Effects of Bigleaf Maple On Site Fertility In Coniferous Forest In the Pacific Northwest.

Bigleaf maple (Acer macrophyllum Pursh) is a large deciduous tree that is abundant in western North America. Its native range extends from northern Vancouver Island, south into California. We examined the influence of bigleaf maple on throughfall, stemflow, and under-canopy and near trunk forest floor chemical properties in a forest dominated by Douglas-fir (Pseudotsuga menziessi (Mirb.) Franco) and western hemlock (Tsuga heterophylla (Raf.) Sarg.). Eight plots with a single bigleaf maple tree in the centre of conifers were paired with eight Douglas-fir plots without bigleaf maple. Compared to conifer plots, bigleaf maple throughfall had higher pH, and concentrations and depositions of P and K. Similarly, stemflow of bigleaf maple had significantly higher pH, and K concentration. The under-canopy forest floor associated with bigleaf maple showed significantly higher total exchangeable bases, CEC and concentrations of exchangeable Ca and Mg. The near trunk forest floor at bigleaf maple plots had a significantly higher pH, total exchangeable bases, CEC, base saturation and concentrations of NO₃-N, exchangeable Ca, and Mg and contents of total N, NO₃-N and S. Throughfall and stemflow beneath bigleaf maple appear to contribute to higher pH and N availability in the forest floor, thus improving the soil fertility under the canopy of bigleaf maple and to a greater extent near bigleaf maple trunks. The results suggest that there is a soil microsite around bigleaf maple stems which is influenced by stemflow. These enriched microsites proximal to bigleaf maple trunks can form fertile spots for conifer growth at later stages of forest succession.