Abstract
Potential net nitrogen (N) mineralization, potential net nitrification, and overstory (boles and branches) biomass were measured in nine forest ecosystems commonly found within the well-drained uplands of northern Lower Michigan. The ecosystem types ranged from oak-dominated forests on coarse-textured outwash sands to mesic northern hardwood forests on sandy glacial till. Overstory biomass was calculated using species-specific allometric equations developed for Lake States hardwood species. Potential net N mineralization and potential net nitrification were measured by a 30-day aerobic laboratory soil incubation. Analyses of (co)variance were used to determine differences in potential N mineralization, net nitrification, overstory biomass, and biomass increment among the nine ecosystem types. Linear and nonlinear regression analyses were used to predict overstory biomass and biomass increment using potential net N mineralization as the independent variable. Overstory biomass ranged from 92 t•ha
−1
in a xeric oak ecosystem to 243 t•ha
−1
in a northern hardwood ecosystem; annual biomass production ranged from 1.3 to 3.5 t•ha
−1
year
−1
, respectively. Potential net N mineralization was lowest in the xeric oak ecosystem (52.0 μg N•g
−1
) and greatest in the mesic northern hardwood ecosystem (127.8 μg N•g
−1
). Potential net nitrification was 45.5 μg NO
3
−
-N•g
−1
in the northern hardwood ecosystem; 10 to 230 times greater than in other ecosystems. A saturating exponential model (y = a(1–e
−kx
) + c) produced the smallest residual mean squares in predicting overstory biomass (R
2
= 0.822) and annual biomass increment (R
2
= 0.847) from potential net N mineralization. Maximum overstory biomass and biomass increment predicted from this equation were 247 t•ha
−1
and 3.7 t•ha
−1
, respectively. In addition, laboratory net N mineralization potentials were highly correlated with annual rates of N mineralization determined by insitu incubation (r
2
= 0.849). Overstory biomass and woody biomass increment were poorly correlated with potential net nitrification. The exponential function used to predict biomass increment from N mineralization suggests that the productivity of some northern hardwood forests in northern Lower Michigan is not limited by N availability.