Large Wood in Small Channels: A 20‐Year Study of Budgets and Piece Mobility in Two Redwood Streams

Abstract

Large wood (LW) influences geomorphic and ecological processes. However, most field data sets describing LW dynamics are conducted over the span of only a few years. We present a unique long‐term data set from northern California, USA of LW volumes, inputs, and transport in two small headwater streams, the North Fork (NF) and South Fork (SF) of Caspar Creek. We used data collected approximately every 2 years from 1998 to 2018 to assess how LW budgets change over time between catchments, what factors influence inputs from standing trees to the streams, and controls on LW piece mobility. We find that the SF, which experienced stream‐side logging and instream wood removal in the 1970s, continued to have lower LW volumes (range of 101–153 m3 km−1 over the 20‐year period) compared to the NF (range of 297–313 m3 km−1), which experienced logging in the 1980s but with buffer strips left near the channel. If current trends continue, it will likely take ∼100–200 years from the time of logging for the SF to reach NF instream wood volumes. We show that windstorms combined with precipitation events, very high winds, and hillslope steepness are strongly associated with LW piece inputs from standing trees. LW moves infrequently in the channel, with piece characteristics, the number of wood pieces per meter surrounding an LW piece, and discharge metrics influencing LW entrainment and displacement lengths. Our data set provides strong support to previously identified controls on LW dynamics in streams while also capturing variability over a 20‐year period.

Current progress in quantifying and monitoring instream large wood supply and transfer in rivers

“…An important constraint in previous investigations on wood transport rate or transport distance is the short monitoring time, which ranged between 5 months (e.g., Jochner et al, 2015) and a few years (e.g., Iroumé et al, 2018; Lienkaemper & Swanson, 1987), with a few exceptions of longer‐term monitoring periods (Lininger & Hilton, 2022; Ghaffarian et al, under review). In most cases, discharge stayed below or close to the bankfull flow conditions during the study period.…”

Why wood should move in rivers

“…Developing longer term datasets of wood dynamics on diverse rivers that employ consistent measurements across studies would be ideal. Decadal (Wohl & Iskin, 2022; Wohl & Scamardo, 2021) and multi‐decadal studies of wood dynamics that have recently been published (Goodman et al, in press; Lininger & Hilton, 2022) help to address this gap. Beyond direct field measurements of wood presence/absence over many years, indirect approaches including physical experiments, numerical modeling, and radiocarbon or other chronologies of wood ages can also provide insight into multi‐decadal wood movement.…”

A call to action: The need for evaluation of carbon storage by lacustrine large woody debris

“…Centuries to millennia of land‐use history and the corresponding shifts in forest age class distributions in most of the world's populated landscapes have substantially reduced wood loading in lakes as compared to historic baselines (Warren et al., 2016). For example, deforestation and/or conversion of primary forests to managed secondary forests has depleted inputs of stream LWD, and reforested or managed secondary forests contribute smaller‐diameter LWD than late‐successional and old‐growth forests (Keeton et al., 2007; Lininger & Hilton, 2022; McHenry et al., 1998). LWD has been manually removed from streams to ‘improve’ habitat, avoid build‐up behind dams, and enhance navigation (Czarnecka, 2016; Wohl, 2014).…”