Compatible volume and taper models for economically important tree species of Turkey Özçelik, John Brooks
To cite this version:
Özçelik, John Brooks. Compatible volume and taper models for economically important tree species of Turkey. Annals of Forest Science, Springer Nature (since 2011)/EDP Science (until 2010), 2012, 69 (1), pp.105-118. 10.1007/s13595-011-0137-4. hal-00930708
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ORIGINAL PAPER
Compatible volume and taper models for economically important tree species of Turkey
Ramazan Özçelik & John R. Brooks
Received: 27 June 2011 /Accepted: 9 September 2011 /Published online: 7 October 2011 # INRA and Springer-Verlag, France 2011
Abstract • Conclusion Based on our results, the taper equation of • Introduction The accurate estimation of stem taper and Clark et al. (1991) is recommended for estimating diameter at volume are crucial for the efficient management of the a specific height, height to a specific diameter, merchantable forest resources. Compatible segmented polynomial taper volume, and total volume for the species considered. and volume equations were developed for Brutian pine (Pinus brutia Ten.), Lebanon cedar (Cedrus libani A. Keywords Segmented models . Form-class profile . Taper . Rich.), Cilicica fir (Abies cilicica Carr.), Scots pine (Pinus Volume . Turkey sylvestris L.), and Black pine (Pinus nigra Arnold.). • Methods In this study, the Clark et al. (USDA For Serv Res Pap SE-282, 1991) segmented taper model was 1 Introduction selected as this model is one of the most tested segmented models and has frequently been well ranked for its excellent Brutian pine (Pinus brutia Ten.), Scots pine (Pinus sylvestris performance. The data for each species were divided into L.), Lebanon cedar (Cedrus libani A. Rich.), Cilicica fir two sets: the majority (about 75%) was used to estimate (Abies cilicica Carr.), and Black pine (Pinus nigra Arnold.) model parameters, and the remaining data (about 25%) are major commercial tree species in Turkey. There are were reserved to validate the models. The performance of nearly 11.64 million ha of commercial Brutian pine (about the models was compared and evaluated by average bias, 5.4 million ha), Scots pine (1.24 million ha), Lebanon cedar standard error of the estimate (SEE), and a fit index (FI). (about 0.5 million ha), Cilicica fir (about 0.3 million ha), and • Results The proposed model generally performed better Black pine (4.2 million ha) forest in Turkey, accounting for than the other equations for the whole tree as well as for almost half of the total forest land with a current standing sections within the tree, based on the ten relative height volume of approximately 750 million m3 (Anonymous classes examined. In addition, tree bole volume estimates 2006). These tree species are an important source of raw were compared to other established tree bole volume material for the forest products industry in Turkey. estimation techniques. With ever-changing market conditions, there is a need to accurately estimate tree volumes to different upper stem Handling Editor: Barry Alan Gardiner merchantability limits. This is not currently possible with Contribution of the co-authors Dr. John Brooks, contributed to selection the existing local volume tables for these five species. One of methods, evaluation of results, and response to comments of reviewers. of the most accurate approaches to estimating upper stem R. Özçelik (*) diameter and volume to any merchantability limit is Faculty of Forestry, Süleyman Demirel University, through the use of compatible volume and taper models East Campus, (Kozak 2004; Jiang et al. 2005). Although merchantable 32260 Isparta, Turkey e-mail: [email protected] volume equations developed from volume-ratio equations are very easy to use and develop, those obtained from taper J. R. Brooks functions are generally preferred probably because they also Forest Biometrics, Division of Forestry and Natural Resources, allow estimation of diameter at a given height (Dieguez-Aranda West Virginia University, 322 Percival Hall, et al. 2006). As reported by Li and Weiskittel (2010); the Morgantown, WV 26506-6125, USA advantage of estimating volume through taper equations over 106 R. Özçelik, J.R. Brooks existing volume tables lies in the ability of taper equations to develop a segment stem taper model based on form-class accurate predict total height (th) diameter over bark (dob) or segmented taper model presented by Clark et al. (1991). diameter inside bark (dib) at any given height of individual Several studies have compared some of the more commonly trees, hence allowing the acquisition of merchantable volume employed taper models. For example, Clark et al. (1991)found information to any desired specification. that their form-class profile model was superior to the Max Numerous tree taper models of various forms and complex- and Burkhart (1976) model, the Cao et al. (1980) model, and ity have been published (Max and Burkhart 1976; Kozak 1988; Schlaegel’s(1983) form class model. Figueiredo-Filho et al. Thomas and Parresol 1991; Newnham 1992;Fangetal.2000; (1996) evaluated five taper models for estimating diameters Lee et al. 2003) indicating the importance of the subject in along the stem for predicting merchantable or total volume. forest management and at least two approaches are used with Most of the statistics indicated that the segmented form-class success today. One expresses variable form as a single model of Clark et al. (1991) performed best for describing the continuous polynomial. The other expresses variable form stem profile and predicting stem volume in their study. Li and utilizing a segmented polynomial in such a way that bole is Weiskittel (2010) compared ten widely used stem taper divided into segments which are then joined at inflection profile models for predicting both diameter and total stem points between segments (Fang and Bailey 1999). volume in the Acadian Region of North America. They found Taper systems do not have widespread use in Turkey and that the segmented taper equation of Clark et al. (1991) different standard volume equations developed (Alemdağ provided the best predictions across all species when upper 1962, 1967;Evcimen1963;Gulen1959) over five decades stem diameter measurements were available for stem volume. ago are still the most common tool used for estimating the The objective of this research was to develop a volume of the five tree species described in this paper. Several compatible volume system based on the Clark et al. studies have been carried out to test the suitability of different (1991) taper model form that accurately describes the stem taper models for describing the stem profile and predicting profile throughout the main bole and provides accurate stem volume of different tree species at the regional level in estimates of the tree volume to any upper stem merchant- Turkey (Yavuz and Saraçoğlu 1999;Sakıcı et al. 2008;Brooks ability limit for five commercially important tree species in et al. 2008). However, additional work is needed in this area Turkey. We evaluated a widely recognized, reliable, and to refine volume estimation. As reported by Kozak and Smith flexible taper model form published by Max and Burkhart (1993): a well behaved taper equation should not only give (1976). In addition, total tree volume estimates, based on unbiased estimates of dib or dob with minimum variance, but the proposed models, were compared to existing total stem also have flexibility to adapt to a wide variety of species and volume tables and the combined variable equation of Spurr give accurate predictions of stem volume. Therefore, it is (1952) which was fit to the same data. necessary and beneficial to further study the characteristics of taper equations and extend their use to other species besides the ones for which they were originally developed. 2 Materials and methods Ideally, a volume estimation system should be compatible, i.e., the volume of the tree bole is obtained through the In total 248 Brutian pine, 124 Lebanon cedar, 196 Cilicica fir, integration of the taper model from the ground to the top of the and 162 Black pine were felled in even-aged forest areas of bole and should be equal to the actual stem volume Isparta Forest Region and 95 Scots pine were felled in even- (Demaerschalk 1972;Clutter1980). A total volume equation aged forest areas of Erzurum Forest Regions in Turkey, on is very easy to use and is therefore preferred when land owned by The Turkish Forest Service. Sample trees were classification of the products by merchantable size is not selected to ensure a representative distribution from both the required. In comparison with single and segmented taper dominant and co-dominant crown classes across a range of models, a variable-form taper model usually provides the height and diameter classes in even-aged sawn-timber stands. lowest degree of local bias and the greatest precision in taper Trees possessing multiple stems, broken tops, obvious cankers predictions (Kozak 1988;Newnham1992; Sharma and or crooked boles were not included in the sample. Trees were Zhang 2004). However, the disadvantages of variable-form felled and total height was measured to the nearest 0.03 m. taper models are that they cannot be integrated analytically to Diameter over bark (dob) at breast height (1.3 m) was calculate total stem or log volume and merchantable height measured and recorded to the nearest 0.25 cm. Diameter over for a given top diameter; it must be obtained by iteration bark was also measured at 0.3, 2.3 m and then at intervals of (Kozak and Smith 1993). 1 m along the remainder of the stem. In each section, two Jiang et al. (2005) reported that segmented polynomial perpendicular diameters over bark were measured and then models appear to be more accurate than other model arithmetically averaged. Actual volumes and section volumes formulations for estimating diameter, height, and volume in cubic meters were calculated using the overlapping bolts estimation. In this study, we used this second approach to method as described by Bailey (1995). Tree volume and taper models in Turkey 107
The scatter plot of relative diameter against relative of sample trees were selected at random and used as the height was examined visually for each species to detect validation data set, while the rest were used for model possible anomalies in data. Extreme data points were fitting. All trees with total height less than 5.3 m were observed in all species, therefore the systematic approach, eliminated because they could not be used to fit the Clark et proposed by Bi (2000) for detecting abnormal data points al. (1991) model. Summary statistics for the both data sets was applied to increase the efficiency of the process. This are shown in Tables 1 and 2. involved local quadratic fitting with a smoothing parameter The following notation will be used hereafter. Other of 0.25 for all species, which was selected after iterative definitions specific to a particular equation will be listed fitting and visual examination of the smoothed taper curves with the equation: overlaid on the data. Using this approach, the number of extreme values accounted for less than 0.2% of data for all D is diameter at breast height (1.3 m species. The plots of relative height against relative above ground) over bark (cm) diameter used for this study, together with the loess d is diameter over bark (dob) at height h (cm) regression line, are shown in Fig. 1. Approximately 25% H is total tree height (m)
Fig. 1 Plot of relative height 1.6 1.6 versus relative diameter over Brutian pine Black pine bark for each species studied 1.4 1.4 1.2 1.2 1.0 1.0 0.8 0.8 d/D d/D 0.6 0.6 0.4 0.4 0.2 0.2 0.0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 h/H h/H
1.4 1.4 Lebanon cedar Cilicica fir 1.2 1.2
1.0 1.0
0.8 0.8 d/D 0.6 d/D 0.6
0.4 0.4
0.2 0.2
0.0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 h/H h/H
1.2 1.1 Scots pine 1.0 0.9 0.8 0.7 0.6 d/D 0.5 0.4 0.3 0.2 0.1 0.0 0.0 0.2 0.4 0.6 0.8 1.0 h/H 108 R. Özçelik, J.R. Brooks
Table 1 Model fitting data summary statistics 2.1 Taper and volume equations Species Mean SD Minimum Maximum Clark et al. (1991) developed a form-class segmented Brutian Pine (n=183 trees) profile model combining the better attributes of Schlaegel’s DBH (cm) 38.19 13.20 12.00 75.00 and Max and Burkhart’s models. Total height (m) 18.48 4.80 6.50 26.50 (1) Butt section, from stump to 1.3 m Disk dob (cm) 23.27 13.54 1.00 79.00 (2) Lower stem, from 1.3 m to 5.3 m Disk height (m) 8.95 5.94 0.30 26.30 (3) Middle stem, from 5.3 m to 40–70% of total height Lebanon cedar (n=95 trees) (4) Upper stem, from 40% to 70% of total height to the tip DBH (cm) 31.32 7.08 14.00 62.00 of the tree Total height (m) 15.67 3.35 7.80 25.90 Disk dob (cm) 19.18 16.45 3.00 64.00 A Schlaegel-type equation is used to estimate diameter Disk height (m) 8.14 5.17 0.30 25.30 in the butt, a Schlaegel form-class equation is used in the Cilicica fir (n=153 trees) lower stem, while an equation of the Max and Burkhart DBH (cm) 34.50 12.35 14.00 70.00 type is used for the other sections. Total height (m) 15.82 19.24 7.60 27.30 The Clark et al. (1991) taper function has the following form: 8 hi9 r r 0:5 > 2 ðcþe=D3Þðð1 h=HÞ ð1 1:30=HÞ Þ > Disk dob (cm) 20.44 19.24 1.00 74.00 > I D ð1 þ r þ > <> S hi1 ð1 1:30=HÞ => p p Disk height (m) 8.35 5.52 0.30 26.30 ¼ 2 ðD2 F2Þðð1 1:30=HÞ ð1 h=HÞ Þ þ ð Þ d IB D ð : = Þp ð : = Þp 1 Scots Pine (n=76 trees) > hi 1 1 30 H 1 5 30 H > :> : 2 : 2 ;> I F2 b h 5 30 1 þ I 1 b a h 5 30 DBH (cm) 28.88 7.74 15.00 44.00 T H 5:30 M a2 H 5:30 Total height (m) 17.04 3.80 9.80 25.00 Disk dob (cm) 17.80 14.62 3.00 46.00 Table 2 Model validation data summary statistics Disk height (m) 8.64 5.51 0.30 24.30 Black pine (n=121 trees) Species Mean SD Minimum Maximum DBH (cm) 33.93 13.07 14.00 66.00 Brutian Pine (n=65 trees) Total height (m) 19.58 4.40 9.00 29.00 DBH (cm) 39.96 14.49 14.00 71.00 Disk dob (cm) 22.42 12.65 2.00 68.00 Total height (m) 18.52 4.35 7.50 26.70 Disk height (m) 9.23 6.02 0.30 27.30 Disk dob (cm) 24.32 14.58 1.00 75.00 Disk height (m) 8.95 5.82 0.30 25.30 Lebanon cedar (n=29 trees) DBH (cm) 31.25 6.32 21.00 46.00 h is height above the ground to the Total height (m) 15.92 3.36 9.60 23.70 measurement point (m) Disk dob (cm) 19.19 16.30 3.00 50.00 V is total stem volume over bark from Disk height (m) 8.24 5.23 0.30 23.30 3 stump (m ) Cilicica fir (n=43 trees) r, c, e are regression coefficients for heights DBH (cm) 36.83 14.63 15.00 73.00 below 1.3 m Total height (m) 16.27 5.05 8.00 26.00 p is regression coefficient for heights Disk dob (cm) 21.74 21.00 1.00 76.00 between 1.3 m and 5.3 m Disk height (m) 8.74 5.85 0.30 25.30 a and b are regression coefficients for heights Scots pine (n=21 trees) above 5.3 m DBH (cm) 30.64 6.49 18.00 43.50 F is diameter over bark (dob) at 5.3 m Total height (m) 16.82 3.46 11.80 22.20 above ground (cm) Disk dob (cm) 17.36 14.30 3.00 43.00 β −β 1 4 are coefficients to be estimated Disk height (m) 8.47 5.35 0.30 21.30 π k is equal to /40,000, a metric constant Black pine (n=41 trees) for converting from diameter squared DBH (cm) 31.80 11.06 13.00 54.00 in square centimeters to cross-sectional Total height (m) 19.32 4.89 9.50 27.20 area in square meters Disk dob (cm) 20.82 11.18 2.00 59.00 a , a are regression coefficients 0 1 Disk height (m) 9.20 6.12 0.30 26.30 b1, b2 are regression coefficients Tree volume and taper models in Turkey 109
The volume equation, derived through integration of the Clark et al. (1991) taper equation, is of the form:
8 hi9 r r > 2 Wðð1 L1=HÞ ðH L1Þ ð1 U1=HÞ ðH U1ÞÞ > > I1D ð1 GWÞðU1 L1Þþ > > hiðrþ1Þ > > ðð = Þpð Þ ð = Þpð ÞÞ > > þI I TðU L ÞþZ 1 L2 H H L2 1 U2 H H U2 > > 2 3 2 2 2 ðpþ1Þ 3 > > ðð : Þ2 ð : Þ2Þ > < bðU L Þ b U3 5 30 L3 5 30 = ¼ 6 3 3 ðH 5:30Þ 7 ð Þ V k 6 = ðð : Þ3 ð : Þ3Þ 7 2 > þ b 3 U3 5 30 L3 5 30 > > 6 2 7 > > þ 26 ðH 5:30Þ 7 > > I4F 6 ð = Þð = 2Þð ð : Þ ð : ÞÞ3 7 > > 6 þ I5 1 3 1 b a a H 5 30 L3 5 30 7 > > ð : Þ2 > > 4 H 5 30 5 > > ð = Þð = 2Þð ð : Þ ð : ÞÞ3 > : I6 1 3 1 b a a H 5 30 U3 5 30 ; ðH 5:30Þ2