Above- and below-ground net production in 40-year-old Douglas-fir stands on low and high productivity sites

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Abstract
Above- and belowground net primary production was estimated for 40-yr-old Douglas-fir (P. menziesii (Mirb.) Franco) stands growing on sites with apparently large differences in productivity potential. Aboveground net production was estimated from direct measurements of tree growth; belowground productivity was derived from data obtained by sorting live and dead roots from soil cores used in combination with measurements of root growth on observation windows. Aboveground net production was 13.7 t[tons]/ha on the high productivity site and 7.3 t/ha on the low productivity site. Belowgound dry matter production on the high productivity site was 4.1 t/ha compared with 8.1 t/ha for the poorer site. On the more productive site, 8% of total stand dry matter production was in fine roots in contrast over 36% on the poorer site. The difference in total net production (aboveground plus belowground) between the 2 sites was small (2.4 t/ha). Apparent differences in aboveground productivity may, to a large extent, result from the need for a greater investment in the fine roots on harsher sites.