Forest floor property controls and consequences for forest soils’ thermal-hydrological functioning

气候条件、空气中的营养物质输入和树种选择等因素控制着森林的地面特性，从而控制着我们森林的生态功能。可用的库存数据使得能够识别基本FF属性（例如，厚度、质量、形态）和生态立地条件。虽然人们普遍认为存在这种密切的关系，但这仍有待于在一个涵盖广泛空间范围的环境中加以证明。测试FF特性、降水量和气温之间的关系是一个特殊的挑战，因为FF特性本身控制着平均气温（MAT）和平均年降水量（MAP）以及FF内的温度和水张力之间的关系。通常，对FF基本特性和物理特性之间的联系知之甚少这些参数包括孔径分布、保水性、水力传导率、导热率，其控制基本的FF服务，例如FF内和通过FF的水、能量、空气和物质的通量。此外，很少有人知道这些属性如何改变气候变化，N-富营养化和树种组成的变化。FF保水性的变化不仅可能影响森林中的水循环，而且可能影响其热状况，因为土壤中的热流取决于孔隙的几何形状和连通性以及水分饱和度。虽然这已被证明为寒带，类似的调查温带森林缺乏。它阻碍了我们对森林下土壤水分和土壤温度的组合状况如何响应非生物和生物驱动因素的变化而改变的理解。森林的热力学和水力学特性变化对森林和下层矿质土壤水热平衡的影响的基于模型的评估，为填补这些知识空白提供了巨大的潜力。然而，尚未采取系统和综合的方法来确定对FF财产和由此产生的FF服务的控制。因此，我们的项目有两个目标：（1）利用森林覆盖层和下层矿质土壤层水热平衡的耦合模型，回答森林覆盖层结构因养分供应和气温变化而发生的变化如何影响森林的热量和水分平衡的问题，以及（2）基于对FF特性与研究单元（RU）和其他监测/清单站点的生态站点条件之间的关系的更好理解，这些新的发现将用于将森林基本特性从林分水平转移到区域和国家水平。

Climatic conditions, airborne nutrient inputs, and tree species selection - among other factors - control forest floor (FF) properties and thus the ecological functions of our forests. Available inventory data enable the identification of relations between basic FF properties (e.g., thickness, mass, morphology) and ecological site conditions. Although it is widely assumed that such close relations exist this remains to be proven in a setting covering a wide spatial range. Testing relations between FF properties, precipitation, and air temperature is a special challenge, because FF properties themselves control the relation between mean air temperature (MAT) and mean annual precipitation (MAP) and the temperature and water tension within FFs.In general, very little is known about the link between basic FF properties and physical properties (pore-size distribution, water retention, hydraulic conductivity, thermal conductivity) that control essential FF services such as the fluxes of water, energy, air, and matter; within and through the FF. Moreover, little is known about how these properties alter under climate change, N-eutrophication and changes in tree species composition. Changes in water retention of FF may impact not only the water cycle in forests, but also their thermal regime, because the heat flow in soils depends on the geometry and connectivity of pores and the degree of water saturation. While this has been shown for the boreal zone, similar investigations for temperate forests are lacking. It hampers our understanding of how the combined soil moisture and soil temperature regime under forests could alter in response to changes in abiotic and biotic drivers.Existing data on FF properties and dynamic site conditions from a number of monitoring sites and inventories (e.g., ICP-Forests Level I and II sites) in combination with a model-based assessment of the impact of changes in thermic and hydraulic properties of FF on the water and heat balance of FF and underlying mineral soil bear huge potential for closing these knowledge gaps. However, a systematic and combined approach to identify the controls of FF properties and resulting FF services has not yet been carried out. The aim of our project is thus two-fold: (1) Answer the question of how changes in the structure of FF as a result of changing nutrient availability and air temperature can affect the heat and water balance of forests, using coupled modelling of the water and heat balance of FF and the underlying mineral soil horizon, and (2) based on an improved understanding of the relationships between FF properties and ecological site conditions at the research unit (RU) and other monitoring/inventory sites, these new findings will be used to transfer basic FF properties from the stand level to the regional and national level.