EARTH, WIND & WATER—TREES AS AGENTS OF PROGRESSIVE ROCK FAILURE

The conversion of fresh bedrock into weathered, intact rock and- subsequently- into detached and thus mobile material that can be transported downhill and into rivers underpins the entire conceptual framework defining the physical structure of the Critical Zone (CZ). In turn, rock weathering- through its production of porosity in rock and soil - drives or limits a vast range of CZ processes, including those related to carbon storage, chemical weathering, water availability, ecosystem attributes, and the pace of erosion and thus landscape evolution. In thin-soiled settings, we presume that trees play a significant role in converting weathered bedrock into mobile sediments, with models centered on tree throw. However, little is known regarding how - or how often - trees damage rock, create fractures or expand fractures in fresh and weathered bedrock. This question is complicated by a paucity of available data and methods to measure forces at the bedrock-root interface. Combining force sensors at the tree-rock boundary with precipitation, solar radiation, wind, tree sway data, acoustic emission sensors, and physical models, I have begun to quantify tree-driven soil-production mechanisms at Observatories with diverse forest types and climate conditions. Data suggests that trees damage and detach rock due to daily water uptake, rain, and wind events, while charismatic tree throw may matter less than belowground damage. The frequency, magnitude and style of wind-driven tree forces varies among species. This suggests that changes in water availability and forest structure, driven by variations in lithology and climate, may greatly influence tree-driven physical weathering.