Soil carbon stocks and forest biomass following conversion of pasture to broadleaf and conifer plantations in southeastern Brazil

• Broadleaf plantations maintain soil C similar to pasture to a 45 cm depth.
• Conifers show only 6% greater soil carbon than broadleaf plantations.
• Aboveground biomass and productivity show no correlation with soil carbon levels.
• Broadleaf–Pasture soil carbon differences indicate potential for soil carbon sequestration.

Increased soil carbon sequestration can potentially mitigate CO2 emission and can indicate sustainable forest management. This study aims to determine the relative influence of commercial plantation tree species on soil carbon following establishment on former tropical pastures. Soil carbon (organic horizon plus mineral soil from 0 to 45 cm) and stemwood productivity were quantified from 6 to 34 year-old conifer and broadleaf plantations in a sandy Oxisol (Typic Hapludox) in southeastern Brazil. Study plots consisted of ten pastures paired with broadleaf plantations and ten additional broadleaf plantations paired with conifer plantations. Pastures primarily consisted of Brachiaria decumbens Stapf., while broadleaf plantations were primarily Eucalyptus, but also included one plot each of three other broadleaf species. Conifer stands were made up of Pinus species. Average stemwood productivity (± standard error) was 9.7 (±1.0) Mg C ha−1 yr−1 for broadleaf and 5.7 (±0.5) Mg C ha−1 yr−1 for conifer plantations, but did not correlate to soil C. The soil C in the paired Pasture–Broadleaf plots averaged 36.0 ± 1.7 Mg C ha−1 in pastures and 36.8 ± 1.9 Mg C ha−1 in broadleaf plantations. The Broadleaf–Conifer plots averaged 38.3 ± 1.9 Mg C ha−1 for broadleaf plantations and 36.0 ± 1.6 Mg C ha−1 for conifers. Our results show little difference in soil C across vegetation types, providing evidence that conifer and broadleaf plantations overall maintain similar levels of soil carbon to pasture land-use up to 34 years following land conversion. Soil C differences between Pasture–Broadleaf pairs indicated a small decline in soil C accretion early after plantation establishment, followed by recovery to slightly higher accretion rates.