The demography of coarse wood in north temperate lakes

1. Exchange of material across habitat boundaries is a key process in riparian zones. The movement of coarse wood from lakeshore forests to the littoral zone, where it provides habitat for aquatic organisms, is not well understood. In 2003, we resampled coarse wood within the littoral zone of four lakes in Northern Wisconsin (U.S.A.), that had originally been surveyed in 1996, to quantify the spatial arrangement of littoral coarse wood and estimate input, loss and movement rates. 2. All four lakes had a clumped pattern of littoral coarse wood, and the locations of clusters were similar in both census years. Littoral coarse wood was more abundant than expected on moderate to steep slopes, on southern shorelines, and in areas with sparse residential development. 3. All four lakes had a net accumulation of coarse wood; rates of wood input ranged from 0.5 to 1.9 logs km(-1) year(-1), i.e. there was more wood in 2003 than 1996. Movement rates of tagged logs varied 14-fold among lakes, with a maximum in one lake of 42% of logs recovered in 2003 more than 20 m from their 1996 location. Median distance moved ranged from 22 to 323 m among the four lakes. 4. Areas of persistently high wood density may be keystone habitats whose presence enables the persistence of populations of certain aquatic organisms. Conservation of locations with high wood density may be important to maintain target densities of coarse wood of lakes with human development.