Management intensification maintains wood production over multiple harvests in tropical Eucalyptus plantations.

Authors: McMahon D, RB Jackson

Intensive management in tropical plantation forestry has increased global wood production 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. By remeasuring plantation soils after 12 years and nearly two rotations, we investigated how established plantations alter soil stocks of important plant nutrients and whether these changes could limit plantation productivity in the future. We hypothesized that the plantations would deplete soil stocks of nitrogen, which is often added in fertilizer at lower rates than it is removed in harvested biomass, and that the balance between harvest and fertilizer would also dictate changes in stocks of other nutrients. In 2004 and 2016, we sampled soils to a depth of 100 cm in plantations and adjacent pastures and native vegetation reserves, and compared total nutrient stocks across time and vegetation type. We found that nutrients were not significantly depleted over time, and that stocks of carbon, nitrogen, and calcium in the plantations all tended to increase in either the top 20 or top 100 cm of mineral soil, particularly in the Cerrado region. We also observed changes in nutrient stocks in non-plantation vegetation, due in part to spatial heterogeneity, highlighting the difficulties of using other vegetation types as static "controls" to assess the effects of plantations on soils. Overall, soil nutrient depletion does not appear to threaten sustainability in these intensive plantation forests.