**1. Introduction**

Brazil is among the world's largest pulp and paper producers and has developed studies aimed at increasing knowledge on forest-to-product raw materials in an attempt to meet the growing demands and economic interest. *Eucalyptus* trees are the most common hardwood

fiber sources for chemical cellulose and paper production in Brazil, with a minimum harvesting age of approximately 4.5 years and average yield of 35 m3 h−1 yr−1 [1]. This major industrial-scale interest has led to a steady increase in the extent of *Eucalyptus* plantations, which has been moved to new frontiers such as north and central-western regions of Brazil. These new frontiers are predominantly characterized by dystrophic soils and very distinct seasonal rainfall compared with traditional regions. The climatic condition specifically for the central-western region is marked by seasonal drought stress of about 5 months [2].

It is well known that water deficit is one of the most challenging factors of our times which threatens *Eucalyptus* plantation production [3]. A slight reduction in average *Eucalyptus* yield was observed in Brazil compared to previous years as a result of advancing planted areas to regions where water deficits are more severe [4]. However, little has been explored regarding the extent of the potential impacts on the wood quality for end use. From that understanding and considering that extreme drought events will happen more frequently around the world [5], new studies aligned to increase knowledge on the changes in forestry which go beyond the influence on stand volume are intended.

*Eucalyptus* wood characteristics may vary substantially among species and clones [6, 7], as well as by the plantation site [8–10]. Wood density and cellular structure of xylem are highly associated when considering the wood characteristics related with adaptation mechanisms to drought [11, 12]. There is a close relationship between density and hydraulic safety in the sense that a greater resistance to the cavitation process (better hydraulic safety) is related to higher wood density [13]. This in turn could be explained by changes in the structure of vessel elements [13], and/or by the contribution that the fiber matrix (nonconductive elements) makes to adjust the necessary equilibrium during water transport under high tension [14]. Hence, since the wood quality for pulp production is strongly influenced by anatomy and density properties [15, 16], the extent to which these adaptive responses determine pulp and papermaking performance has economic relevance [17].

The *Eucalyptus grandis* x *Eucalyptus urophylla* hybrid has been widely used in Brazil, providing most of the raw material which is used for hardwood pulp companies [18]. Additionally, interspecific hybrids from species such as *E. grandis*, *E. urophyla*, *Eucalyptus camaldulensis*, *Eucalyptus pellita* and *Eucalyptus tereticornis* have been utilized as a strategy for dry environments [19]. Researchers in a publicprivate partnership have installed an unprecedented breeding program with several *Eucalyptus* species and hybrids in Goiás state, in the central-western region of Brazil. The objective has been to evaluate the performance of different genetic materials against specific climate and soil conditions, aiming to select superior clones to compose future plantations on an industrial scale in these new *Eucalytpus* plantation frontiers in the country. Therefore, the present work evaluated five elite *Eucalyptus* clones at four-year-old grown in Goiás state, Brazil, regarding their wood properties and their impact on morphological quality indices and pulping process efficiency. The overall objective was to indicate the pulpwood potential of superior genetic materials adapted to the Brazil central-western region, contributing to increase knowledge of drought-tolerant genetic materials available for the pulp and paper industry.
