Recovery and grades of Eucalyptus urograndis sawn timber infected by Chrysoporthe deuterocubensis stem canker disease

Abstract

Global wood demand continues to rise while supply from natural forests declines, increasing the importance of forest plantations as a sustainable timber source. In Malaysia, Eucalyptus urograndis has gained attention as a fast-growing plantation species, but stem canker disease caused by Chrysoporthe deuterocubensis threatens timber recovery and value. This study evaluated the effect of infection severity on sawn timber recovery, grading, and value in 11-year-old E. urograndis trees from Sabah, Malaysia. Twelve trees were classified into four infection-severity classes, felled, and sawn using a back-sawing pattern. A total of 404 boards were assessed for dimensions, recovery, visual grade, and disease-related defects using modified Malaysian Grading Rules. Board size shifted toward smaller dimensions as infection severity increased. However, total recovery remained relatively high across classes, and severely infected logs produced the highest volume recovery. Healthy trees yielded the greatest proportion of SELECT and STANDARD grade boards, whereas infected trees produced more downgraded boards. Infection severity was not significantly correlated with log diameter or board volume recovery. These findings indicate that infected E. urograndis logs can still provide commercially usable timber, although with reduced product quality and value.

Full Article

Recovery and Grades of Eucalyptus urograndis Sawn Timber Infected by Chrysoporthe deuterocubensis Stem Canker Disease

Rasdianah Dahali  ,^a Lee Seng Hua  ,^b Paridah Md Tahir  ,^a Adlin Sabrina Muhammad Roseley  ,^c Mohd Redzuan Abdul Rauf,^d Mohammed Abdillah Ahmad Farid  ,^a and Mohd Zulkhairi Mohd Yusoff  ,^a,e,*

Global wood demand continues to rise while supply from natural forests declines, increasing the importance of forest plantations as a sustainable timber source. In Malaysia, Eucalyptus urograndis has gained attention as a fast-growing plantation species, but stem canker disease caused by Chrysoporthe deuterocubensis threatens timber recovery and value. This study evaluated the effect of infection severity on sawn timber recovery, grading, and value in 11-year-old E. urograndis trees from Sabah, Malaysia. Twelve trees were classified into four infection-severity classes, felled, and sawn using a back-sawing pattern. A total of 404 boards were assessed for dimensions, recovery, visual grade, and disease-related defects using modified Malaysian Grading Rules. Board size shifted toward smaller dimensions as infection severity increased. However, total recovery remained relatively high across classes, and severely infected logs produced the highest volume recovery. Healthy trees yielded the greatest proportion of SELECT and STANDARD grade boards, whereas infected trees produced more downgraded boards. Infection severity was not significantly correlated with log diameter or board volume recovery. These findings indicate that infected E. urograndis logs can still provide commercially usable timber, although with reduced product quality and value.

DOI: 10.15376/biores.21.3.7662-7689

Keywords: Eucalyptus urograndis; Chrysoporthe deuterocubensis; Infection classes; Recovery; Defects; Grades; Values

Contact information: a: Laboratory of Biopolymer and Derivatives, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia; b: Department of Wood Industry, Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM) Cawangan Pahang Kampus Jengka, Lintasan Semarak, Bandar Jengka, 26400 Bandar Tun Razak, Pahang, Malaysia; c: Faculty of Forestry and Environment, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia; d: Sabah Softwoods Berhad, Tawau 91019, Sabah, Malaysia; e: Department of Bioprocess Technology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia; *Corresponding author: mzulkhairi@upm.edu.my

Graphical Abstract

INTRODUCTION

Global demand for wood and wood products continues to exceed the supply that can be sustainably obtained from natural forests. This widening gap has increased interest in forest plantations as an alternative and reliable source of timber. According to the Food and Agriculture Organization (FAO) of the United Nations, the rising demand for wood is driven by population growth, reduced natural forest availability, expanding economies, globalization of the forest products industry, climate change, and the increasing demand for high-quality value-added wood products (FAO 2022). As a result, forest plantations are becoming increasingly important in supplying raw material for both industrial and domestic use (Salleh 1995; Samdin et al. 2020). The promotion of non-native species in forest plantations is one strategy to support the timber industry and reduce pressure on natural forests (Samdin et al. 2020). Among these species, Eucalyptus has attracted considerable attention because of its rapid growth, short rotation, adaptability to a wide range of site conditions, and suitability for both pulp and solid wood production. Plantation grown Eucalyptus can be used for a variety of high-value products, including flooring, furniture, veneer, plywood, mouldings, and structural timber. These characteristics make Eucalyptus one of the most important fast-growing plantation genera in the tropics and subtropics (Rezende et al. 2014; Foroughbakhch et al. 2017; McEwan et al. 2020; Japarudin et al. 2022; Zhang and Jiang 2026).

In Malaysia, forest plantation development has been promoted as part of the strategy to ensure a continuous supply of raw material for the wood-based industry (Bernama 2022; MTIB 2025). Eucalyptus plantations have been highlighted as a potential source of wood supply to support the timber industry and downstream processing (Bernama 2022; MTIB 2025). Plantation species are increasingly viewed as an important supplement to timber obtained from natural forests, especially where natural forest production is declining. In particular, Eucalyptus plantations have gained importance in several regions of the country because of their potential to supply quality wood for industrial processing. Malaysian forestry sources also list plantation Eucalyptus among species used for furniture, mouldings, light construction, and pulp and paper products (Salleh 1995; Khan 2024). Recent studies indicate that Eucalyptus plantations have expanded in Malaysia, particularly in Sarawak. One report showed that Eucalyptus plantations accounted for 19% of the total forest plantation area in Sarawak. This rapid expansion reflects the growing interest in Eucalyptus as a plantation crop, but it also highlights the need to understand production risks that may reduce timber value and recovery (Awing et al. 2023; Awing 2023). Several studies have reported increasing disease incidence and severity in Eucalyptus plantations, posing significant challenges to plantation productivity, wood quality, and economic returns (Wu and Chen 2019; Suzuki et al. 2022).

Eucalyptus species are not highly resistant to disease, and numerous pathogens have been reported in plantation stands including stem canker pathogens (Chrysoporthe spp., Lasiodiplodia theobromae), wilt pathogens (Ceratocystis spp.), leaf pathogens (Teratosphaeria spp., Mycosphaerella spp.), and root pathogens (Phytophthora spp.) (Old et al. 2003; Gezahgne 2010; Wu and Chen 2019; Liao et al. 2022). Among these, stem canker is one of the most damaging diseases because it affects growth, wood quality, and sawmill recovery. The causal fungus Chrysoporthe deuterocubensis has been identified as an important canker pathogen of Eucalyptus in tropical and subtropical regions, including Malaysia (Ambrose 2024). In Malaysian plantations, infected trees have shown symptoms such as swelling, bark cracking, kino formation, sunken lesions, and rotten or deformed stems, all of which can reduce the commercial value of the logs (Samdin et al. 2018).

Several treatment strategies have been evaluated for canker disease management in trees, although the success of each method depends on the host, pathogen, and timing of intervention. In general, sanitation practices such as pruning infected tissues, removing severely diseased trees, avoiding wounding during wet conditions, and destroying infected material are recommended to reduce inoculum and disease spread. Chemical control has also been tested in plantation systems, and recent work in Malaysia showed that prochloraz manganese chloride, thiram, and copper hydroxide could reduce infection or lesion development caused by C. deuterocubensis on Eucalyptus urograndis (Ambrose 2024). Biological control and the use of tolerant planting material have also been proposed as longer-term approaches for managing Eucalyptus canker diseases (Suzuki et al. 2022; Samdin et al. 2018).

Despite the importance of canker disease, there is still limited information on how infection severity affects the recovery, grading, and commercial value of sawn timber from plantation-grown E. urograndis in Malaysia. Most available studies focus on pathogen identification or disease control rather than the impact of stem canker on wood conversion and board quality. Understanding these effects is important because diseased logs may still enter the processing chain, and their wood value may depend on how much material can be recovered in acceptable grades (Awing 2023). Therefore, the present study aimed to evaluate the effect of C. deuterocubensis stem canker severity on the recovery, grading, and value of sawn timber from plantation-grown E. urograndis. The specific objectives were to: (i) determine the influence of infection severity on log and board recovery, (ii) assess the effect of disease-related defects on visual grade classification, and (iii) estimate the economic implications of using infected timber for commercial products. The findings are expected to provide useful information for plantation management, disease mitigation, and the efficient utilization of Eucalyptus timber from infected stands.

EXPERIMENTAL

The Eucalyptus hybrid clone used in this study was E. urograndis (E. urophylla x E. grandis). This hybrid originates from China. The selected plot covers approximately 11.7 hectares and consists of 1,908 E. urograndis stands of 11-year-old trees. The sampling area is located in Block 38 C (coordinates: 4°33’16.3” N, 117°42’58.7” E) at Sabah Softwoods Berhad in Tawau, Malaysia. Visual tree inspections were conducted by assessing the physical characteristics and symptoms of stem canker present on the stems (Table 1), which included swelling, bark cracking, gummosis, sunken lesions, and elongated canker areas, as well as the presence of fruiting structures.

The symptoms and locations of each canker on the infected trees were photographed (Fig. 1). The infected trees were examined by forest pathologist Rauf et al. (2019), who confirmed the presence of C. deuterocubensis based on visual assessment. In addition, the presence of C. deuterocubensis was confirmed through DNA extraction, PCR amplification, and molecular phylogenetic analysis, as reported by Awing et al. (2023). The symptoms observed on the trees served as indicators of stem canker development and severity, as summarized in Table 1. The physical appearance of infected trees according to severity class is shown in Fig. 2.

Tree Assessment, Selection, Pre-Harvest and Harvesting

The trees were chosen based on a rubric of stem canker symptoms that was created prior to sampling. Before felling, each tree chosen for this study was measured for diameter at breast height over bark (DBHOB) being greater than 25 cm (26.8 to 39.7 cm), total height, and height to the lowest green branch. The overall volume of the stand and the volume between the stands were calculated. The selected trees were harvested manually using chainsaw.

Table 1. Classes of Severity for Eucalyptus urograndis Infected with Chrysoporthe deuterocubensis (Dahali et al. 2021)

Due to the logistic constraint during the movement control order (MCO) as Covid-19 and the limited number of man-power/facilities on that time, only three trees from each infection classes were chosen. At a height of 15 cm above ground, twelve trees of E. urograndis were felled for an evaluation of sawn timber recovery and quality grades of timber. This study did not cover a complete analysis of the recovery from individual trees. The conversion is based on total sawlogs/billet volumes. Comprising 36 logs in total, 12 trees felled in this study. Three logs (each 2.5 m in length) were obtained from the bottom part of the stem of each felled tree, as it contained the most obvious infected area of stem canker. The remaining logs were excluded because there were very few defects (almost defect-free) present.

Logs Processing, Sawing Pattern, and Measurement of Recovered Timber

Immediately after the logs were cross-cut, they were coded and colored by oil-based painting at the butt and upper parts of each log to minimize released growth stress after tree felling (Blackburn et al. 2011), to minimize water or moisture run-off, and for easy tracking during processing. Each log end was painted with one of four colors to uniquely identify the infection classes: healthy (green), moderate (blue), severe (yellow), and very severe (red). Log length, together with the small end diameter over bark (SEDOB) and large end diameter over bark (LEDOB), was recorded for volume estimation.

Fig. 1. Symptoms of Chrysoporthe deuterocubensis on Eucalyptus urograndis tree plantation at Sabah Softwoods Berhad in Tawau (Dahali et al. 2021)