100 Years Later; Effects of Logging on Stream Habitat in Colorado's Front Range

Historical documents and recent field studies suggest that logging within the Colorado Rockies during the past two centuries has reduced the wood loads and frequency of wood jams along most forested streams. Log jams provide pool habitat in steep reaches and encourage the storage and uptake of carbon in the riverine environment, and therefore may have effects which extend throughout the stream. To evaluate possible changes wood loads, jam frequency and pool volume are compared based on stream characteristics, forest age, and flow alteration. In addition, sediment samples from reaches with and without log jams are compared based on organic matter (OM) content and Total Carbon (TC) content. Sediment samples taken from behind log jams are compared to samples taken from other backwater areas along a river reach. Preliminary results of the 2010/2011 field seasons indicate that log jams on streams draining old growth forest (more than 200 years since last disturbance) average 45/km, while streams draining younger stands average 15/km. In addition, total pool volume is greater on streams draining forests which were not logged, and sediment samples taken from log jams (regardless of forest age) have an overall average of 5% OM, as compared to an average of 1% OM in samples taken from non-jam areas. Samples taken from log jams on streams draining old growth forests have an average of 12% OM.  These results indicate that historic logging may have an effect on the quantity and quality of pool habitat available in headwater streams.