Spatial extent of impact of red alder on soil chemistry of adjacent conifer stands

RHOADES, C.C., and BINKLEY, D. 1992. Spatial extent of impact of red alder on soil chemistry of adjacent conifer stands. Can. J. For. Res. 22: 1434-1437. We examined patterns in soil N availability and pH along transects extending from mixed stands of conifers (mostly Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)) and red alder (A/nus rubra Bong.) to pure conifer stands at two locations. At the relatively infertile Wind River site, increased N availability was apparent for about 8-12 m downslope of the alder-conifer stand, but no effect was apparent upslope. At the fertile Cascade Head site, no trend was apparent in N availability across the stand boundaries, but soil pH in the conifer stand was depressed for about 5 m from the alder-conifer stand. Overall, the effects of alder on soil chemistry appeared limited to a distance of less than half the height of the trees.