Data from: Tropical forest restoration: fast resilience of plant biomass contrasts with slow recovery of stable soil C stocks

1. Due to intensifying human disturbance, over half of the world’s
tropical forests are reforested or afforested secondary forests or
plantations. Understanding the resilience of carbon (C) stocks in these
forests, and estimating the extent to which they can provide equivalent
carbon (C) sequestration and stabilization to the old growth forest they
replace, is critical for the global C balance. 2. In this study, we
combined estimates of biomass C stocks with a detailed assessment of soil
C pools in bare land, Eucalyptus plantation, secondary forest, and natural
old-growth forest after over 50 years of forest restoration in a degraded
tropical region of South China. We used isotope studies, density
fractionation and physical fractionation to determine the age and
stability of soil C pools at different soil depths. 3. After 52 years, the
secondary forests had equivalent biomass C stocks to natural forest,
whereas soil C stocks were still much higher in natural forest (97.42 t
ha-1) than in secondary forest (58.75 t ha-1) or Eucalyptus plantation
(38.99 t ha-1) and lowest in bare land (19.9 t ha-1). Analysis of δ13C
values revealed that most of the C in the soil surface horizons in the
secondary forest was new C, with a limited increase of more recalcitrant
old C, and limited accumulation of C in deeper soil horizons. However,
occlusion of C in microaggregates in the surface soil layer was similar
across forested sites, which suggests that there is great potential for
additional soil C sequestration and stabilization in the secondary forest
and Eucalyptus plantation. 4. Collectively, our results demonstrate that
reforestation on degraded tropical land can restore biomass C and surface
soil C stocks within a few decades, but much longer recovery times are
needed to restore recalcitrant C pools and C stocks at depth. Repeated
harvesting and disturbance in rotation plantations had a substantial
negative impact on the recovery of soil C stocks. We suggest that current
calculations of soil C in secondary tropical forests (e.g. IPCC Guidelines
for National Greenhouse Gas Inventories) could overestimate soil C
sequestration and stabilization levels in secondary forests and
plantations.