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Creeks and streams are attractive and valuable components of both urban and rural environments. They provide beauty, enjoyment, recreation, and inspiration to the humans who flock to them throughout the year. Yet the dynamics of their healthy functioning are complex and not well understood either by the general public or by those with authority over their maintenance and use.
We have been studying Big Chico Creek here at California State University, Chico for over 20 years now, and reading and talking to scientist studying other streams. The information that follows represents a distillation of what we've learned about streams and the proper management of them. Although our points are based on scientific research, they are presented in a format with which anyone will be comfortable.
This booklet is intended for those entrusted with some aspect of the management of urban or rural creeks, as well as those fortunate enough to have such streams flowing through property they own. It is our hope that the information here will help to guide you to intelligent decisions producing healthy and vigorous creek communities.
1. In creekside areas where natural or near-natural conditions exist, riparian vegetation native to the area should be encouraged, and exotic vegetation should be discouraged.
Native plant species produce specific types of foods which the animals of the
riparian zone are adapted to find and to digest. Specific plants also supply
cover that protects and shades animals, other plants, and the creek. In
addition, certain plants provide habitat in the form of nesting cavities for
animals and growing sites for epiphytes (plants growing on plants), such as
moss and mistletoe. Thus, all the life along the creek has become accustomed
to the native plants naturally growing there, and depends upon them for the
particular type of food, cover, and habitat they provide.
For example, among the key native riparian plants in the Sacramento Valley are white alder (Alnus rhombifolia) and western sycamore (Platanus racemosa). White alder roots form symbiotic associations with soil bacteria that can change gaseous nitrogen (in the air and soil) into organic forms plants can use. Thus alder leaves are high in protein and, when they fall into the creek, are a rich source of nitrogen supporting the food chain for animal life in the creek. Western sycamores contain heartwood which rots easily, so when a branch breaks off, decay often eats into the tree, forming a cavity that becomes home for birds and squirrels. Important plants native to the Sacramento Valley riparian zone.
In modern times, many aggressive plants from other continents or other sites on this continent have invaded our creeksides. These plants crowd out the native species, but do not perform the important functions as well as the natives do. Their leaves, seeds, and fruit are less suitable as food for our native animals, and they do not provide as good cover or habitat. Thus, a creekside full of exotics may look green and flourishing, but the creek life and the bankside animal life will be but a shadow of its former self, lacking, for example, the nitrogen from alder leaves and nesting cavities of sycamores. Common exotic plants that have invaded the Sacramento Valley riparian zone.
Restoration. To restore a riparian zone to its normal richness, exotic species should be removed and natives replanted. For seedlings and small saplings, simply pulling the plants up by the roots is the quickest and surest means of removal. Mature, established vegetation requires a different strategy. Many exotics, notably Tree of Heaven (Ailanthus) and Privet (Ligustrom), stump- sprout vigorously when the mature tree is cut. Application of a systemic herbicide before or at the time of cutting is the quickest way to kill these plants. If you are willing to wait a year or two for results, they can also be killed by girdling, without use of chemicals. Our experience has been that these stump-sprouters require a great deal of diligence and concentrated attention to successfully eliminate.
When revegetating with natives, whether of areas where exotics have been
removed or areas lacking vegetation due to human activity, it is important to
place plants appropriately. In the Sacramento Valley, for example, the alders
typically grow at the very edge of the creek, with their roots extending into
the creek itself. Sycamores typically grow somewhat higher above the level of
the creek, with valley oaks (Quercus lobata) from the adjacent valley
oak savanna extending into the riparian somewhat beyond and above the
sycamores. Local arborists or botanists should be consulted to ensure that
native riparian plants are planted at proper locations. Proper watering
regimes are required for new native plants to become established. For
example, even though our Sacramento Valley native trees are adapted to
waterless summers, the seedlings and even saplings will require several
summers of periodic watering to become established, and arrangements must be
made either for drip systems installed at the time of planting or firm
commitments for hand-watering.
Extent of the Riparian. Although the width of riparian zones vary, the natural zone of even a small creek may extend 100 feet or more to either side of the creek itself. The health and welfare of the creek and the life in it is intimately dependent upon the vegetation beside it. When developers or farmers attempt to create a bit more open space by plowing or bulldozing into the trees and shrubs of the riparian zone, they are gravely damaging not just the vegetation but the animal life and the creek life itself. If you enjoy the creek and fishing in the creek, you must respect the entire riparian zone as well, because they are interconnected.
2. Irrigation in the riparian corridor should be minimized.
Here in California, over-watering in the riparian corridor encourages the establishment and growth of exotic, weedy non- native species. These species compete with the native riparian plants, and do not provide quality food or habitat that native riparian animals need. Our native riparian plants are adapted to our long, dry summers and do not require irrigation to survive or thrive once they are established. In fact, summer watering may actually harm some of our native plants. Many studies have shown that valley oaks in lawn areas are weakened by the summer watering the lawns require. Canopy growth by the oaks is stunted, and oak root fungus is encouraged. This fungus is a common killer of oaks, with resultant danger to humans when the trees fall. A current protective strategy implemented by parks in our area is to remove grass under the oak canopies, replace it with wood chips, crushed rock, or other material and, of course, eliminate the watering in the area.
If there are exotic plants in or along the edge of a riparian corridor and
you wish to maintain them there, then their negative impact upon the native
vegetation can be minimized by providing summer water with drip tubing rather
than spray heads. In addition to causing less damage to native plants, drip
irrigation is also a far more efficient means of irrigation in terms of water
use. Spray heads and the larger volume of water they release also permits the
runoff of pesticides and other pollutants into the riparian zone.
3. Stream bank maintenance should emphasize protection from adverse human impact and restoration of natural conditions.
Barren stream banks permit erosion of soil and perturbation of the creek. Whether these areas result from excessive human use or natural conditions, they should be mitigated or eliminated. If continuation of human access is desired, then stone steps should be put into place and appropriate native vegetation planted to either side of the steps. If human access is not necessary, then build up the soil, if it is extensively eroded, and plant native sedges and shrubs. Fencing may be necessary to discourage humans (or dogs) from using the area.
1. Activities that disturb the stream bed or gravel surface should be limited, since these displace and destroy stream life.
A balance must be struck between our enjoyment of streams and the requirements of the streams for health. Although not readily apparent, the bed of a stream is alive with plants and invertebrate animals living on and under the rocks and sediment there. Vehicles moving through the stream crush and displace this life, to the detriment of the stream and its health. Even when humans or dogs walk in the stream channel, the life there is disturbed. Turning over rocks and building rock dams across the stream are also harmful to stream life. Fish, such as salmon, are disturbed by intensive human use of deep pools in creeks and burn up energy reserves, which may be crucial to their successful migration and reproduction and hence their continued presence in a creek system.
As people use and enjoy streams, they must be aware of the effect of their
activities, and modify their activities to respect and protect the health of
the stream and its life.
2. Bank protection should be accomplished by planting of native riparian shrubs and trees, in preference to riprapping with rocks.
A stream channel and the riparian plants alongside it form an integrated system. The flowing water constantly exerts force on the banks, cutting in some places and depositing in others. At the same time, streamside vegetation resists the water and tends to encroach on the channel. The two forces balance one another in a dynamic way, with vegetation gaining in dry years and the stream gaining in wet years. As a result, the stream stays much the same while constantly changing. Meanwhile, the interplay of flood waters with streamside trees (particularly large sycamores) provides most of the cover and holding pools for fish.
Rocks placed along stream banks to prevent erosion provide limited cover,
habitat, and no food for riparian animal life. These rocks also have a way of
migrating into the stream, due to floods, gravity, and people moving them to
dam swimming holes. Once in the stream, the large rocks armor the bottom,
preventing floods from reworking gravel and fish from digging redds for
egg-laying. In a flow-controlled stream, such as Big Chico Creek through the
city of Chico, the erosive force of the stream will never significantly exceed
the resistance of the streamside vegetation. Accordingly, adequate bank
protection can be provided by the natural growth of riparian vegetation in
flow-controlled systems. To this end, the immediate banks of such streams
should be densely planted with native riparian species and riprapping with
rocks should not occur.
3. Natural fluctuations of stream flow should be permitted, within the limits of safety.
High water flow in streams is necessary for the health of the stream. Even flow-controlled streams must be permitted to experience high water conditions. These floods maintain the flow capacity of the channel, wash and sort gravel and transport it downstream, excavate pools and undercuts, which create fish habitat and cover, often reduce populations of exotic fish species while having little effect on natives, and flush accumulated silt, litter, and toxins from the stream.
4. Materials other than rainwater should not be permitted to enter storm drains.
Storm drains channel runoff from city streets and rooftops into creeks when
it rains (or when cars are being washed). Any chemicals, litter, or debris
deposited on streets or paved areas will end up in the creek. This runoff
frequently contains rubber worn from tires, oil leakage from vehicles,
asbestos worn from brakes, detergents, and fertilizers and pesticides
originally applied to lawns and gardens. All these are harmful to creek life,
some of them lethal. Urban authorities should monitor materials being flushed
from the streets into storm drains (particularly in industrial areas), should
identify storm drain grates with signs indicating that dumping of materials
down the drains is prohibited, and should install settling basins in the
drains to collect some of the pollutants before they enter the streams.
5. Litter should be promptly and systematically removed from streams.
Creeks flow; that is part of their beauty. But this flow convinces some people that the creek is a conveyor belt for removal of garbage. Although the debris may move a bit downstream, the damage to the stream from litter stays behind and involves much more than just the ugliness of the litter.
Quantities of grass or leaves dumped into a stream will, as it decomposes,
deplete the water of oxygen and thus suffocate aquatic life. Many types of
litter leak, leach, or degrade to toxic materials; these include oil filters,
paint containers, certain plastics, printed paper (containing ink), plywood,
sheetrock, and caulk tubes. This litter especially must be removed promptly
if it is spotted in a creek. Chemical toxins are obviously dangerous; old
storage sites for toxins must be monitored to prevent seepage into groundwater
or streams. Even modern disposal regulations for toxins are not always
followed. As you enjoy the creek, you must be alert to spot and report
evidence of toxic dumping.
If you observe suspected toxins in the creek or possible violations of water quality regulations, in northern California, at least, one of the following agencies should be promptly contacted: California Fish and Game Hotline (1-800-952-5400), Regional Water Quality Control Board, Redding (916-224-4845), or your local Environmental Health Department (in Chico, 891-2727) or Fire Department (in Chico, 895-4911).
Cleanups. No matter how much we try to keep streams clean, litter
enters the system through wind, careless people, and storm drains. Regular
litter removal is a must, particularly for urban streams. Periodic public
cleanups of streams have a twofold effect. First, they remove the litter
before it can degrade and harm the stream. And, second, they increase the
community's sense of stewardship of the creek and thereby help to reduce the
incidence of littering and increase the proper care and maintenance of the
creek.
It should be mentioned that fallen branches and trees in the creek are not litter and should not be automatically removed. Branches and fallen trees provide cover, substrate, and food for aquatic organisms. They provide feeding perches for herons and sunning spots for turtles. They also deflect water flow, causing turbulence and scouring, thereby creating stream diversity and fish habitat. In an urban setting, unfortunately, this may result in more displacement of the stream than people are willing to accept. Judgments on removal of fallen trees must, therefore, be made on a case by case basis.
1. Wildlife in the riparian should be encouraged by protecting the riparian
zone from destruction and by encouraging the growth of native vegetation.
A healthy, natural riparian system provides food and shelter for an incredible abundance of wildlife. Invertebrates, reptiles, amphibians, birds, and mammals abound in and along this complex ecosystem. (See terrestrial vertebrates found along Chico Creek on the CSU, Chico campus.) These animals make the riparian zone a stable, more robust system through their interactions with the plant life and other aspects of the system. In addition, this plentiful wildlife makes the riparian zone a stimulating and interesting place for humans of all ages to observe, study, and enjoy the natural world.
Vegetation and animal life. As discussed earlier, the riparian is an integrated system, with the stream, the surrounding vegetation, and the animals all interconnected and dependent on each other. Bulldozing riparian vegetation until only a thin strip is left harms both terrestrial and aquatic life, eliminating most of the animal life normally occurring in the riparian zone. A wide zone of riparian vegetation should be retained or restored in order to support a healthy diversity of animal life. Although the natural width of riparian zones varies, on even a small creek it can typically extend 100 feet to either side of the creek itself.
The vegetation in the riparian zone should consist of native species in order to adequately support the animal life. As detailed under Vegetation Management, native wildlife has evolved to coexist with native vegetation and depends upon it for food and habitat. Thus removal of exotics and planting of native species directly encourages the establishment of a normal healthy diversity of animal life. In planting native species, maximize foliage height diversity by selecting plants that will occupy distinct vertical levels in the forest, from ground cover up to the overstory canopy. Different birds and mammals forage and live in these distinct vertical levels.
Valley Oaks. A particularly important native riparian tree for
wildlife is the valley oak, which naturally occurs at the edge of the riparian
and into the savanna beyond. These oaks provide both cover and food for birds
(such as wood ducks, Aix sponsa, and acorn woodpeckers,
Melanerpes formicivorous) and mammals (such as gray squirrels,
Sciurus griseus, and Beechey ground squirrels,
Spermophilus beecheyi), as well as a wide variety of insects.
Thus valley oaks must be considered an important part of any healthy riparian
community, and the damaging summer watering referred to in Part A should be
diligently avoided.
2. Indiscriminate poisoning of rodents within the riparian zone should not be allowed.
Exotic Rats. Pesticides to control exotic rodents that are considered
health threats (primarily black rats and Norway rats, Rattus rattus
and R. norwegicus) have no place within riparian zones, either in urban
or rural areas. These rat poisons pose a potential threat to native mammals
and birds, as well as the exotics, without entirely eliminating the exotics.
Such indiscriminate poisoning of native wildlife cannot be justified. If the
riparian area is kept natural and clean of litter, then exotic rodent
populations will not pose health threats. Elimination of litter and of thick,
exotic plant cover, such as ivy in the riparian zone, is all that is required
to eliminate any exotic rats that may be living there.
Beaver control. Beavers (Castor canadensis) are common along
certain stretches of streams, even in urban settings. These large
semi-aquatic rodents feed on aquatic plants and the bark of saplings,
occasionally felling mature trees for their branches, as well as to aid in dam
construction. Beaver damage to riparian trees may be unacceptable in urban
settings; wrapping wire screens around the bases of native trees will prevent
such damage. Damming of creeks by beavers may also be unacceptable in urban
or some rural settings. If dams are not causing immediate problems, they may
be left in place; here in northern California they will be removed by winter
and spring floods. Only dams that are barriers to upstream fish migrations
should be removed.
3. Animal habitat should be increased by preserving snags and, where appropriate, by installing nest boxes.
Dead trees, known as snags, are habitat for many species of cavity
nesting birds (e.g., nuthatches, wrens, owls, and woodpeckers), as well as
insects which serve as food for these and other vertebrates. In addition, in
northern California such snags often serve as acorn storage sites (granaries)
for acorn woodpeckers. Existing snags which do not pose a safety hazard to
people or structures should, therefore, be permitted to stand. Further, we
recommend that in areas where acorn woodpeckers occur, but their natural
granary trees have been reduced in number, artificial granaries in the form of
untreated power poles be erected at the edge of the riparian zone.
If a stretch of riparian habitat is healthy and contains some snags and
plenty of native vegetation, especially large sycamores, there is probably
adequate shelter for wildlife. In these areas, nest boxes and bird houses are
probably not advisable, since they may attract more non-native birds than
natives. If the riparian zone is degraded or extensively converted to
ornamental vegetation, then nest boxes and bird houses are probably a good
idea, to give native birds and mammals a place to live and reproduce.
Entrance holes must conform to specific diameters to permit these species and
to preclude exotics such as European starlings (Sturnus vulgaris) and
house sparrows (Passer domesticus). (See list of references.) We
recommend monitoring these nest boxes periodically, and removing any exotics
which may have colonized them.
4. Domestic and feral pets should be controlled within the riparian zone.
Many careful studies have shown that domestic pets can decimate
riparian populations of birds and small mammals. Feral cats should be removed
from the riparian, and dogs should be kept strictly on leash within the
riparian zone.
Creek Day. Our Committee for Stewardship of Chico Creek has organized
an annual Creek Day centered on the campus and open to the larger community.
A large display of living plant, vertebrate, and invertebrate creek life is
gathered under a circus tent one day. Students, school children, and local
citizens learn from the signs and docents telling about the creatures contained
in the numerous aquaria.
The Bidwell Park Nature Center located next to the creek makes numerous
presentations, which cover the plant and animal life in the park as well as
the creek, to elementary school classes. Our committee is considering "Creek
Ecology" presentations through the Nature Center, which would focus on the
natural history of creek life, both for school children and for adults.
* Butte County Fish http://www.csuchico.edu/~pmaslin/ichthy/btfsh.html
* A Management Guide for the Care of Streams with Particular Reference to
Northern California, prepared by The Committee for Stewardship of Chico Creek.
* Barbour, Michael G. and Major, Jack, Terrestrial Vegetation of California.
John Wiley & Son, New York, 1977.
* El-Swaify, S. A., Moldenhauer, W. C., and Lo, Andrew, Soil Erosion and
Conservation. Soil Conservation Society of America.. Ankeny, Iowa,
* Forman, Richard T. T., and Gordon, Michel, Landscape Ecology. John Wiley
& Son, New York, 1986.
* Griggs, F.T., Morris, V. and Denny, E. 1993. Five Years of Valley Oak
Riparian Forest Restoration. Fremontia 22(2): 13-17.
* MacArthur, R.H. 1961. On Species Diversity. Ecology 42(3): 594-598.
* Owen, Oliver S. and Cheras, Daniel D., Natural Resource Conservation. 5th
Ed., MacMilllian Publishing Co., New York, 1990.
* Proceedings for the California Riparian Systems Conference, September 22-24,
1988, Davis, California. Pacific Southwest Forest and Range Experiment
Station, Berkeley, California.
* Riparian Ecosystems and their Management: Reconciling Conflicting Uses,
First North American Riparian Conference, April 16-18, 1985, Tucson, Arizona.
USDA Forest Service, General Technical Report RM-120, Rocky Mountain Forest
& Range Experiment Station, Fort Collins, Colorado.
* Stokes, D. and L., The Complete Birdhouse Book, 1990. Little, Brown &
Co., Boston. This paperback contains information on construction,
entrance-hole dimensions, placement, and use of birdhouses for a wide range of
common species. Macarthur, R. H., on Species Diversity, 1961. Ecology
42(3): 594-598.
* Watts, T., Pacific Coast Tree Finder. 1963. Nature Study Guild, Berkeley.
A pocket manual for tree identification
Index
It is important to educate your local community regarding the precious
resource creeks represent, and the proper means of preserving this resource.
Several types of activities can accomplish this goal. Regular creek cleanups
not only help the creek but also increase public awareness and appreciation of
creeks. In Chico, the Butte Environmental Council and the Bidwell Park Nature
Center have joined with the city's Park and Playground Commission and local
business concerns to promote twice-yearly cleanups of Big Chico Creek. Local
waste disposal companies provide equipment and other businesses donate
refreshments; several hundreds of people participate in these very successful
events. 