Comparison of site index and biomass production of spruce-fir stands by soil drainage class in Maine

Abstract

Site index and biomass production of natural, even-aged spruce-fir ( Picea rubens Sarg., Picea mariana (Mill.) B.S.P., Abies balsamea L.) stands on four soil drainage classes were compared to determine the relationship between site index and biomass production. Biomass yield equations using stand age at breast height and site index as independent variables were developed by soil drainage class. Site index was determined from equations developed for each drainage class and revealed that site index for spruce and fir increased with improved drainage. Site index was found to be a poor predictor of stand biomass production on the soils studied as there was no significant change in the biomass production with increase in site index on the poorer drained soils. However biomass production decreased with increase in site index on the better drained soil suggesting that rates of self-thinning may increase on these soils with increase in site index. Site index, which measures only the height growth of the forest, may not be adequate in classifying sites into productivity classes, as it does not take into account the relation between soil and other stand properties. Stand biomass production was also compared among all soils, revealing that differences in biomass productivity among these soils is not evident at early ages. No significant differences in biomass productivity among stands were found until about stand age 60 years, where production of stands on the better drained soils became greater than those on the poorer drained soils.