Systematic spatial variation of stomatal conductance in a Sitka spruce plantation.
Null balance diffusion porometers were used to estimate the variation of stomatal conductance (gs) in a Sitka spruce plantation. Samples were stratified with respect to tree social status, whorl position, shoot or branch hierarchy and leaf age. Average gs of codominant and dominant trees was 0.66 times the average gs of suppressed and intermediate trees. The sample size requirement for sampling stratified with respect to tree social status was estimated to be 0.75 times that for random sampling. Average gs of terminal shoots was 1.15 that of lateral shoots. Average gs of whorl shoots was 1.28 times that of interwhorl shoots. Stomatal conductance of 2 and 3-year-old foliage was 0.48 and 0.31 times gs of 1-year-old foliage, respectively. Stratification of sampling into three layers and three age classes estimated average gs with a 95% confidence interval of plus or minus 20%. An estimate of average gs with a 95% confidence interval of plus or minus 10% would require a sample size of 155 using an ideal stratified sample.