Jack pine regeneration and crown fires

Abstract

The effect of crown fires on Pinus banksiana Lamb. regeneration was studied in separate forest- and cone-burning experiments. Nine plots (0.56–2.25 ha) of jack pine trees near Fort Providence, Northwest Territories, were burned using crown fires to determine the effects of fire intensity, rate of fire spread, depth of burn, and postfire duff depth on seed viability and regeneration. Fire intensities were 36 902 – 93 476 kW/m, and fire spread rates were 24–70 m/min. Depths of burn were low (2.0–3.6 cm), and postfire duff depths averaged 2.0–5.5 cm. Postfire seed rain was highly variable (64–634 seeds/m2), but seed viability was near 67% on all plots. Jack pine regeneration was also highly variable (7–79 seedlings/m2). In the cone-burning experiment, the germination rate increased from 41% (unheated cones) to 64% after 10 s of burning but decreased sharply after 30 s. Flame temperature did not significantly affect viability. Cone-burning results suggest that the postfire seed rain originated from the upper canopy, where flame duration was 5–15 s, and seed in the lower canopy was consumed by fire. Seed rain and regeneration were primarily influenced by understory fine fuel consumption (and therefore, fire intensity), tree height, and live crown base height.