EuCarbHydro Project: Carbon and Water Balance Trade-offs in Eucalyptus Plantations as a Climate Change Adaptation Strategy

We evaluated the critical ecophysiological trade-offs between carbon sequestration and water consumption in Eucalyptus nitens (En) and the hybrid E. nitens × globulus (Eniglo) under three initial planting densities (700, 900, and 1,100 trees ha⁻¹) in south-central Chile. Amidst increasing aridity driven by climate change, optimizing stand density and selecting resilient taxa are analyzed as strategic tools to secure water sustainability without sacrificing forest productivity. The experiment, established in July 2023 as a complete randomized block design with three replicates, considers Granier sapflow sensors (9 trees x 3 densities x 2 taxas = 54/site), Soil water sensors at 0-20, 20-40 and 40- 60 cm depths (54 per site) and data from a nearby weather station. Seasonal measurements consider stand leaf area index, soil respiration and detailed growth measurements.

After 3 years E. nitens exhibited substantially greater growth than the hybrid. At the maximum density of 1,100 trees ha⁻¹, E. nitens yielded a stand volume of 32 m³ ha⁻¹, which doubled the 16 m³ ha⁻¹ accumulated by the hybrid. This structural development correlated with a higher Leaf Area Index (LAI) in En (4.0 m²/m²) compared to Eniglo (2.8 m²/m²).

Regarding water dynamics, the hybrid exhibited higher average daily transpiration, peaking up to 2.0 mm day⁻¹, whereas En sustained a more conservative water use ranging from 1.6 to 1.7 mm day⁻¹. This led to a significantly higher growth efficiency value (the slope of the LAI vs CAI regression relationship) of 7.45 for En versus 4.69 for the hybrid. Belowground carbon allocation via soil respiration was roughly the same across species and densities (~2.5 Mg ha⁻¹ month⁻¹). Our results suggest that E. nitens successfully optimizes carbon-water balances by maximizing wood production with lower relative transpiration costs. These findings may help guide plantation management strategies aimed at improving productivity and regional water-use sustainable resources.