Physical and Chemical Properties of Highland Bamboo (Yushania alpina) Culms Grown in Ethiopia

• Bamboo is the fastest growing plant currently known on earth, a property that enables it to be the best alternative as a future source of wood ﬁ ber. This study investigated the effect of site and culm height on the physical and chemical properties of Yushania alpina culms grown in Ethiopia. Matured Yushania alpina 3 to 5-year-old samples were harvested from Hagere-Selam and Rebu-Gebeya sites. The culms were subdivided into three equal lengths (bottom, middle, and top), and the variations in physical and chemical properties between the two sites and the culm heights of Yushania alpina were investigated. The results showed that the average values of MC, basic density, tangential and longitudinal shrinkage of Yushania alpina culms for Hagere-Selam and Rebu-Gebeya sites were (91.78 and 80.32 %), (0.65 and 0.63 g/cm 3 ), (6.63 and 5.84 %) and (0.63 and 0.56 %), respectively. The average values of cellulose, lignin, extractive and ash contents in the culms for Hagere-Selam and Rebu-Gebeya sites were (52.84 and 50.71 %), (26.55, and 26.04 %), (8.41 and 8.02 %) and (1.95 and 2.17 %), respectively. The results revealed that the site affected the MC, basic density, cellulose, lignin, extractive, and ash contents of Yushania alpina culms but not the tangential and longitudinal shrinkage. The culm height of Yushania alpina affected MC, basic density, tangential shrinkage, longitudinal shrinkage, cellulose, lignin, extractive, and ash contents. In the case of both sites, the highest percentages of MC, tangential and longitudinal shrinkage, and ash content were observed at the base and lowest at the top of the culms. On the contrary, both sites observed the highest magnitude of basic density, cellulose and extractive at the top and lowest at the base of the culms. The variations in physical and chemical properties at different sites and culm heights in ﬂ uence the utilization of Yusha-nia alpina culms for industries and end products.


INTRODUCTION 1. UVOD
Bamboo is the fastest growing plant currently known on earth, a property that enables it to be the best alternative as a future source of wood fi ber (Liese and Köhl, 2015).Unlike timber, bamboo culms need short rotation (3-5 years) to mature before they can be harvested and utilized (Liese and Köhl, 2015).Bamboo is a perennial plant that belongs to the subfamily Bambusoideae of the family Poaceae (Gramineae), and it contains more than 1,500 species.It provides more than 1,500 applications, from traditional utilization in rural areas to industrial production, construction, and other versatile uses (Liese, 1987;Zhaohua, 2011;Hinde and Kaba, 2018).Bamboo has a higher strength-to-weight ratio than wood, enabling easy harvesting, transporting, and manufacturing of products (Wahab et al., 2009;Anokye et al., 2014).The above characteristics of bamboo have encouraged and intensifi ed bamboo research in recent years.
The utilization of bamboo for various applications is governed by its properties, like any wood material.Moisture content, density, and shrinkage are physical properties that infl uence the dimensional stability, toughness, strength, working properties, and durability of bamboo and bamboo products (Liese and Köhl, 2015).The basic chemical properties found in bamboo are cellulose, hemicellulose, and lignin, which infl uence its utilization for different applications (Liese, 1985).The properties of bamboo culms are mainly affected by culm position, age, topography, and climate (Liese and Köhl, 2015;Tolessa et al., 2019).The physical and chemical properties of bamboo vary between species, sites, age, and different parts of culm positions (Santhoshkumar and Bhat, 2015;Liese and Köhl, 2015;Tolessa et al., 2019).Information on the physical and chemical properties of bamboo is necessary for assessing its suitability for various end products (Kamruzzaman et al., 2008;Tolessa et al., 2019).Such information will also enable increasing the utilization of bamboo species as substitutes for solid wood in woodbased industries.
Recently, Yushania alpina (Y.alpina) culms and splints have been used to construct traditional houses, rudimentary furniture, handcrafts, mats, fencing, beehive, and household utensils (baskets, winnowing trays) (Desalegn and Tadesse, 2014;Desalegn, 2015).The highland bamboo (Y.alpina) is indigenous to Ethiopia and available in the highlands of Kenya, Sudan, Zambia, Zaire, Burundi, Rwanda, Cameroon, and Tanzania (Embaye et al., 2003).This bamboo species is the most cultivated and widespread throughout the country.It is preferred mainly because of its suitability and ease of processing and converting into different products.
In Ethiopia, the multiple uses of bamboo in industrial applications are not getting the most economic advantage, and its utilization is limited to domestic services (Mulatu and Kindu, 2010;Zenebe et al., 2014).This is due to insuffi cient basic information on its properties.Previously, few studies have been done on physical and chemical properties (Muche and Degu, 2019;Tsegaye et al., 2020;Dessalegn et al., 2021).There is still limited information about the variation of physical and chemical properties between sites, within culms, and along the culm heights of Y. alpina grown in Ethiopia.Therefore, this study investigated the effect of site and culm heights on the physical and chemical properties of Y. alpina grown at Hagere-Selam (Sidama Region) and Rebu-Gebeya (Amhara Region).

MATERIJALI I METODE
A total of twenty matured Yushania alpina culm samples (3-5 years old) were harvested from potential sites of Hagere-Selam (Sidama Region) and Rebu-Gebeya (Amhara Region).First, the bamboo culms were harvested, and their branches were removed from the top parts of the culms leaving the entire length to be about 9 m.After that, the culms were subdivided into three equal lengths, labeled bottom, middle, and top portions, with lengths of 3 m (Liese and Köhl, 2015).

Determination of physical properties
2.1.Određivanje fizičkih svojstava 2.1.1Determination of moisture content 2.1.1.Određivanje sadržaja vode Three centimeters long specimens representing two sites (Hagere-Selam and Rebu-Gebeya) and three culm heights (base, middle, and top) were cut from fresh Y. alpina to determine its initial moisture content.Green weight of each specimen was measured using an analytical balance with a 0.01g accuracy (IS 6874, 2008).The specimens were then oven-dried at a temperature of (103±2) °C until attaining constant weight.The moisture content was calculated using Eq 1. (1) Where W g is the green weight of specimens and W od is the oven-dry weight of the specimen

Determination of basic density 2.1.2. Određivanje nominalne gustoće uzoraka
Three centimeters long specimens, (representing 2 sites and three culm heights), were cut from fresh Y. alpina culms for the determination of basic density.The green weights of all specimens were measured using an analytical balance with an accuracy of 0.01 g.The water displacement method was used to determine the volume of each specimen.The specimens were then oven-dried at a temperature of (103±2) °C.The repeated measurement of weight was recorded until the constant weight was reached.Basic density was determined based on ISO 22157-2:2004 and IS 6874 (2008).Basic density was calculated using Eq 2. (2)

Determination of shrinkage 2.1.3. Određivanje utezanja
Specimens representing 2 sites and three culm heights were prepared from round-shaped Y. alpina culms, 3-cm in length, to determine tangential and longitudinal shrinkage.For each specimen, the green weight and dimensions of wall thickness at four points and lengths at four points in green conditions were measured using an analytical balance and digital caliper with an accuracy of 0.01g and 0.01 mm, respectively (Figure 1).The specimens were oven-dried at a temperature of (103±2) °C.The repeated measurements for weight were recorded until constant weight was reached.Shrinkage was determined based on ISO 22157-2:2004 and IS 6874 (2008).The shrinkage was calculated using Eq 3.

(3)
Where D i is the initial dimension of the specimens before oven-drying (mm) and D f is the fi nal dimension of the specimens after oven-drying (mm)

Determination of chemical composition 2.2. Određivanje kemijskog sastava
The harvested bamboo culms were dried and converted into small-size strips suitable for further milling processes.Thereafter, they were placed in a hammer mill and Willey mill to reduce it to the appropriate size.Then the milled powder bamboo samples were fi ltered using a 40 mesh size (425 μm) and 60 mesh sieve (250 μm).The particles were stored in an airtight container labeled with the appropriate code for chemical analysis.
The chemical composition including extractive (alcohol-toluene solubility), ash, and lignin content were determined using the standard procedures of the American Society for Testing Materials (ASTM) (Table 3).Cellulose content was determined according to alkali extraction and Kurchner-Hoffer method (Brown, 1975).Toluene was used instead of benzene and reported as alcohol-toluene extractive (Tolessa et al., 2017).The amounts were expressed on a percentage basis of the starting oven-dry mass.The lignin content test was performed with extractive-free bamboo derived from the alcohol-toluene extractive test.

Statistical analysis 2.3. Statistička analiza
The data were analyzed statistically to assess signifi cant differences between the two sites (Hagere-Selam and Rebu-Gebeya) and along the three culm heights (base, middle, and top) using descriptive statistics and analysis of variance (ANOVA) by R software, version 4.1.3.The least signifi cant difference (LSD) was used for mean comparison at p<0.05.  4. The results revealed that Y. alpina culms harvested from Hagere-Selam had a higher value of initial MC than those harvested from Rebu-Gebeya.These differences may be associated with the age and season of felling of bamboo culms (Liese, 1985).For this study, the culms 3 to 5 years old were harvested during the dry season but in different months.

REZULTATI I RASPRAVA
The results revealed that the values of initial MC for the two sites decreased from the base to the top position of the culms (Table 4).Similar trends to this fi nding were seen in Bambusa balcooa, Bambusa tulda, Bambusa salarkhanii, and Melocanna baccifera, grown in Bangladesh (Kamruzzaman et al. 2008).Other researchers also found similar variations in their studies (Wahab et (2009), the variation of MC along the culm height was due to differences in anatomical structure and chemical composition between locations along the bamboo culms.On the other hand, the decreasing trend of initial MC might be due to a smaller proportion of vascular bundles at the bottom when compared to the top position of culms (Anokye et al., 2014).

Nominalna gustoća
Density is among the main factors that affect the utilization of bamboo culm as raw material.The over- all mean values of basic density for the Hagere-Selam and Rebu-Gebeya sites were 0.65 and 0.63 g/cm 3 , respectively.This shows that the culms harvested from the Hagere-Selam site were signifi cantly denser than those from the Rebu-Gebeya site (Table 4).Generally, the density of bamboo ranges from about 0.4 to 0.9 g/ cm 3 depending on the anatomical structure refl ected in the quantity and distribution of fi bers around the vascular bundles (Zakikhani et al., 2017).The density of this fi nding was in the range of generally recognized values of bamboo density.The result shows that the culm height had signifi cant effects on the basic density at p<0.001 level, whereas the site had a signifi cant effect on basic density at p<0.01 level (Table 4).However, the table shows that the interaction effect between the site and culm height did not signifi cantly affect the basic density at p>0.05 level (Table 4).
The results revealed that the basic density significantly increased along with the height of Y. alpina culms for both sites (Figure 2).Many researchrs reported similar trends to this fi nding.They found an increase in basic density with increasing height of bamboo culms from the base to the top (Wahab et al., 2009;Santhoshkumar and Bhat, 2015;Vetter et al., 2015).The increase of basic density from the base towards the top position of culms was also reported for thirteen bamboo species grown in Malaysia (Siam et al., 2019).This variation is associated with anatomical structure variations at differ-ent bamboo culms heights (Liese, 1985).According to Santhoshkumar and Bhat (2015), the increase in the magnitude of density from the bottom to the top position of the bamboo culm was due to the increase in the proportion of fi brous tissue and increased frequency of the occurrence of vascular bundles.

Utezanje
Shrinkage is another main factor that affects the utilization of bamboo culm as a raw material in different wood industries.Unlike wood, bamboo begins to shrink from the very beginning of drying.The results revealed that the overall mean tangential or culm-wall shrinkage for the Hagere-Selam and Rebu-Gebeya sites was 6.63 % and 5.84 %, respectively (Figure 5).The overall mean longitudinal shrinkage for the Hagere-Selam and Rebu-Gebeya sites was 0.63 % and 0.56 %, respectively (Figure 5).Shrinkage of the Y. alpina culm grown at Hagere-Selam was higher in both tangential (culm-wall thickness) and longitudinal direction when compared to the Rebu-Gebeya site (Figure 5).This variation may be related to the initial MC and the culm-wall thicknesses of the bamboo culms (Siam et al., 2019).
The tangential and longitudinal shrinkage of Y. alpina culm at different heights for Hagere-Selam and Rebu-Gebeya sites is presented in Figure 3 and Figure 4, respectively.The statistical analysis of variance revealed that site and culm height had a highly signifi cant effect on tangential shrinkage at p<0.001 (Table 4).The same table shows that the culm height had a signifi cant effect on longitudinal shrinkage at p<0.001, whereas the site had a signifi cant effect on the longitudinal shrinkage at p<0.05.However, the interaction between the site and the culm height position had an insignifi cant effect on the tangential and longitudinal shrinkage at p>0.05 (Table 4).
The results showed that the tangential and longitudinal shrinkage of the culm decreased from the base to the top positions of Y. alpina for both sites (Figure 3, Figure 4).A similar trend was observed in Bambusa balcooa, Bambusa tulda, Bambusa salarkhanii, and Melocanna baccifera species grown in the Philippines (Kamruzzaman et al., 2008).These variations are associated with higher parenchyma cell content and fewer vascular bundles at the base positions.On the other hand, lower parenchyma cell content and a higher number of vascular bundles are found at the top positions of bamboo culms (Wahab et al., 2009).

Cellulose content 3.2.1. Sadržaj celuloze
Cellulose is the main constituent of lignocellulosic wood material, and it is located predominantly in the secondary cell wall.The analysis of variance shows that the site and culm height had a signifi cant (p<0.001)effect on the cellulose content of Y. alpina bamboo (Table 5).The same table shows that the interaction effect between site and culm height did not show a signifi cant (p>0.05)effect on cellulose content (Table 5).The overall mean value of cellulose content in Y. alpina culms grown at Hagere-Selam was 52.84 %, which is statistically higher than the bamboo culms collected from the Rebu-Gebeya site, which was 50.71 %.The results obtained from this study were higher than those found in the previous study on the same bamboo species (46.76 %) (Tsegaye et al., 2020).The cellulose content of this fi nding was in the range of softwood (40 -52 %) and hardwoods (38 -56 %).Normally, the cellulose content of bamboo ranges from 40 -50 % (Fengel and Wegener, 1984).The results obtained in this study were in the range of the values mentioned above for woods and other bamboo species.Bamboo species with cellulose content in this range are suitable for pulp and papermaking, bioenergy, and biobased composite production (Hammett et al., 2001;Li et al., 2007).It can also be used for applications similar to those of softwood and hardwood.
In the case of both sites, statistically, the highest cellulose contents were observed at the top; followed by the middle and lowest at the bottom position (Figure 8, Figure 9).The percentage cellulose content of Y. alpina culms for both sites showed an increasing trend from the base to the top (Figure 8, Figure 9).The same trend to this fi nding was reported for the same bamboo species at age of three (Tolessa et al., 2019).The in-

Klason lignin content 3.2.2. Sadržaj Klasonova lignina
Lignin is a phenolic substance consisting of an irregular array of variously bonded hydroxyl-and methoxy-substituted phenylpropane units.Statistically, the overall mean values of lignin content of Y. alpina culms collected from the Hagere-Selam (26.55 %) differed insignifi cantly from the culms collected from the Rebu-Gebeya site (26.04 %) (Figure 7).The lignin content in different tropical bamboo species was reported in the range of 24.84 to 32.65 % (Razak et al., 2013).Fengel and Wegner (1984) investigated the ranges of lignin for softwoods (24 -37 %) and hardwoods (17 -30 %).The results obtained from this study were in the range of the above reports for bamboo, softwood, and hardwood.According to Zhang et al. (2022), the high lignin content of bamboo culms can provide excellent physical and mechanical properties.On the other hand, the high lignin content contributes to bamboo rigidity and makes it suitable for structural applications, such as construction and furniture-making.
The analysis of variance shows that the culm height had a signifi cant effect on lignin content at p<0.01 (Table 5).The site showed a signifi cant (p<0.1)effect on lignin content (Table 5).However, the interaction effect between the site and culm height did not show a signifi cant (p>0.05)effect on the lignin content of the culms (Table 5).The results revealed that the highest percentage of lignin content was observed at the bottom; followed by middle and minimum at the top culm positions for both sites (Figure 8, Figure 9).A similar variation pattern to this fi nding was observed in the same bamboo species (Tolessa et al., 2019).A similar variation pattern to this study was reported for Melocanna baccifera (Hossain et al., 2022).

Sadržaj ekstraktiva
Non-structural chemical compositions found in wood and bamboo materials are known as extractive substances.On the other hand, extractives in bamboo are non-cell wall components with diverse chemical compositions such as resins, lipids, waxes, tannins, pentosan, hexosan, starch, and silica (Fengel and Wegener, 1984).According to the analysis of variance, site and culm height showed a signifi cant (P<0.001)effect on the extractive content (Table 5).However, the interaction effect between the site and culm height did not show a signifi cant effect on the extractive content of Y. alpina at p>0.05 (Table 5).
The overall mean value of extractive content in Y. alpina culms collected from Hagere-Selam was 8.41 %, which is insignifi cantly higher than the culms collected from the Rebu-Gebeya site, which was 8.02 %.Extractives in bamboo can enhance the structural rigidity of its cell wall and effectively resist diseases and pests/decay (Zhang et al., 2022).
Statistically, in the case of both sites, the highest extractive contents were observed at the bottom position; followed by the middle and lowest at the top position (Figure 8, Figure 9).The same variation pattern to this fi nding was reported in Y. alpina culms (Tolessa et al., 2019).

Ash content 3.2.4. Sadržaj pepela
Ash is a term generally used to refer to inorganic substances such as silicates, sulfates, carbonates, or metal ions.The analysis of variance shows that the main effects of site and culm height had a signifi cant effect on ash content at p<0.001 (Table 5).However, the interaction effects between the site and culm height did not show a signifi cant effect on ash content at p>0.05 (Table 5).The overall mean value of ash content in Y. alpina culms collected from Rebu-Gebeya was 2.17 %, which is signifi cantly higher than the culms collected from the Hagere-Selam site, which was 1.95 %.Liese and Köhl (2015 stated that bamboo growth sites affect the amount of ash in bamboo.This difference might be due to the topography, soil, and climate of the area where the bamboo culms are grown.Values lower than those determined in this study were reported for highland bamboo, namely 1.87 % (Tolessa Statistically, in the case of both sites, the highest ash contents were observed at the bottom position; followed by the middle and lowest at the top position (Figure 7, Figure 8).The same variation to this fi nding was reported in Y. alpina culms at the age of three (Tolessa et al., 2019).According to Tolessa et al. (2019), the ash content variation along the culm height varied with moisture content.

ZAKLJUČAK
This study investigated the variation of physical and chemical properties in Yushania alpina culm with site and culm height.The Y. alpina culms grown at the Hagere-Selam had higher values of green moisture content (MC) and basic density compared to the culms collected from the Rebu-Gebeya.The green MC of Y. alpina culms decreased from the base toward the top positions for both sites.Similarly, the tangential and longitudinal shrinkage from green to oven-dry conditions of Y. alpina culms showed a decreasing trend from the base to the top for both sites.In contrast, the opposite tendency was observed in the basic density, which decreased from the top to the base positions of the bamboo culms for the two sites.Density is the most important parameter affecting its practical utilization.Based on density, most of the other characteristics of bamboo culms can be predicted.A signifi cant effect of site and culm height on chemical properties was observed.The amount of cellulose and lignin content found was in the range of wood and other bamboo species.Consequently, Y. alpina culm can be a potential source of pulp and paper, and bioenergy, and is suitable for structural applications, such as construction and furniture-making and biobased composite production.Further study should be carried out on other potential bamboo species abundantly available in Ethiopia, such as lowland bamboo (Oxythenatera abyssinica) and other introduced and exotic bamboo culms.

Table 4
Analysis of variance for basic density and shrinkage at different sites and culm heights of Yushania alpina Tablica 4. Analiza varijance nominalne gustoće i utezanja uzoraka Yushania alpina s različitih staništa i različite visine stabljike