Evaluation of the Point Intercept Method for the Estimation of Plant Biomass

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Abstract
With the point intercept method, contacts are registered between plants and the tips of narrow pins passed into the vegetation. The summed number of contacts over a large number of pin positions has been used to estimate plant cover and leaf areas. This study shows that number of point intercepts also correlates highly with biomass. The intercepts can, therefore, be used as a regression variable to predict the mass of both stems and leaves in plant stands. Doubly ln-transformed and untransformed simple regression models yielded high explained variance for biomass of graminoids and dwarf shrubs when regressed on number of pin contacts in quadrat samples. For transformed variables, r2-values ranged from 0.81 to 0.93 in quadrats sampled with 200 pins each, and between 0.67 and 0.80 when sampling intensity was reduced to 50 pins per quadrat. Time studies combined with calculations of how to optimize the sampling effort betweeen 1) number of quadrats to sample and 2) number of pin positions per quadrat, revealed that the time needed for obtaining a regression equation of high precision (including the time for both registrations of pin contacts and destructive biomass estimation) is relatively limited. Subsequent estimation of biomass, from number of pin contacts only, are rapid in comparison with, e.g., destructive estimations, particularly if samples need to be fractionated into different components.

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