Impact of Urbanization on Large Wood Sizes and Associated Recruitment Zones

Abstract

Although the presence of large wood (LW) has long been recognized to enhance watershed function, land use impact on LW remains poorly understood. Using a series of six watersheds, we investigate the relationships between LW recruitment zones, LW size, and LW jam occurrence and land use. Although the results in general show urban land use to severely limit LW, they also stress that agricultural land use may be positively correlated to LW. Occurrence of potentially productive LW recruitment zones is nevertheless best correlated to total forest land cover and forested riparian area. However, the lack of mature forest due to previous widespread deforestation linked to historical agricultural land use is likely a limiting legacy effect. Since the pattern of land use seen in the study area is typical of much of the developed world, our results suggest the limiting of LW may be a major way in which watersheds are impacted in many regions. Accordingly, reintroduction of LW represents a significant opportunity to restore watersheds on a broad scale. Specifically, we propose a mix of passive conservation and active restoration of LW sources and that the targeting of these tactics be planned using the spatial analysis methods of this study.

Keywords

• large wood
• stream restoration
• watershed management
• riparian zone
• land use
• GIS