Succession after fire: variation in \delta13C of organic tissues and respired CO2 in boreal forests

Isotope ratios of carbon dioxide and leaf organic matter were measured in 5 neighboring forests of varying ages: 7, 14, 45, 140, and 160 years. These forests are composed primarily of black spruce (Picea Mariana) and quaking aspen (Populus tremuloides) with a shift in species dominance from aspen to spruce 50 years after fire disturbance. Research on the carbon isotope ratios of leaf material and CO₂ was conducted to look for influences from species composition, forest age, and time after most recent burn. Samples of organic \delta¹³C in whole leaf tissue were collected from the dominant species of each forest. Concurrent aboveground NPP measurements allowed us to estimate total ecosystem \delta¹³C by providing a method for weighting \delta¹³C of individual species and plant tissues. \delta¹³CO₂ and [CO₂] were measured on canopy CO₂ to determine the isotopic ratio of ecosystem respiration. The atmospheric results indicated that the \delta¹³C of ecosystem respiration changes with successional stage. Specifically, the aspen dominating forests showed ¹³C depleted values relative to the spruce dominated forests. Organic results showed more ¹³C-enriched values with increased forest age and vegetation functional type. Specifically, oldest trees within the coniferous species had the most ¹³C-enriched values in leaf tissues. These results suggest that increases in the disturbance regime of northern boreal forests will lead to a decrease in the \delta¹³C of ecosystem carbon with consequences for the atmospheric \delta¹³C budget.