Application of visual surveys to estimate acorn production of Brant's oak (Quercus brantii Lindl.) in northern Zagros Forests of Iran

Acorn production plays a fundamental role in the organization and dynamics of oak forest ecosystems. Regarding acorn importance, visual survey methods have been used to estimate acorn production of oak species throughout the world. In this study, the mast indices of Brant`s oak (Quercus brantii Lindl.) were determined in a section of northern Zagros forests, almost 36 ha area, near Baneh, Kurdistan province. Different types of visual surveys (Whitehead, Christisen-Kearby, Modified Graves and Koenig) were used on 120 trees which were selected using stratified random sampling method. In early September, just prior to acorn fall, each tree was investigated using visual surveys. Furthermore, for each tree, acorn density (acorns number/m2 crown area) was calculated using crown counting to calculate the best regression model in Koenig method. Based on visual estimation indices, fair acorn production of Q. brantii was observed. There was a strong (R2 = 0.73), highly significant (P < 0.001) linear relationship between the Koenig acorn counts (X) and corresponding crown counts. Furthermore, the results of this research confirmed usefulness of the quick visual survey methods to estimate the acorn crop of Q. brantii.