Figure 3.

Increases in Δ¹⁴C between 1959 (1964 for lowest elevation site) and 1992 for (a) low density (<2.0 g/cm³), (b) hydrolyzable (>2.0 g/cm³), and (c) nonhydrolyzable (>2.0 g/cm³) portions of SOM from an elevation transect in the Sierra Nevada (3). The fraction of organic matter with the fastest turnover time will have the highest pre-1963 ¹⁴C values and show the largest increase in ¹⁴C between 1959 and 1992 (a) while the fraction with slowest turnover has lowest initial ¹⁴C values and shows little increase in ¹⁴C over the past 30 years (c).