International Wood Products Journal

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Termite resistance of gabonensis (kruma), a tropical lesser-utilised-species for commercial utilisation

Charles Antwi-Boasiako, Kwadwo Boakye Boadu & Kwasi Frimpong-Mensah

To cite this article: Charles Antwi-Boasiako, Kwadwo Boakye Boadu & Kwasi Frimpong- Mensah (2017) Termite resistance of Klainedoxa￿gabonensis (kruma), a tropical lesser-utilised- species for commercial utilisation, International Wood Products Journal, 8:2, 120-126, DOI: 10.1080/20426445.2017.1317470 To link to this article: https://doi.org/10.1080/20426445.2017.1317470

Published online: 25 Apr 2017.

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Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=ywpj20 INTERNATIONAL WOOD PRODUCTS JOURNAL, 2017 VOL. 8, NO. 2, 120–126 https://doi.org/10.1080/20426445.2017.1317470

Termite resistance of (kruma), a tropical lesser-utilised-species for commercial utilisation

Charles Antwi-Boasiako, Kwadwo Boakye Boadu and Kwasi Frimpong-Mensah Department of Wood Science & Technology, Faculty of Renewable Natural Resources, Kwame Nkrumah University of Science & Technology, Kumasi, Ghana

ABSTRACT ARTICLE HISTORY The paper describes the testing for termite resistance of a lesser-utilised tropical species known Received 14 July 2015 as kruma (Klainedoxa gabonensis) in order to evaluate its potential for the building, construction Accepted 5 April 2017 and related wood-consuming industries. Results suggest that kruma heartwood can be rated as KEYWORDS very durable and the sapwood as durable. It is concluded that utilisation of this wood species Accelerated field test; bio- could reduce over dependence on traditional primary species. deterioration; kruma; mass loss; service-life; subterranean termite; wood utilisation

Introduction Nigeria. Rahman and Chattopadhyay (2003) asserted Timber is a preferred choice for building and furniture that about AU$1500–2500 was incurred per pole as manufacturing (Pakarinen 1999). Wooden furniture is replacement cost for more than 5.3 million wooden sound and thermal-resistant, which makes homes poles used to supply power in the Queensland region cozier and more serene than their plastic and metallic of Australia due to bio-deterioration. Teles and Valle counterparts (Lihra et al. 2008). Natural grain of (2001) also estimated that about ₣300–400 million wood and texture combine beauty and robustness in could be spent yearly to repair or replace wood providing appealing products with elegance, charm destroyed through bio-deterioration alone in France. and sophistication to any room (Newport Furniture Thus, to ensure increased life in service of manufac- Parts 2009). It offers some therapeutic benefits such tured products, promotion of forest/timber conserva- as support and comfort to patients distressed from tion and protection of the environment from the spinal injuries or backache (Phadke 2012). Although harmful effects of preservative-chemicals against bio- wood is a desirable material for construction, as a natu- deterioration, naturally durable timbers (e.g. Quercus ral polymer, it is prone to bio-degradation caused by robur L., Entandrophragma cylindricum (Sprague) bacteria, decay-fungi and insects. Termites, carpenter Sprague, Milicia excelsa (Welw.) C.C. Berg, Cedrus bees, ants and powder-post beetles are the major insect libani A. Rich, Robinia pseudoacacia L. and Tectona pests to wooden structures (Abood 2008). They pene- grandis L.f., Larix decidua var. polonica and Intsia trate wood and decompose its cellulose for biochemical palembanica Miq.) are highly preferred to their non- energy, which reduces the strength and structural rigid- durable and chemically treated counterparts (Humar ity of several manufactured products (Sonowal & et al. 2008). The chemical preservatives could be costly, Gogoi 2010). Thus, such wooden structures have lim- harmful to life and the environment and render wood ited service-lives (Stephan et al. 2006; Lionetto & Fri- unable to receive finishes (International Agency for gione 2009). Ministerial Conference on the Research on Cancer 1995; Nakayama et al. 2000). Protection of Forests in Europe (2007) reported that Increasing unavailability and cost of the ‘well- 80% of the French public surveyed agreed that wood known’, frequently used and naturally durable tra- products required greater maintenance efforts than ditional timbers (e.g. E. cylindricum and M. excelsa) plastics and metals. The report indicated that extremely require the promotion of the abundant secondary tim- low rankings (<2, i.e. poor) were obtained for wood bers or the lesser utilised species (LUS) to meet the useful-life and maintenance intervals in an Austrian incessant wood demand so as to sustain the timber Survey. Adéwolé and Olorunnisola (2010) and DFID industry (Barany et al. 2003). Timber Industry Re- Human Development Resource Centre (2012) structuring Working Group (2008) noted that between observed that wooden school chairs and desks deterio- 2000 and 2004, about 75% of wood exports from rated shortly after their manufacture in Ibadan, Ghana was from only 28 endangered timber species

CONTACT Charles Antwi-Boasiako [email protected] © 2017 IWSc, The Wood Technology Society of the Institute of Materials, Minerals and Mining INTERNATIONAL WOOD PRODUCTS JOURNAL 121 and 25% from the LUS. In 2007, 80% (by volume) of Materials and methods the exported timber was from just 20 wood species Sampling of wood material including T. grandis, Triplochiton scleroxylon Schu- mann, Aningeria robusta (A.Chev.) Aubrév. & Pellegr., Three (3) trees each of kruma and E. cylindricum (70– Ceiba pentandra (L.) Gaertn., Terminalia superba 90 cm wide, of 40–45 years) were randomly harvested A. Chev. and Antiaris toxicaria Lesch. However, (at 1.3 m above the ground) from the Bobiri Forest there are over 500 timber species, which grow to mer- Reserve in the Ashanti Province of Ghana [Latitudes ο chantable sizes but have never been commercially 6 39′S and 6o 44′N; Longitudes 1o 15′E and 1o exploited because their technical properties are 23′W] (Addae-Wireko 2008). Bolts (1 m long) were unknown. Thus, an intensive research into the proper- obtained from each butt. These were quarter-sawn, ties of LUS would be needed in order to increase the processed into boards and the desired sample taken. number of utilisable timber species for domestic supply Forty eight defect-free heartwood samples (within 8– and reduce the over-exploitation of traditional timbers 15 cm from the pith) as well as sapwood (within 40– that already have great export markets (Timber Indus- 50 cm from the pith) were randomly taken from each try Re-structuring Working Group 2008). In , bolt and their field performance (in terms of durability) several LUS (e.g. Podocarpous latifolius R.Br. ex tested against termites. Mirb., Funtumia elastica (P. Preuss) Stapf. and Trichi- lia dregeana E. Mey. Ex Harv. & Sond.) are being pro- gressively used to substitute many of the traditional Determination of termite resistance timbers (e.g. Milicia spp. and Khaya spp.) and for fur- The E. cylindricum and kruma stakes (400 × 40 × niture production (Zziwa et al. 2006). For building and 20 mm) were conditioned at 20°C and 65% rh until furniture-making, Ali et al. (2011) recommended the equilibrium moisture content (EMC) was reached (BS use of the under-exploited tropical timbers (e.g. Acacia EN 252 2014). C. pentandra stakes served as the con- nigrescens Oliv., Pericopsis angolensis (Baker) Meeuwen trol. Each stake was weighed. The moisture content and Pseudolachnostylis maprounaefolia Pax) based on (mc) of 10 other stakes from C. pentandra and each their relative abundance, expected biomass per tree as stem position of kruma and E. cylindricum was well as other important properties (e.g. durability), measured at 103 ± 2°C and used to determine their cal- which are useful determinants of consumers’ choice culated oven-dry masses (CODMs) (Antwi-Boasiako & for wooden products. Thus, Arowosoge and Tee Pitman 2009) (Equation (1)): (2010) mentioned that detailed knowledge about the durability of LUS is needed in order to substitute effec- Calculated oven dry mass (CODM) tively the current highly marketed, primary timber 100 × fresh weight of sample species. = (1) 100 + moisture content of sample Kruma (Klainedoxa gabonensis) is a tropical LUS (Fam.: ). It occurs extensively in , The replicates from each timber were randomly Uganda, and Ghana but it lacks information inserted into the soil to cover one third of their lengths in the Trade Statistics. It has great strength and at the test site (50 × 60 m) of the Demonstration Farm attractive grain pattern; it saws and glues well and of the Faculty of Renewable Natural Resources, Kwame dresses to a smooth finish. It is relatively abundant Nkrumah University of Science and Technology − with a mean basal area of 10.77 m2 km 2 in the Gha- (KNUST), Kumasi-Ghana (Plate 1). The stakes were naian forests (Ghana Forestry Commission 2012). It 50 cm apart from each other. The Demonstration site grows up to 120–150 cm in diameter and 45–50 m lies within the semi-deciduous vegetation zone [6° tall with a straight and cylindrical bole, which 40’N and 1° 33’W] with moderate temperature (25° could be branchless for up to 25 m from the ground. C) and high rh of 83%. It is dominated by Ochrosol Thus, it has much biomass and desirable character- soil (Kumasi Metropolitan Assembly 2006). It contains istics for several structural applications including many termite mounds (Plate 1) and has a high decay flooring and furniture production (Oteng-Amoako hazard index. Common insects at the test field include & Obeng 2012). However, dearth of knowledge on subterranean termites, Anobium spp., Ancistrotermes its durability could hinder its utilisation. This paper spp. and Nasutitermes latifrons (Usher 1975). Accord- sought to examine the durability of kruma, as a ing to Ravenshorst et al. (2013), the use of the field test potential substitute to the threatened primary timbers is mostly preferred to the laboratory type since the for- so as to increase its prospects of utilisation, which mer allows the collective effects of many biotic and would contribute to the widening of the pool of ‘can- abiotic factors of deterioration to be evaluated. didate’ timber species’ from the tropical forests for Antwi-Boasiako and Baidoo (2010) and Sonowal and domestic supply. This would further reduce the Gogoi (2010) explained that duration for field test over-exploitation of the traditional timbers, which could be shortened to produce useful results for reliable have potential export markets. prediction of the durability of LUS. Thus, the stakes for 122 C. ANTWI-BOASIAKO ET AL.

Plate 1. Stakes inserted vertically at the test site (a); a termitarium very close to the test site (b). the current investigation were exposed very close to Experimental design and data analysis termitaria (which harboured the bio-degraders) The stakes were organised into 3 groups of 16 replicates through an accelerated field performance test, which for each timber using split-plot in completely random- lasted for 24 months. ised design. The data were subjected to ANOVA test, while Fisher’s least significant difference (LSD) test (at 95% confidence level) was used to compare the Visual durability ratings treatment means. The stakes were inspected every month and also after the field exposure for termite and other damages caused by bio-deteriogens, particularly termites. The Results stakes were graded as: 0 = no sign of attack, 1 = slight attack, 2 = moderate attack, 3 = severe attack, 4 = fail- Visual durability rating ure (BS EN 252 2014). The heartwood and sapwood of kruma were slightly deteriorated by termites; they recorded a visual dura- bility rating of 1. E. cylindricum heartwood suffered Mass loss (%) moderate attack (rating = 2), while its sapwood was All the debris adhered to each stake were cautiously severely attacked (rating = 3). C. pentandra stakes brushed off. The stakes were oven-dried at 103 ± 2°C were very heavily degraded (rating = 4) (Table 1; and their final masses taken. The mass loss (%) for Plate 2). The differences between the ratings for the each stake was calculated (BS EN 252 2014) (Equation timber species were significant (P < 0.05) (Table 1). (2)) CODM − final mass Mass loss (%) = × 100 (2) CODM Mass loss Mass loss (%) was related to natural durability ratings: Mean mass losses (%) for stakes from the respective 0–5% = very durable, 6–10% = durable, 11–40% = stem positions of the timber species were in this moderately durable, 41–100% = non-durable (BS EN 252 2014). Table 2. ANOVA for the mass losses of stakes from kruma and E. cylindricum bases with C. pentandra as the control. Table 1. Visual durability ratings for stakes from kruma and Mean Source DF Squares square F value Pr > F E. cylindricum bases with C. pentandra as the control. Model 11 33206.6 3018.9 6491 <0.0001 Radial stem Visual durability Replicates 2 0.1 0.1 0.2 0.97 Wood species position rating* Interpretation a Species 2 33169.4 16584.7 12656.5 <0.0001 Kruma Heartwood 1a Slight attack Stem position 1 21.2 21.2 45.7 0.0005b Sapwood 1a Slight attack Replicates*species 4 5.2 1.3 2.8 0.1 E. cylindricum Heartwood 2b Moderate Species*stem 2 10.7 5.3 11.5 0.0089c attack position Sapwood 3c Severe attack Error 6 2.8 0.5 C. pentandra Sapwood/ 4d Failure Corrected total 17 33209.4 (control) heartwood aSignificant: P(<0.0001) < 0.05; bSignificant: P(0.0005) < 0.05; cSignificant: P *Ratings with different superscripts are significantly different (P < 0.05). (0.0089) < 0.05. INTERNATIONAL WOOD PRODUCTS JOURNAL 123

Plate 2. Kruma heartwood (a), sapwood (b), E. cylindricum heartwood (c) and sapwood (d) after field exposure (arrow = termite attack). NB: C. pentandra stakes were completely destroyed at the end of the test. decreasing order: C. pentandra (100%; i.e. non- could also be verified by the Gulfport scale (0 = no durable) > E. cylindricum sapwood (13.1 ± 0.6%; mod- damage, 1 = nibbles to surface etching, 2 = light erately durable) > E. cylindricum heartwood (10 ± damage with penetration, 3 = moderate damage, 4 = 0.7%; durable) > kruma sapwood (8.2 ± 0.6%; dur- heavy damage, and 5 = block failure). It is a tool equally able) > kruma heartwood (4.8 ± 0.3%; very durable). used to explain the extent of timber resistance to ter- The differences between their mass losses were signifi- mites. The current ratings for kruma, E. cylindricum cant (P < 0.05) (Figure 1; Tables 2 and 3). and C. pentandra are in agreement with the standard specified by the Gulfport wood damage scale. Accord- ingly, kruma would be categorised into Durability Class Discussion 1 under the European Standard, EN 252 (BS EN 252 Visual durability rating 2014)] and rated as more durable than the popularly utilised traditional timber under the current study Visual durability rating was employed to examine the (i.e. E. cylindricum) for furniture production and extent of deterioration of the timbers in support of other wooden structures. Thus, kruma could be used their mass losses. This rating assesses the durability for applications in contact with the ground (i.e. Euro- of timber from signs of attack on stakes, which have pean Hazard Class 4). From the Australian Durability previously been exposed in the field to insects and Standard (AS 5604 2005), kruma could be placed in decay organisms (Eaton & Hale 1993). Edlund et al. the same Durability Class (i.e. 1) as Podocarpus totara (2006) reported that the rating could be subjective as var. totara, Manoao colensoi (Hook.) Molloy and Calli- a measurement tool for strength loss. However, it tropsis nootkatensis (D. Don) Oerst. ex D.P. Little, could be an effective and easy-to-use method if meticu- which are used in full weather-exposed applications lously employed (Kasal & Anthony 2004). (and under Hazard Class H1–H4). The current investigation revealed that kruma Ali et al. (2011) indicated that the physico-mechan- heartwood and sapwood were slightly attacked and ical and biological properties of wood could explain its had a visual durability rating of 1. E. cylindricum heart- durability characteristics. Information on the various wood suffered moderate attack (2), while C. pentandra technical properties of kruma is scanty except few − failed completely (4). Wagner et al. (2009) and Ncube characteristics such as its density (940–1150 kgm 3) et al. (2012) mentioned that visual durability rating and cell wall thickness (i.e. thick fibre walls), which have been reported by Oteng-Amoako and Obeng (2012). Eaton and Hale (1993) and Cookson and McCarthy (2013) explained that these properties (den- sity and cell wall thickness) could contribute to the improvement of the resistance of timbers to bio-

Table 3. LSD for the mass losses of stakes from kruma and E. cylindricum bases with C. pentandra as the control. Wood species Stem position Mean mass loss Interpretation Kruma Heartwood 4.8a Very durable Sapwood 8.2b Durable E. cylindricum Heartwood 10c Durable Figure 1. Mass losses for stakes across the bases of kruma Sapwood 13.1d Moderately durable e and E. cylindricum stems with C. pentandra as the control C. pentandra Sapwood 100 Non-durable (Bar = standard error). Means with different superscripts are significantly different (P < 0.05). 124 C. ANTWI-BOASIAKO ET AL. deterioration, as they make browsing by insects in par- which have been earlier identified by Oteng-Amoako ticular difficult. Humar et al. (2008) observed that and Obeng (2012). Q. robur (a very dense and popular furniture-making The commercial utilisation of timbers could be timber) was very resistant to bio-deterioration. The affected by and predicted from their properties includ- thick-walled materials of such timbers retard bio- ing durability (Eaton & Hale 1993). Most architectural degraders from penetrating them and thereby degrad- structures demand timbers with long useful-lives. ing the wood substance. E. cylindricum is lighter, with a While some timbers may be suitable for ground-con- − density of 560–750 kgm 3 (Kémeuzé 2008) than tact applications due to their enhanced durability, kruma. Among the three timbers, C. pentandra was others could be effectively employed only when they found to be the lightest with a density of 380– are protected from the weather and attack by bio- − 450 kgm 3 (Duvall 2011). They all have thin-to-med- degraders (Ani et al. 2005). Kruma is in the same Dura- ium walled-fibres. Based on these characteristics, it is bility Class (i.e. 1) as P. totara, M. colensoi, unsurprising that kruma was more durable than C. nootkatensis, N. diderrichii, C. rodiei and L. alata E. cylindricum as well as C. pentandra. (Australian Standards 2005), which are recommended for wood applications not in contact with the ground such as roofing, window joinery, framing, weather- board and fascia due to their unique durability status Mass loss (Grace & Tome 2005; Kémeuzé 2008). These timbers Usually, natural durability of wood is widely corre- are equally used for structures with extensive ground lated with the biomass, especially in the form of and water contact such as those in buildings, for elec- the amount of cellulolytic materials it loses from tric poles, garden furniture, decking and flooring bio-degradation (Ashaduzzaman et al. 2011). For (Eaton & Hale 1993). Thus, kruma could be a suitable the current investigation, the resistance of wood to substitute to these timbers for indoor and outdoor termite attack was determined from the timber’s structural products. Its abundance and great biomass, mass loss after field exposure. Ashaduzzaman et al. coupled with its durability when used, could contribute (2011) explained that when less biomass is removed, to the reduction of the over-dependence on the few wood marginally loses weight and becomes more durable but over-exploited and threatened commercial resistant to bio-degradation. timbers within the Construction, Wood and other C. pentandra (i.e. the control) lost the greatest related Sectors as well as the promotion of sustainable mass (i.e. 100%) and would be ranked as non-dur- management of the timber resources. able. Kruma heartwood lost the least (4.8 ± 0.3%) and would be rated very durable according to EN Conclusion 252. Duvall (2009) and Antwi-Boasiako and Boadu (2013) reported that C. pentandra contains great Wooden products have preferred characteristics (such amount of carbohydrates and less toxic extractives, as sound and thermal-resistance) to those from artifi- which make it easily susceptible to attack by micro- cial materials employed for similar applications. How- organisms, which use the timber for food. Festus ever, several concerns over the service-lives of wood and Nwala (2012) confirmed that most timber and wood products have been raised, which require species of the family Irvingiaceae as kruma (e.g. careful selection of naturally durable timbers by the glaucescens, I. excelsa and K. trillessii) are wood industry. The present investigation has revealed durable. Based on its current rating, kruma would that: be classified into Use-Classes 3 (i.e. suitable for exterior and above-ground structures) and 4 (i.e. (i) Kruma heartwood and sapwood got slightly dete- for exterior and in-ground applications) under EN riorated in the field and lost the least mass, thus, 335 (Czichos et al. 2011). Thus, its utilisation making them very durable compared to would be comparable to those of Nauclea diderrichii E. cylindricum. Kruma’s natural durability also (De Wild. & T.Durand) Merr., Chlorocardium rodiei compares well with other known timbers such (R.Schomb.) R.R.W. and Lophira alata Banks ex as I. palembanica and Q. robur used for sleepers, P.Gaertn., which are traditional timber species, used axe and tool handles and furniture. for bridge construction, decking and flooring (Mea- (ii) Based on its natural durability, kruma could be den et al. 2011). Pitman et al. (1999) and Cookson used effectively as stakes and posts for outdoor and McCarthy (2013) observed that durability is structures in contact with the ground (such as improved with the presence of tyloses, which makes flooring and doors) and above-ground (e.g. win- wood impermeable to micro-organisms since they dows, roofing and furniture). block the passage-ways such as cell lumina and (iii) The dwindling supply of the preferred naturally pits. Thus, the durability rating for kruma could durable traditional timbers requires the pro- further be attributed to the presence of tyloses, motion of LUS with excellent durability ratings INTERNATIONAL WOOD PRODUCTS JOURNAL 125

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