Floodplain Succession and Soil Nitrogen Accumulation on a Salmon River in Southwestern Kamchatka

We documented riparian primary succession on an expansive floodplain (Kol River, Kamchatka, Russian Federation) that receives large nitrogen subsidies from spawning Pacific salmon. As is typical of primary succession, new alluvial deposits in the lower Kol floodplain were nitrogen poor (200 kg persulfate N/ha to 10 cm soil depth); however, nitrogen accumulated rapidly, and soils contained 1600 kg N/ha (to 10 cmþ the litter layer) by 20 years. Soil nitrogen approached an asymptote at ;2500 kg N/ha by 80 years. Nitrogen-fixing Alnus trees were a minor component of the forest community during the first 20 years of succession. However, salmon carcasses were a substantial nitrogen source during this period of rapid nitrogen accumulation. Similar to other northern Pacific Rim floodplains, we found that new alluvial deposits were colonized by Salix, Chosenia, and Alnus trees; but, unlike other described chronosequences, the community transitioned into meadows of tall forbs (some .2.5 m in height) dominated by Filipendula camtschatica after ;100 years. Foliage of all the major vascular plants occurring in the modern floodplain was exceptionally nitrogen rich (i.e., mean molar C:N for each species was 12–27, and the range for all samples was 8–36); therefore we suggest that salmon allow nitrophilic vegetation to proliferate in the Kol floodplain by ameliorating nitrogen infertility during early succession and building nitrogen rich soils.