Kelp Forest Canopy Light Competition

Stand Setup

Stand density 70 stipes

Canopy extinction coeff. k 0.045

Surface irradiance I₀ 100%

Simulation speed 1.0×

Canopy State

Mean stipe height

0.0 m

Canopy closure

Sub-canopy light

100%

Self-thinning events

How it works

Each stipe grows toward the sea surface at position (x,y) with height h. Its blades form a canopy disc of radius r(h) = 0.12 + 0.34·(h/H_max). Any taller neighbor whose disc overlaps stipe i intercepts light before it reaches i, so light attenuates through the overlapping canopy exactly as it does through leaf area in a Beer-Lambert light profile:

I_i = I0 · exp( -k · Σ_j  overlap(i,j) · A_j )   for every j with h_j > h_i
overlap(i,j) = fraction of stipe i's footprint shaded by stipe j's disc
A_j = π r_j²  (blade/canopy area of the taller neighbor)

Growth follows a saturating (Monod) light-response curve, offset by a fixed respiration/frond-loss cost — the classic photosynthesis-vs-respiration balance that defines a plant's light compensation point:

dh/dt = g_max · I_i /(I_i + I_k)  −  r_resp
I_k = half-saturation irradiance,  r_resp = respiration + tissue-loss cost

Stand density — how many stipes seed the plot; denser stands self-shade sooner.
Extinction coefficient k — how opaque the canopy is per unit blade area (turbid, blade-dense canopies use a higher k).
Surface irradiance I₀ — ambient light at the sea surface (season / water clarity).
When dh/dt stays negative for a sustained stretch, a shaded stipe has spent longer under its compensation point than it can survive — it dies back and a new recruit germinates nearby, the same self-thinning process that stratifies real kelp and forest canopies into a few dominant individuals over many suppressed ones.

This mirrors the canopy self-shading term used in giant-kelp (Macrocystis pyrifera) population models, where sub-canopy light — not nutrients — is usually the limiting factor for understory growth once a forest closes its canopy.

Well-lit, growing Light-stressed Dying / recruiting

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