Light Attenuation in a 14-year-old Loblolly Pine Stand as Influenced by Fertilization and Irrigation

Abstract

We examined empirical and simulated estimates of canopy light attenuation at SETRES (Southeast Tree Research and Education Site) a 2x2 factorial study of water and nutrients. Fertilized plots had signiticantly lower under-canopy PAR transmittance (T_c) when compared to non-fertilized plots. Light interception efftciency as measured by the canopy cosine-corrected light extinction coefficient G was significantly lower in irrigated plots for all dates examined. Estimates of G ranged from a low of 0.36 in irrigated plots in September to a high of 0.64 in March for control plots. Study-wide analyses indicate that a G of 0.50 and a k (uncorrected light extinction coefficient) of 0.69 may be reasonable parameter estimates of canopy light extinction in intermediate-aged loblolly pine plantations across a range of stand condittons and seasons when site-specific data are unavailable. Simulated T_c from our version of the BIOMASS model corresponded well to the empirical estimates. Varying the vertical distribution of foliage in simulations from 10:60:30 to 40:40:10% in the upper middle and lower cantlpy positions respectively) resulted in only a +7% change in total PAR intercepted. whereas varying G from 0.3 to 0.7 resulted in 67% and 31% increase in light interceptcd for control und fertilized plots respeciivcly. Decreased G resulted in an increased proportion of beam radiation intercepted- 63-67% of total PAR intercepted - by the middle canopy where 55-60% of the foliage was found. We hypothesize that propportionally increased porductibity observed in irrigated treatments may be attributed to increased beam radiation intercepted deeper into the canopy by a greater foliage ares.

Citation

Sampson, D.A.; Allen, H. Lee. 1998. Light Attenuation in a 14-year-old Loblolly Pine Stand as Influenced by Fertilization and Irrigation. Trees (1998) 13:80-87