From vegetation to soil: Organic matter dynamics in young temperate riparian forests

The future of wetland forests in temperate regions interests many nature conservationists. Indeed, due to a mosaic of environments influenced by the availability and the dynamics of water, these ecosystems have a specific biological diversity and a potential to store carbon. Sadly, wetland forests are threatened and increasingly rare in Europe, due to human pressure on land, in a context of biodiversity loss and climate change. An important part of these ecosystems is now only semi-wild, and the dynamics of their organic matter is still poorly known. This study focuses on the riparian forests in nature reserves along the lake of Neuchâtel (Switzerland). These forests colonised newly available areas, emerged from the lake after a 3-m drop of the water level at the end of the 19^th century.

The aim of the project is to better understand the dynamics of different types of wetland forests along a gradient of water level. Vegetation communities, organic matter and soil were studying in four forest types: wet black alder forests, humid alluvial white alder forests, ash forests and summer dry pine forests. Measured factors include water table fluctuations, soil litter inputs, organic matter decomposition rate, soil respiration, and soil organic matter characteristics, in relation to vegetation type. The first results show a difference in the organic matter pathways between the four habitats. Water dynamics appears to be one of the main drivers in the fate of organic matter. Wet black alder forests have low soil respiration, but a high rate of organic matter decomposition, as contrarily to the drier ash forests. This project will contribute to improve the conservation of these threatened ecosystems.