|[Manual Home] [Chapter Sections]|
|S I T E P R E P A R A T I O N|
Raised planting spots improve drainage and aeration on wet sites and result in improved seedling performance. Well-drained soil warms faster than waterlogged soil. In zones with cool temperatures, the enhanced soil temperature of raised planting spots may improve seedling performance even on mesic sites. In comparison, raised planting spots may desiccate more than planting spots level with the original soil surface on sites with seasonal moisture deficits.
Raised planting spots may be formed as discrete mounds, as continuous or discontinuous ridges, or as berms.
While all types of raised planting spots enhance soil temperature and aeration, their effectiveness in providing adequate soil water, nutrients, vegetation control and light varies with forest site series.
Inverted Humus Mounds or Ridges with Mineral Soil Capping
Mineral soil capped inverted humus mounds or ridges are particularly useful when soil textures are fine. Seedling roots proliferate in the mineral soil/humus interface because soils are friable, warm, and well supplied with nutrients.
It is important that the configuration and position of the mound is conducive to roots growing beyond the raised area. Roots of some species experience difficulty in raised planting spots with vertical sides, and in mounds surrounded by scalped soil. Trees with root systems confined to a ridge and extended in only two directions are susceptible to blow down.
When deep mineral soil cappings are required to control competing vegetation, it is important that seedling roots are planted well into the inverted surface organic matter, even if this means planting seedlings below the root collar. Seedlings should not be planted close enough to the edge of the mound to be shaded by surrounding vegetation or susceptible to snow press.
The double organic layer beneath the mineral soil cap can act as an impediment to planting seedling roots straight and deep. J-rooted seedlings with root systems confined to the mineral soil capping are prone to drought stress.
Heaps of mineral soil dropped on bare mineral soil may be favorable for seedling growth in dry but cool climates. Soil temperature is enhanced, but the absence of surface organic layers below the mound favors the transfer of moisture from the ground to the mound. When the mineral soil in the mound is medium-textured (loam to sandy loam), root extension is promoted and nutrients (especially nitrogen) from undisturbed soil surrounding the mound may be reached soon after planting. Mineral soil on mineral soil mounds is not appropriate on fine-textured soils.
Mixed Humus and Mineral Soil Mounds
Raised planting spots consisting of mineral soil and humus elevate soil temperature, avoid possible problems of capillary discontinuity, improve aeration, and provide accessible nutrients in humus fragments. Where competing vegetation is not a problem, coarsely mixed, raised planting spots can be favorable for seedling performance. However, coarse mixing does not generally control vigorous competing vegetation.
Peat Mounds and Ridges
Creating mounds or ridges in deep peat soils may be the only way of increasing soil temperature, improving drainage, and controlling competing vegetation. The frequency of chlorotic seedlings during the first few years after planting suggests that peat mounds have a poor nutrient status. However, as the peat mineralizes, seedling color improves. Seedlings should be planted deeply to avoid the possibility of drought stress.
For further information on raised microsites, refer to the video Mounding: A Site Preparation Technique in Review , FRDA Memo 100 [Haeussler 1989], FRDA Memo 160 [Coates and Haeussler 1990], FRDA Report 178 [von der Gönna 1992], and FRDA Report 105 [Örlander et al. 1990].
Planting spots below the general soil surface level are generally favorable for seedling performance in dry zones or sites. Snow and rainfall will accumulate in depressions and can extend the period of moisture availability. Seedlings may also be sheltered from desiccating winds.
Depressions in fine-textured soils may accumulate moisture and result in waterlogged seedlings.
The mineral soil covered inverted humus planting spot, more or less level with the surrounding terrain (e.g., a plowed field), is a favorable planting spot for relatively dry climates (e.g., BWBSmw1). Seedlings are not as exposed to drying winds as when they are planted on raised spots and planting may be easier.
|[Manual Home] [Chapter Sections]|
Copyright 1999 Province of British Columbia