Da. Sampson et Hl. Allen, Light attenuation in a 14-year-old loblolly pine stand as influenced by fertilization and irrigation, TREES, 13(2), 1998, pp. 80-87
We examined empirical and simulated estimates of canopy light attenuation a
t SETRES (Southeast Tree Research and Education Site), a 2x2 factorial stud
y of water and nutrients. Fertilized plots had significantly lower under-ca
nopy PAR transmittance (T-C) when compared to non-fertilized plots. Light i
nterception efficiency, as measured by the canopy cosine-corrected light ex
tinction coefficient, G, was significantly lower in irrigated plots for all
dates examined. Estimates of G ranged from a low of 0.36 in irrigated plot
s in September to a high of 0.64 in March For control plots. Study-wide ana
lyses indicate that a G of 0.50 and a k (uncorrected light extinction coeff
icient) of 0.69 may be reasonable parameter estimates of canopy light extin
ction in intermediate-aged loblolly pine plantations across a range of stan
d conditions and seasons when site-specific data are unavailable. Simulated
Te from our version of the BIOMASS model corresponded well to the empirica
l estimates. Varying the vertical distribution of foliage in simulations (f
rom 10:60:30 to 40:40:10% in the upper, middle, and lower canopy positions,
respectively) resulted in only a +/-7% change in total PAR intercepted, wh
ereas varying G from 0.3 to 0.7 resulted in a 67% and 31% increase in light
intercepted for control and fertilized plots, respectively. De creased G r
esulted in an increased proportion of beam radiation intercepted - 63-67% o
f total PAR intercepted by the middle canopy where 55-60% of the foliage wa
s found. We hypothesize that proportionally increased productivity observed
in irrigated treatments may be attributed to increased beam radiation inte
rcepted deeper into the canopy by a greater foliage area.