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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]

• Deadwood volume ranged from 23 m3 ha−1 in larch forests to 109 m3 ha−1 in spruce-fir-beech forests. • Deadwood diversity was high in beech and spruce forests and low in floodplain forests, pine forests and larch forests. • Deadwood availability was mainly driven by tree- and stand related factors. • Deadwood proportion should be considered as additional forest biodiversity indicator. Deadwood is an important structural feature in forests providing essential resources for various organisms. Both forest management and conservation are increasingly focusing on the integration of deadwood into forest management. Deadwood volume and composition are driven by forest type, stand age, natural tree mortality, tree species composition and harvesting intensity. Here, we used inventory data from 28 unmanaged natural forest reserves (NFR) in Austria to analyse the patterns and drivers of: (i) the volume of standing and lying deadwood, (ii) the diversity of deadwood in different forest types. Eight forest types are located in the investigated NFRs covering a wide range of vegetation types with altitudes of 140–1825 m asl. The volumes of living wood and deadwood differed markedly between forest types. The average deadwood volume per forest type ranged from 23 m3 ha−1 in larch forests to 109 m3 ha−1 in spruce-fir-beech forests. Likewise, deadwood diversity (species diversity as well as diversity in diameter classes and degree of decomposition) differed significantly among forest types, with the highest deadwood diversity found in beech and spruce forests and the lowest in hardwood floodplain forests, carbonate pine forests and larch forests. Our results show that volume and composition of deadwood vary greatly among different forest types. Regression models revealed that the availability of deadwood was mainly driven by tree- and stand related factors (e.g. forest type, diameter at breast height and volume of living stand), whereas site-related (e.g. altitude) and climatic factors (e.g. mean annual precipitation) had a minor influence. The variables tree species diversity, aspect and slope showed no significance and were therefore not integrated into the final model. This study provides insights into deadwood availability and diversity in NFRs on a national scale, providing reference data for unmanaged temperate forests and aiding decision-making in nature conservation and forest management, since NFRs are reference areas for close-to-nature forestry. [ABSTRACT FROM AUTHOR]