Combining partial cutting and direct seeding to overcome regeneration failures in dune forests

• Published in: Forest ecology and management 2020-11, Vol.476, p.118466, Article 118466
• Main Authors: Guignabert, Arthur, Augusto, Laurent, Delerue, Florian, Maugard, Francis, Gire, Céline, Magnin, Clément, Niollet, Sylvie, Gonzalez, Maya
• Format: Article
• Language: English
• Subjects: Biodiversity and Ecology; Direct seeding; Drought; Ecology, environment; Environmental Sciences; Forest management; Germination; Life Sciences; Partial cutting; Pinus pinaster; Seed availability; Seedling survival; Tree regeneration
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/j.foreco.2020.118466

•Germination was the main bottleneck stage of the regeneration process.•Summer drought was the main cause of death for pine seedlings.•Partial cuts reduced biotic and abiotic stresses through microhabitat modification.•Positive effects of partial cutting were greatest in areas with poor regeneration.•Both direct seeding and partial cutting enhanced regeneration 3 years after harvest. Stand regeneration is a crucial step in the management of many forests and its failure can jeopardize future forest growth and production. Thus, adapting forestry practices to improve seedling establishment is of prime importance to maintain sustainable forest management. In the coastal dune forests of maritime pine in SW France, regeneration failure after clear-cutting has greatly increased in the last decades. The aim of this study was to quantify the different stages involved in the regeneration process (seed rain, germination, survival), and to assess the impact of harvesting methods (partial cutting vs. clear-cutting) and of the use of direct seeding (seeding vs. no seeding) on these stages. We established five trials located in areas with contrasting regeneration statuses (of which two sites were in an area characterized by chronic regeneration failure), and we investigated the effect of the harvesting method and the use of direct seeding in a factorial design. We monitored the seed rain, germination and first-year survival for three years. Due to the transient nature of the seed bank, we found that the seed rain of the previous year was the only possible seed source for tree regeneration, and it increased with the proximity and size of surrounding mature trees. Nonetheless, seed rain did not limit regeneration in these stands. In fact, germination was the bottleneck stage of the regeneration process in all sites because it was short-lived and consequently exposed to failure in case of unfavourable conditions. Once established, seedling death was mainly due to summer drought. Clear-cutting without seeding resulted in severe regeneration failures in 4 out of 5 sites, with the most severe in the failure area. Direct seeding increased seedling emergence only in the first year, while partial cutting had a longer-lasting effect by providing a regular seed supply over several years. Partial cutting also decreased biotic and abiotic stresses through microhabitat modification under the tree canopy, resulting in a higher number of germinations and greater seedling survival. This