Assessment of the resilience of Eucalyptus grandis W. Hill trees under severe water stress conditions

Author(s)

Nathália Cardoso Pereira

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2024-06-19

Examining board members

Mario Tommasiello Filho; Gilles Christophe Chaix; Fernanda Trisltz Perassolo Guedes

• Advisor: Mario Tommasiello Filho

Abstract

Existing eucalyptus plantations and those planned for expansion include regions of the country with water scarcity and high risk of severe drought, making it a crucial factor for the sustainability of the plantations. Therefore, the objective was to assess the resilience of Eucalyptus grandis W. Hill ex Maiden trees in relation to their growth in basal area affected by severe water stress and wood density. The experiment included two groups of trees: a control group (C) under normal rainfall conditions and an exclusion group (E), both evaluated at three periods: Stage 0 (normal precipitation conditions), Stage 1 (80% reduction in precipitation for the E group), and Stage 2 (return to normal precipitation conditions). Growth monitoring was conducted using band dendrometers installed on 20 eucalyptus trees for periodic measurement of the increment in basal area (IBA) of the trees. Additionally, periodic forest inventories of diameter at breast height (DBH) and total height (TH) were performed. At the end of the experiment, the trees were felled, and their trunks were sectioned every 2 meters to obtain volume using the Smalian method. Discs were then collected from different heights (base, DBH, and 25%, 50%, 75%, and 100% of the commercial height) to estimate basic density, biomass, and carbon content of the tree trunks. Biomass was measured directly, with green and dry weights obtained by oven drying the trees. Of the biomass results, 48% was considered as carbon. For growth values, average, accumulated, and annual increments were obtained, and IBA values were correlated with climate data to determine the equation that best predicts growth based on climatic variables. Discs collected in the field were used to obtain apparent density profiles through X-ray densitometry. The growth results showed differences between groups and stages of the experiment, with the trees under water exclusion decreasing their growth by 41.8% during the first year, 37.3% in the second year, and 37.5% in the third year of the experiment. Among the climatic variables studied, precipitation and minimum temperature had the greatest influence on growth. Biomass accumulation showed a significant difference between groups, with a p-value of 0.03, indicating 1% significance. At the end of the experiment, trees under water stress grew 30% less than the control group. There was also a significant difference in apparent density values between treatment groups, indicating that water stress affects the final wood density. In conclusion, intense and prolonged water stress affects tree growth, but the trees become resilient with a great capacity for recovery once water availability is restored, showing progressive increases in growth in the following years. However, they exhibited lower biomass increments and, consequently, lower carbon stocks. (AU)

• FAPESP's process: 22/16209-5 - EVALUATION OF THE RESILIENCE OF EUCALYPTUS GRANDIS TREES UNDER SEVERE WATER STRESS CONDITIONS
• Grantee: Nathália Cardoso Pereira
• Support Opportunities: Scholarships in Brazil - Master