Relaciones hídricas en dos especies de Eucalyptus en sistema silvopastoril

The forestry sector in Uruguay has shown remarkable growth, achieving an economic impact of 2.5 billion dollars in 2022, representing 4% of the national GDP. Meanwhile, livestock farming, a historical cornerstone of the country, boasts 12 million head of cattle and remains one of the primary export sectors. In this context, silvopastoral systems (SPS), which integrate forestry and livestock production, offer significant benefits such as income diversification, reduced fire risks, improved animal welfare, and a contribution to environmental sustainability. However, their adoption faces challenges related to technical management. This work aims to provide key information to foster the implementation of SPS in Uruguay. The interaction between the tree and pasture components in SPS generates complex dynamics, especially concerning competition for resources like water. Therefore, studying the water relations and stomatal conductance of Eucalyptus is essential to evaluate tree performance under different arrangements, their impact on water availability for the pasture, and ultimately, the overall sustainability and productivity of the system. The main objective was to characterize the water relations and stomatal conductance of Eucalyptus grandis and Eucalyptus dunnii in silvopastoral systems with single and triple row arrangements. To achieve this, soil water conditions, the trees' response to these conditions, and variables such as diameter at breast height (DBH) and total height were studied in contrasting seasons. The study was conducted in 2024 at the Bernardo Rosengurtt Experimental Station, located in Cerro Largo, Uruguay, on Subeutric Brunosol soils, characterized by their pastoral use. A randomized block experimental design was used, evaluating E. grandis and E. dunnii in single and triple row arrangements with 14-meter alleys. Measurements included water potential, stomatal conductance, crown characterization, DBH, and height, taken during the summer and winter seasons. The results indicated that Eucalyptus grandis showed better performance in total height and DBH, as well as a lower percentage of live crown under the triple row arrangement. On the other hand, E. dunnii, although less efficient in growth and light transmission to the soil, showed less growth in total height and DBH (Diameter at Breast Height) in single-row arrangements, possibly due to the favorable microclimatic conditions that this design offers. In terms of water relations, no significant differences were found in water potential and stomatal conductance between the different arrangements, but there were differences between species and seasons. E. grandis generally exhibited higher levels of stomatal conductance than E. dunnii, which could be attributed to species-specific characteristics. Most of the significant differences found in the study were associated with the species rather than the type of arrangement or orientation. Finally, climatic conditions, such as precipitation and water demand, significantly influenced the water potential and performance of both species. This study highlights the potential of E. grandis in silvopastoral systems and underscores the importance of proper species selection management to optimize production in these systems.