5. Conclusion
Our study highlights the importance of considering variation in
C concentration when estimating live tree C stocks, which has
broad implications for global C accounting and validation of C
accounting models. Carbon concentration is significantly higher
in bark than in stemwood tissue, and varies among tree species.
Tree size and shade tolerance also have effects on C concentration,
but more empirical studies are needed to identify the generality of
these effects. Understanding variation in total C concentration
within and among tree species and incorporating it when quantifying
forest C stocks and validating C accounting models is important
to successfully predict future global C emission scenarios.
Moreover, we observed that much of the variation in total C concentration
is attributed to volatile C concentration, providing
new insight that volatile C plays a key role in variation of total C
concentration. Our results indicate that volatile C concentration,
rather than C-rich elements (e.g., lignin), is the dominant driver
behind size-associated changes in tree C concentration, and the
dominant factor underlying the difference in total C concentration
between bark and stemwood tissue for major boreal tree species.
However, the underlying mechanisms of why volatile C concentration
showed different size-associated relationships between species
is not clear, and whether these results can be generalized to
other species, especially tree species in other biomes, requires further
testing.