Pr. Frédérik Doyon (Département des sciences naturelles, Université du Québec en Outaouais, Canada) will give this seminar, organized by the ELI-E department.

Abstract

The SylvAdapt experiment uses a Before-After-Control-Effect design for comparing two adaptation strategies: 1) the  “Champion species” (CS) that favors the most robust species in the face future global change threats or 2) the “Diversity insurance policy” (DIP) that promotes structural, taxonomic, and functional diversity.  

The experiment has been conducted in southern Quebec in mixed red maple stands, across 26 sites. Each site comprises three treated ¼-hectare plots with partial cuts at three thinning levels (residual G: 20 m²/ha, 12 m²/ha, and 6 m²/ha) and one control. In each plot, tree regeneration (seedlings and saplings) response has been monitored in terms of abundance and diversity 5 years after thinning within 16 microplots (4m2).  

Total seedling cover is almost two times greater in the 12 and 6 m²/ha thinning treatments than the two other ones. Tall seedlings cover and sapling density are two times and four times greater in the 12 and the 6 m²/ha, respectively, and greater in the CS adaptation strategy.  

This result is mostly explained by regeneration coming from red maple stump sprouts. Tree seedling alpha diversity follow the same pattern as the abundance ([control = 20 m²/ha] < [12 m²/ha = 6 m²/ha]). DIP strategy promotes greater tree seedling and sapling diversity than CS. 

Species turnover (beta diversity) was not different between thinning levels and adaptation strategies. 

The results identify an apparent threshold in abundance and diversity occurring between 20 and 12 m²/ha thinning levels and suggest that a partial cut with an intermediate harvest level of 12 m²/ha residual promotes better recruitment, greater diversity, and increased habitat heterogeneity, while keeping competition for forest regeneration at a manageable level.