Global wood cascades from terrestrial sources to terrestrial, freshwater, and marine sinks

Abstract

Forests cover nearly one third of Earth’s land. Dead, downed wood plays a critical role in the planet's physical, biogeochemical, evolutionary, and ecological processes. Wood from terrestrial source areas moves into freshwater and marine environments in wood cascades. Cascades embody a ‘source-to-sink’ approach emphasizing the details of connectivity between production and eventual recycling and can be applied at local to global scales. We lack quantitative studies of specific source-to-sink wood movement, including volumes of wood involved in the cascade, timespans of transport and storage, or partitioning of terrestrial wood from a particular forested area into diverse potential sinks. Characterizing wood cascades can highlight differences in wood dynamics from source to sink and identify geographically specific wood cascades disrupted by human activities, the potential consequences associated with this disruption, and strategies for mitigating the disruption. We review existing understanding of wood production at terrestrial sources, transport processes and rates in freshwater and marine settings, and wood abundance in sinks, and highlight knowledge gaps. Wood dynamics in forests and rivers are the best understood components of wood cascades. Global deforestation and freshwater and coastal management have drastically altered wood cascades. Despite the documented importance of wood, contemporary understanding of wood abundance and quantitative prediction of transport processes and pathways or wood accumulation sites is limited. An integrative conceptualization of wood from source to sink and research targeted at known gaps can advance our understanding of the importance of wood and inform efforts to manage wood for human and environmental benefits.