Individual tree crown and stand development in Pinus taeda under different fertilization and irrigation regimes

Abstract

We examined individual tree foliage mass and branch demography for 13 years in a Pinus taeda L. stand growing on a nutrient poor, well drained sandy soil with a 2 × 2 factorial of fertilization and irrigation treatments replicated four times. Branch level foliage mass was estimated using equations derived from 2500 destructively sampled branches with branch basal diameter, crown location, age and treatment as independent variables. Branch diameter and crown location were measured for all live branches on 80 trees (20 in each treatment) each year for 13 years. Maximum dormant season individual tree foliage mass was 5.4 and 10.7 kg tree −1 in the control and fertilized and irrigated treatments, respectively. The maximum fertilized and irrigated individual tree foliage mass was achieved 3 years after treatment initiation when apparent light and space limitations prevented additional increase in individual tree foliage mass. Individual stem volume increment was linearly related to individual tree foliage mass and individual tree foliage mass was reduced by the presence of large nearby trees. Branch diameter and number were significantly increased by fertilization (52 branches tree −1, 11% increase, 19.8 mm branch −1, 14% increase). Branch longevity was significantly reduced by fertilization; branches survived 6.6 and 5.4 years for the non-fertilized and fertilized treatments, respectively. Branch size, number and longevity in the fertilized treatments would not be likely to reduce stem quality. In stands where nutrients and water were adequate and light and space limitations developed, individual tree foliage mass development could be increased with thinning. However, individual tree foliage mass development was limited much earlier in stand development than heretofore thought. Waiting to thin until stand conditions currently used to trigger thinning (to avoid density dependent mortality) would promote overall stand growth at the expense of crop tree growth. Individual tree foliage mass was correlated with branch development and branches in the lower crown half were more likely to die, had a lower carbon balance due to low light and high respiring tissue relative to photosynthesizing tissue. This combination of factors indicated that pruning may be a likely tool to manage crown development and insure that crop trees have a high value stem. The balance between individual stem growth and stand growth may need to be reevaluated in the context of currently used intensive silvicultural regimes.