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ŠUMARSKI LIST 3-4/2017 str. 28     <-- 28 -->        PDF

Exploratory Data Analysis – Istraživačka analiza podataka
In table 1 the basic descriptive statistics of the variables of all data are given.
Importance of the estimators – Važnost procjenitelja
The term importance refers to the relative importance of each estimator in the forecasting model for the given accuracy of the model. The importance can take values from 0 and 1. The rank of estimators (the predictors) as to their relative importance is given in figure 1. If we focus on the accuracy of the classification of the stands in site qualities (the meaning of the boosting algorithm), most important, with importance equal to 0.79 is the canopy density, followed by the topography (importance = 0.21) and age (materiality < 0.01) (Figure 1).
The correct classification rate reached 98.59%, in site quality III (properly classified the 280 of the 284 stands). The correct classification of stand in site qualities I and II was 4% and 77%, respectively. For a more analytical presentation of classification, one can refer to Table 2, which is derived from the confusion matrix (Table 3).
The main tool for the evaluation of site productivity or site quality is site index (Van Laar and Akca 2007). In site index models, the height growth of dominant, codominant or of trees having certain characteristics are used (Van Laar and Akca 2007). There is a huge number of publications regarding site index models (Huang 1997; Krumland and Eng 2005). However, site quality is related to topographic features (see Dafis 1986; Vanclay 1992; Barnes et al. 1998; Papalexandris and Milios 2010; Milios et al. 2012) as well as to other environmental indicators like understory vegetation, soil physical and chemical properties, foliar nutrients, climatic data, soil properties etc. (see Kayahara et al. 1995, McKenney and Pedlar 2003, Bontemps and Bouriaud 2014, Watt et al. 2015). In Greece, soil depth is strongly related to site productivity, since it acts as a water storing reservoir during dry period (Dafis 1986; Hatzistathis & Dafis 1989) and it has been used in research studies for the site quality determination (Papalexandris and Milios 2010; Stamboulidis et al 2013). Adamopoulos et al. (2009) and