Stage 0 |
Tree growth and litter decomposition are limited by nitrogen.
No nitrate leaches into stream water because the forest has sufficient
capacity to retain nitrogen. |
Stage 1 |
When the nitrogen supply increases chronically, the foliar
nitrogen content increases temporarily. Although the fine root mass
changes a little, foliar biomass increases gradually, and trees grow.
The forest can retain more nitrogen with increased biomass, and little
nitrate leaches into stream water. |
Stage 2 |
The nitrogen supply exceeds the forest’s absorption capacity,
and forest ecosystems are limited by water and phosphorus instead of
nitrogen. Foliar nitrogen content increases, and fine root mass
decreases. Rapidly increased nitrification rates accelerate nitrate
leakage into stream water and N2O emissions into the
atmosphere. |
Stage 3 |
Nitrate leakage into stream water and N2O
emissions into the atmosphere further increase, and the forest declines
because of a decrease in foliar biomass and fine root
mass. |