Editing Tillage (section)

===Burning===
Broadcast burning is commonly used to prepare clearcut sites for planting, e.g., in central British Columbia,<ref name="Macadam 1987">Macadam, A.M. 1987. Effects of broadcast slash burning on fuels and soil chemical properties in the sub-boreal spruce zone of central British Columbia. Can. J. For. Res. 17(12):1577–1584.</ref> and in the temperate region of North America generally.<ref name="kii">{{Cite journal |last1=Kiil |first1=A. D. |last2=Chrosciewicz |first2=Z. |date=1970-12-01 |title=Prescribed Fire — Its Place in Reforestation |journal=The Forestry Chronicle |language=en |volume=46 |issue=6 |pages=448–451 |doi=10.5558/tfc46448-6 |issn=0015-7546|doi-access=free }}</ref>

Prescribed burning is carried out primarily for slash hazard reduction and to improve site conditions for regeneration; all or some of the following benefits may accrue:

:a) Reduction of logging slash, plant competition, and humus prior to direct seeding, planting, scarifying or in anticipation of natural seeding in partially cut stands or in connection with seed-tree systems.

:b) Reduction or elimination of unwanted forest cover prior to planting or seeding, or prior to preliminary scarification thereto.

:c) Reduction of humus on cold, moist sites to favour regeneration.

:d) Reduction or elimination of slash, grass, or brush fuels from strategic areas around forested land to reduce the chances of damage by wildfire.

Prescribed burning for preparing sites for direct seeding was tried on a few occasions in Ontario, but none of the burns was hot enough to produce a seedbed that was adequate without supplementary mechanical site preparation.<ref name="scott">{{Cite journal |last=Scott |first=J. D. |date=1970-12-01 |title=Direct Seeding in Ontario |url=http://pubs.cif-ifc.org/doi/10.5558/tfc46453-6 |journal=The Forestry Chronicle |language=en |volume=46 |issue=6 |pages=453–457 |doi=10.5558/tfc46453-6 |issn=0015-7546}}</ref>

Changes in soil chemical properties associated with burning include significantly increased pH, which Macadam (1987)<ref name="Macadam 1987" /> in the Sub-boreal Spruce Zone of central British Columbia found persisting more than a year after the burn. Average fuel consumption was 20 to 24 t/ha and the forest floor depth was reduced by 28% to 36%. The increases correlated well with the amounts of slash (both total and ≥7&nbsp;cm diameter) consumed. The change in pH depends on the severity of the burn and the amount consumed; the increase can be as much as 2 units, a 100-fold change.<ref name="holt">Holt, L. 1955. White spruce seedbeds as related to natural regeneration. Pulp Paper Res. Instit. Can., Montreal QC. 28 p.</ref> Deficiencies of copper and iron in the foliage of white spruce on burned clearcuts in central British Columbia might be attributable to elevated pH levels.<ref name="Ballard 1985">Ballard, T.M. 1985. Spruce nutrition problems in the central interior and their relationship with site preparation. Proc. Interior spruce seedling performance: state of the art Symposium. Northern Silviculture Committee Workshop, Feb. 1985, Prince George BC.</ref>

Even a broadcast slash fire in a clearcut does not give a uniform burn over the whole area. Tarrant (1954),<ref name="tarr">Tarrant, R.F. 1954. Effect of slash burning on soil pH. USDA, For. Serv., Pacific Northwest For. and Range Exp. Sta., Portland OR, Res. Note 102. 5 p.</ref> for instance, found only 4% of a 140-ha slash burn had burned severely, 47% had burned lightly, and 49% was unburned. Burning after windrowing obviously accentuates the subsequent heterogeneity.

Marked increases in exchangeable calcium also correlated with the amount of slash at least 7&nbsp;cm in diameter consumed.<ref name="Macadam 1987" /> Phosphorus availability also increased, both in the forest floor and in the 0&nbsp;cm to 15&nbsp;cm mineral soil layer, and the increase was still evident, albeit somewhat diminished, 21 months after burning. However, in another study<ref name="tay">Taylor, S.W.; Feller, M.C. 1987. Initial effects of slashburning on the nutrient status of Sub-boreal Spruce Zone ecosystems. ''In'' Papers presented at the Fire Management Symposium, April 1987, Prince George BC, Central Interior Fire Protection Committee, Smithers BC.</ref> in the same Sub-boreal Spruce Zone found that although it increased immediately after the burn, phosphorus availability had dropped to below pre-burn levels within 9 months.

Nitrogen will be lost from the site by burning,<ref name="Macadam 1987" /><ref name="tay" /><ref name="litt">Little, S.N.; Klock, G.O. 1985. The influence of residue removal and prescribed fire on distribution of forest nutrients. USDA, For. Serv., Res. Pap. PNW-333.</ref> though concentrations in remaining forest floor were found by Macadam (1987)<ref name="Macadam 1987" /> to have increased in two out of six plots, the others showing decreases. Nutrient losses may be outweighed, at least in the short term, by improved soil microclimate through the reduced thickness of forest floor where low soil temperatures are a limiting factor.

The ''Picea/Abies'' forests of the Alberta foothills are often characterized by deep accumulations of organic matter on the soil surface and cold soil temperatures, both of which make reforestation difficult and result in a general deterioration in site productivity; Endean and Johnstone (1974)<ref name="end">Endean, F.; Johnstone, W.D. 1974. Prescribed fire and regeneration on clearcut spruce–fir sites in the foothills of Alberta. Environ. Can., Can. For. Serv., Northern For. Res. Centre, Edmonton AB, Inf. Rep. NOR-X-126. 33 p.</ref> describe experiments to test prescribed burning as a means of seedbed preparation and site amelioration on representative clear-felled ''Picea/Abies'' areas. Results showed that, in general, prescribed burning did not reduce organic layers satisfactorily, nor did it increase soil temperature, on the sites tested. Increases in seedling establishment, survival, and growth on the burned sites were probably the result of slight reductions in the depth of the organic layer, minor increases in soil temperature, and marked improvements in the efficiency of the planting crews. Results also suggested that the process of site deterioration has not been reversed by the burning treatments applied.