Establishment of riparian forest buffers
Phyllis Bongrad, Extension educator in agriculture production/water quality and
Gary Wyatt, Extension educator in agroforestry
Illustration by Robin Freese
Minnesota is home to more than 450 miles of Department of Natural Resources designated trout streams. As a cold water species, trout are sensitive to warm stream temperatures. Establishing trees in riparian buffers is widely recognized as a significant tool for stabilizing stream temperatures and improving trout habitat. Riparian forest buffers (RFBs) provide other benefits, as well. They filter sediment, nutrients and pesticides, thus preventing movement of these nonpoint pollution sources downstream. Trees in the buffer zone provide woody debris for the stream, an important component of trout habitat. The woody roots also help stabilize stream banks and help with flood control.
Multi-species, multi-use RFBs offer landowners an opportunity to not only improve stream habitat and water quality, but to explore income producing options from the buffer itself. Currently, the most accepted design includes three zones: an unmanaged woody zone nearest the stream, a second zone of trees and shrubs that can be managed for income, and finally, a warm-season grass zone adjacent to cropland.
Once the buffer has been designed and any problem areas repaired, the site can be prepared for planting. Control of competing vegetation is essential for good seedling establishment and will vary somewhat depending on the zone being prepared and its land use.
When the land being prepared is pasture, burndown of the vegetation with glyphosate (e.g. Roundup®, many others) is recommended in the fall before planting. This may be followed by tillage, if desired. However, a recent Wisconsin study suggests that a single fall application of glyphosate with no follow-up tillage is a good option since it requires relatively little labor or equipment. For site preparation in the tree zones (Zones I and II), glyphosate should be applied in three to four foot strips or circles where the trees will be planted. A second spring burndown may be recommended if perennial weed populations are strong or if problem weeds are emerging. When a pasture area will be planted to Zone III grasses, the fall glyphosate application should be followed with a spring treatment and the desired grasses seeded with a prairie seed drill.
Figure 1. Example of a three-zone riparian forest buffer that is bordering cropland on the left side of the stream and pasture on the right. A strip of alfalfa may be substituted for the warm-season grasses in Zone III when the buffer borders pasture. Illustration by Robin Freese.
When cropland is being prepared for Zones I and II, light tillage, such as disking, is recommended to control the early spring weed flush. Planting this area with a mixture of perennial ryegrass and timothy (five and seven pounds per acre, respectively) will provide soil protection without competing with the young trees. Spring disking is also recommended if cropland will be planted to Zone III grasses. In addition, the area should be cultipacked to prepare a good seedbed for switchgrass or other native grasses.
Planting trees and shrubs
Potential plant materials for the woody zones include both seeds and seedlings. Tree seeds can be collected in the fall and planted by hand or specialized machine. Direct seeding of hardwood nut trees (with nuts) is generally done in the fall. Planting depth should not exceed two to three times the seed diameter. Large seeds, such as acorns and walnuts, can also be broadcast with a fertilizer spreader and disked in to a depth of one to two inches. Lighter seeds, such as maple, can be broadcast and dragged in lightly. For more details about direct seeding, visit www.dnr.state.mn.us/treecare/maintenance/collectingseed.html.
Trees can be purchased as unrooted cuttings (sticks) and bareroot or container seedlings, but the most common is the bareroot seedling. Bareroot seedlings are generally less expensive than container trees and studies have found no differences in their survival rates. Bareroot seedlings need to be kept moist until planting. In addition, the seedling roots should be submerged in water for two to four hours before planting.
Bareroot seedlings are available mainly in the early spring. Both bareroot and unrooted cuttings (sticks) should be planted in the early spring after the last frost date. Container stock can be planted almost any time if watered correctly; however, the spring and fall are best.
The planting hole for both bareroot and container seedlings should be large enough to contain the entire root system without turning any roots up. Roots need to be covered and packed with soil and watered after planting.
Unrooted cuttings (sticks) should be placed in the ground with one bud (poplar) and two to three buds (shrubs) above the soil surface and watered immediately. In general, tree cuttings are difficult to establish with the possible exception of willow.
Minimizing wildlife damage
Protecting tree seedlings from animal damage in the first few years of establishment is important for their long-term survival. Significant damage from browsing deer, rabbits, voles and gophers can be minimized with an integrated pest management (IPM) approach. It can include exclusion, habitat modification, repellents and population management.
Solid, translucent tubes that surround the seedling are among the most common exclusion tools. These tree tubes provide protection from wind damage, animal browsing and girdling. Tree shelters also provide a greenhouse-like environment that promotes rapid growth and long-term seedling survival. Fences can also be used to exclude animals from tree and shrub seedlings but this can be expensive.
Managing vegetation to minimize herbivore habitat can be included in the integrated pest management approach. Late fall mowing is recommended in the buffer rows to reduce habitat for rodents. Other IPM options include using repellents and controlling the herbivore populations through hunting or trapping. Wildlife damage management is truly a diverse and complex topic. To learn more about the wildlife that can damage your property and ways to manage the wildlife-human conflict for the betterment of both, see the Prevention and Control of Wildlife Handbook.
Watering trees and shrubs
Providing adequate water the first year or two is essential for establishment. Seedlings should have adequate water each week. Newly planted seedlings should be watered one or two times per week depending on rainfall. If no rain occurs, watering two to five gallons per plant per watering is recommended.