Assessing the growth gaps of Eucalyptus plantations in Brazil - Magnitudes causes and possible mitigation strategies

Eucalyptus growth (stemwood volume, m(3) ha(-1) yr(-1)) is conditioned by biotic and abiotic factors, which are related to the climate, genotype, chemical and physical soil conditions, silvicultural practices and forest management. These factors a huge temporal and spatial variability of Eucalyptus growth, leading to growth gaps. Therefore, identifying Eucalyptus growth gaps (GG), their magnitudes and causes may be a powerful tool for establishing strategies to increase forest resiliency and productivity. In this context, the aims of this study were to determinate the Eucalyptus growth gaps by a multimodel approach for different production locations in Brazil and to identify their main causes, possible solutions and mitigation strategies. Three Eucalyptus simulation models (FAO, APSIM and 3PG), properly calibrated and validated, were used for simulating the potential and attainable growth. Actual growth data were obtained from 30 producing locations in Brazil from experimental plantations of the TECHS Project. The growth gaps at all locations in Midwest and Northeast regions of the country were predominantly caused by water deficit. In Southeast and North regions, the water deficit was the main cause of GG in 87% and 67% of the locations, respectively. On the other hand, in Southern Brazil, the suboptimal forest management was the main cause of growth gap at all locations, since water deficit is very low in this region. In general, the water deficit represented the main cause of Eucalyptus growth gap in Brazil; therefore, the use of drought-tolerant genotypes, wider spacing, deeper subsoiling for heavy and cohesive soils, and soil conservation practices (such as maintaining harvest residue on site) for improving water infiltration and root growth are the main strategies to reduce this kind of gap. On the other hand, for reducing the growth gap caused by sub-optimal forest management, the main strategies are better nutrition management, use of high-quality seedlings (improved genetic materials and high nursery quality), and weed control, pests and diseases. In addition to these practices, better monitoring of forest fires, windstorms and waterlogging events by integrating climate, management and genetic strategies also could help to improve Eucalyptus productivity in Brazil.