Notes: Nitrogen Accretion and Availability in Some Snowbrush Ecosystems
We examined two chronosequences in the Oregon Cascade Mountains to assess nitrogen accretion and availability in relation to snowbrush (Ceanothus velutinus Dougl.). In two 12-year-old snowbrush ecosystems, total soil nitrogen to 30-cm depth exceeded levels in adjacent old-growth stands by 500 and 570 kg ha-1. Inclusion of the approximate nitrogen content of aboveground snowbrush and forest floor biomass raised the estimate of nitrogen fixation to 94 to 100 kg ha-1 yr-1 over 12 years. Snowbrush also increased the availability index of soil nitrogen, but nitrogen availability appeared high in all ecosystems. We speculate that nitrogen fixation by snowbrush during early succession in these ecosystems has been sufficient to prevent nitrogen limitation throughout the entire successional sequence. The presence of snowbrush for 12 years also increased soil carbon 40 and 60 percent in the two chronosequences. Forest Sci. 28:720-724.
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