High planting density and leaf area index of masson pine forest reduce crown transmittance of photosynthetically active radiation

Abstract High planting density of Masson pine (Pinus massoniana) is perceived to have a major impact on timber production as well as understory biodiversity through changed leaf area index (LAI) and reduced understory photosynthetically active radiation (PAR). However, the quantitative relationship between planting density and LAI and understory PAR for Masson pine is unknown. To study the effects of planting density on LAI and understory PAR, we measured LAI and percentage of PAR (PPAR) transmitted through the crown of 15-year-old Masson pine at three planting densities. Total tree LAI varied between different planting densities, ranged from 2.43 to 3.85 m2/m2 at the crown level and from 1.28 to 1.67 m2/m2 at the stand level. Comparing to low planting density, high planting density reduced LAI at the crown level by 37% and PPAR by 49%. As a result, planting density had considerable effects on tree growth. High planting density reduced crown diameters (0.27 m and 0.47 m smaller than that of trees in medium and low density, respectively) and diameter at breast height (0.55 cm and 1.15 cm smaller than that of trees in medium and low density, respectively), but had no effect on tree height. Thus planting density may be used as a management technique for production of different sized timber for Masson pine.