Quantity is foremost but quality matters: A global meta-analysis of correlations of dead wood volume and biodiversity in forest ecosystems

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Dead wood is crucial for forest biodiversity. Previous analyses support a positive relationship between dead wood volume and biodiversity, but the strength and direction of the correlation may differ across biomes, forests, dead wood traits, and among taxa and functional groups. Therefore, an up-to-date quantitative synthesis of general patterns and global trends of correlations between dead wood and the biodiversity of common and rare species is needed. Here we present the findings of a global meta-analysis that synthesized 213 correlations from 40 studies using random effects models.The correlations between dead wood volume and all species and rare species were significantly positive and moderate, however, there were noticeable differences between taxa. The summary effects by bioclimatic regions, forest types, stands and management regimes were generally positive and moderate with no statistically significant differences, suggesting a consistent positive effect of dead wood volume on biodiversity. Dead wood types and decay stages have statistically significant differences in correlations regardless of species' rarity status, where the volume of logs and the intermediate decay stage have the strongest correlations with biodiversity. Our results support the idea that dead wood volume can largely be considered an indicator of forest biodiversity, however, dead wood quality attributes are critically important, and hence, should be given priority in forest management and biodiversity conservation interventions. More research is needed in the (sub-)tropics and concerning the relationships between dead wood and rare, threatened, and red-listed species.