Becker, Jackson, Biology Department, Bucknell University, 1 Dent Drive, Lewisburg, PA, 17837, jtb034@bucknell.edu; McTammany, Matthew, E, Biology Department, Bucknell University, 1 Dent Drive, Lewisburg, PA, 17837, mmctamma@bucknell.edu.
Large woody debris (LWD) is an important feature of streams in forested regions, where it structures stream channels and increases habitat variability by influencing water flow. Logging in the 19th and early 20th centuries resulted in dramatic reductions of LWD in streams and correspondingly incised stream channels with simplified habitat. Despite reforestation, these physical changes to stream channels from historical logging remain. Introducing LWD to channels affected by historical logging and allowing natural hydrological processes could reshape channels and restore in-stream habitat. We compared the volume of LWD in streams flowing through old-growth (OG) and mature second-growth (SG, >80 y) forests in northwestern Pennsylvania and between stream reaches where LWD addition projects have been conducted using “chop-and-drop” (CD) or “designed” (D) restoration approaches. We quantified LWD volume for 2 OG, 3 SG, 1 CD, and 1 D stream reaches by measuring diameter and length of wood (>10 cm diameter, >1 m length) that intersected a 100-m long transect down the center of each stream channel. LWD volume was quantified in four vertical zones based on how much was in the water, within stream banks but above water, or intercepting the channel but above or outside banks. OG streams had approximately 8x more LWD than SG streams, likely because logging never occurred to remove LWD and mature trees provided a continuing source of new LWD. Second-growth forests have experienced logging, which resulted in removal of LWD from SG stream channels, and younger trees do not contribute as much new LWD to streams. LWD addition resulted in similar total LWD volumes between D reach and OG streams, but the CD reach had 2x more LWD than OG streams. LWD in the D reach was distributed more evenly across different vertical zones, with over 70% of LWD in the active stream channel where it can interact with stream flow and contribute to channel processes. In contrast, over 99% of LWD in the CD reach was above the channel or outside the stream banks, so it was not actively interacting with the stream. Much of the LWD above and outside the channel will enter the stream eventually and could then modify water flow leading to improved in-stream habitats in CD stream reaches. Despite this delay, chop-and-drop might be a more cost-effective restoration approach due to its relative speed and ease compared to designed installation of LWD, particularly in remote stream reaches.
stream, restoration, logging, large woody debris