Contrasting patterns of biomass allocation in dominant and suppressed loblolly pine

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Abstract
We investigated above- and below-ground biomass allocation and allometric relationships of canopy dominant and suppressed loblolly pine (Pinus taedaL.) trees from a range of diameters at breast height (DBH = 3.5-35.6cm) to determine if shifts in allocation may influence the growth and persistence of suppressed trees in the understory. Using mass and volume conversions from harvested trees (15 dominant and 15 suppressed), we developed regressions to predict total and component biomass from DBH. Bole, branch, needle, and total mass differed between dominance categories (ANCOVA, P < 0.10). For a representative size (15cm DBH), dominant trees allocated 63.4, 13.2, 11.3, and 12.0% of biomass to bole, branch, needle, and root tissue compared with 75.9, 6.7, 5.6, and 11.7% for suppressed trees. At any given DBH, suppressed trees were also taller than dominant trees and had a greater porportion of heterotrophic (bole plus branch plus root mass) to autotrophic (needle mass) tissue. Percent carbon and nitrogen of tissues did not differ between dominance categories. Unlike the increased investment in leaf area observed for seedlings and saplings of shade-tolerant species, suppressed loblolly pine increased allocation to bole mass and height growth. An increase in height for this shade-intolerant species may enable some suppressed individuals to escape competition for light. However, increased allocation to heterotrophic versus autotrophic tissue in suppressed trees may confer a cumulative disadvantage over time because of increased respiratory load.

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