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Roots play a fundamental role in forest ecosystems, but obtaining samples from deep layers remains a challenging process due to the methodological and financial efforts required. In our quest to understand the dynamics of Eucalyptus roots, we raise three fundamental questions. First, we inquire about the average extent of the roots of two contrasting Eucalyptus genotypes. Next, we explore the factors that directly influence the growth and depth of these roots, addressing elements such as soil type, climate, and water availability. Lastly, we investigate how the variation in Eucalyptus species may impact root growth patterns, biomass, and carbon stock. In this study, we observed that the maximum root depth increased by an average of 20% when genotypes were grown on sites with higher water availability (wet site). E. urophylla stands had a higher biomass and carbon stock (5.7 Mg C ha−1) of fine roots when cultivated on dry sites (annual rainfall~727 mm) than the wet sites (annual rainfall~1590 mm). In E. grandis × E. camaldulensis stands, no significant differences were observed in the stock of fine root biomass (3.2 Mg C ha−1) between the studied environments. Our results demonstrated that genotypes with greater drought tolerance (E. grandis × E. camaldulensis) tend to maintain higher stocks of fine root biomass (3.2–6.3 Mg ha−1) compared to those classified as plastic (E. urophylla), regardless of the edaphoclimatic conditions of the cultivation site. Finally, our research helps understand how Eucalyptus trees adapt to their environment, aiding sustainable forest management and climate change mitigation. We also provide a practical tool to estimate underground biomass, assisting forest managers and policymakers in ensuring long-term forest sustainability. [ABSTRACT FROM AUTHOR]

Lack of generalized equations has prevailed in Brazil, because it is assumed that localized or climate-specific equations are needed. This study aimed to develop generalized stem taper and volume equations applicable to 11 eucalyptus clones and evaluate if climate variation impacts the accuracy of the estimates. A total of 693 trees evenly distributed across 11 clones at 21 sites were used for model fittings and predictive validation. The penalized mixed spline (PMS) approach was developed for predicting stem taper and volume along the stem profile. The Schumacher and Hall (1933) equation was used to predict total tree volume, while volume ratio equations were applied to predict merchantable volume. For every fitted equation, an annual climatic variable was included to assess the improvement in model performance. The overall results highlighted that climatic variation does not need to be accounted for in stem taper and volume modeling. All of the equations displayed desirable accuracy, but the generalized PMS equation may be preferred when the forestry enterprise looks to furnish a range of multiple forest products. The generalized total tree volume equation, combined with the ratio equations, is highly recommended when the forestry enterprise produces a single product. Key words: penalized mixed spline, volume ratio, climate. Des equations generalisees n'ont pas ete developpees au Bresil, car on assume que l'utilisation d'equations locales ou specifiques au climat est necessaire. Cette etude vise a elaborer des equations generalisees de defilement des tiges et de leur volume applicables a 11 clones d'eucalyptus et a evaluer si les variations du climat ont une incidence sur la precision des estimations. Au total 693 arbres, repartis uniformement parmi 11 clones sur 21 sites, ont ete utilises pour ajuster les modeles et valider les predictions. L'approche par fonction spline mixte penalisee (SMP) a ete developpee pour predire le defilement de la tige et le volume le long du profil de la tige. L'equation de Schumacher et Hall (1933) a ete utilisee pour predire le volume total de l'arbre, tandis que des equations de rapport de volumes ont ete appliquees pour predire le volume marchand. Pour chaque equation ajustee, une variable climatique sur une base annuelle a ete incluse pour evaluer l'amelioration de la performance du modele. Globalement, les resultats ont mis en evidence qu'il n'etait pas necessaire de prendre en compte les variations climatiques dans la modelisation du defilement et du volume des tiges. Toutes les equations avaient une precision adequate, mais qu'il pourrait etre preferable d'utiliser l'equation SMP generalisee lorsque l'entreprise forestiere cherche a fournir une gamme de produits forestiers differents. L'equation generalisee du volume total des arbres, combinee aux equations de rapport de volumes, est fortement recommandee lorsque l'entreprise forestiere produit un seul produit. [Traduit par la Redaction] Mots-cles: fonction spline mixte penalisee, rapport de volumes, climat., 1. Introduction Stem taper and tree volume equations are valuable tools that enhance the efficiency of forest management decision making and maximize profit of a forestry enterprise (Burkhart and Tome [...]