IngentaConnect Origin of the lichenspruce woodland in the closed-crown forest zo...

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Abstract:

Aim

We investigate the timing and factors responsible for the transformation of closed-crown forests into lichen-spruce woodlands. Location

The study area extends between 70° and 72° W in the closed-crown forest zone from its southern limit near 47°30′ N to its northern limit at the contact with the lichen-spruce woodland zone around 52°10′ N. A total of 24 lichen-spruce woodlands were selected. Methods

Radiocarbon dating of charcoals at mineral soil contact and within the organic horizons allowed the principal factors causing the degradation of the closed-crown forest to be identified, i.e. light fires, successive fires and the occurrence of a spruce budworm epidemic followed by a fire. Results

Charcoals dated in the organic horizon were less than 200 years old, suggesting a recent transformation of the closed-crown forest following surface fires. Before their transformation into lichen-spruce woodlands, stands were occupied by old, dense forests that originated from fires dating back to 1000 yrbp. The radiocarbon dating of charcoals in the organic horizon indicated that several stands burned twice in less than 50 years, while others burned shortly after a spruce budworm epidemic. Light fires are frequent within the lichen-spruce woodlands according to multiple charcoal layers found within the organic matter horizon. Main conclusions

While closed-crown forests are predicted to expand under climate warming, compound disturbances diminish the natural regeneration of the closed-crown forests in the south and favour the expansion of lichen-spruce woodlands. As black spruce germinates on mineral soils, surface fires accentuate the expansion of the lichen-spruce woodlands southward. Under global warming, warmer springs will lead to earlier low-intensity fires that do not remove as much organic matter, and hence prevent conditions suitable for black spruce regeneration. Also, spruce budworm reduces seed production for a certain time. The occurrence of fire during this period is critical for regeneration of black spruce.

Keywords: Black spruce; boreal forest; charcoal; climate change; disturbances; eastern Canada; ecological succession; fire severity; lichen-spruce woodland

Document Type: Research article

DOI: 10.1111/j.1466-8238.2009.00449.x

Affiliations: 1: NSERC Northern Research Chair, Centre d'Études Nordiques and Département de Biologie, Université Laval, Québec, Canada G1K 7P4 , 2: Département des Sciences Fondamentales, 555 Boulevard de l'Université, Université du Québec à Chicoutimi, Chicoutimi, Québec, Canada G7H 2B1

Origin of the lichen-spruce woodland in the closed-crown forest zone of eastern Canada