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All Journal MANAJEMEN HUTAN TROPIKA Journal of Tropical Forest Management
M Muhdin
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Agriculture, Biological Sciences & Forestry

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Analisis Beberapa Rumus Penduga Volume Log: Studi Kasus pada Jenis Meranti (Shorea spp.) di Areal HPH PT Siak Raya Timber, Propinsi Riau M Muhdin
Jurnal Manajemen Hutan Tropika Vol. 5 No. 2 (1999)
Publisher : Institut Pertanian Bogor (IPB University)

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Abstract

Determining the stem volume of a tree, both a standing or felled tree, has long been a chronic problem for foresters, whereas, the need for an accurate estimate of wood volume is becoming more important. The use of Brereton’s formula in Indonesia, nowadays, was based solely on practical consideration in obtaining the data which comprise diameter of the large and small ends of logs; and logs length. However, the relative accuracy of this formula in comparison with other formulae still needs to be tested.  The result of this study by using 499 logs in PT Siak Raya Timber (Riau Province) showed that Centroid and Newton’s formulae have the best performance (seen from bias, accuracy and precision) for estimating the log volume of meranti in Sumatera. Bias of both formulae is around zero and very small, therefore it could be neglected. Huber’s formula tends to underestimate the volume, but it has still better performance than Brereton’s, Smalian’s and Bruce’s formulae. Brereton’s and Smalian’s formulae tend to overestimate the volume, whereas Bruce’s formula tends to underestimate. Deviation of errors for Brereton’s is consistently smaller than Smalian’s, and for Bruce’s is the largest one. But, precision for Brereton’s, Smalian’s and Bruce’s formulae are nearly the same.
Determining the stem volume of a tree M Muhdin
Jurnal Manajemen Hutan Tropika Vol. 9 No. 1 (2003)
Publisher : Institut Pertanian Bogor (IPB University)

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Abstract

Determining the stem volume of a tree has long been a problem for foresters, whereas, the need for an accurate estimate of wood volume is becoming more important. six volume equations were used and compared, for both constructing and validating models using data collected from Gmelina arborea Roxb. in the area P.T. Wanaksita Nusantara, Province of Jambi, Indonesia. The best equation obtained from model construction (fitting) step for a data may not necessarily be the best performance (shown from bias, precision and accuracy) for another data set though collected from the same population. For testing the occuracy of model, model validation is an important step in model construction process in order to get the best tree volume equation.
Penentuan Jumlah Pohon Contoh Minimal untuk Penyusunan Persamaan Volume Melalui Fungsi Taper: Studi Kasus pada Jenis Pinus Merkusii Jungh Et De Vriese di Hutan Pendidikan Gunung Walat, Sukabumi, Jawa Barat M Muhdin; Arif Rakhman Hakim
Jurnal Manajemen Hutan Tropika Vol. 10 No. 2 (2004)
Publisher : Institut Pertanian Bogor (IPB University)

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Abstract

The study departs from the fact that the most difficult activity in constructing tree volume table is measurement of diameter and length of section of standing sample trees. Besides, the number of sample trees to represent the population is also another problem. This study examines the construction of the volume equation through taper function by reducing the quantity of sample trees. Validation was also conducted for testing the accuracy of such volume equation. The study found that the best taper function was the third order polynomial model i.e., d/D=f{(h/H),(h/H)2,(h/H)3. The volume equation, constructed using only three sample trees by such taper function (V=0.3573337D2H), has almost the same good performance to equivalent the best model (V=6.14 10-5D1.8249H1.0342), that was constructed using 30 sample tree.Key words: taper function, tree volume equation, validation, accuracy, precision
Penggunaan Analisis Regresi Terboboti dalam Penyusunan Model Pertumbuhan Peninggi Acacia mangium Willd. M Muhdin; Endang Suhendang
Jurnal Manajemen Hutan Tropika Vol. 15 No. 1 (2009)
Publisher : Institut Pertanian Bogor (IPB University)

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Abstract

The compilation of growth stand model usually uses the regression analysis. Homoscedasticity or residual kind homogeneity is one assumption which underlying the use of this regression analysis.  Breaking this assumption causes the low of model accuracy which is shown by the low of determination coefficient and the height of error standard. The problem of heteroscedasticity can be solved by using weighted regression analysis.The Selected Raiser Growth Model equation in this research was transformed into a model equation: ln P = a + b/A, where there was a significant correlation between the growth and the age (R2  = 55.04%, sb0 = 0.041, and sb1 = 0.171).  From the use of weighted regression analysis with weightier wi = 1/”Xi, it can be concluded that there was no real correlation between the growth and the age (R2 = 0.55%, sb0 = 0.572, and sb1 = 2.560).  The use of weightier shows much lower accuracy than without weightier.  However, from the use of weighted regression analysis with weightier: wi = 1/si2, where si2 = residual kinds at free variable group to I (X1) shows that there was significant correlation between the growth and the age (R2 = 45.46%; sb0 = 0.084, and sb1 = 0.205).  There fore it can be said that the accuracy was much better than regression without weightier.  Furthermore,  the use of weighted regression analysis with weightier wi = 1/si2, where  si2 is residual kind at free variable to i (X) which is estimated through second orde polynomial regression model shows a very significant correlation between the growth and the age (where R2 = 87.22%, sb0 = 0.029, and sb1 = 0.072). The last result shows a better accuracy than the preceding treatments.  From this research, it can be concluded that by using a suitable weightier, the use of weighted regression analysis in compiling raiser growth model can improve the model accuracy.
Co-Authors Arif Rakhman Hakim Endang Suhendang