How Many Trees Does It Take to Protect a Stream?
A literature review conducted by the Stroud Center asked how wide a streamside forest buffer needs to be to protect water quality, habitat, and plant and animal life in small streams.
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The Stroud Preserve riparian reforestation project is a demonstration of the three-zone Riparian Forest Buffer System (RFBS) developed by the U.S.D.A. Forest Service.
Initiated in 1992, the project involves three experimental agricultural watersheds in the Stroud Preserve, a southeastern Pennsylvania farm protected by conservation easements. The streams are in the drainage of the Brandywine River, which flows into the Delaware Estuary.
Prior to 1992, all three watersheds were primarily in crop production (maize, soybeans, hay) under a soil conservation plan including contouring and crop rotation. Water quality was compromised by elevated nutrients and suspended sediments.
The primary objectives of this project are to:
- evaluate the non-point source reductions of the RFBS in the relatively high-relief terrain of the Mid-Atlantic Piedmont
- assess the time required after reforestation to achieve significant mitigation
- establish specific guidelines for planting and managing forest buffers zones in the mid-Atlantic region.
The RFBS consists of: Zone 1, a streamside strip (~ 5 m) of permanent woody vegetation for stream habitat protection; Zone 2, an 18-20 m strip of managed forest upslope from Zone 2; and Zone 3, a 6-10 m wide grass filter strip. The RFBS was established between 1992 and 1994 in a 16-ha watershed (Morris Run) that is primarily in row crop production. Zone 1 included existing streambank trees; Zone 2 was converted from hay and crops to hardwood seedlings; and a level-lip spreader (to disperse concentrated overland flow) was constructed in Zone 3. A second treatment watershed (Half Way Run) was taken out of agricultural production and reforested in its entirety. The third watershed (Mine Hill Run) is being maintained in agricultural production comparable to that of Morris Run, as a long-term reference watershed.
The monitoring design uses paired watersheds supplemented by mass balance estimates of nutrient removal by the riparian forest buffer. Water quality monitoring for nutrients and suspended solids includes grab samples collected every 14 days from all three streams, intensive sampling storm runoff eight times a year (Morris Run and Mine Hill Run), sampling of overland flow (Morris Run), and quarterly sampling of groundwater (Morris Run).
Newbold, J. D., S. Herbert, B. W. Sweeney, P. Kiry, and S. J. Alberts. 2010. Water quality functions of a 15-year-old riparian forest buffer system. Journal of the American Water Resources Association. 1-12. DOI: 10.1111 ⁄ j.1752-1688.2010.00421.x. Request PDF.