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Arthur Guignabert
UMR 1391 ISPA, Bordeaux Sciences Agro, INRAE, 33140 Villenave d’Ornon, France

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Journal article
Published: 03 August 2020 in Forest Ecology and Management
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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 positive effect was more pronounced in the two sites within the failure area, suggesting that conditions were more stressful in this part of the forests. Consequently, we recommend avoiding clear-cutting in favour of partial cutting in all parts of these forests, and ensuring the maintenance of sufficient forest cover to promote regeneration. Direct seeding could be used in addition to partial cutting to maximize the chances of success, but only in areas where natural regeneration is low.

ACS Style

Arthur Guignabert; Laurent Augusto; Florian Delerue; Francis Maugard; Céline Gire; Clément Magnin; Sylvie Niollet; Maya Gonzalez. Combining partial cutting and direct seeding to overcome regeneration failures in dune forests. Forest Ecology and Management 2020, 476, 118466 .

AMA Style

Arthur Guignabert, Laurent Augusto, Florian Delerue, Francis Maugard, Céline Gire, Clément Magnin, Sylvie Niollet, Maya Gonzalez. Combining partial cutting and direct seeding to overcome regeneration failures in dune forests. Forest Ecology and Management. 2020; 476 ():118466.

Chicago/Turabian Style

Arthur Guignabert; Laurent Augusto; Florian Delerue; Francis Maugard; Céline Gire; Clément Magnin; Sylvie Niollet; Maya Gonzalez. 2020. "Combining partial cutting and direct seeding to overcome regeneration failures in dune forests." Forest Ecology and Management 476, no. : 118466.

Research article
Published: 23 April 2020 in Journal of Applied Ecology
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1.Using nurse shrubs to improve tree seedling establishment in stressed environments is a common practice in forestry. Recent refinements of the stress‐gradient hypothesis suggest that positive nurse effects occur under intermediate stress and decline in the harshest conditions. Additionally, indirect facilitation (e.g. protection from herbivory) is expected in low‐stressed/productive systems according to the initial stress‐gradient hypothesis. However, there have been fewer investigations into the use of nurse shrubs to decrease herbivore impacts in stressed systems compared with the role of nurses on stress alleviation. This raises the need to clarify conditions in which the use of nurse shrubs would be most appropriate. 2.We conducted a field experiment in the sand dune forest of southwest France characterised by severe summer water shortages and the presence of different types of wild herbivores. In 2015 and 2016, Pinus pinaster seedlings were planted under shrubs (Arbutus unedo) or in shrub‐removed locations, in fenced/unfenced areas. Survival, cause of mortality, and water stress were monitored for one year after plantation. 3.Summer drought was the main cause of mortality. Water stress increased in both years as summer progressed. We found direct facilitation only in July 2016 at intermediate water stress, due to a decrease in vapour pressure deficit under shrubs. These positive effects declined in late summer when stress was at a maximum. Rodent damage occurred under shrubs in spring whereas ungulate browsing was observed in open areas in autumn/winter. Overall seedling survival was equivalent under or outside shrubs during the first year, but was better under shrubs in the second one. 4.Synthesis and applications. Our results partially validate the refinement of the stress‐gradient hypothesis, with a decline of positive interactions in the most water‐stressed conditions. This draws attention to the difficulty of using shrubs as nurses to improve tree regeneration in the most xeric systems. In addition, we show that indirect associational effects, both positive and negative, could be as important as abiotic stress alleviation in a stressful ecosystem, and using shrubs to facilitate seedling survival could be efficient depending on the type of herbivore involved. This highlights the fact that considering plant‐plant interactions can help in the design of management options, providing that up‐to‐date ecological theories are considered and that the different biotic and abiotic constraints are accurately evaluated.

ACS Style

Arthur Guignabert; Laurent Augusto; Maya Gonzalez; Christophe Chipeaux; Florian Delerue. Complex biotic interactions mediated by shrubs: Revisiting the stress‐gradient hypothesis and consequences for tree seedling survival. Journal of Applied Ecology 2020, 57, 1341 -1350.

AMA Style

Arthur Guignabert, Laurent Augusto, Maya Gonzalez, Christophe Chipeaux, Florian Delerue. Complex biotic interactions mediated by shrubs: Revisiting the stress‐gradient hypothesis and consequences for tree seedling survival. Journal of Applied Ecology. 2020; 57 (7):1341-1350.

Chicago/Turabian Style

Arthur Guignabert; Laurent Augusto; Maya Gonzalez; Christophe Chipeaux; Florian Delerue. 2020. "Complex biotic interactions mediated by shrubs: Revisiting the stress‐gradient hypothesis and consequences for tree seedling survival." Journal of Applied Ecology 57, no. 7: 1341-1350.

Journal article
Published: 03 May 2018 in Forests
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Symbiosis with ectomycorrhizal (ECM) fungi can be important for regeneration success. In a context of increasing regeneration failures in the coastal forest of maritime pine in Southwest France, we tried to identity whether differences in ECM communities could partly explain the variation of regeneration success and how they are influenced by forest practices and stand characteristics. In particular, we focused on the effects of harvesting methods (comparing mature forest with seed-tree regeneration and clear-cuts) and topography (bottom-, mid-, and top positions). Five field trials (two in regeneration failure areas and three in successful areas) were used to sample 450 one-year-old seedlings. Assessments of ECM of seedling nutrient concentrations and of seedling growth based on exploration types were made. ECM root colonisation was similar in all harvesting treatments, suggesting that enough inoculum remained alive after logging. Harvesting-induced effects modifying soil properties and light availability respectively impacted ECM composition and seedling growth. Topography-induced variations in water and nutrient availability led to changes in ECM composition, but had little impact on seedling growth. Contact, short-distance, and long-distance exploration types improved the nutritional status of seedlings (Ca, K, and N), showing that mycorrhization could play an important role in seedling vitality. However, neither ECM root colonisation nor exploration types could be related to regeneration failures.

ACS Style

Arthur Guignabert; Florian Delerue; Maya Gonzalez; Laurent Augusto; Mark R. Bakker. Effects of Management Practices and Topography on Ectomycorrhizal Fungi of Maritime Pine during Seedling Recruitment. Forests 2018, 9, 245 .

AMA Style

Arthur Guignabert, Florian Delerue, Maya Gonzalez, Laurent Augusto, Mark R. Bakker. Effects of Management Practices and Topography on Ectomycorrhizal Fungi of Maritime Pine during Seedling Recruitment. Forests. 2018; 9 (5):245.

Chicago/Turabian Style

Arthur Guignabert; Florian Delerue; Maya Gonzalez; Laurent Augusto; Mark R. Bakker. 2018. "Effects of Management Practices and Topography on Ectomycorrhizal Fungi of Maritime Pine during Seedling Recruitment." Forests 9, no. 5: 245.