Stand density and age affect tree-level structural and functional characteristics of young, postfire lodgepole pine in Yellowstone National Park

• Stand density and age explain much of the variation in postfire tree characteristics.
• Partitioning of biomass to bole wood increases with stand density and age.
• Tree-level leaf area and productivity decrease with stand density and increase with age.
• Variation in tree characteristics has changed little in the past 13 years of stand development.
• Variation in postfire tree regeneration continues to influence tree characteristics 24 years after fire.

More frequent fire activity associated with climate warming is expected to increase the extent of young forest stands in fire-prone landscapes, yet growth rates and biomass allocation patterns in young forests that regenerated naturally following stand-replacing fire have not been well studied. We assessed the structural and functional characteristics of young, postfire lodgepole pine (Pinus contorta var. latifolia) trees across the Yellowstone subalpine plateaus to understand the influence of postfire stand density and age on tree-level aboveground biomass (AB), component biomass (bole, branch, foliage), partitioning to components, tree-level aboveground net primary productivity (ANPP) and leaf area (LA). Sixty 24-year-old lodgepole pine trees were harvested from 21 sites ranging from 500 to 74,667 stems·ha−1 for development of allometric equations to predict biomass, ANPP and LA. All traits increased nonlinearly with increasing tree basal diameter. Tree-level total AB and component biomass decreased with increasing stand density and increased with age when compared with measurements from 11-year-old trees. Bole partitioning increased with stand density, while foliage and branch wood partitioning declined. Tree-level ANPP and LA decreased significantly with stand density and age. Overall, our results indicate that stand density and age explain much of the variation in tree characteristics and that 24 years after fire, the initial postfire regeneration density is still exerting significant influence on the structure and function of individual trees.