Modelling natural recruitment of European beech (Fagus sylvatica L.)

In the study, data from a Slovenian forest inventory (67,563 plots, 200 m2 each) were used to develop a two-stage beech recruitment model. In the first stage a probability model of beech recruitment was estimated with binary logistic regression, while in the second stage a conditional model for beech recruitment rate was derived. A tree was classified as recruited if it had crossed a threshold of 10 cm in its diameter at breast height. On average, 2.5 beech ha−1 y−1 overgrew the measurement threshold, representing 38% of the total recruitment. High variability in beech recruitment was observed (CV = 274%). Among 21 variables selected for possible inclusion into the models, three stand, one site, two climate, two forest management, and one wildlife variable were chosen; eight were included in the probability model, seven in the conditional model, six of which were included in both models. Beech recruitment was negatively related to stand basal area and mean diameter and positively related to the proportion of beech in the stand basal area. Beech recruitment was most successful in young even-aged and uneven-aged stands and on sites of medium productivity. Tree mortality in a stand, resulting mainly from harvesting, was positively related to beech recruitment, while the opposite was true for large ungulate density index. Among climate variables, mean annual temperature and mean annual precipitation influenced the probability of beech recruitment, a result that could be useful for exploring the future potential of beech in a changing environment.

► The study represents one of the first attempts to model natural beech recruitment.
► Forest inventory data were used to develop a two-stage model of beech recruitment.
► Stand variables most strongly affected beech recruitment.
► Beech recruited with the highest success in young even-aged and uneven-aged stands.
► Climate variables had significant influence on probability of beech recruitment.