Plant establishment at three ponds created for gravel extraction along the lower Mad River, Humboldt County, California

Three ponds were constructed in gravel bars along the lower Mad River in Humboldt County, California. They were excavated in the gravel bars to mitigate impacts on salmonid spawning habitat in the main channel and allow for the removal of gravel for commercial use. I mapped the vegetation in order to investigate its distribution, character, and the abundance of plant species around these ponds. I gathered species abundance data while mapping patches of vegetation. Mapping recorded the vegetation assemblages as polygons and I analyzed their relations by using TWINSPAN. A moderate environmental gradient related to the existing vegetation was evident. There were eight vegetation types on the banks around two ponds on the Christie Bar. The Lower Christie pond had five types and had more well-developed emergent and submergent aquatic populations. The newer Upper Christie pond had two main types, with incidence of two others in a very small area. The third pond on the Blue Lake Bar was almost barren of vegetation and was not mapped for plant assemblages. A thick blanket of fine sediment from the original construction sites was reserved prior to excavating the ponds. After the excavation was completed, the sediments were spread on the banks of the Christie Bar ponds. The barren pond did not have this available. The blanket of fine sediment contributed to the vegetation development. The maps illustrated a concentric pattern of vegetation groups around the ponds, showing the effects of water level changes. The pattern suggested the influence on the distribution of propagules and their survival. Seasonal patterns of precipitation providing moisture late in the spring probably also influenced plant germination and survival. Diversity in the distribution of plants was highest at the oldest pond. The distribution of species around the ponds was evidence of the dominant effect the pond had over riverine influences. The species order from the TWINSPAN analysis paralleled their wetland indicator categories. Facultative upland species occurred along the outer banks bordering the excavation. Obligate species occurred predominantly at the shore. A transitional area of facultative species had a medial distribution.