Relationships Between Tree Ring Width and Slope Position: Can the Source Location and Species of Downed Wood in Gordon Gulch be Identified by Tree Ring Width?

Large downed wood in rivers and on the floodplain impact both ecological and geomorphic processes; determining the source of the large wood deposited in the river corridor during flood events remains complicated. In the semi- arid Western United States climate change could lead to increased flood events, which often result in the entrainment and deposition of large downed wood (>10 cm in diameter, >1 m in length) in rivers and floodplains (river corridors). To advance methods for identifying the source position and the species of the large wood deposited in the river corridor, we used tree ring analysis to study how tree growth differs with the tree position on hillslopes within the Gordon Gulch Catchment in the Colorado Rocky Mountains. We also assess changes in tree growth due to climate using Palmer's Drought Severity Index (PDSI) as a proxy. We used both Ring Width Indices (RWI) and Basal Area Increments (BAI) to analyze tree core and downed wood samples. There are no significant relationships between RWI and either position or species for downed wood. However, relationships between BAI and hillslope position, PDSI values, and tree growth exist, and these variables can be used to identify the species and hillslope position of large downed wood in the catchment. The two species in the study area, lodgepole pine (Pinus contorta) and ponderosa pine (Pinus ponderosa), typically put on less radial growth the drier the growing season and the further away from the channel that the tree is located, indicating that tree growth will likely be impacted as Colorado becomes drier. Using tree ring width to identify the source of deposited wood could advance understanding of wood dynamics in watersheds and help constrain wood budgets.