Changes in understory plant communities following soil scarification and amendments in a Northern Hardwood Forest

The regeneration dynamics of sugar maple-dominated stands in northeastern North America are intricately influenced by global changes such as soil acidification, invasive species, forest management, and climate shifts. A notable challenge is the expansion of American beech and its bark disease, threatening mature trees and ecosystem services. Although sylvicultural practices aim to control beech regeneration and enhance high-value species, their impact on understory plant communities remains poorly documented. In Valcartier, eastern Canada, we conducted a field experiment to assess the short-term effects of soil scarification and diverse soil amendments (nitrogen fertilization, liming, wood ash) on understory plant communities in a beech-invaded sugar maple stand. Over four years, we inventoried vegetation and measured various biotic and abiotic variables. Results showed that soil scarification significantly reduced diversity metrics like Simpson dominance, functional diversity, and redundancy (a metric correlated to community stability and resilience to disturbance). Negative effects of scarification were exacerbated by nitrogen, lime, or wood ash additions. Lime amendment without scarification enhanced diversity, suggesting its potential to support understory community stability. While scarification and amendments can promote sugar maple, yellow birch, and pin cherry seedling establishment, they have collateral effects on the understory, impacting productivity, diversity, and resilience in the short term. Land managers should exercise caution when combining these treatments, as they may transiently alter the stability and resilience of the understory and other forest functions. A more sustainable approach involves applying scarification and amendments on small, well-distributed patches within the targeted stands for treatment, avoiding extensive application over large areas.