Fighting Invasives: The Best Defense is a Good Offense

Maria DeLaundreau, Project Coordinator, Mississippi Park Connection

When it comes to fighting invasive species, the old adage of “The best defense is a good offense,” has been well studied. We keep finding proof that the ecosystems most resilient to invasives are those that are healthy and intact. Once they become degraded it can be very difficult to restore. 

A stand of reed canarygrass.

On the shores of the river and riverine backwaters, reed canarygrass (Phalaris arundinacea) has been infiltrating and in many places becoming dominant. This environment faces a lot of disturbance. It’s a floodplain. It floods. Flooding reshapes the landscape by moving sediment, submerges and sometimes drowns vegetation, and changing the level of the water table, sometimes creating new backwater lakes and ponds. Sometimes these changes are a perfect entry point for reed canarygrass. 
Once reed canary grass invades it forms dense thickets that are difficult to defend against. Land managers often use burns, mowing, and herbicide to keep it at bay, but something needs to change if you want to prevent it from growing back or re-establishing. 

Reed canarygrass (Phalaris arundinacea)

This is where we come back to needing a good and native offense to protect the floodplain, like planting cottonwood trees. Research has suggested that trees taller than reed canarygrass can shade out this invasive grass. Cottonwoods and reed canarygrass have very similar habitat preferences. They both do best along rivers and other wetlands where the water table is high and they may be flooded for a few weeks each year.

Forest and field both have their place in the floodplain, but not reed canarygrass.
Photo credit: Allie Holdhusen, MISS/NPS

Of course, here at Mississippi Park Connection, we get very excited when there’s an opportunity to do good for the river with cottonwood trees! This spring, we are partnering with Three Rivers Park District at Carver Park Reserve to collect planting material and Coon Rapids Dam Regional Park to plant in a reed canarygrass field. Three Rivers staff will prep the site by mowing down the invasive grass and we will put mulch around the trees to help prevent it from growing back and to help the soil around the thirsty young trees retain moisture. As our cottonwoods grow to be taller than the reed canarygrass, which can grow 2-6 feet in height, the trees will shade out the invasive grass. We are so excited that this native and majestic tree can be used to fight off invasive species and help restore a healthy and resilient floodplain forest habitat in more ways than we realized. 

Intact floodplain forest at Coon Rapids Dam Regional Park.
Photo credit: Allie Holdhusen, MISS/NPS