50-YEAR BIOGEOCHEMICAL EFFECTS OF GREEN ASH, WHITE-PINE, AND NORWAY SPRUCE IN A REPLICATED EXPERIMENT

Few long-term, replicated experiments are available to provide information on the effects of tree species on soil chemistry and ecosystem biogeochemistry. We examined replicated, 50-year-old plots of green ash (Fraxinus pennsylvanica Marsh), white pine (Pinus strobus L.), and Norway spruce [Picea abies (L.) Karst.] that had been planted in an abandoned agricultural field. The pH(water) of the 0-5-cm soil layer under green ash was 4.6, compared with 4.2 under white pine and 3.8 under Norway spruce. The Norway spruce soil was substantially less-well buffered against further acidification than the soil under green ash, and contained less than half the quantity of exchangeable Ca2+ + Mg2+ + K+ in the 0-15-cm depth. The decline in these cations under Norway spruce was accompanied by higher concentrations of exchangeable Al3+. The most important factor in the lower pH under Norway spruce was the greater acid strength of the soil organic matter, with a secondary role played by the higher saturation of the exchange complex with aluminum. Nitrogen mineralization in resin cores averaged 40 kg/ha under green ash, 84 kg/ha under white pine, and 56 kg/ha under Norway spruce. The only significant difference in litterfall biomass and chemistry was a greater content of aluminum and lower content of magnesium in litterfall in the Norway spruce plots relative to green ash plots. These major biogeochemical differences between tree species demonstrate the need for replicated experiments for assessing the mechanisms that drive long-term changes in ecosystems relative to differing species, management regimes, and atmospheric deposition.