MAINTENANCE RESPIRATION AND STAND DEVELOPMENT IN A SUB-ALPINE LODGEPOLE PINE FOREST

We examined a chronosequence of subalpine lodgepole pine stands to test the hypothesis that low net primary production in older forest stands is caused by higher maintenance respiration costs of woody tissues. We predicted that respiration of woody tissues (particularly stem sapwood) would be greater in older stands and that the higher maintenance costs would account for observed low wood production. For a unit of ground surface, the carbon flux involved in wood production and associated construction respiration was 210 g-m 2-yr-1 in a 40-yr-old stand, but declined to 46 g.m-2.yr-1 in a 245-yr-old stand. However, maintenance respiration of woody tissues in stems and branches consumed only 61 g.M-2.yr-1 in the 40-yr-old stand and 79 g.M-2.yr-1 in the 245-yr-old stand. The slight, nonsignificant increase in maintenance respiration of woody tissues could not explain the dramatic decline in aboveground wood production in the old-growth stand.