Comparing the Slope-Area Threshold for Stream Initiation in Primeval and Managed Forests of Northern Michigan

Abstract

Forest management and other land uses can alter hydrological pathways and affect stream initiation along draining hillslopes. To evaluate this potential effect, primeval forests at the Huron Mountain Club in northern Michigan were compared to surrounding forest lands historically logged. A total of 59 stream channel heads (19 in primeval forests and 40 in managed forests) were mapped using GPS. Per the slope-area method, channel heads were plotted within a digital elevation model to determine drainage area and local slope, which were used to discern a threshold of channel initiation. A watershed Hydrologic Soil Index (representing the tendency for surface runoff) was also determined and evaluated for its importance for channel formation. Consistent with the slope-area method, a significant relation was detected between drainage area and local slope for both managed (R2 =. 29) and primeval forest watersheds (R2 =. 56). However, no significant difference in relation was detected between forest types. This was noteworthy because soils mapped in the primeval forests had a significantly higher Hydrologic Soil Index indicating thinner soils more prone to surface runoff. Results suggest that forest management has likely varied throughout the region but has sustained forest drainage densities comparable to primeval forests.