Watersheds and Forest Management
Riparian Forest Buffer Restoration: Maryland Stream ReLeaf
MD DNR Forest Service provides staff support for Maryland Stream ReLeaf, a statewide initiative supporting riparian forest buffers. Stream ReLeaf coordinates the efforts of a wide variety of state, local, federal, and nonprofit agencies and groups, all of whom play a part in expanding or maintaining streamside and shoreline forests.
Stream ReLeaf began in 1996, carrying out the State’s commitment to the Chesapeake Bay Riparian Forest Buffer (RFB) Initiative . Mature buffers had been found to reduce nitrogen by 60 to 90+ percent, a major benefit for the efforts to reduce nutrients to the Chesapeake Bay by 40% . The RFB Initiative was developed to increase the rate at which forest buffers were established and conserved throughout the Bay Watershed, and adopted by Maryland, Virginia, and Pennsylvania in 1996.
The initial goal, 2010 miles by the year 2010, was ambitious, representing a tripling of the previous rate of buffer planting prior to 1996. Maryland committed to 600 of the 2010-mile goal. In late 1997, the first Conservation Reserve Enhancement Program (CREP) was announced in Maryland, an approach newly authorized by the 1996 USDA Farm Bill. The generous incentives stimulated a 10-fold increase in the rate of landowners signing up for buffer plantings (Fig. 1). An increase in incentive rates in 1998 raised sign-up rates even more. Consequently, Maryland met its 600-mile commitment in 2001 and doubled the commitment to 1200 miles. As Virginia and Pennsylvania began CREP as well in 1999 and 2000, the entire 2010-mile goal for the Chesapeake Bay watershed was met in 2002, eight years early. The 2000 Chesapeake Bay agreement anticipated this early achievement, and called for an expanded goal, which was set in 2003.
Directive 03-1 set a new goal of establishing 10,000 miles of buffers in the Chesapeake Bay Watershed by 2010, of which Maryland is accountable for 2032 miles. Additional goals include establishing buffers along 70% of streams and rivers, working with five other jurisdictions to increase urban tree canopy cover, and to restore, promote and protect riparian forest buffers on public and private land.
The Stream Releaf Implementation Plan for 2005-2010 is currently available. The plan outlines the new goal for the Stream Releaf program, which is an additional 1,200 miles between 2003 and 2010, and the strategy for reaching the goal. NOTE: the plan is an Adobe Acrobat file (330 KB). For the free Acrobat viewer go to Adobe.com.
To include a forest buffer in the statewide accounting, please send the buffer reporting form to:
Chesapeake Watershed Forestry Coordinator:
580 Taylor Avenue, E-1
Annapolis, MD 21401
(410) 260-8531 or -8509
Riparian Forest Buffer Survival and Effectiveness
Streamside forests are a valued tool for nutrient reduction, and they simultaneously provide other benefits for wildlife, aquatic habitat, air quality, streambank stability, and carbon sequestration. When we plant seedlings and young trees to create a riparian forest buffer, the intended benefits and functions develop over time. Several investigations have helped quantify the rate of development of new forest buffers in Maryland.
The first measure of success for riparian forest buffer restoration is whether the trees initially survive. Survival is routinely measured in buffers established using cost-share programs like the Conservation Reserve Enhancement Program. In addition, tree survival has been monitored statewide using random sampling in 1999 and 2002. The rate of development of a variety of functions has been measured on long-term monitoring sites in focus watersheds as part of the Potomac Watershed Partnership and USDA Forest Service Clean Water Action Plan funding.
The 1999/2000 survival study was funded by a USDA Forest Service Clean Water Action Plan grant. It included baseline measurements of characteristics indicative of expected riparian buffer functions on 14 long-term monitoring sites in the Monocacy and Antietam watersheds. The study also evaluated stream temperatures along a stream system, and found that once streams exited fully forested areas, temperatures rapidly rose above tolerances for cold-water fisheries. This suggests that cold-water fisheries will depend on very extensive shading to maintain viability under current climate trends.
The 1999/2000 statewide stocking survey of 130 buffer sites found that 82% met acceptable stocking levels (greater than 200 trees/acre). Just over half of the sites exceeded preferred stocking levels of 400 trees/acre. Average stocking was 488 trees/acre, slightly lower than the average planting density of 511 trees/acre. Survival of planting seedlings was estimated to average only 60%, with naturally regenerated volunteer seedlings making up a third (36%) of the surviving seedlings. The new buffers are fairly diverse in composition, with an average of over 8 species per site. Weed competition was identified as the most common stressor for the young seedlings, with drought, deer, machinery such as mowers, and insects also being noted with lesser frequency.
A follow-up survey in 2002 found survival rates improved to 78%, attributed to greater attention to and support for maintenance by the CREP program. With increased mowing and spraying, the contribution of natural regeneration was reduced but still significant at 25% of total stocking.
The USFS Clean Water Action Plan project also measured baseline conditions for riparian forest buffer functions in 2000 and 2001, including vegetation composition, stream temperature, buffer cross-section and plan section, stream nitrogen and phosphorus, and benthic macroinvertebrate index of biotic integrity. Initial measurements found an average of 59 plant species per site (herbaceous and woody) and average daily maximum stream temperatures that rose from 21.4oC to 22.0oC from upstream to downstream, compared to standards of 20oC for natural trout reproduction and 23.7oC for a recreational trout fishery. Grab samples of streamflow (baseflow) nitrate and phosphate averaged 3.4 mg/l and 0.13 mg/l respectively. Water samples were within drinking water standards for nitrate (none are set for P), but higher than would be expected from a forested watershed. The Index of Biotic Integrity for benthic macroinvertebrates averaged 2.65, a rating of poor. These indices show that there is room for substantial improvement in water quality and habitat conditions in the future.
Riparian buffer conditions were re-measured after five years, supported by a grant from the Harry R. Hughes Center for AgroEcology, Inc. Riparian buffer conditions were measured annually on an additional 20 sites in the Monocacy, Catoctin, and Antietam watersheds from 2001 to 2008 through the Potomac Watershed Partnership and US Forest Service Large-Scale Watershed funding. The full report is available here. Seedling survival generally stabilized after five years at an average of 50%, just over 200 trees/acre. Vegetation richness, the number of plant species within the sample area, increased from 167 to 276 species, a 67% increase. Most of the new species were trees and shrubs, some planted and some from natural regeneration. Invasive exotic plants also increased, with some of the species newly invading the region, not just these sites.
Nitrate and phosphate generally showed improving trends, but variability among sites and years resulted in differences that were not considered significant at five to seven years of age. Average instream nitrate declined 1 to 2 mg/l from 2001, averaging less than 4 mg/l in 2008. Turbidity did not show any discernable trends. Dissolved oxygen levels were consistently in the healthy ranges for aquatic life, and pH values were neutral to slightly alkaline, reflecting the limestone geology in the valleys.
The diversity of aquatic insects (benthic macroinvertebrates) was used to assess stream health. An average of two additional taxa per site were found in 2006, a significant increase only five years after buffer establishment. Index of Biotic Integrity based on the benthic macroinvertebrate data increased on 64% of forest buffer sites, but the modest changes were not statistically significant at this time. The Pfankuch Streambank Stability rating significantly improved between 2003 and 2008, although the more urbanized watershed with 66% impervious surfaces upstream was consistently less stable.
Values for functions of riparian forest buffers were estimated using data from the long-term monitoring sites. Potential income at 30 years averaged $974/acre for pines, with thinning. Hardwoods averaged $1170/acre at 80 years and ranged up to $4300/acre, but most sites had little potential for thinning. Half of the hardwood sites sampled had such low stocking (<60 ft2/ac.) that they were unlikely to yield enough to be harvested economically. Values for water quality and air quality were estimated at $419/year and $60/year, respectively. Adding some hunting lease income for $10/year and annualizing timber income ($15/year for hardwoods) gives $504/acre/year for these values alone.
Based on these results and other longer-term studies, faster growth, denser tree stocking, and greater biomass appear to be associated with earlier production of expected benefits. Hardwoods on sites with heavy grass competition experienced lower survival and growth. Significant benefits may take 15 to 20 years to develop, coinciding with expected crown closure by the young trees. With fast-growing densely planted trees, some other studies have seen significant nutrients reductions in two to seven years.
Timely riparian restoration and development of expected ecological functions depend on sufficient site preparation, matching species to site conditions and actively maintaining good growing conditions around planted trees for at least 3 to 5 years. Given the array of existing and new pests and diseases that are likely to attack common riparian species, planting a diversity of species is an important step to build in long-term resilience. Natural regeneration can add even more species and diversity, but shifting ecological conditions, particularly in deer browse levels and fire exclusion, mean that some important native species are sparse or absent unless planted.
Invasive plants can be a major problem for early growth and survival of trees. Japanese hops is a recent invader that is most prolific in floodplains, and has been spreading rapidly along the streams of the Maryland Piedmont. To improve knowledge on how to control this problem in riparian plantings, Philip Pannill led a study and developed a Cooperative Weed Management Area for the Monocacy and Antietam watersheds. The project was funded through the National Fish and Wildlife Foundation with USDA Forest Service support. The results are presented in a report on the study results and recommendations, and a Powerpoint presentation that details plant biology and identification as well as results of different mechanical and chemical treatment methods.