Nutrient dynamics of the southern and northern BOREAS boreal forests

The objective of this study was to compare nutrient concentration, distribu tion, and select components of nutrient budgets fur aspen (Populus tremuloi des), jack pine (Pinus banksiana), and black spruce (Picea mariana) forest ecosystems at the BORcal Ecosystem Atmosphere Study (BOREAS), southern and northern study areas near Candle Lake, Saskatchewan and Thompson, Manitoba, Canada, respectively. The vegetation (excluding fine roots and understory) in the aspen, black spruce, and jack pine stands contained 70-79%, 53-54%, and 58-67% of total ecosystem carbon content, respectively. Soil (forest f loor and mineral soil) nitrogen (N), calcium (Ca), and magnesium (Mg) conte nt comprised over 90% of the total ecosystem nutrient content, except for C a and Mg content of the southern black spruce stand and Ca content of the s outhern aspen stand which were less than 90%. Annual litterfall N content w as significantly greater (p < 0.05) for trembling aspen (30-41 kg N ha(-1) yr(-1)) than for jack pine (5-10 kg N ha(-1) yr(-1)) or black spruce (6-7 k g N ha(-1) yr(-1)), and was generally greater, brit not significantly, for the southern than for the northern study area. Aboveground net primary prod uction was positively correlated (R-2 = 0.91) to annual litterfall N conten t for the BOREAS forests, and for all boreal forests (R-2 = 0.57). Annual a boveground nutrient (N, Ca, Mg, and K) requirements (sum of the annual incr ement of nutrient in foliage, branches, and stems) were significantly great er (p < 0.05) for trembling aspen than for jack pine or black spruce forest s. Annual aboveground N requirements ranged from 37-53, 6-14, and 6-7 kg N ha(-1) yr(-1) fur trembling aspen, jack pine, and black spruce forests, res pectively. The greater nutrient requirements of deciduous than evergreen bo real forests was explained by a greater annual production of biomass and lo wer use efficiency of nutrients. Nutrient cycling. characteristics of borea l forests were influenced by climate and forest type, with the latter havin g a greater influence on litterfall N, annual nutrient requirements, nutrie nt mean residence Lime, and nutrient distribution.