The Effects of Forest Harvesting on Forest Hydrology and Biogeochemistry

Abstract

The hydrological consequences of forest harvesting are arguably the longest-studied aspect of interactions between hydrology and land cover or land use. Chang (2003) notes that increased understanding of interactions between forest management and hydrology led to enactment of forest protection laws in China as early as 300 BC, while the Swiss initiated the establishment of forested watershed reserves in Europe in 1342 (Kittredge 1948). The earliest documented basin-scale comparison of streamflow and erosion from forested and agricultural lands (1902) also comes from Switzerland (Whitehead and Robinson 1993). Numerous studies of forest harvesting effects on various aspects of the hydrological cycle (particularly streamflow) followed, complemented in the past several decades by research on the biogeochemical impacts of forest harvesting. Aspects of this work (particularly related to harvesting effects on streamflow) were summarized in classic reviews by Hibbert (1967), Bosch and Hewlett (1982), and Sahin and Hall (1996). Recent summaries of the hydrologic and biogeochemical impacts of forest harvesting have focused on individual countries (e.g., USA – Stednick 1996, National Research Council 2008; Canada – Buttle et al. 2005, 2009), specific regions (e.g., Pacific Northwest – Moore and Wondzell 2005; Feller 2005), or particular environments (e.g., tropical forests – Bruijnzeel 2004). Rather than restate these reviews, this chapter attempts to synthesize the results of studies of the hydrologic and biogeochemical effects of forest harvesting from a more global perspective. In particular, it focuses on areas of consensus that have arisen from this work, caveats to that consensus that arise from specific environmental conditions or forest management practices, and areas of controversy, both in terms of the results of this research and the methods employed to obtain them. The latter is an important but often overlooked issue in attempts to assess the consequences of forest harvesting, and some of the ongoing debates regarding these outcomes can be linked to the experimental and analytical approaches used in various studies. This assessment of consensus, caveats, and controversies begins with a review of the effects of forest harvesting on hydrological processes and water partitioning, links these effects to harvesting impacts on various aspects of streamflow at the basin scale, and then turns to the biogeochemical consequences of forest harvesting. The chapter concludes with an outline of major research issues that should be addressed in future work.