Agroforestry deliberately grows woody trees or shrubs together with crops and/or livestock on the same plot. Three classic layouts are modeled here: alley cropping (tree rows bordering crop strips), forest farming (a multi-storey stand of tall trees, understory shrubs and shade-tolerant crops) and silvopasture (scattered trees over grazed pasture).
Canopy shade cover (Poisson overlap model):
cover ≈ 1 − e^(−n · A_crown / A_field)
n = trees on stage, A_crown = π·r_crown², r_crown grows with stand age
Carbon sequestration (per hectare, idealized square grid):
trees/ha = 10 000 / spacing² (spacing in metres)
tCO₂/ha/yr ≈ trees/ha × 0.03 × min(age, 20) / 20 (0.03 t CO₂/yr = mature per-tree rate, reached by year 20)
Windbreak reduction (approximate, porosity-style model):
reduction ≈ shade_cover × 0.75 × min(1, age / 15)
taller, denser, more mature canopies block more wind energy downwind
- System — switches the planting geometry: rows for alley cropping, layered clusters for forest farming, open scatter for silvopasture (with grazing animals).
- Tree spacing — closer spacing means more trees per hectare, more shade and a stronger windbreak, but more competition for light, water and nutrients.
- Stand age — young trees have small crowns and thin trunks; as the stand matures the canopy closes, litterfall builds soil organic matter and carbon storage accumulates.
- Wind speed — sets the open-field wind; the ground cover visibly sways less downwind once the windbreak effect from the tree rows kicks in.
These curves are simplified teaching approximations, not a substitute for site-specific agronomic modeling — but the underlying trends (denser + older stands shade more, sequester more carbon, and block more wind) match the literature on alley cropping, forest farming and silvopasture systems.