Intensive management in tropical plantation forestry has increased global wood production, in total and per unit of time and land. Eucalyptus trees in southeastern Brazil can grow exceptionally fast, even on the highly weathered and nutrient-poor soils of the Atlantic Forest and Cerrado biomes. Based on current management practices, we hypothesized that repeated harvests in these eucalypt plantations would deplete soil stocks of nitrogen, which is often added in fertilizer in lower quantities than are removed in wood. We also hypothesized that the balance between harvest and fertilizer would alter stocks of phosphorus, potassium, and calcium. In 2004 and nearly two harvest cycles later in 2016, we sampled soils to a depth of 100 cm in plantations and adjacent pastures and native vegetation reserves, and measured soil nutrient and carbon stocks to assess how plantations had changed the soil and whether these changes could limit the productivity of future vegetation.
Results/Conclusions
We found that none of the nutrients analyzed were significantly depleted over time, and that soil stocks of carbon and nutrients in the plantations all tended to increase, with mean increases in the top 20 cm of 20% for potassium in the Atlantic Forest biome and 23% for carbon and more than 500% for calcium in the Cerrado. Changes in nutrient stocks can be attributed to the combination of fertilizer inputs and transfer from aboveground biomass, reinforcing the importance of retaining litter and harvest residues on site. Nutrient stocks generally changed less under unmanaged than managed vegetation, suggesting minimal nutrient supply or loss from environmental processes such as atmospheric deposition and leaching. Overall, soil nutrient depletion does not appear to threaten sustainability in these intensive plantation forests over the time period studied.