B A S E Non-linear height-diameter models for oriental beech (Fagus orientalis Lipsky) in the Hyrcanian forests, Iran

The relationship between tree height and diameter is an important element in growth and yield models, in carbon budget and timber volume models, and in the description of stand dynamics. Six non-linear growth functions (i.e. Chapman-Richards, Schnute, Lundqvist/Korf, Weibull, Modified Logistic and Exponential) were fitted to tree height-diameter data of oriental beech in the Hyrcanian mixed hardwood forests of Iran. The predictive performance of these models was in the first place assessed by means of different model evaluation criteria such as adjusted R squared (adj R 2 ), root mean square error (RMSE), Akaike information criterion (AIC), mean difference (MD), mean absolute difference (MAD) and mean square (MS) error criteria. Although each of the six models accounted for approximately 75% of total variation in height, a large difference in asymptotic estimates was observed. Apart from this, the predictive performance of the models was also evaluated by means of cross-validation and by splitting the data into 5-cm diameter classes. Plotting the MD in relation to these diameter at breast height (DBH) classes showed for all growth functions, except for the Modified Logistic function, similar mean prediction errors for small-and medium-sized trees. Large-sized trees, however, showed a higher mean prediction error. The Modified Logistic function showed the worst performance due to a large model bias. The Exponential and Lundqvist/Korf models were discarded due to their showing biologically illogical behavior and unreasonable estimates for the asymptotic coefficient, respectively. Considering all the above-mentioned criteria, the Chapman-Richards, Weibull, and Schnute functions provided the most satisfactory height predictions. However, we would recommend the Chapman-Richards function for further analysis because of its higher predictive performance. Keywords. Forest trees, Fagus orientalis, simulation models, growth, Iran. Modèles non linéaires de diamètre de hauteur pour le hêtre oriental (Fagus orientalis Lipsky) dans les forêts Hyrcaniennes en Iran. La relation entre la hauteur des arbres et le diamètre est un élément important pour les modèles de croissance, de rendement, du budget de carbone et de volume du bois, et pour la description de la dynamique des peuplements. Six fonctions de croissance non linéaires (Chapman-Richards, Schnute, Lundqvist/Korf, Weibull, fonctions logistiques et exponentielles modifiées) ont été ajustées aux données de diamètre de hauteur des arbres de hêtre oriental dans les forêts mélangées hyrcaniennes d'Iran. La performance prévue des modèles a été évaluée à l'aide du R² ajusté (adj R²), de l'erreur quadratique moyenne (RMSE), du critère d'information d'Akaike (AIC), de la différence moyenne (MD), de la différence absolue moyenne (MAD) et de l'erreur quadratique moyenne (MS). Les résultats ont montré que chacun de ces six modèles représente environ 75 % de la variation totale de hauteur, mais produit différentes estimations asymptotiques. La performance prévue a également été évaluée à l'aide des validations croisées et par séparation des données en classes de 5 cm de diamètre à hauteur de poitrine (DBH) afin de calculer le MD pour chaque classe. Les visualisations de MD pour toutes les classes DBH ont montré que les six fonctions de croissance, sauf la logistique modifiée, produisent des erreurs de prédiction moyennes similaires pour les arbres de tailles petites et moyennes. Cependant, pour les arbres de grande taille, l'erreur de prédiction moyenne est plus élevée. La fonction de logistique modifiée est la moins performante, en raison d'un large biais. Les modèles exponentiels et de Lundqvist/Korf ont été rejetés en raison, respectivement, de leur comportement biologique illogique et des estimations déraisonnables pour les coefficients asymptotiques. En envisageant tous les critères mentionnés ci-dessus, les fonctions Chapman-Richards, Weibull et Schnute fournissent les prédictions de hauteur les plus satisfaisantes, mais la fonction de Chapman-Richards pourrait être recommandée pour une analyse plus approfondie en raison de sa meilleure performance

The effect of biochar amendment on the growth, morphology and physiology of Quercus castaneifolia seedlings under water-deficit stress

Water stress is one of the most important environmental stresses which can adversely affect soil fertility and plant growth in arid and semiarid regions. In this study, biochar was used as a type of soil amendment to improve the physiology of Chestnut-leaved oak (Quercus castaneifolia C.A.M.) seedlings and soil quality in water-deficit conditions. A randomized complete block design was conducted using three water regime treatments [100, 70 and 40% field capacity (FC)] and four application rates of produced biochar from hornbeam wood chips (control without biochar, B1, B2 and B3 with 10, 20 and 30 g kg−1 soil, respectively) in potted seedlings. The soil water-holding capacity in the 30 g kg−1 biochar was found to be higher than that in the non-biochar treatment under 100 and 40% FC. Water supply reduction to 40% FC decreased the soil total N, the available P and K, CEC, SOC and microbial respiration, as compared to the non-biochar soil used as the control; however, an increase in the B3 treatment was detected in the soil P and K at 100% FC. Severe water deficit (40% FC) induced a significant decrease in photosynthesis, transpiration, stomatal conductance and xylem water potential seedlings; even, in this case, the addition of the highest dose of biochar under the lowest water supply increased photosynthesis and stomatal conductance by 38% and 39%, respectively. Leaf nutrient concentration was also influenced by the treatment. The highest diameter and height growth and dry weight of the seedlings were observed in 100 and 40% FC under the B3 treatment. Plant biomass of the seedlings treated by B3 was increased by 55, 70 and 73%, in comparison with those attained by the control under 100, 70 and 40% FC irrigation, respectively. Generally, the use of the 30 g kg−1 biochar in the soil could alleviate the negative effects of water deficit and improve the growth of Q. castaneifolia seedling and soil quality with increasing the soil water-holding capacity, organic carbon and nutrient

Change in biochemical parameters of Persian oak (Quercus brantii Lindl.) seedlings inoculated by pathogens of charcoal disease under water deficit conditions

Drought alone or in combination with charcoal disease pathogens led to modifications in some biochemical characteristics of Persian oak seedlings. Drought conditions enhances the effects of charcoal fungus with effects at biochemical level.AbstractCharcoal disease is one of the common diseases in oak forest of Zagros in western Iran that has increased in the recent years. The disease is associated with abiotic stress, especially drought, and contributes to the decline of Persian oak (Quercus brantii Lindl.), the major oak species in this forest association. Persian oak seedlings were exposed to a factorial combination of two irrigation levels and inoculation with either Biscogniauxia mediterranea or Obolarina persica (agents of charcoal disease). Proline, total soluble sugar and soluble protein contents in seedling foliage were increased in response to charcoal pathogen inoculation, especially when combined with water stress, while starch, chlorophyll a+b and carotenoid contents strongly declined. Pathogen inoculation stimulated malondialdehyde content, electrolyte leakage, and hydrogen peroxide and superoxide radical contents in oak leaves, and were increased by water stress. The combination of charcoal disease agents and water stress increased peroxidase and superoxide dismutase activity while, for catalase and ascorbate peroxidase activities, the interaction between the two factors of variability was not significantly increased. Ascorbate peroxidase activity was at maximum level in seedlings infected with O. persica independently of water stress. Glutathione reductase had the highest activity in inoculated seedlings under soil moisture stress while those under higher soil moisture levels, the enzyme was increased only when inoculated with O. persica. Contents of non-enzymatic antioxidants including ascorbic acid and glutathione increased in response to combined pathogen inoculation and water stress and was higher when seedlings were inoculated with O. persica than with B. mediterranea. Chitinase activity significantly increased because of pathogen inoculation. Furthermore, foliar phenylalanine ammonia lyase activity was higher under all treatment combinations, as compared to the controls. The effects of B. mediterranea or O. persica pathogens on foliar biochemical responses of Q. brantii seedlings were more severe under water-stress and it was more sensitive to B. mediterranea than O. persica