N2-fixation by Sitka alder in a young lodgepole pine stand in central interior British Columbia, Canada

Annual N-2-fixation by Sitka alder (Alnus viridis (Chaix) DC. ssp. sinuata (Regel) A.&D. Love) was estimated at 1015 kg N ha(-1) over three growing seasons in a young lodgepole pine (Pinus contorta Dougl. ex Loud.) stand in the Sub-Boreal Spruce biogeoclimatic zone of British Columbia (BC), Canada. Unlike the ambiguous evidence provided by 15 N natural abundance, the isotope dilution method indicated that >90% of the N in new alder tissues was derived from the atmosphere. Despite low light levels (18.1% of open sky values), alders growing under a mature lodgepole pine canopy (>150-year-old) obtained a similarly high proportion of their N requirements by N-2-fixation. (C) 2002 Elsevier Science B.V. All rights reserved.