Early growth and nutrient dynamics of planted Pinus banksiana seedlings after slash-pile burning on a boreal forest site

Containerized jack pine (Pinus banksiana Lamb.) seedlings were planted in 10 paired slash-pile-burn and control plots established on a recent clearcut in northeastern Ontario to assess early impacts of intensive fire on soils and plant growth and nutrition. Root zone soil and seedlings were sampled one growing season after planting. The control seedlings exhibited modest growth without gain in N content, indicating reliance on internal nutrient reserves for growth on this low-fertility site. Slash-pile burning reduced seedling mortality, and markedly increased height, root-collar diameter, and biomass growth, as well as uptake of N, P, K, Ca and Mg. The response was attributed to greatly improved soil fertility following fire, characterized by increased pH, extractable NO(3)(-) and NH(4)(+), available P, and exchangeable K, Ca and Mg. Significant correlations between corresponding soil tests and seedling nutrient composition indicated that laboratory extractions effectively reflected nutrient availability to plants. The highest correlations were associated with N. Vector diagnosis identified N as the most limiting nutrient constraining growth on the burns, even though base cation increases (mainly from ash) were relatively larger than extractable N in the soil. These early responses in soils and plants to intensive fire may have long-term effects on plantation development.