Where does wood come from? Using dendrochronology and isotopic methods to identify the watershed origin of wood in the river corridor

Floods impact the forest carbon cycle and wood loads in channels and floodplains by causing erosion and deposition in the valley bottom and recruiting downed trees to the river corridor. Determining the origin of large wood (LW) from the watershed is challenging. LW can come from the riparian corridor or from hillslopes, through tree recruitment from slope failure during a flood or from previously downed pieces. Here, we examine the source of LW deposited in valley bottoms in the Colorado Front Range, USA following a flood that occurred in 2013. We use dendrochronology and stable isotope methods to answer if the LW in the valley bottoms was sourced from hillslopes or riparian areas. We sampled cores from trees in different landscape positions (riparian, mid-slope, and upslope), measured ring widths, and standardized tree ring chronologies. We sampled pieces of LW in the valley bottom deposited by the flood. After analyzing radial growth over time, we found that trees higher upslope showed greater variability in growth. Our results indicate that variability in radial growth may be useful for identifying the source of LW recruited and deposited during floods.  In addition, we found that growth was correlated with spring and summer climate indicators (precipitation, temperature, and vapor pressure deficit), which will help us age and cross-date LW deposited by floods. Since d¹¿O records climate conditions and tree conditions vary by position, we plan to complete d¹¿O isotope analysis of tree core rings across landscape position to determine if isotopic signature differs depending on position. Comparing radial growth and isotopic signature of standing trees in different positions to downed LW will allow us to determine the source of deposited LW. Understanding the sources of downed LW deposited in river corridors is important for constraining wood budgets and determining potential wood supply. Our work could provide a unique approach for quantifying LW sourcing.

Impact/Purpose

Large wood in streams provides critical habitat for aquatic organisms and influences channel and floodplain morphology.  Understanding the sources of downed large wood deposited in river corridors is important for constraining wood budgets and determining potential wood supply. Our work could provide a unique approach for quantifying large wood sourcing. 

Citation

Cromratie Clemons, S., H. Barnard, K. Lininger, AND J. Renee Brooks. Where does wood come from? Using dendrochronology and isotopic methods to identify the watershed origin of wood in the river corridor. AGU Annual Fall Meeting, Chicago and virtual, IL, December 12 - 16, 2022.