Crossing a threshold: The legacy of 19th century logging on log jams and carbon storage in Front Range headwater streams

Instream wood has an important effect on the geomorphic and ecological function of streams, but human impacts have altered both the forests that supply wood and the streams themselves. These changes may have pushed many stream systems over a threshold past which the stream morphology and ecology do not return to their pre-disturbance state, but instead settle into a "new normal." This dissertation addresses the question of whether logging which took place in the 19th century has had lasting and significant effects on the instream wood and carbon storage of headwater streams in Colorado's Front Range. The distribution of logs within the headwaters of the Big Thompson River, North Saint Vrain Creek and Cache la Poudre River in northern Colorado were assessed to quantify the ways in which logs and forest characteristics relate to carbon storage within a stream. Characteristics of jams (size, number per kilometer) and carbon storage correlate most closely with reach-scale variables, implying that management would be most effective at the reach scale. Increased total wood load and decreased spacing between key pieces are the most important changes that can be made to promote the formation of jams within a reach. Old growth forest creates significantly different total carbon storage and partitioning of carbon storage, which extends previous work on the effects of old growth forest on terrestrial carbon to riverine environments.