Nowakowski Amy L, Wohl Ellen
Department of Geosciences, Colorado State University, Ft. Collins, CO 80523-1482, USA.
Environ Manage. 2008 Oct;42(4):557-71. doi: 10.1007/s00267-008-9140-4. Epub 2008 Jun 6.
We documented valley and channel characteristics and wood loads in 19 reaches of forested headwater mountain streams in the Bighorn National Forest of northern Wyoming. Ten of these reaches were in the Upper Tongue River watershed, which has a history of management including timber harvest, tie floating, and road construction. Nine reaches were in the North Rock Creek watershed, which has little history of management activities. We used these data to test hypotheses that (i) valley geometry correlates with wood load, (ii) stream gradient correlates with wood load, and (iii) wood loads are significantly lower in managed watersheds than in otherwise similar unmanaged watersheds. Statistical analyses of the data support the first and third hypotheses. Stream reaches with steeper valley side slopes tend to have higher wood loads, and reaches in managed watersheds tend to have lower wood loads than reaches in unmanaged watersheds. Results do not support the second hypothesis. Shear stress correlated more strongly with wood load than did stream gradient, but statistical models with valley-scale variables had greater explanatory power than statistical models with channel-scale variables. Wood loads in stream reaches within managed watersheds in the Bighorn National Forest tend to be two to three times lower than wood loads in unmanaged watersheds.
我们记录了怀俄明州北部大角国家森林中19条源头山区森林溪流的河谷和河道特征以及木材负载量。其中10条溪流位于上舌河流域，该流域有包括木材采伐、枕木漂流和道路建设在内的管理历史。9条溪流位于北岩溪流域，该流域几乎没有管理活动的历史。我们利用这些数据来检验以下假设：（i）河谷几何形状与木材负载量相关，（ii）溪流坡度与木材负载量相关，以及（iii）管理流域中的木材负载量显著低于其他条件类似的未管理流域。对数据的统计分析支持了第一个和第三个假设。河谷边坡较陡的溪流河段往往有更高的木材负载量，并且管理流域中的河段往往比未管理流域中的河段木材负载量更低。结果不支持第二个假设。与溪流坡度相比，剪切应力与木材负载量的相关性更强，但包含河谷尺度变量的统计模型比包含河道尺度变量的统计模型具有更大的解释力。大角国家森林中管理流域内溪流河段的木材负载量往往比未管理流域低两到三倍。
