Canopy architecture, light interception, and above-ground productivity of lodgepole pine forests

The influence of canopy architecture on light interception, and the relationship between light interception and above-ground net primary productivity (ANPP) in lodgepole pine (Pinus contorta var latifolia) stands of southeastern Wyoming was examined. Estimates of the light extinction coefficient, G, (k corrected for solar angle), were inversely related to leaf area index (LAI), and negatively correlated with the percent canopy in gap. Simulation results that were supported by empirical analyses suggested that light interception depended strongly on the efficiency of light capture. Increased foliage aggregation from increased LAI and increased crown disengagement associated with canopy architecture of lodgepole pine reduced the effectiveness of light capture.; Estimates of above-ground biomass (AGB), and ANPP were obtained from local allometries and litter trap collections. AGB ranged from 19 to 252 Mg ha{dollar}sp{lcub}-1{rcub}{dollar} over an age range of 36 to 100 yrs. ANPP varied considerably, and ranged from 3.6 Mg ha{dollar}sp{lcub}-1{rcub}{dollar} yr{dollar}sp{lcub}-1{rcub}{dollar} to 8.0 Mg ha{dollar}sp{lcub}-1{rcub}{dollar} yr{dollar}sp{lcub}-1{rcub}{dollar} across all stands. ANPP decreased with age. Stemwood production ranged from 0.9 to 3.6 Mg ha{dollar}sp{lcub}-1{rcub}{dollar} yr{dollar}sp{lcub}-1{rcub}{dollar} and also decreased with age. Foliage production was not correlated with age or stand density. Branch production did not correlate with stand density, but proportional branch production increased with a concomitant decrease in relative stemwood increment in low density stands. The production of reproductive structures was not correlated with any attribute of stand structure examined.; Interception of photosynthetically active radiation (IPAR) showed remarkably little variation among stands ranging from 69 to 77% of incident. ANPP increased with good estimates of intercepted PAR, but IPAR explained only 30% of the variation in ANPP. IPAR and age together explained 79 percent of the variation in ANPP. Estimates of the canopy efficiency in light energy conversion for total production (g MJ{dollar}sp{lcub}-1{rcub}{dollar} of ANPP), and stem plus branch biomass increment (g MJ{dollar}sp{lcub}-1{rcub}{dollar} stemwood plus branch production) ranged from 0.20 to 0.43 g MJ{dollar}sp{lcub}-1{rcub}{dollar} and 0.05 to 0.19 g MJ{dollar}sp{lcub}-1{rcub},{dollar} respectively, and were negatively correlated with age. Site differences in light conversion efficiency, biomass respiration, and allocation to below-ground structures are likely correlated with age.