Differential growth response to increasing growing stock and structural complexity in even-and uneven-sized mixed picea abies stands in southern Finland

Widespread application of the selection system will depend on whether creating stands with uneven-sized (UES) structures comes at the expense of net periodic annual basal area increment (PAI) compared with stands with even-sized (ES) structures. I modeled PAI on growing stock and structural complexity over 12 years in midrotation stands with ES and UES structure types. Average PAI of the largest trees did not differ among types and decreased with increasing stocking, whereas PAI of the smallest trees in the UES type declined with stocking. Trees ≥ 10 cm in diameter grew more slowly in the ES type than the UES type, but no difference was seen after incorporating small trees (down to 5 or 2 cm). In the ES type, PAI of most trees increased linearly with increasing stocking, whereas in the UES type, it increased only up to 20 m²·ha⁻¹. As structural complexity increased, PAI of the largest trees increased in the ES type, whereas PAI of all but the largest trees decreased in the UES type. Neither silvicultural system was innately more productive, as each can outperform the other under optimal levels of stocking and structural complexity. However, optimizing increment of only large trees would undermine the UES type.