities, from large to small, are recognizing the benefits of reestablishing the physical and emotional linkage between the river, trees and the community. For instance, San Antonio has its iconic River Walk, Chicago has just completed its riverfront, Washington DC has its Southwest Waterfront neighborhood, and Pittsburgh has reconnected neighborhoods to its three rivers via a network of urban trails. Furthermore, Hartford, Nashville, Providence, Denver, and Detroit all offer events on their downtown riverfronts that draw thousands, and Cincinnati, Columbus, Owensboro and many more are rediscovering their community-to-river reconnection. But when you look at images of these urban riverfronts, you notice they all have one thing in common: a lot of hardscape. Hard engineered solutions are meant to reduce maintenance and accommodate maximum access.
The trend in revitalizing urban riverfronts is a giant step forward, but our urban riverfronts also need soft green edges. They need the green space and trees that humans and fish, and all living things, require to thrive. It isn’t possible or desirable to return our urban rivers to forested watersheds, but we can reintroduce trees to our river corridors provide while also adding value to our urban communities.
Healthy for fish, healthy for people. Give trees to fish, and we’re also giving them to ourselves.
I’ve decided there needs to be a song about how fish grow on trees. Remember this folk song?
“…Oh, the limb on the tree,
And the tree in a hole
And the hole in the ground
And the green grass grew all around, all around
And the green grass grew all around…”
Let’s add “…and the green trees grew all around, all around…and big fish in the river are found.”