By the Numbers: 100

With more than 150,000 miles of riparian forest buffers growing in the Chesapeake Bay watershed, it’s clear that planting trees and shrubs along rivers and streams is a popular practice for protecting waterways. While it stands to reason that wide forest buffers could generate more benefits than narrow ones, it was not until 2014 that the Stroud Water Research Center set about to determine just how wide a buffer needed to be to work.

When Stroud Water Research Center President, Director and Senior Research Scientist Bernard W. Sweeney and Research Scientist J. Denis Newbold dove into research on forest buffer width, they were already decades into forest buffer history. In the seventies, wide zones of streamside vegetation were known to protect streams from the impacts of logging. In 1985, the sixth U.S. Farm Bill funded the planting of streamside vegetation to slow farmland erosion. And seven years later, research from Sweeney himself revealed the quality of streamside vegetation was likely the single most important human-altered factor affecting the structure, function and quality of our streams. But would width amplify all the benefits a forest buffer has to offer? And how wide is wide enough?

After examining eight ecosystem functions streams are known to support—including nutrient removal, sediment trapping and the health of macroinvertebrates and fish—Sweeney and Newbold found that the integrity of small streams can only be protected by forest buffers at least 30 meters—about 100 feet—wide. In other words, the ideal width of a forest buffer is only slightly shorter than three school buses laid end to end!

Of course, Sweeney and Newbold recognized the layout of a particular piece of land could limit the width of any forest buffers that may be planted there. The scientists also acknowledged forest buffer policies may need to accommodate site-specific factors. In the Chesapeake Bay watershed, a forest buffer must be at least 35 feet wide to count as a pollution-reducing practice that supports work toward the Bay’s “pollution diet.” Even so, the average forest buffer in the watershed is almost three times this size, and the benefits of a wide forest buffer are clear.

According to Sweeney and Newbold’s literature review, which synthesized the results of hundreds of scientific studies, effective nitrogen removal requires buffers that are at least 30 meters wide. Buffers of this size can also be expected to trap about 85 percent of any sediment delivered by water moving over the land (which is 30 percent more than a buffer only 10 meters wide!). A 30-meter width can also ensure a buffer protects streams from measurable increases in water temperature during summer months; sends a natural level of stems, branches and other large woody debris into a waterway; and supports natural macroinvertebrate and fish communities.

In our watershed, the planting and care of forest buffers can be limited by a lack of technical assistance and maintenance support. Indeed, buffer restoration has slowed in recent years. While the Chesapeake Bay Program has set a goal to restore 900 miles of buffers every year until at least 70 percent of the watershed’s riparian areas are forested, plantings continue to fall short of this annual target: last year saw the lowest restoration total of the last 16 years.

As part of our work to restore forest buffers, our partners have committed to increasing efforts to teach landowners about buffer establishment and care. Our partners have also committed to better tracking and spending technical assistance funds, seeking out additional funding for the suppression of interfering weeds and determining whether current payments that support buffer care should be raised.

Learn about our work to restore forest buffers.