Abstract To determine the effect of resource availability on efficiency of stemwood production, we calculated radiation use efficiency (Εstem = stem production/photosynthetically active radiation [PAR] interception) and production efficiency (PEstem = stem production/leaf area index [LAI]) from measurements of LAI, intercepted photosynthetically active radiation (IPAR), and stem production on stands of Pinus taeda, Pinus elliottii, Liquidambar styraciflua, and Platanus occidentalis during the sixth growing season. Treatments were control, irrigation only, and irrigation plus 57, 85, or 114 kg N ha−1 y−1. Compared to the control, irrigation plus 85 kg N ha−1 increased stem production: 8.7–15.0 Mg ha−1 y−1 (loblolly), 6.0–10.7 Mg ha−1 y−1 (slash), 1.2–12.8 Mg ha−1 y−1 (sweetgum), and 0.5–9.6 Mg ha−1 y−1 (sycamore). Annual PAR capture and LAI were correlated with stem production (r2 = 0.80, r2 = 0.66, respectively, average of 4 species). Fertilization and irrigation increased Εstem and PEstem for sycamore, whereas only fertilization increased efficiencies for sweetgum. Irrigation increased PEstem for the pines. Foliar [N], often a surrogate for photosynthetic efficiency, was positively correlated with both efficiency variables for the hardwoods (r2 from 0.65 to 0.79). For the pines, canopy size was the primary growth determinant. FOR. SCI. 51(6):556–569.