Monday, January 9, 2017

Restoring the Floodplain

Post contributed by Brett Stolpestad and Brad Chatfield, Conservation Corps of Minnesota:

Great Horned Owls are one of the many species that use Saint
Paul's floodplain parks to raise their young.
The Mississippi River floodplain is Minnesota’s centerpiece. A patchwork of cottonwood, maple, boxelder, hackberry, and ash make up the forest ecosystem, providing critical habitat for migratory birds and other river-dependent wildlife. The City of  Saint Paul is home to a beautiful winding chain of parks along the Mississippi and uses a variety of management practices to augment the health of the floodplain ecosystem. One particularly useful and beneficial technique is shelterwood harvesting, the process of gradually removing mature trees in a given area with the goal of establishing the next generation of desirable tree species. This process has the potential to increase biodiversity, improve wildlife habitat, and eliminate invasive species.

How does shelterwood harvesting work?

Step one: Land managers begin by surveying forest transects using satellite images, GPS units, and GIS software. At this stage, typically called a forest composition survey, surveyors attempt to create a map that clearly illustrates the distribution of tree species, the total canopy cover, the average size of the trees and perhaps their age.  

Step two: Surveyors identify potential shelterwood harvest sites by analyzing sections of forest that may lack diversity or contain undesirable species like buckthorn, white mulberry, or Siberian elm.  

Step three: Through several gradual stages, foresters begin removing trees that lie within the designated shelterwood harvest area. Removing these trees helps to open the canopy, allowing sunlight to reach the forest floor where the next generation of saplings can become established.

Step four: Native tree species can then be planted in the newly created pockets, adding to the biodiversity of the ecosystem and improving wildlife habitat. Trees or shrubs such as cottonwood, silver maple, sugar maple, black willow, elderberry, and red osier dogwood might be selected!

A Conservation Corps member completing a canopy survey at Hidden Falls
Regional Park.
In recent years, prominent Saint Paul Parks including Hiddens Falls, Lilydale, and Crosby Farm Regional Parks have all been selected as sites for shelterwood harvest. The decision to focus on these parks has been, in part, a response to ecological threats including the encroachment of emerald ash borer. The threat of emerald ash borer has led to the preemptive removal of ash tree throughout the floodplain, followed by several large-scale volunteer planting events. Over the past few years, volunteers have helped plant hundreds of trees and shrubs throughout Crosby, Lilydale, and Hidden Falls. If you visit these parks today, you will undoubtedly see dozens of young maple, cottonwood, and black willow standing straight in their “tree-tubes,” along with an understory smattering of black willow, dogwood, and elderberry.
Shelterwood harvest areas are replanted with native tree
species. These young trees are protected with tree tubes, which
facilitate growth and protect the saplings from hungry animals.
The Mississippi River floodplain remains a gorgeous and dynamic landscape in the heart of our state. The floodplain parks of the Twin Cities offer the opportunity for city-dwellers to walk the long winding paths through towering floodplain giants, and to become immersed in the wildlife sanctuary that the floodplain provides.