River distance, stand basal area, and climatic conditions are the main drivers influencing lying deadwood in riparian forests.

Description: Scheme of the riparian zone in the Mura-Drava-Danube Transboundary Biosphere Reserve–the largest riverine protected area in south-eastern Europe–covering a gradient of softwood, transition and hardwood forests. Softwood floodplain forests grow in the lower parts of floodplains, they are hygrophilous, regularly flooded forests dominated by willow and poplar, while hardwood floodplain forests occur in the higher parts of current or former floodplains, dominated by elm, ash, or oak. The average lying deadwood volume per forest type ranges from 55 m³ha⁻¹ in hardwood forests to 94 m³ha⁻¹ in softwood forests. As distance from the river edge increased, the volume of lying deadwood decreased, ranging from 0.7 to 990 m³ha⁻¹ in total. Deadwood in fresher decay stages was found mainly at greater distances to the river, while advanced decay stages dominated close to the river. [Display omitted] • With increasing distance from the river edge, both the occurrence and volume of lying deadwood in riparian forests of south-eastern Europe decreased significantly. • High stand basal area had a positive effect on the volume of lying deadwood, while extensive silvicultural management practices increased the occurrence probability of lying deadwood. • Moist and warm climatic conditions led to a larger amount of deadwood in advanced decay stages. Riparian forests are among the most diverse terrestrial ecosystems, yet their biodiversity is increasingly threatened by habitat degradation, climate change, river regulation and invasive species. We investigated deadwood, widely recognized as an indicator for forest biodiversity, in riparian forests of the Mura-Drava-Danube Transboundary Biosphere Reserve. The Biosphere Reserve is a conservation area that spans five countries and three rivers located in south-eastern Europe. In detail, we analyzed the drivers of lying deadwood volume, occurrence and decay related to floodplain type, silvicultural management, and climatic conditions using regression models. Lying deadwood occurrence and volume significantly decreased as distance from the river edge increased, indicating that river dynamics likely play a role in deadwood accumulation in riparian forests. Deadwood volume was also positively influenced by stand basal area, a parameter that can be directly addressed by silvicultural management. Deadwood decay was affected positively by temperature and negatively by precipitation, highlighting the importance of climatic conditions on decay progression. However, in order to draw more accurate conclusions about the drivers and dynamics of deadwood in riparian forests, further monitoring efforts that consider river flooding and flow regime, deadwood transport and saproxylic organism activity in addition to forest management and site conditions, are needed. [ABSTRACT FROM AUTHOR]