Forest Growth Projector

Projected Volume is built from a sigmoid (S-shaped) growth curve calibrated so it passes exactly through your entered Current Stand Volume at your entered Current Stand Age, then projected forward by Projection Period years along that same curve. Site Index — a standard forestry measure of site productivity (dominant tree height at a reference age, typically 50 years) — sets the curve's volume ceiling directly (Site Index × 3, a rough approximation), and the curve's climb-rate constant is then solved for so it fits your entered current volume and age against that ceiling. Because a higher Site Index means a taller ceiling for the exact same entered current volume and age, that starting point represents proportionally less of a high-Site-Index stand's total potential — more headroom below the ceiling — which is what makes a higher Site Index produce a higher Projected Volume and more Volume Growth over the same Projection Period, not a faster raw per-year growth-rate constant.

From the projected volume the calculator derives Mean Annual Increment (MAI, total volume divided by stand age) both now and at the projection point, Periodic Annual Increment (PAI, volume gained divided by the projection period), and an Optimal Rotation Age found by scanning ages 10 through 200 for wherever MAI peaks — the classic forestry rule that maximum sustained yield occurs where MAI and PAI cross. This is a simplified single-curve yield model, not a species-specific or region-calibrated forest growth-and-yield table — real projections should draw on regional volume tables or growth simulators (e.g. FVS) calibrated to your species and site.