Soil chemical changes and plant succession following experimental burning in immature jack pine

Abstract

In 1975 and 1976, an experimental burning program was conducted in an immature stand of boreal jack pine (Pinus banksiana Lamb.) growing on level, granitic outwash sands in northern Ontario. Nine 0.4-ha plots were burned under a range of fire weather conditions and sampling was conducted to examine the effect of fire on soil chemical changes and revegetation. Results indicated that depth of burn (DOB) affected both soil chemical changes and plant succession on these pine sites. Vaccinium angustifolium Ait., Oryzopsis spp,. Waldsteinia fragarioides (Michx.) Tratt, Salix spp. and Viola adunca Sm. increased in cover at two levels of DOB but the increase was greatest at the lower DOB and decreased to pre-burn levels after 10 yr. Comptonia peregrina (L.) Coult., Epilobium angustifolium L., Polytrichum commune Hedw. and Amelanchier sanguinea (Pursh) DC. were not found in the pre-burn surveys but appeared after burning. Vegetation cover for these species was always higher at the deeper DOB but decreased almost to zero after 10 yr. Other species such as Pleurozium schreberi (Brid.) Mitt., Linnaea borealis L., Corylus cornuta Marsh., Cladina rangiferina (L.) Nyl. and Aralia nudicaulis L. were eliminated from the site and did not recover even after 10 yr. Soil pH increased 0.3 to 1.0 pH units in the organic and mineral soil layers. The rate of increase in pH was always steeper at the higher DOB and pH returned to pre-burn levels in the mineral soil layers after 10 yr. Immediately after burning, exchangeable Ca in the mineral soil layers doubled but 10 yr later, Ca returned to pre-burn levels. Phosphorus and K increased in the mineral soil, leveled off and were still elevated after 10 yr. Total Kjeldahl N was reduced by 50% in the organic soil while N in all mineral soils increased, and was still increasing after 10 yr. Except for immediate post-fire increases in pH, Ca and N, soil chemical changes were small or they rebounded to pre-burn levels 10 yr after burning. Therefore it is unlikely that these changes were the cause of the plant cover changes that persisted to 10 yr. Key words: Soil nutrients, plant succession, fire, depth of burn, jack pine