The purposes of site preparation are to:
- reduce the competition of unwanted vegetation in order to increase the survival and growth rate of the desired trees,
- remove slash and logging debris if the site has been harvested, and
- to prepare or modify the soil.
Ultimately, we want to provide better light, nutrients and moisture to make conditions favorable for germination, survival and growth.
For information about prescribed burns, see our Fire page.
Mechanical site preparation with heavy equipment can be divided into three categories:
- breaking or crushing vegetation in place
- moving vegetation from the planting site
- manipulating soil structure or microtopography of the site
The most frequently-used tool used to crush existing vegetation in place is the rolling drum chopper, which comes in varying sizes. The largest choppers weigh about 80 tons and are capable of crushing a 20-inch diameter tree at 2.5 miles per hour!
Small to medium-sized choppers are sufficiently adequate tools for handling a large number of stems up to 5-inches in diameter. Rolling chopper drums of this size are usually pulled by a rubber-tired skidder or a crawler tractor.
Chopping normally progresses in a circular manner from the tract edge to the center, except where steep terrain only allows downhill passes or where equipment operation is prohibited by wet areas or drainages.
The procedure for a standard chopping operation would be:
- a single pass with a chopper
- a hot fire
- a second pass with a chopper
A significant advantage of rolling choppers is that they do not displace the topsoil and they have a minimal effect on soil runoff. Chopping can be combined with shearing by mounting a shearing blade to the tractor or skidder.
A more intensive treatment is the use of a shearing blade: a horizontal knife blade mounted on a large crawler tractor which shears vegetation at the ground line. The cut material is piled or raked into piles or windrows.
Caution: This treatment can cause topsoil and seedbed displacement.
The purpose of disking is to break up or till the soil surface, improving soil aeration and moisture movement, and helping young trees to root. Disking also incorporates organic surface layers into the underlying mineral soils and prepares the surface for bedding where appropriate. Disking can significantly reduce hardwood sprouting when the site is treated in summer when the soil is dry. The disks can sever all but the largest roots and uproot small stems and vines.
Disking for forestry purposes involves a stronger, larger version of the agricultural disk. It consists of a series of large, saucer-shaped steel blades joined at the center of an axle that allows them to roll when the unit is pulled. The blade edges are sharpened and serated to allow deeper penetration into the soil. Soil tilling and depth cut are enhanced by setting the axle at an angle to the direction of travel and adding weight to the disks. Disks are usually pulled by crawler tractors or rubber-tired skidders.
Bedding is the formation of a continuous mound of soil with a narrow 2-axled disk or bedding plow. This treatment is usually done on sheared and piled sites with poor surface drainage, but is also common on sites with good surface drainage. Soils near the top of the bed are drier and warmer sooner in the spring than unbedded areas, which promotes early root growth. Early root growth increases the chance of successful establishment and accelerates seedling growth.
Bedding plows are often pulled by crawler tractors or rubber-tired skidders. On the lower coastal plain, phosphorus fertilizer is often applied just ahead of bed formation and from the tractor or skidder pulling the bedding plow.
Bedding with the contour of the land (against the slope) is essential to minimize soil erosion on upland sites. On well-drained upland sites, first-season seedling growth and survival may be limited more by late-season soil moisture deficits on bedded than on comparable nonbedded sites.
Ripping or subsoiling is done on rocky upland soils that have developed from consolidated rock and on other soils with dense, high-strength clay horizons that may inhibit root development. The latter type of soil must be ripped when dry to maximize fracturing. When wet, the ripping shank may only cut a narrow vertical slit through the clay layers.
Ripping is carried out with 1 or 2 vertically-mounted rock-ripping shanks on a crawler tractor. The shanks are equipped with a replaceable wear shoe and drawn or pushed through the soil at a depth of 40 to 60 cm. Horizontal "wings" near the tip may be used to enhance the fracturing of soils with high clay content. Tractor power requirements depend on soil strength, ripping depth, and the number and size of residual vegetation on the site.
Ripping encourages more deep root development than any other of the other soil treatment methods above, a great advantage in areas with summer droughts.
Why Use Herbicides?
Herbicides Can Herbicides Cannot
- bring longer-lasting control of competing vegetation = increased economic return for landowner.
- control tough invasive exotic plants.
- retain biomass for soil protection.
- avoid soil compaction.
- be costly.
- reduce slash accumulations after harvest.
- regenerate fire-dependent species.
- be used without caution:
- application failure
- drift to non-target crops
- surface runoff
The use of herbicides for site preparation has increased in the last two decades:
- several effective compounds are now available,
- the use of most of these compounds has minimal impact on soils,
- increased machinery and fuel costs have made mechanical methods less attractive economically,
- foresters are generally observing increased plantation growth rates on herbicide-treated sites, and
- herbicide treatments usually kill the root systems of treated trees, significantly reducing the potential for sprouting of undesired species.
The primary objective of chemical site preparation is to reduce sprouting of competing hardwoods that usually grow in established plantations.
More Information on Herbicides:
Florida Forestry Information