Simple Two-stock model for a grazing field. If the root stock is destroyed, the system is much slower to recover from overexploitation
Plants root stock are growing slowly. The growth is proportionnal to plant perimeter (sqrt of stock). Finally it is bounded due to area limitation.
Plant stems grows a bit faster, proportionnaly to the root stock. Stems are bounded due to sun limitation i.e. the stock ratio stem/root < 2.
Goats eat the stems if any, then the roots. A "stop grazing period" is decided if the total stock is too low.
