Downed wood dynamics in the riparian and littoral zone of small lakes in tolerant hardwood forests

Abstract

Large wood (LW) is an important structural feature in forested lake ecosystems, but little is known about the production of LW in riparian forests and its movement across the forest–lake ecotone, both of which we describe here for eight small (<30 ha) lakes in Ontario, Canada. The creation of snags through live-tree death varied by species, ranging from 0.24% year−1 for eastern white cedar to 5.60% year−1 for balsam fir. Snag breakage was best described as a function of snag height and snag fall described as a function of tree species, decay stage, and diameter. Long LW pieces and pieces generated close to the lake were more likely to be deposited at the shoreline. The density of LW at the shoreline was 125–550 pieces·km−1, and density and volume of LW were positively related to riparian slope. LW was a stable resource at the shoreline, with a recruitment rate about equal to the loss rate and average movement along the shoreline of 2.89 cm·year−1. LW volumes at the shoreline and in the littoral zone of the lake were positively related to lakebed slope. LW could reside in the littoral zone for centuries, providing physical structure for multiple generations of aquatic organisms in these small lakes. Our results indicate that critical habitat for fish that need aquatic LW extends at least 5 m into riparian forest and that removal of trees within 5 m of the forest edge would reduce LW input to the littoral zone.