Eucalyptus plantation effects on soil carbon after 20Â years and three rotations in Brazil

How will shifting land use from row crops and pasture to intensively managed forests alter soil carbon storage? Demand and profitability has led to a dramatic increase in Eucalyptus production with a total planted area over 20 million hectares worldwide. The impacts of these short-rotation (6- to 8-year harvest cycle) Eucalyptus plantations on soil carbon appear to be variable, and the available case studies are typically too short term to support generalization. Spatial heterogeneity of soils across landscapes requires repeated sampling for reliable documentation of soil carbon changes over multiple rotations. We characterized soil carbon stocks and change over two decades in 306 operational Eucalyptus plantations across a 1200-km gradient. Across all sites, soil C (0-30 cm depth) in 2010 averaged 29 Mg ha−1 (± 0.70 Mg ha−1), tending to increase with increasing soil clay content, precipitation, and mean annual temperature. Average soil C from the original sampling to 2010 (ranging from 18 to 26 years or approximately 3 to 4 rotations) showed a slight decrease (−0.22 ± 0.05 Mg ha−1 yr−1, P < 0.0001). Tropical sites in Region 1 (Bahia state) showed no net change (−0.11 Mg ha−1 yr−1, P = 0.1874, whereas tropical and subtropical sites in Region 2 (Espirito Santo state) lost soil carbon stocks (−0.87 Mg ha−1 yr−1, P < 0.0001), and subtropical sites in Region 3 (São Paulo state) also remained the same (0.06 Mg ha−1 yr−1, P = 0.3969). Soil carbon change tended to increase with precipitation during the dry season, and had weaker associations with soil order and mean annual temperature.