Site preparation is the creation of a favorable growing environment for tree seeds or seedlings. The biggest obstacle facing seedling establishment is competition from other vegetation. Effective site preparation will reduce competing vegetation and create a sufficient number of suitable growing sites without causing excessive soil disturbance.
Learn more by viewing the video Green Side Up: Site Preparation.
Mechanical site preparation
Mechanical site preparation typically disturbs the soil and reduces competing vegetation by plowing, disking, raking, chopping, scalping and trenching, among other approaches. In some cases, mechanical site preparation can be valuable, as exposing and disturbing mineral soil can have the added benefits of increasing root zone temperatures, aerating the soil and improving drainage. However, when mechanical site preparation is done incorrectly, it can result in soil erosion, compaction and rutting.
Also consider the potential competing vegetation that may develop from dormant seeds after the soil is exposed. A combination of both mechanical and chemical techniques can be used for added control.
Chemical site preparation
Chemical site preparation can be an effective method to control vegetation and increase the amount of sunlight and water available for plant growth. Chemical methods may involve simple equipment, can be less expensive and provide longer control than mechanical site preparation. However, chemical effectiveness depends on the appropriate herbicide selection, the timing of application, application rate and weather conditions. Herbicide applications may need to be repeated for several years to ensure stand establishment.
For private lands enrolled in the Managed Forest Law, where forest certification standards may apply, some chemicals may be restricted. See the Forest Stewardship Council's (FSC) list of highly hazardous pesticides for more information. All herbicides must be applied in accordance with label recommendations and their registered use. Detailed forestry herbicide information is available online.
Prescribed burning, or controlled ground fires, can be an effective and inexpensive means of removing or reducing vegetation and preparing a suitable seedbed. Burning can also improve soil nutrient levels and ectomycorrhizal development.
Prescribed burning, however, can reduce the effectiveness pre-emergent herbicides and can increase solar heating at ground line, leading to seedling mortality. The use of fire as a vegetation management technique is very appealing to many small landowners because it appears "natural," but it can be dangerous. Effective and safe use of prescribed fire requires appropriate equipment and training.
Cover crops are appropriate for afforestation sites where they are grown to prevent invasion by noxious weeds, non-native invasive species or other competing vegetation. Cover crops can also control soil erosion, improve soil condition and increase water-holding capacity.
When selecting a cover crop, choose a species that will accomplish the site preparation objectives but not adversely impact tree growth. Legumes are sometimes selected as cover crops because they can enhance soil nitrogen. Small grain crops such as winter wheat and rye can inhibit weed growth and add organic matter to soils while providing limited competition for tree seedlings. Winter wheat can be spring seeded to produce a less vigorous but effective cover crop.
Former agricultural fields
Former agricultural fields present a unique set of site preparation challenges. Fields that were in row crops such as corn or soybeans the previous year generally require a pre-emergent herbicide after planting to control germination of stored weed seed.
Cover crops may also be used to control invasive weeds. Alfalfa, clover or some perennial grasses provide fierce competition for tree seedlings and seeds. Alfalfa and sod are easiest to control during the year prior to planting with an early fall application of herbicide when the plants are still actively growing. Alternatively, rotation into a row crop or other desirable cover crop, followed by planting of seedlings, has been especially effective for hardwood plantings on heavy soils.