Aboveground Biomass Estimation with the Canopy Intercept Method: A Plant Growth Form Caveat

The canopy intercept method estimates aboveground biomass with hits by a pin passed through vegetation. Here we demonstrate a strong plant growth form effect on the technique. Slopes of linear regressions of clipped biomass on mean hits per pin for five plant growth forms were positively correlated with plant structure size (e.g., leaf size). Two potential reasons for this trend are: 1) an interaction of leaf size and pin diameter that monotonically reduces the relationship of foliage surface area to pin contact as leaf size declines, and 2) a probable positive relationship between leaf size and leaf thickness. Both would result in an increase in the biomass: contact ratio (and slope) as leaf size increases. The range of r2s for the five groups was 0.831 to 0.956. Results indicate that canopy intercept provides good precision to estimate standing crop, and separate calibrations for plants of different growth forms may be useful to reduce systematic error in biomass estimation.