Axial variation of color and shore d hardness in cedrus libani wood Uğur Özkan, Burak Koparan, Onur Alkan, Nazlı Öğüt, Şerife Kalkanlı, Candan Kuş Şahin Maderas Ciencia Y Tecnologia, 2026 This study examines the limited understanding of axial variation in color and hardness properties of Cedrus libani wood. In this context, the variation in color parameters and Shore D hardness across heart, heartwood, and sapwood sections was systematically investigated. Wood disc samples obtained from different axial positions of a 102-year-old tree were used to evaluate color properties, including lightness (L*), redness (a*), and yellowness (b*), together with hardness values. A total of 480 measurements were conducted across the three anatomical sections. The results demonstrated that both color and hardness properties vary systematically along the axial direction of the tree. Sapwood exhibited higher lightness values, whereas heart and heartwood showed comparatively lower L* values. Redness was more pronounced in heartwood and heart sections, while yellowness values were relatively similar across sections, with slightly higher values observed in the heart. In terms of mechanical properties, Shore D hardness increased from sapwood toward the center of the tree, reaching its maximum in the heart section. Additionally, axial differences were evident, with upper sections displaying higher hardness values compared to lower sections. These findings provide new insights into the axial variation of physical and mechanical properties in Cedrus libani wood, contributing to a better understanding of its material behavior. This knowledge is important for optimizing utilization strategies and improving performance-based classification of wood depending on its position within the tree.
Characterizing diameter distribution of Pinus nigra stands in Türkiye with a Weibull distribution Onur Alkan, Quang V. Cao, Ramazan Özçelik Canadian Journal of Forest Research, 2025 The objective of this study was to identify the most effective system for predicting parameters of the Weibull function that characterize diameter distributions of black pine ( Pinus nigra Arn.) stands in Türkiye. We examined three Parameter Recovery methods: the Moment Recovery method, based on diameter moments (diameter variance and quadratic mean diameter), the Percentile Recovery method, relying on diameter percentiles (the 31st and 63rd percentiles), and the Hybrid method, which combines elements of both approaches. Within each of the three methods, we derived regression coefficients from four estimation approaches: Seemingly Unrelated Regression (SUR), Cumulative Distribution Function Regression (CDFR), Maximum Likelihood Estimator Regression (MLER), and Stand Table Regression (STR). Our findings demonstrated that the Moment Recovery method exhibited superior performance compared to the Percentile Recovery and Hybrid methods. Additionally, the MLER approach surpassed the other three estimation techniques. Notably, the Moment Recovery method, coupled with regression coefficients estimated through MLER, emerged as the top-performing combination overall. These results hold significant implications for the development of a diameter distribution growth and yield model tailored to black pine stands in Türkiye.
Stem Profile Patterns of Pinus nigra and Pinus sylvestris Growing in Mixed Stands Ramazan Özçelik, Krishna P Poudel, Felipe Crecente-Campo, Bora Kaya, Onur Alkan Forest Science, 2023 Taper equations provide one of the most successful approaches of calculating tree volume to specified top diameters from standing tree measurements. This study assessed the stem profile patterns of Black pine (Pinus nigra Arnold.) and Scots pine (Pinus sylvestris L.) trees growing in mixed stands in northwestern Türkiye using a segmented polynomial taper equation. Models were fitted with the continuous second-order autoregressive structure to correct for the autocorrelation. The models fit the data well, describing more than 99%, 98%, and 97% of variation in diameter, merchantable volume, and total stem volume, respectively. However, the prediction errors were slightly larger for black pine than for Scots pine. Results also revealed that the model coefficients for these species were significantly different. Models developed in this study should provide more accurate upper stem diameter and volume estimates when the objective is to estimate such attributes for black pine and Scots pine growing in the mixed stands. Study Implications: Estimates of total and merchantable tree volume in a stand are essential for forest management and planning. Taper models are one of the most accurate approaches to estimating upper stem diameters and volume to any merchantability limit. There has been an increasing interest in managing mixed-species stands but limited work has been done on taper equations for trees growing in mixed stands. This study assessed the stem profile patterns of black pine and Scots pine trees growing in mixed-species stands in northwestern Türkiye. As has been reported for pure stands, species-specific taper equations were more accurate upper stem diameter and volume estimations in mixed-species stands. The developed taper models should play an important role in planning and inventorying mixed Black pine and Scots pine stands in Türkiye.
Artificial intelligence as an alternative modelling strategy for reliable height-diameter predictions of mixed-oaks species MARIA J. DIAMANTOPOULOU, RAMAZAN ÖZÇELİK, BURAK KOPARAN, ONUR ALKAN Turkish Journal of Agriculture and Forestry, 2023 Forest management and sustainable timber production rely on forest measurements that include tree height. However, the fieldwork needed for tree height measurements is time-consuming, and several times, hard to obtain. The solution to this problem is the construction of reliable height-diameter (h-d) models that can provide accurate tree height predictions. To this direction, a modified Gompertz model that included dominant height and diameter at breast height was used to predict tree height. In order to investigate the most promising modelling method, six alternative approaches were evaluated; these involved both regression and artificial intelligence techniques and produced the (i) fixed-effects (FE), (ii) mixed-effects (ME), (iii) three-quantile regression (3QR), (iv) five-quantile regression (5QR), (v) general regression neural network (GRNN), and (vi) support vector regression (SVR) models. The accuracy of the developed h-d models was studied in this work for mixed-oak stands (Quercus cerris L., Quercus petraea (Matt.) Liebl. and Quercus frainetto Ten.) in Türkiye. For this purpose, 1735 trees were measured in 52 sample plots in total. The tree variability among sampling plots was incorporated in the constructed models through the dominant heights and the tree height variance in each sample plot, while the models were localized using one to five oak trees, as calibration samples, per plot. The study showed that the ME constructed model with root mean square value equal to 1.8331 was constantly superior to nonlinear regression methods used, while the GRNN and the SVR models with root mean square values equal to 1.8330 and 1.8279, respectively, showed similar predictive ability with the later to prevail, as compared to the rest of the models tested. Finally, five trees per plot were found to be an acceptable trade-off between sampling cost and predictive capacity and reliability.
Fitting and calibrating a mixed-effects segmented taper model for brutian pine Ramazan Özçelik, Onur Alkan Cerne, 2020 Taper models are one of several necessary tools in modern forest inventory, giving information on diameter at any point along the tree stem and this information can also be used to estimate stem volume. In this study, we used nonlinear mixed-effects (NLME) modeling approach to minimize existing statistical problems in constructing taper equations. A segmented taper model of Max and Burkhart (1976) was fitted using this approach to consider for withinand between-tree variation in brutian pine (Pinus brutia Ten.) stem taper. Based on evaluation statistics, the model including random-effects parameters β1, β3 and β4 were found to be the best. Inclusion of random parameters were not completely eliminated heterogenous variance and autocorrelation in residuals. Incorporating variance function and a continuous autoregressive error structure (CAR(1)) to NLME Max and Burkhart model removed the heteroscedasticity and autocorrelation in residuals. Upper stem diameters were used to localized stem taper model to individual tree. For this, two different measurement scenarios were evaluated as one and two upper stem diameter measurements. Inclusion of random parameters were improved the predictive capability of taper model in particularly the middle and lower sections of stem based on upper stem diameter measurements. The calibration using upper stem diameter measurements can improve the tree-level accuracy of stem taper model is therefore recommended. 1Isparta University of Applied Sciences, Faculty of Forestry, 32260, Isparta, Turkey, ORCID: 0000-0003-2132-2589a, 0000-0001-5798-3421b
RECENT SCHOLAR PUBLICATIONS
Axial variation of color and Shore D hardness in Cedrus libani wood U Özkan, B Koparan, O Alkan, N Öğüt, Ş Kalkanlı, CK Şahin Maderas: Ciencia y tecnología 28, 3 , 2026 2026
Dip çaptan göğüs çapının tahmini: Bilecik yöresi karışık meşe meşcereleri B Koparan, L Ertaş, O Alkan, R Ozçelik Turkish Journal of Forestry 26 (4), 475-485 , 2025 2025
Evaluating optimal percentile pairs for a Weibull-based diameter distribution in European black pine stands O Alkan Dendrochronologia 91, 126341 , 2025 2025 Citations: 1
Estimation of diameter at breast height from stump diameter: Mixed oak stands in Bilecik region B Koparan, R Ozçelik, O Alkan, L Ertaş Turkish Journal of Forestry 26 (4), 475-485 , 2025 2025
Doğal karaçam meşcereleri için yöresel karışık etkili çap-boy modellerinin geliştirilmesi O Alkan, R Ozçelik Turkish Journal of Forestry 25 (4), 399-407 , 2024 2024
Tek ağaçta göğüs çap artımının periyot süresi, yaş sınıfı ve sosyal sınıfına göre değişimi: Sarıkamış yöresi sarıçam meşcereleri örneği B Koparan, O Alkan, S Carus, Y Çatal, R Ozçelik Turkish Journal of Forestry 25 (4), 437-446 , 2024 2024 Citations: 3
Characterizing diameter distribution of Pinus nigra stands in Türkiye with a Weibull distribution O Alkan, QV Cao, R Özçelik Canadian Journal of Forest Research 55, 1-12 , 2024 2024 Citations: 2
Variation of diameter at breast height increment values of single tree by planning period, age class, and social class: Study case of Scots pine stands from Sarıkamış region R Ozçelik, Y Çatal, S Carus, O Alkan, B Koparan Turkish Journal of Forestry 25 (4), 437-446 , 2024 2024
Development of regional mixed-effects height–diameter models for natural black pine stands R Ozçelik, O Alkan Turkish Journal of Forestry 25 (4), 399-407 , 2024 2024
Almus yöresi doğal doğu kayını meşcerelerinin çap dağılımının Weibull dağılımı ile modellenmesi O Alkan, R Ozçelik, Ş Kalkanlı Turkish Journal of Forestry 24 (3), 197-207 , 2023 2023 Citations: 1
Stem Profile Patterns of Pinus nigra and Pinus sylvestris Growing in Mixed Stands R Özçelik, KP Poudel, F Crecente-Campo, B Kaya, O Alkan Forest Science 69 (6), 610-618 , 2023 2023 Citations: 4
Kızılçam (Pinus brutia Ten.) meşcerelerinde uygulanan ilk aralama çalışmalarının değerlendirilmesi: Sütçüler örneği E Bayar, O Alkan Turkish Journal of Forestry 24 (1), 11-17 , 2023 2023 Citations: 1
Evaluation of first thinning in brutian pine (Pinus brutia Ten.) stands: A case study in Sütçüler O Alkan, E Bayar Turkish Journal of Forestry 24 (1), 11-17 , 2023 2023
Modeling diameter distribution of natural oriental beech stands in the Almus region using the Weibull distribution O Alkan, R Ozçelik, Ş Kalkanlı Turkish Journal of Forestry 24 (3), 197-207 , 2023 2023 Citations: 1
Artificial intelligence as an alternative modelling strategy for reliable height-diameter predictions of mixed-oaks species MJ Diamantopoulou, R Özçelik, B Koparan, O Alkan Turkish Journal of Agriculture and Forestry 47 (2), 228-241 , 2023 2023 Citations: 16
Height-diameter model for natural black pine stands in eğirdir region: quantile regression approach. O Alkan, R Ozçelik 2022
Eğirdir yöresi doğal karaçam meşcereleri için çap-boy modeli: Kantil regresyon yaklaşımı O ALKAN, R ÖZÇELİK Turkish Journal of Forestry 23 (3), 187-195 , 2022 2022 Citations: 1
Antalya-Gebiz Yöresi Kızılçam Meşcereleri için Uyumlu Gövde Hacmi ve Gövde Çapı Modelleri M TURGUT, R ÖZÇELİK, O ALKAN Bartın Orman Fakültesi Dergisi 24 (2), 289-303 , 2022 2022
Compatible stem volume and stem diameter equations for Brutian pine stands in Antalya-Gebiz region. M Turgut, R Özçelik, O Alkan 2022
Estimating the tree bole volume of Brutian pine (Pinus brutia Ten.) and Taurus cedar (Cedrus libani A. Rich.) using paracone and centroid methods in Turkey R ÖZÇELİK, O ALKAN Journal of Biometry Studies 1 (2), 45-48 , 2021 2021
MOST CITED SCHOLAR PUBLICATIONS
Stem taper equations for diameter and volume predictions of Abies cilicica Carr. in the Taurus Mountains, Turkey O Alkan, R Özçelik Journal of Mountain Science 17 (12), 3054-3069 , 2020 2020.0 Citations: 18
Artificial intelligence as an alternative modelling strategy for reliable height-diameter predictions of mixed-oaks species MJ Diamantopoulou, R Özçelik, B Koparan, O Alkan Turkish Journal of Agriculture and Forestry 47 (2), 228-241 , 2023 2023.0 Citations: 16
Mapping forest stand structural diversity using Rapideye satellite data I Ozdemir, K Ozkan, A Mert, UY Ozkan, O Senturk, O Alkan Recuperado de Recuperado de http://congrexprojects. com/docs/12c04_docs2 … , 2012 2012.0 Citations: 12
Toros göknarı için uyumlu hacim ve gövde çapı modelleri O Alkan, R Ozçelik Turkish Journal of Forestry 22 (4), 408-416 , 2021 2021.0 Citations: 5
Stem Profile Patterns of Pinus nigra and Pinus sylvestris Growing in Mixed Stands R Özçelik, KP Poudel, F Crecente-Campo, B Kaya, O Alkan Forest Science 69 (6), 610-618 , 2023 2023.0 Citations: 4
Fitting and calibrating a mixed-effects segmented taper model for Brutian pine R Özçelik, O Alkan Cerne 26 (4), 464-473 , 2020 2020.0 Citations: 4
Türkiye’nin bazı önemli ağaç türleri için yöresel gövde çapı modellerinin geliştirilmesi: Bucak örneği O Alkan, R Ozçelik, H Alkan Turkish Journal of Forestry 20 (4), 333-340 , 2019 2019.0 Citations: 4
Toros Göknarı (Abies cilicica carr.) meşcereleri için gövde çapı, çap-boy, çap dağılım ve bonitet endeks modellerinin geliştirilmesi O Alkan Doktora Tezi, Isparta Uygulamalı Bilimler Üniversitesi Fen Bilimleri … , 2019 2019.0 Citations: 4
Tek ağaçta göğüs çap artımının periyot süresi, yaş sınıfı ve sosyal sınıfına göre değişimi: Sarıkamış yöresi sarıçam meşcereleri örneği B Koparan, O Alkan, S Carus, Y Çatal, R Ozçelik Turkish Journal of Forestry 25 (4), 437-446 , 2024 2024.0 Citations: 3
Dikili ağaçların hacim tahmini için bazı metotların karşılaştırılması R Özçelik, H Alkan, O Alkan Turkish Journal of Forestry 19 (4), 380-385 , 2018 2018.0 Citations: 3
Characterizing diameter distribution of Pinus nigra stands in Türkiye with a Weibull distribution O Alkan, QV Cao, R Özçelik Canadian Journal of Forest Research 55, 1-12 , 2024 2024.0 Citations: 2
Meşcere bazlı orman envanterinde optimal örnekleme tasarımı; Sinop-Ayancık orman işletme şefliğinde bir uygulama çalışması O Alkan Süleyman Demirel Üniversitesi Fen Bilimleri Enstitüsü , 2013 2013.0 Citations: 2
Evaluating optimal percentile pairs for a Weibull-based diameter distribution in European black pine stands O Alkan Dendrochronologia 91, 126341 , 2025 2025.0 Citations: 1
Almus yöresi doğal doğu kayını meşcerelerinin çap dağılımının Weibull dağılımı ile modellenmesi O Alkan, R Ozçelik, Ş Kalkanlı Turkish Journal of Forestry 24 (3), 197-207 , 2023 2023.0 Citations: 1
Kızılçam (Pinus brutia Ten.) meşcerelerinde uygulanan ilk aralama çalışmalarının değerlendirilmesi: Sütçüler örneği E Bayar, O Alkan Turkish Journal of Forestry 24 (1), 11-17 , 2023 2023.0 Citations: 1
Modeling diameter distribution of natural oriental beech stands in the Almus region using the Weibull distribution O Alkan, R Ozçelik, Ş Kalkanlı Turkish Journal of Forestry 24 (3), 197-207 , 2023 2023.0 Citations: 1
Eğirdir yöresi doğal karaçam meşcereleri için çap-boy modeli: Kantil regresyon yaklaşımı O ALKAN, R ÖZÇELİK Turkish Journal of Forestry 23 (3), 187-195 , 2022 2022.0 Citations: 1
Development of regional stem taper models for some important tree species of Turkey: Case study of Bucak O Alkan, R Özçelik, H Alkan Turkish Journal of Forestry 20 (4), 333-340 , 2019 2019.0 Citations: 1
Kantil regresyon ile gövde çapı modelinin geliştirilmesi R OZÇELİK, O ALKAN, Ş KALKANLI Turkish Journal of Forestry 22 (3), 250-256 , 0 Citations: 1
Axial variation of color and Shore D hardness in Cedrus libani wood U Özkan, B Koparan, O Alkan, N Öğüt, Ş Kalkanlı, CK Şahin Maderas: Ciencia y tecnología 28, 3 , 2026 2026.0
