2-PHASE SAMPLING OF WOODY AND HERBACEOUS PLANT-COMMUNITIES USING LARGE-SCALE AERIAL PHOTOGRAPHS

A two-phase sample design employing large-scale aerial photographs was used to quantify early successional woody and herbaceous plant commun ity structures. Two conventional 35-mm cameras were mounted on a boom and suspended from a helium-filled blimp to obtain low-cost 1:366 scal e stereo photographs (1:80 scale prints) of seven experimental vegetat ion complexes. Estimates of woody crown volume index and herbaceous pe rcent cover were generated for 5 x 5 m plots by calibrating photo meas urements to a limited ground-truth sample. The method offered signific ant increases in estimation precision (> 35%) over ground sampling alo ne, as well as attractive cost advantages (0 to 40%). The highest leve ls of precision were obtained by measuring entire plots on the photogr aphs. This procedure added approximately 10% to the cost of photo eval uations but resulted in estimates with standard errors that were, on a verage, 78% smaller than those of ground samples. Simulation trials su ggested that more than nine ground-truth sample units per vegetation c ommunity type provided only marginal increases in estimation precision . If individual species or species groups of interest are well represe nted in sample areas, large-scale photographs, employed in a two-phase sample design, can be an effective tool for quantifying and monitorin g vegetation community structures in silvicultural and related field s tudies.