Crack willow leaves. Credit: Robert Vidéki, Doronicum Kft., Bugwood.org, CC BY-NC 3.0 US. Cropped for use.
Background
Non-native, invasive crack willow trees are some of the largest trees in northern Minnesota and have invaded miles of stream banks around Duluth. Their name comes from the excessive dropping of limbs and trunks from these multi-stemmed trees, creating large debris dams often mistaken for beaver dams. Their roots invade the stream bed and banks, altering response to stream flow.
Almost no research has been done in North American stream ecosystems, but fisheries managers are requesting assistance to investigate effects on stream fish and ecosystems.
Confounding decisions about control, these trees may have both positive and negative effects on stream ecosystems. They appear to provide most of the shade to invaded streams, likely keeping water temperatures cooler and benefitting species like trout. Their roots may prevent stream bank erosion. Negatively, the large debris dams may alter water flow, cause stream beds to “silt in” (bad for fish and fish food habitat), impede fish ability to move up and down stream, and alter the fish food resources.
Research questions
- What are the effects of crack willow on stream fish, their habitat, and their food resources?
- Does removing debris dams and root masses effectively mitigate the negative impacts for in-stream?
Practical implications
Currently, there is only anecdotal information about whether and how to manage crack willow. This research will provide land managers with data on the effects and feasibility of managing the non-native species. This project team will work in collaboration with another investigation into crack willow.
Findings
This project began in January 2026 and is in progress for the next several years. Please check back at a later time for updates.
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