2010-12-29_REPORT - M1988044 - Laserfiche WebLink

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reached a plateau in its development and has now achieved a good deal of maturity. Once this point is achieved the vegetation patterns are well established and not much additional change will occur in the vegetation until other factors in the complex competition equation begin to have an effect on the growth. In this type of vegetation those other factors primarily relate to available room and light. The victors in the competition for space goes to those plants whose growth can limit the growth of others vying for the same space. Sometimes it will be willow; other times it will be cottonwood, and in some cases it may be an herbaceous species such as grass. The advantage cottonwood has over willow though lies in its ability to capture light resources and thus shade sun loving plants which hinders those plants' ability to retain dominance. Thus cottonwood, by gaining height and width can shade willow and reduce its dominance while selecting for more shade tolerant grasses that can out compete willow in the understory and capitalize on resources the willows need to maintain dominance. The primary modifier of this type of competition for dominance, in this case, would be water. If the soil is wet enough, willow, especially obligate wetland species, can maintain dominance simply because cottonwood and grass may not be capable of sustaining themselves in a soil that is too wet. However, as has been seen in the large wetland adjacent to Exclosure 2, even obligate wetland willows cannot out compete such wetland plants as the rushes and bullrushes which so thoroughly dominate the wet soils there that willow plants, if present, are usually small and in poor condition or are living on small hummocks. As for Exclosure 1, this competition pattern will probably follow a path leading to strong overall willow dominance with localized cottonwood dominance. That will continue until the streambed declines in elevation resulting in a falling water table that harms willow and favors cottonwood. But that is decades away and there is always the possibility that the streambed will become aggradational which will raise the water table favoring willow even more and limiting cottonwood. This would occur if development upstream increases sediment loads to a point where it arrives faster than it can be removed. One fact is clear in the development patterns seen within this exclosure as well as outside this exclosure in adjacent streambed areas - the removal of grazing was key to initiating the recovery. Without that recovery would not have occurred under any circumstances. EXCLOSURE2- General Description for 2010: This exclosure is located about a mile, as the stream flows, north and downstream from Exclosure 1. It is located in a large embayment off the main channel and most of it is drier than Exclosure 1. There is a very large and highly productive wetland just to the west of the exclosure and the eastern edge of that wetland encroaches into the western side of the exclosure. That wetland contains very few woody plants and is mostly composed of rushes, bull rushes, a few sedges, and a minor amount of wetland grasses and forbs. 2010 Annual Report Coal Creek Wetland Mitigation Permit DA 198811488 Page 11