A global large-sample synthesis of large wood (LW) dynamics based on catchment descriptors and hydrological drivers

The body of research on large wood (LW) dynamics in rivers has been gaining momentum in line with the increasing recognition of the multifaceted morphological and ecological roles that wood exerts on fluvial systems. Although processes constituting LW dynamics (e.g., recruitment, mobility, storage, and export) have been extensively explored at the reach scale, understanding remains scarce at the catchment scale, which requires a systematic, landscape-level approach to identifying broader risks and developing targeted action plans. This contribution synthesizes a three-decade scholarly corpus and presents a nuanced meta-analysis on catchment-scale LW dynamics across different geographical and climatic regions. The final database encompasses 248 distinct catchments globally, classified according to the specific LW process documented and indexed with a common parameter for each process: recruitment per channel area (m³ ha^-1) for recruitment, stability index– equal to wood length to channel width ratio (m m^-1)– for mobility, LW load (m³ ha^-1) for storage, and unit LW export rate (m³ ha^-1 a^-1) for export. Regression modelling was rigorously employed, with the aforementioned LW parameters from the four processes as response variables. Meanwhile, predictor variables were systematically chosen to represent the effect of catchment characteristics and hydrological forcing on the LW parameters, thereby adopting a large-sample hydrology perspective across diverse environmental settings. Quantitative results from the regression analyses suggest that drainage area, mean catchment slope, mean annual precipitation, and percentage forested area are statistically significant predictors of LW parameters across the studied LW processes. For the recruitment phase, higher mean annual precipitation and steeper slope are generally associated with greater LW recruitment. In terms of mobility, an increase in drainage area corresponds to a decrease in the stability index, suggesting lower LW stability in larger catchments. LW storage patterns show that higher mean annual precipitation is linked to a greater LW load, while smaller catchments generally exhibit lower stored LW volumes. Finally, the unit LW export rate is significantly influenced by the percentage forested area and slope within each catchment, with both higher percentages of forestation and steeper slopes leading to greater LW export per unit drainage area. These results highlight the extent to which catchment-scale characteristics affect LW processes in a way that studies conducted at the reach scale could easily overlook. This meta-analysis also represents the first systematic attempt to quantify catchment-scale variability in LW parameters at a global level, a dimension that previous reviews have not explored. Finally, the analyses suggest that a disproportionate number of studies on LW dynamics are concentrated on catchments in temperate and continental climatic regions. This highlights a profound need for more studies on LW patterns in underrepresented areas, including tropical catchments in the Southern Hemisphere and the boreal and Arctic rivers in high latitudes– all of which are increasingly altered and subjected to anthropogenic pressures as well as climate change ramifications.