Crown radius of pedunculate oak (Quercus robur L.) depending on stem size, stand density and site productivity

Abstract

Crown size is a good indicator of the growth potential of trees and is often used in forest management for outlining thinning guidelines or constructing forest growth models. The aim of this study was to analyse mean crown radius as a function of stem size, stand density and site productivity in even-aged stands of pedunculate oak (Quercus robur L.). Data included measurements of 620 trees from 53 plots in nine thinning experiments and one operational stand in Sweden, Denmark and Great Britain, representing a wide spectrum of thinning practices ranging from the strictly unthinned control to extremely heavy thinning with essentially solitary trees. Three sets of models were constructed based on different predictor variables, including indicators of individual stem size (diameter at breast height, DBH), stand density/thinning grade (quadratic mean diameter and stand basal area) and site productivity (stand top height). Preliminary results indicated a significant effect of DBH and (nominal) thinning grade on crown radius. The response pattern of the final models indicated an increasing crown radius with increasing DBH, with increasing thinning grade (decreasing stand density) and with decreasing site productivity. The models are valid for predicting the crown radius of pedunculate oak in even-aged forest stands.

Keywords:

• silviculture
• oak
• crop trees
• thinning
• crown radius

Acknowledgements

The authors would like to thank numerous students and colleagues who with great enthusiasm and energy contributed to the fieldwork and collection of data. University of Copenhagen provided institutional support for the experiments in Denmark, Swedish University of Agricultural Sciences (SLU) for the experiment in Sweden and Forest Research for the experiment in Great Britain. The Danish Nature Agency most kindly provided historical inventory data for the oak stand in Bjerge Meadows. Comments from Dr Gary Kerr (Forest Research, UK), Professor Peter Savill (University of Oxford, UK) and an anonymous reviewer helped improve the final presentation.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The Wallenberg Foundation and SLU grants for internationalization supported the collection of data in the experiment Crumbland 7. The establishment and maintenance of experiment 1516 and 1517 were supported during 2002–2007 by two grants from the Danish Nature Agency's fund for experimental silviculture. The research presented was supported during 2010–2014 by basic funding from the Swedish University of Agricultural Sciences.