Riparian forest buffers serve several important functions, including reducing non-point source pollution in streams; reducing erosion from surface water runoff; and maintaining a habitat for wildlife and plants, both on the land and in the water. With careful planning, three-zone buffers can also provide profitable sources of income from timber and horticultural products, like decorative woody florals and forest farming plantings.
However, regular maintenance is essential if a riparian forest buffer is to accomplish these functions. Controlled burning can be an important tool for maintenance of the grass portion of a riparian buffer practice. As a “living filter,” it is essential that each buffer component be managed to maintain vigorous growth and maintain uptake and nutrient storage. For example, where warm season grasses are used, it is recommended to use a spring burn every couple of years in order to reduce the accumulated dead leaf matter and lessen competition from weeds and cool season grasses.
Spring is also the season to consider replanting or reseeding of riparian buffers. Warm season grasses work well in the outer zone (zone one) of a riparian buffer and can be planted densely to reduce runoff. In most cases, grasses with stiff stems work best to reduce water flow rates. Always use flood tolerant grasses. A good example of a flood-tolerant warm season grass is Switchgrass, a good choice because its deep roots filter well and will over time add organic matter to the soil. Indiangrass and big bluestem are other warm season grasses well-suited for riparian buffers. For a list of additional warm and cool season species to use in riparian settings, contact your local Natural Resource Conservation Service, University Extension agent or the Department of Conservation.
For zone two of a riparian buffer, consider smaller trees and shrubs adjacent to large trees (zone three) to provide long-term retention of nutrients. Red osier dogwood and curly willow planted in this zone can provide additional income when marketed to local florists.
Replanting and reseeding:
Replanting and reseeding are important maintenance practices during the first
few years following establishment of a riparian buffer and can be done in the
spring or fall. An annual inspection should be made to identify areas in need
of replanting or reseeding. Woody plants should be replanted within a row if
more than three or four consecutive seedlings have died. Spot planting can be
done quickly with just a bucket full of water, seedlings and a shovel.
Replanting in the native grass/forb zone may be a bit more involved, depending on the density and quality of grass and establishment. If there is poor establishment, a herbicide like Glyphosate can be used, followed by redrilling. If there is some establishment, but not as dense as desired, the site can be directly redrilled. If the areas needing reseeding are small, handspreading the seed and raking it into the ground is acceptable.
During the life of a riparian buffer, trees will begin to compete with each other as they do in a natural forest, and without pruning and thinning they will not maintain an optimal growth rate. Depending on spacing, fast-growing trees such as cottonwoods and poplars will be competing with each other within 5- 10 years of planting. Some time between year five and year ten, every second or third tree may have to be harvested to increase water and growth space for remaining trees.
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A spring prescribed burning of a riparian buffer will reduce weed competition and accumulated dead leaf matter. |
Prescribed burning:
Fire is a good maintenance tool for native grasses and forb plantings in riparian
buffers and filter strips. To reduce weed competition during the year, prescribed
burns are usually performed early in the spring. During this time, many of the
competing cool-season grasses, weeds and woody plants begin growing while the
native prairie plants are still dormant. Always develop a prescribed burn plan
prior to burning. Assistance is available through NRCA and DNR.
While different burning frequencies may be used, an annual spring-burn for the first three or four years is recommended.
Following establishment of a good stand of desired grasses and forbs, a burning cycle of once every three to four years can be used. The burning cycle is usually defined by the accumulation of dead plant material on the ground, weed species invasion and general vigor of the plant community. Fall burns also can be used to stimulate forb growth more than the grass growth. However, they may be problematic if adjacent crops are not harvested.
Burning the riparian prairie component of a riparian buffer can be tricky due to the close proximity of shrubs and trees. Such a burn requires numerous people, careful planning, attention to fuel sources and amounts, and attention to wind. Using a small, slow backfire (a fire that burns into the wind) helps to keep the fire more controlled while it is close to neighboring shrubs and trees. A fire break is often mowed or raked between the shrubs and/or trees and the native prairie component. The fire break can be wetted if the fuel is dry.
When performing a prescribed burn, keep the fires small and monitor the wind speed. |
Ideally, you should burn in sections; burn only one side of the creek or break a prairie stand into three or four sections and burn one each year. Fall burns eliminate winter cover and late spring burns can destroy nests. However, fire helps to maintain native plant health. Most native prairie plants will grow more vigorously, produce more flowers and produce more seeds after a fire. The active growing points of most prairie plants are below the soil surface, and are therefore unaffected as the fire rapidly passes over. After the fire, these plants are stimulated by warmth of the blackened ground and the nutrients that were released from burned plant material.
Replanting and Prescribed Burning sections reprinted with permission from Iowa State University Extension; for more information visit www.extension.iastate.edu
