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Site index curves for European Chestnut (Castanea sativa Mill.) in Belasitsa mountain Krivulje indeksa staništa za pitomi kesten (Castanea sativa Mill.) na planini Belasici Tzvetan Zlatanov1, Ivaylo Velichkov1, Georgi Hinkov1, Margarita Georgieva1, Olafur Eggertsson2, Saevar Hreidarsson3, Magdalena Zlatanova1, Georgi Georgiev1 Abstract Richards, Lundqvist-Korf and Hossfeld growth functions were fitted to age-height data of European chestnut (Castanea sativa Mill.) dominant trees on the northern slopes of Belasitsa mountain, Southwest Bulgaria. The model prediction performance was evaluated using quantitative as well as qualitative examinations. Goodness of fit of each model was estimated by the coefficient of determination, F-test for significance of the regression and t-tests for significance of the coefficients of the model. Models were further compared by the evaluation of the standard error of the model and Akaike’s Information Criteria. Site index curves were constructed following the "guide curve method" procedure. In accordance with the evaluation tests, the Richards function was chosen as most adequate to express the age-dominant height relationship. Accordingly, it was further employed as a guide function to derive site index curves for studied chestnut population. It was recommended that the growth model and the site index curves elaborated in the current study are used within the data range 10−110 years. Key words: Castanea sativa, height growth, site index curves, Guide curve method, Richards function Introduction Uvod European chestnut (Castanea sativa Mill.) represents one of the most important broad-leaved plants in South Europe, even though both socio-economic changes and pathologies reduced the importance it had till the first decades of the last century (Haltofová, et al. 2005). The ecological and economical relevance of chestnut has been related to its multipurpose character and presence across different domestication forms: mixed forests, coppices and orchards (Lauteri et al. 2009). Until recently there were uncertainties with respect to the origin of chestnut in Belasitsa mountain. It was reckoned to be either artificial, the species having been introduced from its southern localities (Dobrev 1914; Stoyanov 1921), or related to its broader relict distribution (Bratanova-Doncheva et al. 2005). Zlatanov et al. (2011) revealed genetic congruence between studied chestnut population and those located in Northern Greece, and found (by pollen analyses and C14 dating of samples) that chestnut was present in the mountain as early as 8000 years BP. These findings support the theories that Belasitsa mountain is most likely a refugium area of chestnut, hence the importance of this species in the mountain. For many centuries chestnut dominated stands in Belasitsa mountain used to be intensively managed for nut and firewood production, and grazing. Human impact over chestnut stands diminished after nationalization of forests in 1948. Only the interest of the local people in collection of chestnut fruits remained though it became more unorganized and uncontrolled (Kostov 1979). The consistent increase of the demand for wood and the subsequent outbreaks of the exotic pathogen Cryphonectria parasitica (Murrill) Barr. during the last 15 to 20 years brought about interest of targeted management of chestnut stands. 1 Forest Research Institute – Sofia, 132 "St. Kliment Ohridski" blvd., 1756 Sofia, Bulgaria 2 Iceland Forest Research, Mogilsa, Is-116 Reykjavik, Iceland 3 The Agricultural University Of Iceland, Is-311 Borgarnes, Iceland Corresponding author: Tzvetan Zlatanov: tmzlatanov@gmail.com |