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Adequate Site Preparation Can Enhance Productivity of New Forest Stands

Planning how to reforest a stand should begin prior to scheduling a final timber harvest. One of the most important components of the reforestation plan is selecting the appropriate site preparation technique.

What is Site Preparation?

Site preparation is the reduction of logging debris and residual vegetation, including non-merchantable stems, and the treatment of undesirable regeneration and competition from woody and non-woody species. It is used to facilitate planting of artificial regeneration or to release natural regeneration of desired species and to improve initial growth rate of a new stand. Intensive site preparation practices began in the mid-20th century. These practices were designed to improve seedling survival rates in plantation forestry, which was implemented throughout the south to support a growing need for pine pulpwood.1 As site preparation practices evolved, efficiency of treatment techniques and reduction in soil disturbance to treated sites has improved, further enhancing practice results.

Types of Site Preparation

Site preparation practices vary depending on site characteristics and vegetation to be controlled, as well as cost, availability of equipment, and labor. Three methods are used alone or in combination: fire, mechanical, and chemical.

Fire

Fire has been used by man for thousands of years to alter natural site characteristics. Periodic burning during specific times of the year, and under fairly controlled conditions, can enhance certain plant and animal communities while eliminating others. The use of prescribed fire is a cost-effective method of site preparation. Depending on time of year and intensity of the fire, it can improve conditions for natural regeneration; reduce competition from hardwood regeneration, shrubs, and herbaceous species; reduce residual logging debris; and create better tree planting conditions.2 Once the most feasible method of improving site condition before reforestation, prescribed fire is now primarily used in conjunction with mechanical or chemical site preparation treatments.3

Mechanical

Mechanical site preparation techniques were initially designed to mimic the clearing of an agricultural field to plant a crop and can be completed in a variety of combinations.4 Shearing standing stems and stumps is used on areas that have a significant number of residual trees or high stumps. This process utilizes a large blade on the front of a bulldozer to cut off stems and stumps at ground level. Chopping downed debris can be done at the same time as shearing, or as a single operation. Large drums with cutting teeth that can be filled with water for added weight are pulled behind a bulldozer to flatten and chop small diameter standing stems and logging debris. Chopping followed by a prescribed fire is often sufficient to facilitate hand planting on sites with light to moderate residual vegetation and logging debris. Additional operations, including root raking, pushing debris into large piles, and disking to further reduce competing vegetation is often done on sites with heavy residual stems and logging debris, especially if the reforestation area will be machine planted. On sites with poor drainage, an additional implement is utilized to create raised beds (figure 1). This ensures the roots of planted seedlings are above the water table, improving soil aeration.5 Bedding, which plows up and packs the topsoil and organic matter on a site, can also be utilized to increase seedling survival and growth rate even on sites that aren’t prone to poor drainage.

Seedlings on raised beds are put in sites with poor drainage.

Figure 1. Raised beds for seedlings on a site with poor drainage. Photo credit: Bill Steele, Southeastern Forestry.

It was eventually determined that not only were these combinations of treatments expensive, they could adversely impact site quality since mechanical site preparation could require as many as three passes across a reforestation area with heavy equipment. Pushing logging debris and sheared stems and stumps into piles often moved organic matter and topsoil, reducing site fertility. Multiple passes with heavy equipment compacted soils and piling of logging slash on upland sites increased soil erosion rates by removing natural sediment barriers.5 Development of site preparation equipment which integrate two or more operations resulted in implements which serve dual purposes, reducing costs and site disturbance from multiple passes.6

Chemical

Skidder applying chemicals

Figure 2. Chemical site preparation using broadcast foliar herbicide. Photo credit: TJ Savereno, Clemson Extension.

Chemical site preparation has become the favored method on most sites within the last twenty to thirty years. Research on forest herbicides has led to the development of compounds which have a variety of modes of action, as well as species on which they are most effective.3 These herbicides can be used alone, or in combination to target a broader range of species. Fifteen formulations are commonly prescribed for site preparation prior to planting southern pine species.7 Treatment recommendations are based on vegetation to be controlled, time of year of application, and soil type. Application method can be foliar spray, injection, cut-stump, or granular soil application. For site preparation, foliar sprays are the most common and can be applied by helicopter, skidder (figure 2) or tractor, or backpack. Chemical site preparation is generally less expensive than mechanical site preparation and causes less soil compaction and erosion in a reforestation area. Adhering to labeled rates and application instructions, and considering weather factors such as wind speed, wind direction, and air temperature, will reduce the risk of misapplication. Applying forestry herbicide inappropriately can result in drift of chemicals into untreated areas, volatilization of chemical, or reduction in effectiveness of herbicides on target species.

Cost of Site Preparation

Several factors can impact the cost per acre of any site preparation prescription. These include the number of acres to be treated; type and density of existing vegetation; availability of site preparation contractors; and time of year for treatment. Every two years the Alabama Cooperative Extension Service conducts a survey of the cost of implementing forestry practices to private landowners in the South. The results are derived based on costs for forestry practices conducted in the Northern Coastal Plain, Southern Coastal Plain, and the Piedmont physiographic regions of the southeastern United States. Table 1 reflects the 2016 results based on average cost per acre across all three regions.8 These averages do not include the cost to purchase or plant seedlings. Also, with a questionnaire completion and return rate of only 11% for the 2016 survey, these averages may not be as representative of the cost of site preparation treatments as those obtained from a larger sample size.

Table 1. Average site preparation costs.

Treatment Practice Avg. Cost/Acre (2016)
Site Prep. Burning $28.94
Mechanical Site Prep. (1 pass) $105.73
Mechanical Site Prep. (2 pass) $217.87
Mechanical Site Prep. (3 pass) $252.09
Chemical Site Prep. (Ground) $78.47
Chemical Site Prep. (Aerial) $79.70

Source: Estimates derived from Maggard and Barlow.8

Site Preparation Recommendations

To obtain recommendations for site preparation to reforest a clearcut stand, forest landowners in South Carolina can contact their local Clemson University Cooperative Extension office, South Carolina Forestry Commission office, or a forestry consultant. State and federal cost-share assistance may be available to assist with reforestation expenses.

References

  1. Allen AW, Bernal YK, Moulton RJ. Pine plantations and wildlife in the southeastern United States: an assessment of impacts and opportunities. Washington DC: U.S. Department of the Interior, National Biological Service; 1996 Jan; Information and Technology Report 3.
  2. Waldrop TA, Goodrick SL. Introduction to prescribed fire in southern ecosystems. Asheville (NC): U.S. Department of Agriculture Forest Service, Southern Region Station; 2012 Aug [slightly revised 2018; accessed 2019 Nov 5]:11–17. https://www.srs.fs.usda.gov/pubs/su/su_srs054.pdf.
  3. Wade DD, Lunsford JD. A guide for prescribed fire in southern forests. Atlanta (GA): U.S. Department of Agriculture Technical, Forest Service Southern Region; 1989 Feb. R8-TP 11. [accessed 2019 Nov 22]. http://www.gfc.state.ga.us/forest-fire/prescribed-fire-guide/index.cfm.
  4. Fox T, Jokela E, Allen HL. The evolution of pine plantation silviculture in the Southern United States. Asheville (NC): U.S. Department of Agriculture, Forest Service, Southern Research Station; 2004. In: Gen. Tech. Rep. SRS–75. In: Gen. Tech. Rep. SRS–75. [accessed 2019 Jul 2]. https://www.srs.fs.usda.gov/pubs/9647.
  5. Smith D, Hawley R. The practice of silviculture. (8th ed.) New York (NY): John Wiley & Sons; 1986.
  6. Callaghan DW, Khanal PN, Straka TJ. An analysis of costs and cost trends for southern forestry practices. Journal of Forestry. 2019;117(1):21–29.
  7. Lambert C, Megalos M, Jeuck J. 2017 Quick guide to forestry herbicides used for softwood and hardwood site preparation and release. Raleigh (NC): NC State Extension; 2016 [accessed 2019 Nov 6]. https://content.ces.ncsu.edu/quick-guide-to-forestry-herbicides-used-for-softwood-and-hardwood-site-preparation-and-release#.
  8. Maggard A, Barlow R. Costs and trends for southern forestry practices. Forest Landowners. 2016 Sep;76(5):31–39.

Publication Adapted from:

Richardson B. Why site prepare after a clearcut. Clemson Cooperative Extension. 2016; FW 07.

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NEWSLETTER

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