Culm characteristics and volume-weight relationship of a forest bamboo(Melocanna baccifera(Roxb.)Kurz)from northeast India

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ORIGINAL PAPER

Culm characteristics and volume-weight relationship of a forest bamboo(Melocanna baccifera(Roxb.)Kurz)from northeast India

Pator Singnar1?Arun Jyoti Nath1?Ashesh Kumar Das1

?Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2015

Culm characteristics ofMelocanna baccifera, locally‘muli’,culms at f i ve different culm ages of 11 girth classes(5–6 to 15–16 cm)were studied from Cachar District of southern Assam,northeast India.We recorded internode length,internode diameter,number of internodes per culm,total culm height,total culm green weight and total culm volume of all f i ve culm age classes.Data were gathered on 165 culms,each culm age class containing 33 culms with 3 culms per girth class.Culm height ranged from 3.2 to 15.3 m with highest mean of 9.15 m(in threeyear old culms)and maximum culm height was recorded in four-year old culms.Highest mean and maximum internode length(27.45 and 54.2 cm,respectively),internode diameter(3.12 and 4.75 cm,respectively)and total culm green weight(5.42 and 12.87 kg/culm,respectively)were recorded in three-year old culms and lowest in current-year culms.Best f i tted regression models for all parameters were developed.Signif i cant linear relationships between culm green weight and culm solid volume were documented for all f i ve culm age classes.Their corresponding best-f i t regression models were also developed.

Regression model?Volume equation?Age class?Girth class?Yield determination

Introduction

The physical and environmental properties of bamboo make it an exceptional economic resource for a wide range of uses,including poverty reduction.It is one of the fastest growing plants and can be harvested annually without depletion or deterioration of the soil.Bamboos complete their height growth within 2–4 months and have quick renewal capacity(Nath et al.2004;Yen and Lee 2011). Therefore,the biomass of mature bamboo stands can be assumed to be steady-state(Chen et al.2009).Bamboo is widely used in construction,for making woven wares and is becoming popular as an excellent substitute for wood in producing pulp,paper,board and charcoal.

Study of culm characteristics of bamboos at different age and diameter classes helps in selection of plus clump or culm which improves the commercial utilization of a particular species(Inoue et al.2013).Characterization of bamboo in relation to its anatomical,physical,mechanical and chemical properties helps to determine the maturation age,and this enhances processing and utilization(Hisham et al.2006).The anatomical structure of a bamboo culm determines its properties and characterizes the culm in relation to its end product(Latif 2001).Certain attributes, such as culm size and culm wall thickness inf l uence the range of their usage(Wong 1982).Strength,straightness, lightness combined with hardness,variation in size,ease of propagation,its short growth period to maturity and its availability for harvesting have expanded the range of uses of bamboo(Sharma 1982).Generally bamboo culm matures at two to three years,reaching its maximumstrength(Espiloy 1987,1994;Latif et al.1990).However, bamboo properties differ by species,age,location and external factors(Hisham et al.2006;Nath et al.2015a). Correal and Arbelaez(2010)reported that the age of bamboo is a key factor that affects its mechanical properties.The length of internodes determines the load bearing capacity of bamboo as well as its ability to peel,which in turn inf l uences its use(Pattanaik et al.2004).Guan et al. (2012)suggested that muli bamboo can be processed into high-value hardwood f l ooring due to its high-strength. Management strategies can also affect the end use of bamboo(Yen 2015;Nath et al.2015b).

The genus,Melocannahas two species and is one of the 10 genera of the Paleotropical woody bamboo subtribeMelocanninaeunder the tribe Bambuseae(BPG 2012).Melocanna baccifera,commonly known as‘muli’bamboo, is native to India,Bangladesh,Myanmar(Burma)and Nepal(Watson and Dallowitz 1992;Banik 2000).In India, it is mainly distributed in the northeastern states(Assam, Manipur,Meghalaya,Mizoram and Tripura)(Biswas et al. 1991).This species is included among the 20 priority bamboo species identif i ed by INBAR and IPGRI(Rao et al. 1998).Of 145 bamboo species found in India,M.bacciferaconstitutes about 20%of the total bamboo resource and it is the second largest afterDendrocalamus strictus(45%) (NCDPD 2010).It is one of the most important bamboo species in terms of its distribution,high economic and ecological values particularly in northeast India.It is the dominant forest bamboo in the hilly tracts of Cachar District with some cultivated stands in the homegardens of the local peoples(Nandy et al.2004).Knowledge of the mensurational properties of muli bamboo from this region is important for sustainable commercial utilization of this species.The physical characteristics and culm green weight relationship of muli bamboo based on different culm ages and diameter classes has not been reported.The present study was undertaken to investigate culm characteristicsof M.bacciferaby age class and to develop corresponding regression models.These regression models will be helpful for yield estimation of a stand without harvesting the culms. Our results can facilitate culm selection,yield estimation, and sustainable commercial utilization of the species.

Materials and methods

The Barak Valley region,the southern part of Assam,covers an area of 6922 sq.km.The region shares its border with Dima Hasao District and the state of Meghalaya to the north, the state of Manipur to the east,the state of Mizoram to the south and the state of Tripura and the Sylhet district of Bangladesh to the west(Roy and Bezbaruah 2002).Barak Valley consists of three districts(Cachar,Hailakandi and Karimganj)that support large natural stands of muli and isolated stands in homegardens(Nandy et al.2004).Forest vegetation of the district is categorized as Cachar tropical evergreen and semi-evergreen forest(Champion and Seth 1968).The presentstudy wasconducted in a privately owned forest stand at Innerline Reserve Forest(24°40.392′N and 92°45.292′E)of Cachar District.The muli stand selected for the present study was extensively managed with culm age ranges from current-year to four-year of age.The climate of the area issubtropicalwarm and humid with average rainfall of2300 mm,mostofwhich is received during the southwest monsoon season(May to September).Stand characteristics were studied in seven randomly located 5×5 m quadrats. The number of culms within the quadrat was recorded according to the age of the culms and culm density was calculated per hectare.Our study area was an extensively managed,homogenous stand with culm ages ranging from current-year to four-year old in ratios of 4:2:2:1:1 and culm size(circumference)ranges from 5–6 cm to 15–16 cm.

Tagging the bamboo culms every year for age determination isa time consuming and laboriousmethod.Moreover,itis very diff i cult to tag all the culms in forested areas.Culm age can be determined based on the colourofthe outline,status of the culm sheath,the outward appearance of culms,and the development of branches and leaves(Banik 2000).A brief summary of age determination is as follows:(1)A currentyear(6 month to 1 year)culm has culm-sheaths attached and the culm surface is covered with a clear white powder,only a few leaves are developed;(2)A 1 year(1-2 year)culm bears culm sheaths that are beginning to rot,white powder on the surface of the culm disappears gradually,and the culm turns lightgreen;(3)On a 2-year-old(2-3 year)culm,the sheath has begun to drop,and the culm bottom hasbeen invaded by mold and turnsdark green;(4)On a 3-year-old(3-4 year)culm,the sheath has disappeared from the surface ofthe culm,which is moldy and has become yellowish green in color;(5)On a 4-year-old(4-5 year)culm,the culm surface is coarse,covered with mold and moss,and turnsbrownish green.Pattanaik et al.(2004)suggested that the issue of diameter at breast height(DBH)measurement in bamboos needs some investigation.Therefore,the point 1.3 m above ground level where DBH is typically recorded can fall on different positions respectto internodesand on differentinternodenumbersofthe culm which can lead to false diametermeasurement.To avoid thisproblem,culm diameterwasmeasured atthemiddlepoint ofthe internode nearestorabove to the heightof1.3 or1.37 m from the ground.

The required data forthe present study was gathered from freshly harvested culms.After the selection of culms by age, girth of the culms was measured at the height of 1.3 m from theground and culmswere separated into 11 sizeclasses,viz. 5–6,6–7,7–8,8–9,9–10,10–11,11–12,12–13,13–14, 14–15,and 15–16 cm.Three culms were harvested fromeach available size class of each age class.Height of the culms,internode length and internode diameterfrom bottom to top were measured and the number of nodes in each culm wascounted.Each culm wascutinto three equalsectionsand the fresh weight was recorded separately using a digital scale.Culm wall thickness of the base and apex of each section ofthe culmswere measured using a verniercaliperto the nearest mm.Average culm wall thickness in all four directions and average diameter were calculated.The solid volume was determined for each section.

The solid volume of each section of the culms was calculated using the formula given by Tandug and Torres (1985),which is given below:

where:Vis the solid volume in cubic centimeter of the section,Bathe area in square centimeter at the large end of the section,Bhthe area in square centimeter at the large end of the hollow portion,bsthe area in square centimeter at the small end of the section,bhthe area in square centimeter at the small end of the hollow portion,andLis the length in centimeter of the section.

The total green weight was derived by summing the values obtained for each section.The total solid culm volume and culm green weight for each culm were determined and used in the f i tted regression model.

Statistical analyses were performed using Microsoft Excel (version 2010)and SPSS(version 19).Tukey’s test was used to identify signif i cantdifferencesbetween means(at5%level of signif i cance)of culm characteristics by culm age. Descriptive statistical analysis was performed for different parameters.Regression models were developed for each parameter.Culm circumference was converted into diameter and it was categorized into three classes,viz.small(diameterof 2–3 cm),intermediate(diameter of 3–4 cm)and large (diameter of 4–5 cm).Regression equations for internode length and internode diameter on internode number of each age class was developed according to the three diameter classes.Regression equations were also developed for the following relationships:(1)Culm height and culm DBH,(2) Culmgreen weightand culm DBH,(3)Culmsolid volume and culm DBH,and(4)Culmgreen weightand culmsolid volume.

Table 1 Descriptive statistics for the various parameters of different culm age classes

Fig.1 Scatter plot of the f i tted function for internode length(a,b,c,d and e are for current-,one-,two-,three-and four-year old culm respectively;a,b,and c represent for smaller,intermediate and higher diameter class respectively in each age class)

Results and discussion

Culm characteristics

Culm height ranged from 3.2 to 15.3 m with a mean of 9.15 m in three-year-old culms and highest culm height was recorded for four-year-old culms(Table 1).Mean culm height for the different age classes were similar.Number of internodes per culm ranged from 14 to 49 with a mean of 35.2 in 1-year-old culms.Krishnaswamy(1956)reported that bamboos vary considerably in size depending on the species,locality and vigour of the clump.Among our f i ve culm age classes,three-year-old culms had the highest mean internode length,internode diameter,total culm height and culm green weight whereas current-year culms had the lowest means for all parameters.Certain attributes,such as culm size and culm wall thickness inf l uence the range of potential culm usage(Wong 1982).Sattar et al.(1990) reported thatM.bacciferaandBambusa balcooaattain maturity with respect to bending strength at 3 years.

Internode length and internode number

Internode length ofculmsin the smalldiameterclass(DBHof 2–3 cm)increased from the basal part of the culm to the 7–10th internode(atheightsof2.30–2.91 mfromtheground), and then itdecreased gradually to the 18–23rd internode,after which a slight increase was noticed(Fig.1).Internode length ofculms in the intermediate diameterclass(DBH of3–4 cm) increased from the basal part of the culm to the 12–15th internode(at heights of 3.32–3.89 m from the ground),and then decreased gradually to the 31–37th internode,afterwhich a slightincrease wasagain recorded(Fig.1).Internode length of culms in the large diameter class(DBH of 4–5 cm) increased from the base of the culm to the 16–20th internode (at heights of 4.81–5.09 m from the ground),and thendecreased gradually to the 39–46th internode,after which a slight increase was again recorded(Fig.1).The relationship was best represented by a third order polynomial regression model in all diameter classes of each age class(Fig.1).

Fig.2 Scatter plot of the f i tted function for internode diameter(a,b,c,d and e are for current-,one-,two-,three-,and four-year old culm respectively;Y1,Y2and Y3are for internode diameter(cm)of smaller,intermediate and higher diameter class culm respectively)

Table 2 Regression of height(m)on diameter at breast height (DBH)(cm)of different culm age classes

Table 3 Regression of culm green weight(kg)on diameter at breast height(DBH)(cm)of different culm age classes

Internode length varied from base to top and this variation was specif i c to culm diameter class.The relationship between internode length and number of internodes was best represented by a third order polynomial regression model in three culm diameter classes of each culm age class.Shigematsu(1958)reported that internode length of bamboo is species specif i c but there is also intraspecif i c variation.

Internode diameter and internode number

Internode diameter was greatest at the f i rst internode and gradually declined towards the tip of the culm of the smaller and intermediate diameter class in all age classes (Fig.2).A slight increase in internode diameter was recorded in higher diameter class culms at the basal portion to the 12–15th internode,beyond which it gradually declined towards the tip of the culm(Fig.2).A second order polynomial regression model(Fig.2)accounted for 96.4–98.6,98.4–100 and 98.1–99.2%of the variation in smaller,intermediate and higher diameter class culms, respectively(Fig.2).For current-year culms:Model:

where,Y1,Y2,Y3internode diameter(cm);Xinternode number;aconstant;b1,b2regression coeff i cients.

The regression models for other culm age classes are given in Fig.2.Unlike internode length,which increased until a considerable height from ground level,internode diameter gradually decreased towards the tip of the culm in smaller and intermediate diameter class culms.Internode diameter varied from base to top of the culm and this variation was specif i c to culm diameter classes.Pattanaik et al.(2004)developed a third order polynomial regression model for internode diameter that yielded anR2value of 0.826.However,in this study the relationship between culm diameter and internode numbers is best represented by a second order polynomial regression model for all culm age classes(withR2values of 0.96–0.99,0.98–0.99 and 0.98–0.99 for small,intermediate and large diameter class culms,respectively,of all culm age classes).

Culm height and culm DBH

Mean culm heightwashighestforthree-yearold culms(with 9.15 m and maximum of 14.58 m),but four-year old culms had maximum mean culm height of 15.3 m(Table 1). Lowest mean culm height was recorded for current-year culms(8.37 m).The regressions developed for the f i ve age classes of height(HT)on DBH are shown in Table 2.Pattanaik et al.(2004)developed a third order polynomial regression for culm height as the best f i t with a correlation coeff i cientr=0.69(culm diameter was taken at the eighth internode).Watanabe and Ueda(1976)developed an exponential model for culm height of Japanese bambooPhyllostachys bambusoides.In our study the relationshipbetween culm height and DBH was best represented by a linear regression model and the model explained 79.7–93.3%of variability in the dependent variable.

Fig.3 Scatter plot of the f i tted function for culm volume(cm3) of f i ve different age classes of Muli bamboo(Y1,Y2,Y3,Y4andY5are for culm volume of current-,one-,two-,three-,and four-year old culms respectively;X=culm diameter)

Table 4 Regression equations of culm solid volume on culm green weight of different culm age classes

Culm green weight and culm DBH

Fig.4 Fitted regression lines of culm volume on culm green weight(a,b,c,d and e are for current-,one-,two-,three-,and four-year old culm respectively)

Culm green weight was highest in three-year-old culms (mean=5.42 kg/culm and maximum=12.87 kg/culm) and lowest in current-year culms(mean=3.66 kg/culm and maximum=7.61 kg/culm)(Table 1).Regression ofculm green weight on culm DBH is shown in Table 3.All regression equations and intercepts of culm green weight were signif i cant atp＜0.01.DBH was highly correlated (r=0.93–0.98)with total culm green weight within culm age classes.A linear regression model best f i tted culm green weight and was highly signif i cant(p＜0.01).The model accounted for 87.1–96.8%of the variation in the dependent variable.

Culm volume and culm DBH

Mean culm volume was highest in one-year old culms (6533.93 cm3/culm)followed by three-year(6438.62 cm3/ culm),four-year(6222.43 cm3/culm),two-year(5903.35 cm3/ culm)and current-year-old culms(5735.65 cm3/culm) (Table 1).For f i ve age classes of muli bamboo the regression equationsdeveloped between culm volume and culm DBHare presented in Fig.3.Athird orderpolynomialregression model wasf i tted forcurrent-,two-and three-yearold culms,whereasa second order polynomial regression model best f i tted the oneand three-year old culms(Fig.3).The models accounted for 94.6-98.4%of the variation in the dependent variable.

Culm green weight and culm volume

The highest coeff i cient of determination(R2=99.2%) was obtained for three-year old culms followed by fouryear(R2=98.8%),two-year(R2=97.2%),one-year (R2=97.2%)and current-year culms(R2=92.4%) (Table 4).The regression results shown in Table 4 indicate a highly positive linear relationship between culm volume and culm green weight for all culm age classes.The f i tted regression lines are shown in Fig.4.Tandug and Torres (1985)and Mohamed et al.(1991)suggested that this type of information could be applied in determining the pulp yield of bamboos for paper manufacture.

Conclusions

M.bacciferahas high economic value and therefore,culm characteristics studied forf i ve differentculm age classes can help in culm selection proceduresforbetter utilization of the species.Lower green weight and solid volume in currentyear culms ref l ects their unsuitability for diverse uses.Age specif i c regression models for culm DBH on culm green weight and culm solid volume will guide researchers,forest departments and resource managers in sustainable stand management and accurate yield prediction of the species.

AcknowledgmentsSenior author is grateful to Mohan,Appu and Mukta for their help during the f i eld study.Financial assistance from University Grants Commission,New Delhi is acknowledged.We thank two anonymousreviewersfortheircommentsto improve the manuscript.

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2 September 2014/Accepted:16 April 2015/Published online:14 July 2015

Project funding:This study was f i nancially supported by University Grants Commission,New Delhi.

The online version is available at http://www.springerlink.com

Corresponding editor:Hu Yanbo

?Arun Jyoti Nath

arunjyotinath@gmail.com

1Department of Ecology and Environmental Science,Assam University,Silchar 788011,India