Thinning Target TPA From a Target SDI
The residual-stand number the prescription needs.
Example
You enter
- Species maximum SDI 450
- Target percent of maximum (%) 35
- Quadratic mean diameter (in) 10
- Current trees per acre (0 to skip) 300
You get
- Sdi target 157.5
- Residual target 157.5
- Trees to cut 142.5
- Ba target 85.9005
Details, formula, and sources
TPA_target = (SDI_max x target%) / (QMD/10)^1.605, the trees to cut from the current TPA, and the residual basal area. A ponderosa stand (SDI_max 450) thinned to the 35% competition floor at a 10 in QMD keeps 157 trees per acre - a 300-TPA stand marks 143 for cutting at about 86 ft2/acre residual. The inverse of the Reineke stand density index; thinning from below raises the QMD, so the residual lands conservatively below the target. A management aid, not a prescription.
SDI_target = SDI_max x target% / 100; TPA_target = SDI_target / (QMD/10)^1.605; cut = max(0, TPA_current - TPA_target); BA_target = TPA_target x 0.005454 x QMD^2.
Reineke Stand Density Index inverted to a stocking target (Reineke 1933; USDA FS stocking-guide practice), by name.
The Reineke SDI relation is a public forest-mensuration result; the maximum SDI is species-specific from published tables.
Estimate. AHJ and licensed professional govern.
Field names used by the API: sdi_max, target_pct, qmd_in, current_tpa, sdi_target, tpa_target, cut_tpa, ba_target
- Inverse Reineke TPA_target = SDI_target / (QMD/10)^1.605 at the pre-thin QMD; thinning from below raises QMD, making the target conservativeReineke 1933
- Species maximum SDI_max comes from published species tables (e.g. ~450 ponderosa pine, ~600 Douglas-fir)USDA FS stocking guides