PARENT SESSION
Contributed Oral Session 66: Disturbance Ecology : Water, Wind, and Ice
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 520 B, Level 5, Palais des congrès de Montréal

Coarse woody debris piles as browsing refuges for aspen and willow regeneration.

de Chantal, Michelle^*,1, Granström, Anders², ¹ University of Helsinki, Helsinki, Finland² Swedish University of Agricultural Sciences, Umeå, Sweden

ABSTRACT- We conducted an inventory in Tyresta National Park, central Sweden, to determine whether coarse woody debris piles are effective refuges against browsing for seedlings. A large area of the Park′s natural forest burned in 1999, and numerous woody debris piles were formed by windthrow. The area contains 10-15 Populus tremula seedlings/m² that regenerated naturally from seeds in 2000. The area also comprises 30 Salix seedlings/m². In 2004, we measured the height, stem base diametre, diametre at current browsing height, and height of past browsing events for the three tallest Populus and Salix seedlings growing in debris piles and in adjacent open areas. The protection offered by debris piles was evaluated by the distance from seedlings to the nearest debris stem, the diametre and height above ground of that stem, and debris pile height and width from the seedling position. Four years after establishment, Populus height was 60.2 ± 9.0 cm in open areas and 153.0 ± 40.6 cm inside debris piles. The respective values for Salix were 53.9 ± 11.9 cm and 166.9 ± 27.3 cm. Stem base diametre was wider for seedlings growing inside debris piles than in open areas. Backward regression analysis showed that debris pile height and width, and distance to the nearest debris stem influenced Populus seedling height. In contrast, the height of Salix seedlings was affected by debris pile height only. The results show that debris piles are an effective tool to protect seedlings against herbivory. Accordingly, natural or man-made debris piles could be integrated into silvicultural methods and forest restoration activities to promote seedling regeneration.

Key words: Populus tremula, Salix, Natural disturbances, Height