Impact of the thinning regime on the mean diameter of the largest stems by diameter at breast height in even-aged Picea abies stands

Abstract

The increases in the arithmetic mean diameter at breast height (dbh) of the 100, 200, 300 and 400 largest stems ha−1 by dbh associated with six different thinning regimens for periods up to 35 years were compared, by analyses of variance, to the corresponding stem fractions in unthinned stands using permanent sample plot data. In addition, the expected mean dbh of these stand fractions at future points in time was modelled, based on site and stand data obtained at the time of the first thinning. Thirty-five years after the first thinning, the thinning from below regimens resulted in actual increases (a measure affected by both the thinning intensity and the thinning method), compared with the unthinned stands, in the mean dbh for the 100, 200, 300 and 400 largest stems ha−1 of 2.6–9.0 cm. The corresponding genuine increases (a measure principally affected solely by the thinning intensity) were 4–11 cm. The functions predicting the future dbh of these stand fractions yielded good fits.