Regeneration silviculture of birch: A review

Abstract

The birches are most commonly regenerated using even-aged systems, primarily clearcutting. Clearcut sizes range from 16 ha down to 0.4-ha patches. Seed trees or shelterwoods are sometimes used to provide additional seed and site protection. Uneven-aged systems are not recommended, with the exception of group selection for yellow birch. Coppice systems do not provide full stocking except in short-rotation biomass culture, but coppice provides acceptable supplemental regeneration. Natural regeneration by seeding prevails because it is economical and highly reliable where the water balance is favorable. Yellow birch sometimes regenerates in advance, but otherwise the canopy, understory, and seedbed must be manipulated to meet germination and seedling-establishment requirements. Suitable seedbeds are prepared by burning, by mechanical site-preparation equipment, and sometimes by the logging process itself. Draining often is all that is necessary to regenerate peatlands. Seedlings should be protected from grazing or browsing. Relatively few stands are regenerated artificially. Direct seeding (either broadcast- or spot-sowing) is usually reliable. Planting is more common and gives the opportunity to introduce exotic or genetically improved stock. In species trials, silver birch has consistently grown faster - and yellow birch slower - than eeitherhairy birch or paper birch. Phenotypically selected natural stands and controlled pollination produce progeny that grow in volume from 30 to 80% faster than average. Thorough site preparation, fertilization, mulching, weed control, and protection from animals benefit seedling growth. Both bare-root and container-grown stock are planted successfully. Birch is highly regarded for afforesting mine spoils, drained or worked-out peatlands, abandoned and abused agricultural lands, heaths, previously flooded lands, and areas with high air pollution. Fertilizers are often applied to improve site quality. Birch nurse crops benefit conifers by protecting them from frost, insects, and pathogens; by improving the soil through nutrient cycling; and by increasing stand wind-firmness on shallow soils. The optimum proportion of birch in mixed stands is 17–25%. Overly dense birch should be controlled with chemicals, by hand, or with machinery to allow optimum conifer development.