Recently, natural resource researchers have been looking into the role of trees in protecting water quality. They found that trees, their canopies and root systems play an important role in protecting water quality, even if the trees are not next to a lake, river or stream.
Trees and forests serve our watershed by slowing rainfall, preventing erosion, filtering contaminants before they enter a waterway, absorbing rainfall and snow melt, recharging aquifers, and slowing storm water runoff.
In the Grand Traverse Bay watershed, the biggest threats to our water quality are from the cumulative impacts of stormwater flowing over land and through storm drains to our lakes, rivers, and streams, carrying pollutants with them. Trees are one of the most cost-effective, efficient and pleasant tools we can use to help manage stormwater.
The Watershed Center started a Watershed Forestry Initiative this year to raise awareness about the need to maintain forests and tree cover to protect our water quality generally and the role trees play in managing stormwater specifically.
Through a grant from the Michigan Department of Natural Resources and Environment Urban and Community Forestry Program and the U.S. Forest Service State and Private Forestry Program, the Watershed Center developed a data set of tree canopy cover for the years 2001 and 2009. We partnered with the Northwest Michigan Council of Governments to run that data through specialized CITYgreen software for the watershed as a whole and for nine sub-watersheds.
The results indicate a loss in total tree cover in the Grand Traverse Bay Watershed between 2001 and 2009 of more than 4,000 acres, a 1.3 percent decrease. Those trees helped manage more than 30 million cubic feet of stormwater during a 2.25-inch rain, such as the rainfall we had in the third week of September this year.
Because of the loss of those trees, more stormwater made its way to surface waters in the watershed without being slowed, filtered, or absorbed.
The largest total amount of decline by sub-watershed occurred in the Boardman River sub-watershed. Its tree canopy cover decreased by 2,573 acres, or 2.5 percent, between 2001 and 2009. This translates to a decline in stormwater management capacity of more than 19 million cubic feet. Surprisingly, the largest percentage loss occurred in the Yuba Creek sub-watershed, which lost more than 7 percent of its tree cover.
The smallest percentage lost was in the Old Mission subwatershed, where less than 0.2 percent of its tree cover was lost while the area gained in other vegetated land covers. That means that Old Mission Peninsula increased its capacity to manage stormwater over the eight-year period. That's a great thing for water quality!
As we continue this initiative, we will work with citizens and officials to share and refine this information. This will help inform decisions about how our freshwater community manages our landscapes and the potential impacts of those decisions on water quality and our Up North quality of life.
About the author: Andy Knott is executive director of the Watershed Center Grand Traverse Bay, whose mission is to protect water quality in the bay and its 1,000 square-mile watershed.
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