Schroder J.,Hochschule fur Nachhaltige Entwicklung FH Eberswalde
Allgemeine Forst- und Jagdzeitung | Year: 2012
The study analyzes the relations between individual crown vitality and basal area increment for sessile oak (Quercus petraea [MArr.] LIEBL.). Investigations were carried out from 2006 to 2011 in five stands of mature sessile oak (table 1) on terrestrial, moderately dry sites with average nutrient supply. The trial stands are located in a geographic sequence with increasingly continental climate from the western border of Brandenburg into Eastern Poland (table 2, fig. 1). To quantify oak vitality, two different approaches were compared: (i) the European standard procedure for annual assessment of crown transparency in summer, and (ii) a method to assess winter crown structure according to KÖRVER et al. (1999; fig. 2). Basal area increment was derived from consecutive diameter measurements at the start and after five years. - A comparison between 2006 and 2011 shows significant improvements in crown condition in all trial stands for both summer and winter assessment (table 3, fig. 3). Spearman rank correlation coefficients between crown transparency and crown structure are relatively small but significant (fig. 4). As a result, the two approaches are seen as complementary methods which allow conclusions on different phenomena and processes: While crown transparency mirrors short-term (mostly annual), volatile influences such as extreme weather periods or insect attacks, crown structure is a measure of environmental changes or vitality problems on a larger time scale of more than one year. Although crown structure is significantly related to basal area increment on four out of five plots (fig. 5), correlations between tree growth and crown vitality are rather weak for both assessment methods and do not follow any spatial trend (table 4). Initial basal area and relative crown size were identified as the most imfluential factors for variation in basal area increment. Low but significant correlations exist between relative crown size and crown vitality: Trees with identical dbh values tend to show less crown transparency and a healthier crown structure with increasing horizontal crown area (fig. 6). All these results show that the investigated crown vitality parameters alone do not completely reflect basal area increment variation and, vice versa, increment values can only partially predict crown development. The geographic gradient covered by the sequence of trial stands does not lead to any detectable spatial trend in the results.