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The Value of Riparian Zones for Protecting Aquatic Systems:
General Concerns and Recent Studies in Maine1
2
John R. Moring 3
Greg C. Garman '+
Dennis M. Mullen
Abstract.--Riparian zones serve important functions for
fisheries and aquatic systems: shading, bank stability,
prevention of excess sedimentation, overhanging cover for
fishes, and energy input from invertebrates and allochthonous material. Impacts from loss of riparian areas are discussed in relation to aquatic ecosystems, and the results of
two recent studies in Maine are reviewed.
INTRODUCTION
Any land disturbance in a watershed, whether
due to logging activities, road or other construction, agriculture, or other activities, can directly
or indirectly affect stream ecosystems. In forested
watersheds, aquatic life is most affected by logging and related activities in the nearby areas.
The more extensive such cutting, the greater the
potential for environmental and biological changes
in streams.
Use of a buffer strip of intact riparian vegetation can be an effective deterrent to many of the
changes in streams brought about by land disturbances. Riparian vegetation acts to shade streams,
provide bank stability, provide overhead cover and
food for fishes (via insect drift), and provide
allochthonous input to fuel the aquatic ecosystem.
The forest canopy/riparian zone thus effectively
becomes part of the aquatic ecosystem, as changes
in the riparian component can directly alter the
aquatic component.
In Maine, where 89% of the land is forested,
land use regulations in unincorporated territories
allow only limited cutting within riparian zones.
But, because of extensive damage from spruce budworm in fir and spruce stands (approximately 10
million acres are moderately to severely infested
in Maine &.lone) , there have been increa~ed numbers
of applications submitted for exclusion permits to
cut close to streams. Thus, knowledge of the
potential impacts of removing riparian vegetation
1
Paper presented at the North American Riparian C2nference (Tucson, Arizona, April 16-18, 1985).
John R. Moring is Associate Professor of
Zoolo~y, University of Maine, Orono, Maine.
Greg C. Garman is a Post-Doctoral Fellow,
Northeast Atlantic Fisheries Center, Fisheries and
Ocean~, St. John's, Newfoundland.
Dennis M. Mullen is a Zoology Research Technician, University of Maine, Orono, Maine.
315
to fish and other aquatic life is becoming increasingly important to resource managers. Two recent
studies in Maine addressed these concerns. One, on
School Brook, examined aquatic primary production
before and after cutting. The other, on the East
Branch Piscataquis River, dealt with changes in
physicochemical and biological conditions following
salvage cutting.
The objectives of this paper are to (1) review
the beneficial characteristics of riparian zones
with respect to aquatic life, and indicate how the
removal or alteration of such vegetation can affect
stream ecosystems, and (2) briefly summarize the
results of the two recent studies in Maine where
riparian vegetation was removed along streams during
logging.
BENEFITS OF RIPARIAN ZONES
Physicochemical Conditions
Studies concerning environmental changes fol-lowing removal of riparian vegetation are relatively
extensive from western North America and the Appalachian Mountains. But, with the exception of
studies by Martinet al. (1981), Englert et al.
(1982), and a few others, such riparian-related
studies have been rare in New England. With soil
excavation, sediment levels can increase, particular:y in steep terrains and during road construction
(Brown and Krygier 1971, Krammes and Burns 1973,
Platts 1974, Moring 1975, Beschta 1979). The Haine
Land Use Regulation Commission (1979) concluded
that equipment used in riparian areas was largely
responsible for the increased levels of sedimant
entering areas of low gradient in Maine.
These increased levels of sediment fines have
been directly linked to decreased survival of developing fish eggs and energing alevins (Cooper
1965, Koski 1966, Phillips et al. 1975). Though
riparian zones act to filter excess sediment from
entering streams, significant increases can still
occur in areas of steep terrain, heavy rainfall or
snowmelt, or in watersheds with large disturbed
areas. When riparian vegetation is removed, streambank stability is low, and sedimentation may enter
streams over an extended period of time. With the
removal of vegetation, stream flow often increases,
particularly if riparian areas are cut (Rowe 1963,
Meehan et al. 1969, Rothacher 1970, Swank and
Helvey 1970, Moring 1975, Graynoth 1979, Verry et
al. 1983).
Levels of intragravel and surface dissolved
oxygen often decline following logging, particularly
if riparian vegetation is diminished (Iwanaga and
Hall 1973, Moring and Lantz 1974, Moring 1975,
Ringler and Hall 1975). Although levels eventually
return to pre-cutting values (dependent on water
temperature, stream flow, and other factors), the
period of depressed values of dissolved oxygen and
permeability can be sufficiently low to result in
mortalities of developing eggs and alevins (Moring
1981,1982) as well as adult and juvenile fishes in
streams (Hall and Lantz 1969, Moring and Lantz 1975,
Moring 1981).
If overstory vegetation near streams is opened,
water temperatures can increase dramatically (Chapman 1962; Brown and Krygier 1967,1970; Gray and
Edington 1969; Meehan 1970; Narver 1972; Moring 1975;
Welch et al. 1977; Lynch et al. 1984). The magnitude
of this increase depends on the presence or absence
of a riparian buffer strip, the size of the cut area,
the adoption of slash burning or debris clearance,
and the soil type. These temperature changes can
be long term (Moring 1975, Feller 1981). Even a
partial buffer of riparian vegetation may not be
enough: a study by Hewlett and Fortson (1982) indicated a significant increase in water temperature
when only a partial riparian strip remained after
logging.
Biological Conditions
Aquatic communities in woodland streams depend
on the surrounding forest for energy. This allochthonous input drives the aquatic ecosystem
(Minshall 1967, Benke and Wallace 1980). When the
riparian canopy is removed, this basic energy source
is altered. Allochthonous input and insect input
decreases. When environmental conditions change,
invertebrate numbers and diversity often change
(Gurtz et al. 1980, Murphy and Hall 1980, Newbold
et al. 1980, Martin et al. 1981, Murphy et al. 1981).
A direct relationship has often been noted between
land use practices, invertebrate density and diversity, and the presence or absence of intact
riparian zones.
Fishes are the highest order consumers in
woodland streams, and are directly dependent on
invertebrates for food and indirectly dependent on
physicochemical constraints for acceptable habitat
and conditions for metabolism. When riparian
vegetation is removed, environmental conditions
in streams (particularly temperature, dissolved
oxygen, sedimentation, and stream flow) often change,
significantly affecting fish populations (Hall and
tantz 1969, Meehan et al. 1969, Burns 1972, Moring
and Lantz 1975, Reed and Elliott 1978, Horing 1981).
316
Th~ presence of an intact riparian zone is
essential for mitigating wide variations in environmental conditions. The approximate width of such
"buffer" riparian strips has been the subject of
some studies (Brazier and Brown 1973, Erman et al.
1977, Newbold et al. 1980, Erman and Mahoney 1983,
etc.), though most federal and state agencies,
where riparian cutting policies are in force, use
a 23 m (75 ft) intact riparian zone, on each side
of a stream, within which all cutting or other
activity is prohibited. Several states are now
encouraging landowners to retain riparian zones,
even when not legally required to do so, by utiliztax incentives.
THE SCHOOL BROOK STUDY
School Brook, a small tributary to the
Aroostook River, is located near Oxbow, Maine. The
spruce-fir canopy provided shading to this important
nursery stream for brook trout (Salvelinus fontinalis). A salvage clearcut, extending along
1,500 m (4,920 ft) of one bank of the stream, was
undertaken in winter 1983-1984. The objective of
the study was to measure instream primary productivity to determine if autochthonous energy input in~
creased after cutting in the watershed.
Primary production was measured in June and
August 1983, and June, August, and October 1984 at
each of four sections in the control and experimental
sections. Details of techniques have been reported
by Mullen (1985), but production rates were estimated using closed recirculating chambers similar
to those described by Bott et al. (1978).
No significant differences were noted in production by periphyton communities before and after
cutting and between control and experimental sections.
Rather than being a rejection of the hypothesis of
increased primary production following logging, the
results were inconclusive because the removal of
riparian vegetation along only one side of the
stream resulted in just a 5% reduction in effective
canopy. And, the orientation of the cut was such
that the angle of the sun did not allow sunlight to
directly penetrate forest cover.
Population estimates of brook trout indicated
no significant differences between cut and uncut
sections in the stream. Populations in both control
and experimental sectiwns increased after logging.
However, any changes in water temperature were mitigated by cool spring water entering the brook at
several locations. Together with the limited removal
of the canopy, brook trout populations were essentially not affected by changes in environmental conditions. Thus, under the conditions of that stream
and that individual, limited cut, the aquatic system
was little changed.
EAST BRANCH PISCATAQUIS RIVER STUDY
The few studies conducted in New England dealing with removal of riparian vegetation have dealt
with nutrient loss (Bormann et al. 1970, Likens et
al. 1970, Hallet al. 1980, etc.), or on a limited
scale with macroinvertebrates (Martinet al. 1981).
Most such studies have also been within deciduous
forest areas (e.g. Hubbard Brook). As a consequence,
a study was conducted from autumn 1980 to autumn
1982 on the East Branch Piscataquis River, near
Greenville, Maine. The stream is within a typical
northeastern spruce-fir forest of the type described
by Gibbs (1979).
The river is approximately 15 m wide in the
affected area. A canopy of spruce and fir provided shading to approximately 90% of the stream
surface prior to loggin'8· About 90% of the standing timber was removed in the cut block, resulting
in the removal of 70-80% of the canopy shading the
stream. Pre-cutting measurements were conducted
in 1981, and post-cutting measurements were conducted in 1982--a total of 24 months of study.
hold for forested areas of Maine as well. It should
be noted that, though 23 m (75 ft) intact riparian
strips are often recommended for stream protection,
wildlife biologists are often recommending even
wider zones (as much as four times wider: Johnson
and Small 1985), as riparian areas have value as
animal corridors and winter deer yards. These terrestrial wildlife concerns extend beyond the immediate areas near streams.
The presence of intact riparian areas provides
a "cushion" of protection for stream ecosystems.
The riparian zone is a critical component for
aquatic systems, and the alteration of that-terrestrial zone can have serious implications to
aquatic communities.
Details of the study have been reported by
Garman (1984), but benthic particulate organic
matter and suspended particulate matter significantly increased.after logging, resulting in higher
levels of sediment fines in the gravel of pools.
Particulate organic matter in the stream was ten
times higher after logging and the ratio of coarse
to fine substrate particulates was reduced by almost 100 percent following cutting in the watershed.
Annual stream flow remained similar after cutting, but spring stream flow was higher following
logging. Water temperatures were significantly
higher after logging, and these alterations were
linked to many of the biological changes. Mean
daily temperature maxima were significantly greater
in every month of 1982, exceeding 30°C (86°F) on
several dates in summer. Waters warmed earlier and
retained heat later in the year, probably due in
part to supplemental warming of runoff across the
clearcut area.
ACKNOWLEDGMENTS
This research was conducted in cooperation with
the International Paper Company, and conducted on
Company lands. Funding was principally from the
Maine Department of Inland Fisheries and Wildlife,
with additional grants from International Paper
Company and the Evelyn Murphy Fund of the Appalachian Mountain Club. \ve appreciate the assistance
and expertise of fishery biologists David Easley
and Paul Johnson.
LITERATURE CITED
Insect and fish communities after logging were
dominated by hardier species. Most groups were
still represented after cutting, though mean annual
densities of Plecoptera and Odonata were reduced,
and eurythermal insects (e.g. Oecetis, Cyrnellus,
and Psilotreta) increased in number. Brook trout
disappeared from the stream, and non-game fishes
(e.g. white sucker, Catostomus commersoni; northern
redbelly dace, Phoxinus eos; blacknose dace,
Rhinichthys atratulus; and creek chub, Semotilus
atromaculatus) dominated the post-logging stream
community. The common shiner (Notropis cornutus),
not present prior to removal of riparian vegetation,
became a significant component of the post-cutting
fish population.
CONCLUSIONS
Intact riparian zones have several inherent
values to aquatic systems. They insure stability
and integrity of stream banks. Vegetation and root
structures help to retain soil and reduce erosion
to the stream. Intact riparian vegetation can also
provide shading to streams, overhanging cover,
terrestrial drift, and allochthonous drift for energy.
The study on the East Branch Piscataquis River
demonstrated that many of the concerns expressed by
riparian scientists in other parts of North America
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