The influence of forest floor changes on the success and composition of tree regeneration

气候变化将极大地影响树种组成，从而影响森林的生物多样性和生态系统功能。到目前为止，间接影响，如种子发芽的基质条件改变，营养物质供应或种子捕食的变化，以及随后的树种之间的竞争变化，导致再生成功的变化，很少受到关注，尽管它们可能对未来森林的复原力和适应能力至关重要。在中欧，诸如温度升高、落叶物种比例增加和持续的富营养化等驱动因素可能导致森林地面质量和其他森林地面特性的减少，对树种的再生产生未知的后果。大多数关于FF对树木再生影响的研究可以追溯到20世纪60 - 70年代，早在广泛的缺磷和气候变化成为重要考虑因素之前。我们的项目旨在通过研究FF特性变化对温带欧洲山毛榉混交林重要树种再生成功的影响来缩小这一知识差距。具体而言，我们将解决气候变化和FF变化对三个目标物种，森林山毛榉，云杉，槭pseudoplatanus再生成功的综合影响。 除了这两个因素的直接影响，我们将分析间接影响，通过变化的营养物质和水或菌根化，生物因素的变化，如真菌病原体和种子捕食，以及树种之间的竞争，以及幼苗和其他林下植被之间的变化。为此，我们将评估发芽率以及死亡率，生长（e。例如，在一个实施例中，密度、高度、根和枝的生物量）、竞争状态以及菌根化和营养的实验方法。在围隔实验中，不同的土壤磷状况，因此FF质量的网站的土柱，我们专注于发芽和初步建立的过程。在这里，我们将测试降低FF厚度是否会影响种子和萌发体对1）随着降水季节分布（潮湿的冬季）的变化而发生真菌侵染的敏感性，以及2）在干燥期发生干燥的敏感性。我们进一步检验了3）FF结构是否决定了建立的成功。在田间试验中，这三个物种的种子播种在6个地点对比P的有效性平均年温度，我们测试是否降低FF厚度促进4）竞争树苗从林下和5）增加竞争P和其他养分之间的成熟树木和幼苗。如果成功，我们的项目将为了解不断变化的环境条件下森林生态系统的再生动态做出重要贡献。

Climate change will greatly impact tree species composition and hence biodiversity and ecosystem functioning of forests. So far indirect effects such as changes in regeneration success as a result of altered substrate conditions for seed germination, modifications in nutrient availability or seed predation and subsequent shifts in the competition among tree species have received very little attention, although they may be crucial for future forest resilience and adaptive capacity. In central Europe, drivers such as increasing temperatures, increasing proportions of deciduous species and ongoing eutrophication may lead to a reduction in forest floor (FF) mass and other FF properties with unknown consequences for the regeneration of tree species. Most research on the influence of FF on tree regeneration dates back to the 1960-1970s, long before widespread P deficiency and climate change were important considerations. Our project aims to close this knowledge gap by studying the influence of changes in FF properties on the regeneration success of important tree species in temperate mixed European beech forests. Specifically, we will address the combined influence of climate change and FF changes on the regeneration success of three target species, Fagus sylvatica, Picea abies, Acer pseudoplatanus. In addition to the direct influence of these two factors, we will analyse indirect influences through changes in the availability of nutrients and water or mycorrhization, changes in biotic factors such as fungal pathogens and seed predation, and changes in the competition among tree species as well as between seedlings and other understorey vegetation. For that purpose, we will assess the germination rates as well as the mortality, growth (e. g., density, height, biomass of roots and shoots), the competitive status as well as mycorrhization and nutrition of seedlings in an experimental approach. In mesocosm experiment with soil columns from sites differing in soil P status and hence FF mass, we focus on the germination and initial establishment process. Here we will test whether decreasing FF thickness influences the susceptibility of seeds and germinants to 1) fungal infestation with changes in seasonal distribution of precipitation (wetter winters) and 2) to desiccation in dry periods. We further test whether 3) the establishment success depends on FF structure. In a field experiment, where seeds of the three species are sown at six sites contrasting in P availability mean annual temperature, we test whether decreasing FF thickness promotes 4) competition for tree seedlings from understorey and 5) increases competition for P and other nutrients between mature trees and seedlings. If successful, our project will provide an important contribution to understanding the regeneration dynamics in forest ecosystems under changing environmental conditions.