903S93001 CBP/TRS 91/93
February 1993
The Role and Function of
Forest Buffers in the
Chesapeake Bay Basin
for Nonpoint Source
Management
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The Role and Function of
Forest Buffers in the
Chesapeake Bay Basin
for Nonpoint Source
Management
Prepared by:
Forestry Work Group
of the
Nonpoint Source Subcommittee
Chesapeake Bay Program
Produced under contract to the U.S. Environmental Protection Agency
Contract No. 68-WO-0043
February 1993
Printed by the U.S. Environmental Protection Agency for the Chesapeake Bay Program
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THE ROLE AND FUNCTION OF FOREST BUFFERS
IN THE CHESAPEAKE BAY BASIN
FOR NONPOINT SOURCE MANAGEMENT
Prepared by:
Forestry Work Group
of the
Non-Point Source Subcommittee
Chesapeake Bay Program
February 1993
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FOREWORD
The Forestry Work Group has recognized the enormous
value of streamside forests in providing quality
aquatic habitat, a measure of water quality, and in
enhancement of other living resources of the Bay. We
equally acknowledge the important role that forest
buffers play in planning for and achieving greater
control over nonpoint source pollutants reaching the
Chesapeake Bay and its many tributary rivers and streams.
With this in mind, a discussion of riparian forest
buffers is timely.
This position ptiper provides useful information for
consideration in current planning efforts. The
recommendations offer a focus for discussion of
remaining issues related to use of forest buffers
and a guide for further work and study.
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INTRODUCTION
When colonists first arrived in the Chesapeake Bay they found vast forests covering over 95%
of the watershed. As the natural ecosyste/n, these forests provided a biological and physical
system which yielded high quality waters and a productive Chesapeake Bay. Unfortunately
much of the historic forest, especially along streamsides, has been lost or altered by human
activities. Farmers found streamside soils to be highly fertile and many were cleared for
agriculture. Uncontrolled access to streams and rivers by livestock also destroyed riparian
forests. And increasingly, urban and suburban development is contributing to the permanent
loss of forests. Although today's forests have been reduced to less than 60% of their original
extent, they are just as important in maintaining the purity of water and quality of life in the
Chesapeake Bay watershed as they were in the 1600's.
THE ROLE OF FOREST BUFFERS
The problems of the Chesapeake Bay are largely the result of non-point source (NPS)
pollutants. It is unquestionable that the conversion of forests to other land uses throughout
the watershed and particularly adjacent to streams and rivers, has adversely affected the
vitality of our water resources. Now, there is an increasing recognition of the role that forests
can play to help reduce pollution when combined with other management practices. Research
results from a variety of sources have documented the effectiveness of the riparian forest in
reducing NPS loading from runoff and groundwater. Most of this research has been done in
agricultural watersheds or in connection with silvicultural activities. Forests have many uses
within systems of best management practices (BMP's) in agriculture, silviculture, land use
planning, and stormwater management. Most attention is now, however, focussed on the
use of riparian forest buffer strips as a management practice. However, forest buffers are
difficult to address in the same context as other common best management practices. Forest
buffers are also recognized for their high value in wildlife and fish habitat and maintaining
ecosystem integrity. This paper primarily discusses elements of the relationship between
forests and water quality in the context of the forest buffer.
Definitions
A Riparian Ecosystem is a complex assemblage of plants and other organisms in an
environment adjacent to and near flowing water. Without definitive boundaries, it may include
streambanks, floodplains, and wetlands as well as sub-irrigated sites forming a transitional
zone between upland and aquatic. Mainly linear in shape and extent, they are characterized
by laterally flowing water that rises and falls at least once within a growing season
(Lowrance, Leonard and Sheridan, 1985).
A Forest Buffer is an area of trees, shrubs, and other vegetation designed to intercept surface
runoff, wastewater, subsurface flow and deeper groundwater flows fr
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Components of a Forest Buffer
All forest buffers are not created equal. A forest buffer has three basic components whose
characteristics determine its effectiveness in terms of NPS pollution control: soil structure and
composition, the extent of surface litter/organic layer, and the species, diversity, and age of
forest vegetation.
1. Soil Structure. Forest soils are generally regarded as highly effective in nutrient
removal however their degree of efficiency can be variable. The ability
of a forest soil to function in removing nutrients in surface and groundwater is partially
dependent upon its depth and position in the landscape, relationship to geologic
structure, permeability, presence of subsurface clay and gravel layers, extent and
duration of shallow water table, and function as a groundwater discharge zone (Pionke
and Lowrance, 1991).
2. Organic Litter Laver. The organic litter layer in a forest buffer provides a physical
barrier to sediments, maintains surface porosity and high infiltration rates, increases
populations of soil mycorrhizae, and provides a rich source of carbon essential for
denitrification. The organic soil provides a reservoir for storage of nutrients to be later
converted to woody biomass. A mature forest can absorb as much as 14 times more
water than an equivalent area of grass (NCASI, 1992). The absorptive ability of the
forest floor develops over time. Trees release stored moisture to the atmosphere
through transpiration while soluble nutrients are used for growth.
3. Vegetation. Trees have several advantages over other vegetation in improving water
quality. Trees aggressively convert nutrients into biomass. They are not easily
smothered by sediment deposition or inundation during periods of high water level.
Their deep spreading root systems resist erosion, stimulate biological and chemical soil
processes, and draw water and nutrients from deep within the soil profile. Trees
produce high amounts of carbon needed as an energy source for bacteria involved in
the denitrification process. All species do not perform equally, but hardwoods are
generally considered essential to maximum efficiency. Perkey (1990) summarized the
effectiveness of tree species in biological uptake of nutrients. A forests' effectiveness
in NPS pollution control will vary with the age, structural attributes and species
diversity of its trees, shrubs and understory vegetation.
PHYSICAL AND BIOLOGICAL FUNCTIONS
Sediment Filtering. The forest floor is composed of decaying leaves, twigs and branches
forming highly permeable layers of organic material. Large pore spaces in these layers catch,
absorb, and store large volumes of water. With buffers of adequate size, 50% to 100% of
sediment and its adsorbed nutrients has been shown to settle out in the streamside forest as
the speed of runoff is reduced by the many obstructions encountered. Suspended sediment
is further removed as runoff and sediments are readily incorporated into the forest floor. With
a well developed litter layer, infiltration capacities of forest soils generally exceed rainfall and
can absorb overland flows from adjacent lands. Grass stands may have only 1/1 Oth this
capacity and may actually be smothered by sediment deposition (Cooper, et al., 1987).
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Nitrogen and Phosphorus Removal. Forest ecosystems and forest buffers function similar to
wetlands by serving as filters, sinks, and transformers of suspended and dissolved nutrients
(Richardson, 1 989). The forest ecosystem retains or removes nutrients by rapid incorporation
and long term storage in biomass, improvement of soil nutrient holding capacity by adding
organic matter to the soil, reduction in leaching of dissolved nutrients in subsurface flow from
uplands by evapotranspiration, bacterial denitrification in soils and groundwater, and
protection of the soil during heavy rains and runoff events.
Studies of forest buffer performance by Peterjohn and Correll (1984) on the coastal plain of
Maryland showed reductions of up to 88% of nitrate and 76% of phosphorus after agricultural
runoff passed through a forest buffer. On the coastal plains of Georgia, Lowrance and others
(1984) credited riparian forests with removing 80-90% of nitrate, 50% of phosphorus and
99% of sediments generated from adjacent agricultural fields. Cooper, Gilliam and others
(1985,1987) studied the role of riparian forests in sediment and nutrient reduction on the
middle coastal plain of North Carolina and found reductions of as much as 93% of nitrate and
50% of phosphorus over a 20 year period. Each of these studies was conducted using a
water balance approach incorporating surface and groundwater components.
O 10 20 30 40 50 60 70 80 90 10O
% removal
Figure 1. Summary of studies in various states regarding nutrient
removal efficiency of riparian forests.
Additional studies conducted in Indiana (Karr and Gorman, 1975), by the Corps of Engineers
on the Cache River in Arkansas, and in France (Piney, et.al., 1988) support these findings.
In general, a third or more of nitrogen was accumulated in woody biomass while denitrification
and other processes accounted for the remainder of the reduction. Phosphorus was removed
with the particulate matter. No studies directly represented urban runoff situations, although
potential exists for nutrient removal in developed settings. The above figures reflect the
nutrient removal potential of riparian forests primarily based in the coastal plain. Preliminary
results from research studies currently in progress in the piedmont and hill/valley terrain
characteristic of uplands in the Bay watershed generally support these findings.
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Stream Channel Stability. Streams and rivers are highly dynamic systems that are prone to
change even without human interference. In-channel stream stability and streambank erosion
at a given point are heavily influenced by the land use and condition in the upstream
watershed (Heede, 1980). However, vegetation is essential for stabilizing stream banks,
especially woody vegetation (Karr, J. R. and I. J. Schlosser, 1978). Forest buffers alone can
rarely be expected to control existing stream erosion problems but forests have an indirect
effect on streambank stability by providing deep root systems which hold the soil in place
more effectively than grasses and by providing a degree of roughness capable of slowing
runoff velocities and spreading flows during large storm events. Karr and Gorman (1975)
explained, that while slowing velocities of flood heights may increase headwater flood height,
downstream flood crest and flood damage is dramatically reduced. These processes are also
critical for building floodplain soils.
Shade and Temperature. The shade provided by a riparian forest buffer moderates stream
temperatures and levels of dissolved oxygen. These factors are critical for fisheries and
submerged aquatic vegetation, but also have water quality implications. Temperature
increases the rate at which nutrients attached to suspended solids are converted to readily
available (soluble) forms. As stream temperature increases above 60° F significant increases
in phosphorus release from sediments occurs (Karr and Schlosser, 1978). In this way, the
loss of forest shade may exaggerate nonpoint pollutant effects by reducing the streams ability
to assimilate organic wastes and inducing algae blooms and low oxygen levels.
Habitat. A great variety of habitats are found in structurally diverse riparian woodlands. In
many cases, their value to wildlife and fish alone may be substantial enough to justify forest
buffers. Forested corridors function as connectors between isolated blocks of habitat and
provide shelter for insects beneficial to control of agricultural pests. Fallen and submerged
logs and the root systems of woody vegetation provide cover for fish and invertebrates while
forest detritus is the basis of the food web for the stream. Energy cycles in the aquatic
system are often critically dependent on interaction with streamside woody vegetation. As
such, fish and habitat are important indicators of good water quality. In many agricultural and
urbanized areas, even narrow forest buffers can be essential to the survival for many
important species. Human habitat is also important. Forest buffers in urban areas provide a
unique linkage between people and their environment. Forests can enhance quality of life and
increase community involvement and activism by planting and caring for urban forests.
THE PRACTICAL USE OF FOREST BUFFERS
Forest buffers present an emerging challenge. Opportunities exist for preserving, enhancing
and restoring riparian forest ecosystems. Improved land use planning can preserve forest
buffers and greenbelts during development and land clearing. Narrow or intermittent forest
buffers along streams and rivers can be expanded and connected through planting and better
management. Thousands of miles of riparian forest, now lost, can be restored. Restoring
forests along our streams and rivers, however, will not be an easy task. Compatibility with
historic farm and pasture management, potential loss of cropland, small farm sizes, long term
protection of buffers, and social acceptance may be difficult barriers to overcome in parts of
the farming community. Stormwater engineering needs, high land values, and vandalism or
other physical damage in urban areas can make urban reforestation challenging.
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Agricultural Lands. Cropping practices, fertilization, pesticide application, field drainage and
livestock grazing and confinement all have the potential to seriously degrade water quality.
Forest buffers can be used as a linear break in the pattern of row crops and pastures to
manage sediment, wind and runoff problems. Riparian forests form a buffer between
agricultural uses and streams and can control nonpoint source pollution while producing
numerous additional benefits. In some situations, non-riparian forests safely removed from
areas of high water table can be used for disposal of manure or in treatment of leach field
effluent. When properly protected from livestock use, forests can help protect streambanks.
Forests and forest buffers are used in conjunction with other nutrient and erosion control
practices. For example, a best management system for a farm may combine conservation
tillage, fencing, grass waterways, forest buffers, and a nutrient management plan.
Urban and Suburban Development. Forests should be retained as greenbelts along streams and
drainageways during development. Forests and forested wetlands can also be used as part
of treatment systems for urban runoff, where design requirements can be met. Forests can
be used as infiltration zones. Urban forest buffers filter runoff, air pollutants, and noise.
Forests cool the air and provide corridors for movement of birds and other wildlife. In urban
areas, these buffers may provide the only available habitat for many organisms.
Silvicultural Activities. Much like their use on agricultural lands, forest buffers are used during
timber harvest operations to prevent sediment from logging roads, skid trails, and site
preparation activities from reaching streams and rivers.
Specifications for Establishment. The USDA Forest Service and Soil Conservation Service
jointly established guidelines and practice specifications for use in establishing forest buffers
(Welsch, 1991). Although implementation is flexible, these specifications discuss components
and uses of the forest buffer that should be taken into consideration by field consultants and
landowners prior to buffer establishment. Location, width, placement, fencing option,
management objectives (such as water quality improvements, wildlife habitat, wood products,
recreation, etc.), species selection and more will be taken into consideration during forest
buffer design. The SCS NE Regional Technical Center has issued interim standards and
specifications on forest buffers for states in the northeast region.
MANAGEMENT OF FOREST BUFFERS
Although maintenance-free for most of their existence, forest buffers may be designed and
managed to accomplish many different resource objectives. Once established, management
options for the riparian forest ecosystem range from strict preservation to the complete
removal of streamside trees. However, neither of these extremes represents the optimum
management of these areas to enhance water quality. With proper management, riparian
forest buffers can be more productive and provide better NPS pollution control (Lowrance,
1985). Studies have shown that both old growth and young growth forests alone have less
potential to remove nutrients than a vigorous forest of mixed ages. Hardwood species must
be predominent enough to perpetuate developed organic litter layers. Wildlife habitat
concerns, such as those for old growth trees, must be integrated with water quality needs.
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A challenge exists for forestry professionals. Current silvicultural systems for evenage or
unevenaged management are designed primarily to provide a sustained yield of wood
products. Systems which focus on a variety of landowner desires while protecting riparian
values are more appropriate. Pionke and Lowrance (1991), have recommended that uneven-
aged silvicultural systems should be employed in forest buffers to maximize water quality
benefits. However, trees should be periodically harvested to sustain this growth and diversity
and remove nutrients sequestered in tree stems and branches. In this way, forests can
benefit both the landowner and the environment (Welsch, 1991).
NEEDED RESEARCH
A general conclusion can be made that forested riparian buffer strips are effective in reducing
nutrient, temperature and sediment levels in runoff and that riparian ecosystems can exert
major control on N03-N concentrations in riparian zone groundwater, especially when
subjected to shallow water tables (Pinoke and Lowrance, 1991). However, it is generally
accepted that nitrate removal efficiency varies in different geographic provinces. Research
should continue to document forest buffer effectiveness in mountain, hill and valley, piedmont
and coastal plains and to compare performance of various forest types, and with other
practices such as grass filters. In each case additional quantification of expected performance
is needed.
The age and degree of development of the forest buffer and its attendant litter layer is also
likely to have an effect on buffer efficiency. This comparison is important in relating forest
buffers to grass filters over time. Although grass filters in the riparian zones contain less
organic matter in their surface soils, no data is currently available to determine the levels
necessary for optimal denitrification. The role of organic carbon in this process needs further
study.
Studies of the minimum width of riparian forest necessary to achieve effective nutrient
reductions has not been.done. In addition, management prescriptions for forest buffers to
improve their nutrient removal effectiveness over the long term need additional study and
development. Information is also needed on species mix and nutrient uptake and the time
necessary to establish a functioning forest buffer.
SUMMARY AND CONCLUSIONS
Streams and rivers are the focal point of increasing public interest. Their quality affects most
residents of the Bay watershed. Riparian forests play a significant and demonstrable role in
protecting and improving these ecosystems' quality. The restoration of a healthy aquatic
ecosystem from the tributary streams to the Chesapeake Bay will require the reestablishment
of significant amounts of riparian forest. It will also require the enhancement and repair of
many existing forest buffers. Although additional research and study is necessary to better
quantify the effectiveness of forest buffers in a variety of field conditions, and provide a
comparison with other vegetation types, sufficient studies currently exist to document the
value of this practice in nonpoint source control.
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The restoration of forested buffers along the streams and rivers in agricultural and urbanizing
watersheds in conjunction with other nutrient and runoff management practices has enormous
potential for the long term improvement of aquatic resources in the Chesapeake Bay
watershed. Increased emphasis should be focussed on the implementation and study of this
available cost effective management practice and the development of targeting programs to
increase its implementation in agricultural and urban settings. This management practice
brings tangible benefits to both water quality and living resources.
It is essential to the Bay's long term water quality and living resource goals to ensure
conservation of forests and especially streamside buffers during land use planning arid
development. Large amounts of forests are currently being converted to other land uses such
as residential and commercial development, transportation, and agriculture. Replanting trees
as mitigation following construction alone should not be considered as a substitute for proper
conservation and management of existing forests. Otherwise forest losses will quickly offset
gains made through tree-planting programs.
Although forest buffer design and use is ongoing in the Bay watershed, work is still needed
to bring specifications and standards for use to the ground level. Flexible forest buffer
specifications need to be readily available to soil conservationists, farm planners, engineers,
and consultants so that this practice can be effectively used to meet differing site objectives.
There is a need to enhance the level of training and experience in the value and uses of forest
buffers and to work closely with landowners and planners at the local level. Pilot projects
which demonstrate forest buffers need to be implemented and publicized.
RECOMMENDATIONS
The need to protect and enhance beneficial land uses and the ability to target nonpoint source
control implementation was clearly recognized in the 1990 NPS Evaluation Panel Report. The
current state of our knowledge clearly illustrates the value of forest cover in protecting water
quality and providing essential habitat for wildlife and fish. Clearly, forest buffers should be
a priority tool in most best management systems. It is essential to integrate the role of forest
and especially forest buffers into the development of tributary strategies, nutrient
management planning, and local land use planning.
Recognizing these findings, the Forestry Work Group makes the following recommendations
to the Nonpoint Source Subcommittee of the Chesapeake Bay Program.
General Recommendation
Forest buffers should be actively promoted as a practice which can provide water quality
protection and be integrated into farm planning, operation, and management. The retention,
enhancement, restoration, and management of forest buffers should be actively promoted in
urban areas and during residential and commercial development.
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Specific Goals
The following provides a synopsis of the types of actions that would be needed to fully
implement an effective program of forest buffer use Bay-wide. The Forestry Work Group is
working on several of these topics at the present time.
1. Identify and evaluate existing state and local land use regulations and ordinances to
determine which are effective at ensuring forest buffers are retained or restored during
residential and commercial development.
2. Develop highly visible pilot demonstration projects to illustrate and evaluate the proper
uses of forest buffers on working farms or pastures.
3. In high density urban areas, wherever feasible when implementing BMP retrofits, include
the use of pilot demonstration projects which illustrate the uses of forests in stormwater
management systems.
4. Review existing manuals, handbooks and technical specifications in each jurisdiction such
as those used by forestry departments, conservation districts and extension, to ensure that
guidelines are in place to effectively promote and implement forest buffers.
5. Working together, the U.S. Forest Service and State Forestry agencies will provide input
to tributary strategy development which addresses conservation of forest resources, and
restoration of forest buffers and corridors in each tributary basin in the Chesapeake Bay
Watershed.
6. Coordinate and enhance forest inventory efforts of the U.S. Forest Service, State Forestry
agencies and state and local conservation agencies/districts, to better assess pressure on
existing forest resources, target critical areas for restoration of forest buffers, and provide
consistent information to modeling efforts needed to evaluate changes in the Bay's forests.
7. Coordinate existing federal, state, and local incentive programs to provide the flexibility
and maximum targeting for accomplishment of forest buffer establishment or enhancement.
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8. Determine the feasibility of establishing forest buffer goals (by stream mile) in Bay
tributaries. Particular attention could be placed on enhancing and connecting portions of
existing buffers to provide corridors for movement of wildlife.
9. Develop materials and strategies needed to conduct a Bay-wide program for education and
training on implementation of forest buffers in different field situations.
10. Conduct an analysis of current research on forest buffers and initiate a Bay Program
workshop or symposium to present current knowledge, comparisons of forest and other buffer
use, and future-research priorities.
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REFERENCES
Cooper, J.R. and J.W. Gilliam, 1987. Phosphorus Redistribution from
cultivated Fields into Riparian Areas. Soil Science Society of America Journal 51(6),
pp 1600-1604.
Cooper, J.R., J.W. Gilliam, R.B. Daniels, and W.P. Robarge, 1987.
Riparian area as filters for agriculture sediment. Soil Science Society of America
Journal 51(6) 417-420.
iHeede, Burchard, 1980. Stream Dynamic: An Overview for Land
Managers. Technical Report RM-72, USDA Forest Service, Rocky Mountain Range and
Forest Experiment Station, Fort Collins, CO.
Karr, James R. and O.T. Gorman, 1975. Effects of Land Treatment on
the Aquatic Environment. Nonpoint Source Pollution Seminar, EPA 905/9-75-007, U.S.
Environmental Protection Agency, Washington, D.C., 4-1 to 4-18.
Karr, J. R. and I. J. Schlosser, 1978. Water resources and the land-water
interface, in "Science" #201: 229-234.
Lowrance, Richard, Ralph Leonard, and Joseph Sheridan, 1985.
Managing riparian ecosystems to control nonooint pollution, in "Journal of Soil and;
Water Conservation", January-February, pp 87-91.
NCASI, National Council of the Paper Industry for Air and Stream Environment, Inc., 1992.
The Effectiveness of Buffer Strips for Ameliorating Offsite Transport of Sediment-
Nutrients. and Pesticides from Silvicultural Operations. Technical Bulletin No. 631,
New York, NY.
Perkey, Arlyn W., 1990. Forest Management Update Number 11.
Morgantown Field Office, USDA Forest Service, Northeastern Area State and Private
Forestry, 24 pages.
Peterjohn, William T. and David L. Correll, 1984. Nutrient Dynamics in an Agricultural
Watershed: Observations on the Role of a Riparian Forest, in Ecology 65(5), pp 1466-
1475.
Pinay, G. and H. Decamps, 1988. The Role of Riparian Woods in
Regulating Nitrogen Fluxes Between the Alluvial Aouifer and Surface Water: A
Conceptual Model, in Regulated Rivers: Research and Management, Vol. 2, 507-516.
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Pionke, H.B. and R.R. Lowrance, 1991. "Fate of Nitrate in Subsurface
Drainage Waters", in Managing Nitrogen for Groundwater Quality and Farm
Profitability. Soil Science Society of America, Madison, Wl.
Richardson, C.J., 1989. Freshwater Wetlands: Transformers, filters, or
sinks?. FOREM 11(2), Duke University School of Environmental Studies.
Welsch, David, 1991. Rioarian Forest Buffers-Function and Design
for Protection and Enhancement of Water Resources. USDA Forest Service Technical
Publication 0NA-PR-O7-91, Northeastern Area State and Private Forestry, Radnor, PA.
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