Water: Coastal Zone Act Reauthorization Amendments
F. Site Preparation and Forest Management Measure
Confine on-site potential NPS pollution and erosion resulting from site preparation and the regeneration of forest stands. The components of the management measure for site preparation and regeneration are:
- Select a method of site preparation and regeneration suitable for the site conditions.
- Conduct mechanical tree planting and ground-disturbing site preparation activities on the contour of sloping terrain.
- Do not conduct mechanical site preparation and mechanical tree planting in streamside management areas.
- Protect surface waters from logging debris and slash material.
- Suspend operations during wet periods if equipment used begins to cause excessive soil disturbance that will increase erosion.
- Locate windrows at a safe distance from drainages and SMAs to control movement of the material during high runoff conditions.
- Conduct bedding operations in high-water-table areas during dry periods of the year. Conduct bedding in sloping areas on the contour.
- Protect small ephemeral drainages when conducting mechanical tree plag.
This management measure pertains to lands where silvicultural or forestry operations are planned or conducted. It is intended to apply to all site preparation and regeneration activities conducted as part of normal silvicultural activities on harvested units larger than 5 acres. Under the Coastal Zone Act Reauthorization Amendments of 1990, States are subject to a number of requirements as they develop coastal nonpoint source programs in conformity with this measure and will have some flexibility in doing so. The application of this management measure by States is described more fully in Coastal Nonpoint Pollution Control Program: Program Development and Approval Guidance, published jointly by the U.S. Environmental Protection Agency (EPA) and the National Oceanic and Atmospheric Administration (NOAA) of the U.S. Department of Commerce.
Regeneration of harvested forest lands not only is important in terms of restocking a valuable resource, but also is important to provide water quality protection from disturbed soils. Tree roots stabilize disturbed soils by holding the soil in place and aiding soil aggregation, decreasing slope failure potential. The presence of vegetation on disturbed soils also slows storm runoff, which in turn decreases erosion.
Leaving the forest floor litter layer intact during site preparation operations for regeneration minimizes mineral soil disturbance and detachment, thereby minimizing erosion and sedimentation (Golden et al., 1984). Maintenance of an unbroken litter layer prevents raindrop detachment, maintains infiltration, and slows runoff (McClurkin et al., 1987). Mechanical site preparation can potentially impact water quality in areas that have steep slopes and erodible soils, and where the prepared site is located near a waterbody. Use of mechanical site preparation treatments that expose mineral soils on steep slopes can greatly increase erosion and landslide potential. Alternative methods, such as drum chopping, herbicide application, or prescribed burning, disturb the soil surface less than mechanical practices (Golden et al., 1984).
Mechanical planting using machines that scrape or plow the soil surface can produce erosion rills, increasing surface runoff and erosion. Natural regeneration, hand planting, and direct seeding minimize soil disturbance, especially on steep slopes with erodible soils (Golden et al., 1984).
3. Management Measure Selection
This measure is based in part on information and experience gained from studies and from the use of similar management practices by States. The information summarized provides comparisons and relative levels of effects and costs for site preparation and regeneration. The majority of the data in Tables 3-42 through 3-46 compare sediment loss or erosion rates for shearing, chopping, root-raking and disking. Many of the data are site-specific, and site characteristics and experimental conditions are provided (when available) in the text below. Regional differences in effects are summarized by Dissmeyer and Stump (1978); however, most of the experimental information is from the Southeast and Texas.
a. Effectiveness Information
Effects of different site preparation techniques depend greatly on care of application and site conditions. Beasley (1979) studied the relative soil disturbance effects of site preparation following clearcutting on three small watersheds in the hilly northern Mississippi Coastal Plain. Slopes were mostly 30 percent or greater. One site was single drum-chopped and burned; one was sheared and windrowed (windrows were burned); and the third was sheared, windrowed, and bedded to contour. The control watershed was instrumented and left uncut. The treatments exposed soil on approximately 40-70 percent of the three watersheds (Table 3-42). A temporary cover crop of clover was sown after site preparation to protect the soil from rainfall impact and erosion. Similar increases in sediment production were measured for the three treatments in the first year after site preparation, with amounts decreasing during the second year except for the bedded site, which was attributed to gully formation from increased stormflow. During the second year, the clover and other vegetation covered 85-95 percent of the surface, effectively decreasing sediment production.
A summary of work on erosion from site preparation by Dissmeyer and Stump is presented in Golden et al. (1984)(Table 3-43). These erosion rates were compiled from the Erosion Data Bank of the U.S. Forest Service and are based on observations throughout the Southeast. The rates reflect soil movement measured at the bottom of the slope, not sediment actually reaching a stream. Therefore, the numbers estimate the worst-case erosion if the stream is located directly at the toe of the slope with no intervening vegetation. Rates are given as tons per acre per year average for 3- to 4-year recovery periods.
The degree of erosion produced by site preparation practices is directly related to the amount of soil disturbed and the percentage of good ground cover remaining. Dissmeyer (1980) showed that disking produced more than twice the erosion rate of any other method (Table 3-44). Bulldozing, shearing, and sometimes grazing were associated with relatively high rates of erosion. Chopping or chopping and burning produced moderate erosion rates. Logging also produced moderate erosion rates in this study when it included the impact of skid and spin roads. The lowest rate of erosion is associated with burning.
Beasley and Granillo (1985) compared stormflow and sediment losses from mechanically and chemically prepared sites in southwest Arkansas (Table 3-45). Mechanical preparation (clearcutting followed by shearing, windrowing, and replanting with pine seedlings) significantly increased sediment losses in the first 2 years after treatment. A subsequent decline in sediment losses in the mechanically prepared watersheds was attributed to rapid growth of ground cover. Windrowing brush into ephemeral drainages and leaving it unburned effectively minimized soil losses by trapping sediment on-site and reducing channel scouring. Chemical site preparation (herbicides) had no significant effect on sediment losses.
Water quality changes associated with two site preparation methods were studied by Blackburn, DeHaven, and Knight (1982). Table 3-46 shows that shearing and windrowing (which exposed 59 percent of the soil) can produce 400 times more sediment loadings than chopping (which exposed 16 percent of the soil) during site preparation. Total
.nitrogen losses were nearly 20 times greater from sheared than from undisturbed watersheds, and three times greater from sheared than from chopped (Table 3-47).
b. Cost Information
The way a site is prepared for reforestation can make a 3- to 14-foot difference in site index for pine in the Southeast (Dissmeyer and Foster, 1987). In an analysis of different site preparation techniques, Dissmeyer and Foster concluded that maintaining site quality yields larger trees and more valuable products (Table 3-48). The heavy site preparation methods required a greater initial investment than did the light site preparation methods, but did not yield a greater harvest. The cost-benefit for light site preparation was a 2.3 percent greater internal rate of return than that for heavy site preparation. Dissmeyer (1986) evaluated the economic benefits of erosion control with respect to different site preparation techniques. Increased timber production and savings in site preparation costs are returns the landowner can enjoy if care is taken to reduce soil exposure, displacement, and compaction (Table 3-49). Using light site preparation techniques such as chopping and light burn reduces erosion, increases the site index and the value of timber, and costs less per unit area treated. Heavy site preparation techniques such as shearing and windrowing remove nutrients, compact soil, increase erosion and site preparation costs, and result in a lower present net value for timber.
The U.S. Forest Service (1987) examined the costs of three alternatives to slash treatment: broadcast burn and protection of streamside management zones, yarding of unmerchantable material (YUM) of 15 inches in diameter or more, and YUM of 8 inches in diameter or more (Table 3-50). YUM alternatives cost approximately $435-$820/acre, in comparison to broadcast burning at $900/acre. In addition, the YUM alternatives protect highly erodible soils from direct rainfall and runoff impacts, reduce fire hazards, meet air and water quality standards, and allow for the rapid establishment of seedlings on clearcuts.
Tables 3-51 and 3-52 present comparisons of estimated total costs for different site preparation and regeneration practices, respectively, for which cost-share assistance is provided by the State of Minnesota through its Stewardship Incentives Program (SIP) (Minnesota Department of Natural Resources, 1991). Table 3-53 presents total costs of forest regeneration by various methods, along with the cost-share amount provided by the State of Illinois' SIP.
As discussed more fully at the beginning of this chapter and in Chapter 1, the following practices are described for illustrative purposes only. State programs need not require implementation of these practices. However, as a practical matter, EPA anticipates that the management measure set forth above generally will be implemented by applying one or more management practices appropriate to the source, location, and climate. The practices set forth below have been found by EPA to be representative of the types of practices that can be applied successfully to achieve the management measure described above.
a. Site Preparation Practices
- Mechanical site preparation should not be applied on slopes greater than 30 percent.
On sloping terrain greater than 10 percent, or on highly erosive soils, operate mechanical site preparation equipment on the contour.
- Mechanical site preparation should not be conducted in SMAs.
- Construct beds along the contour (Huff and Deal, 1982). Avoid connecting beds to drainage ditches or other waterways.
- Use haystack piling where possible instead of windrows.
Leave sufficient slash and duff on the site to provide good ground cover and minimize erosion from the harvest site. If the soil Basic Erosion Rate (BER) is low, leave at least 40 percent good ground cover; if the BER is medium, leave at least 50 percent good ground cover; if the BER is high, leave at least 60 percent good ground cover.
- Minimize incorporation of soil material into windrows and piles during their construction.
This can be accomplished by using a rake or, if use of a blade is unavoidable, keeping the blade above the soil surface and removing only the slash. Rapid site recovery and tree growth are promoted by the retention of nutrient-rich topsoil, and the effectiveness of the windrow in minimizing sedimentation is increased.
- Locate windrows and piles away from drainages to prevent movement of materials during high-runoff conditions.
- Avoid mechanical site preparation operations during periods of saturated soil conditions that may cause rutting or accelerate soil erosion.
- Do not place slash in natural drainages, and remove any slash that accidentally enters drainages.
Slash can clog the channel and cause alterations in drainage configuration and increases in sedimentation. Extra organic material can lower the dissolved oxygen content of the stream. Slash also allows silt to accumulate in the drainage and to be carried into the stream during storm events.
- Provide filter strips of sufficient width to protect drainages that do not have SMAs from sedimentation by the 10-year storm.
b. Practices for Regeneration
- Distribute seedlings evenly across the site.
- Order seedlings well in advance of planting time to ensure their availability.
- Hand plant highly erodible sites, steep slopes, and lands adjacent to stream channels (SMAs)(Yoho, 1980).
- Operate planting machines along the contour to avoid ditch formation.
- Soil conditions (slope, moisture conditions, etc.) should be suitable for adequate machine operation.
- Slits should be closed periodically to avoid channeling flow.