Laboratoire de Biomathématiques et d'Estimations Forestières, Université d'Abomey Calavi, 04 BP 1525, Cotonou, Benin.
Department of Environmental Science and Ecological Engineering, Korea University, 145 Anamro, Seongbukgu, Seoul, 02841, South Korea.
J Environ Manage. 2020 Dec 15;276:111268. doi: 10.1016/j.jenvman.2020.111268. Epub 2020 Sep 1.
Biotic and abiotic drivers of seedling establishment and survival are fundamental not only for elucidating processes occurring at plant early life stages, but also for assisting species natural regeneration. Keystone, multipurpose and economically important tree species such as Afzelia africana Sm. are reportedly facing recruitment constraints, yet little is known about how abiotic and biotic factors shape the species seedling dynamics. Here, we monitored the species seedlings over one year across three seasons in West Africa savannahs to determine how conspecific and heterospecific biotic neighborhood and habitat heterogeneity correlate with initial seedling density, leaves' fungal infection and herbivory and how all these factors combined, influence the species seedling survival. Seedling densities increased with increasing conspecific adult densities, and were highest in tree savannahs and on sandy-silt soils. Leaves' fungal infection and herbivory were also positively associated with conspecific adult density, but were more abundantly observed in tree savannahs than in shrub savannahs. Seedling survival was constrained on higher slope, and negatively affected by conspecific adult density, especially in shrub savannahs. There was a strong evidence for negative density-dependence effects of conspecific adults on seedling survival, which operated through negative effects of herbivory and fungal infection. Habitat heterogeneity was also an important driver, which modulated biotic factors' effects on seedling survival: tree savannahs promote positive conspecific density-dependence of seedling fungal infection and herbivory more than shrub savannahs. Nonetheless, seedlings were more sensitive to natural enemies in shrub savannahs, suggesting increased negative conspecific density-dependence effects on seedling survival in less dense vegetation, possibly as a result of enhanced specialization of predators and pathogens on a limited set of species. The study brings important insights into the mechanisms that drive the establishment and survival of the species seedling, which should be considered in the design of management activities aiming at the conservation of this endangered species.
生物和非生物因素是影响幼苗建立和存活的基础，不仅对于阐明植物早期生命阶段的发生过程至关重要，而且对于协助物种自然再生也至关重要。据报道，阿弗列西亚非洲种（Afzelia africana Sm.）等重要的关键种、多用途和经济树种正面临着繁殖限制，但人们对生物和非生物因素如何塑造物种幼苗动态知之甚少。在这里，我们在西非萨凡纳的三个季节中对该物种的幼苗进行了一年的监测，以确定同种种群和异种种群的生物群落以及生境异质性如何与初始幼苗密度、叶片真菌感染和食草动物的发生相关，以及所有这些因素如何共同影响物种幼苗的存活。幼苗密度随着同种成年树密度的增加而增加，在树木萨凡纳和沙质粉土上最高。叶片真菌感染和食草动物也与同种成年树密度呈正相关，但在树木萨凡纳中比在灌木萨凡纳中更为普遍。幼苗的存活率受到较高坡度的限制，并受到同种成年树密度的负面影响，特别是在灌木萨凡纳中。有强有力的证据表明同种成年树对幼苗存活存在负密度依赖性效应，这种效应通过食草动物和真菌感染的负面影响起作用。生境异质性也是一个重要的驱动因素，它调节了生物因素对幼苗存活的影响：树木萨凡纳比灌木萨凡纳更能促进同种种群密度依赖性的幼苗真菌感染和食草动物的发生。尽管如此，幼苗在灌木萨凡纳中对天敌更为敏感，这表明在植被密度较低的情况下，对幼苗存活的负密度依赖性效应更大，这可能是由于捕食者和病原体对有限物种的特化程度增加所致。该研究为驱动该物种幼苗建立和存活的机制提供了重要的见解，在设计旨在保护这一濒危物种的管理活动时应予以考虑。
