LOG JAMMING: QUANTIFYING THE RELATIONSHIP BETWEEN FORESTS AND STREAMS IN THE COLORADO FRONT RANGE

Historical documents and recent field studies suggest that resource use within the Colorado Rockies during the past two centuries has reduced the wood loads and frequency of wood jams along most forested streams. This study attempts to quantify the effects of past and present resource management on instream wood loads and logjam frequency along Colorado’s Front Range.

Wood loads and jam frequency are compared based on stream characteristics, forest age, and streamflow alteration. We hypothesize that more highly impacted reaches (as measured by recent fire, logging, and streamflow regulation) will demonstrate lower wood loads and jam densities. We investigate the relationship between jam density and overall wood load in streams, and develop an equation to characterize that relationship. In addition, we investigate the effect that piece position has on wood density and the existence of a threshold effect, where increased frequency of key anchored pieces results in a non-linear increase in total stream wood loads.

The preliminary results of the 2010/2011 field seasons indicate that streams draining old growth forests (more than 250 years since last disturbance) have an average of 45 jams per kilometer of river, while streams draining areas which have been logged or otherwise altered by humans have an average of only 20 jams per kilometer. In addition to having fewer total jams, there are fewer channel spanning jams (which create standing pools of water), and less sediment stored behind jams. Overall, this study links forest characteristics with instream wood characteristics, quantifying the links between forest health and river health