Rooting of Sitka spruce (Picea sitchensis (Bong.) Carr.) in ploughed peatland tends to be restricted to the layer between upturned planting turf and undisturbed peat. This is mainly a response to aeration levels in the turf patterns. Roots will extend along the aeration gradient, or up it, but not down into anaerobic peat (Anderson 1967). Improvement of rooting depth is of major concern for the nutrition and stability of stands established on peat. A highly specialized technology has evolved in northern European forestry practice through the use of special ploughs to provide local drainage, an aerated planting site, and vegetation suppression. Cross-draining collects run-off and intercepts lateral water flow within the soil, often at the peat/mineral soil interface. Long-term effects of forest wetland improvement in the United Kingdom are now apparent. Stands established in the 1920s by using the Belgian spaced turf and shallow sliced turf with hand draining are now reaching exploitable size but are often windblown on high-risk sites before they can be cut. Shallow rooting is a feature of spruce growth on peats and always of the windblown trees. Tree-pulling studies carried out by Fraser & Gardiner (1967), to determine wind-firmness, revealed that Sitka spruce on peaty gley soils did not root below 16-5 in. (42 cm) or below 25 in. (63-5 cm) on deep peat. The studies of Day (1962, 1963) show that Sitka spruce in Britain is not inherently shallowrooted and will produce a deep fibrous root system on well-drained soils. On drained peatlands there is a progressive extension of rooting down the profile because of drying, shrinking, and cracking of the peat, but the rooting is not deep enough to ensure stability and is often offset by a rising water-table where drains have become blocked by roots or debris. Natural regeneration of Sitka spruce in the Forest of Ae in southern Scotland was studied as an index of wet site improvement. Seedlings examined by the writer in 1967 on peaty podsol (peat 8 in. (20 cm)), peaty gley (peat 15 in. (38 cm)) and deep peat (peat 15-36 in. (38-91 cm)) were rooted mainly in the litter layer from a 40-year-old Sitka spruce overwood. The roots did not often penetrate the underlying Molinia peat. An assessment of available pore space in the top 7 in. (18 cm) of peat on these sites demonstrated a sharp drop in the percentage of air-filled pores at about 3-4 in. (7-5-10 cm) (Lees 1969). To examine responses of Sitka spruce seedlings to a soil aeration gradient in peat, a field experiment was designed in the Forest of Ae, Dumfriesshire, Scotland.
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J. C. Lees (1972) studied this question.