Diameter-Height Models for Fast-growing Poplar Plantations on Agricultural Land in Sweden

There is increasing interest in using poplar plantations as sources of bioenergy in many countries, but optimizing their management, robust models for estimating and monitoring their structure, growth and biomass are required. The presented study explores the diameter-height relationships of poplars in 40 plantations on agricultural land located in central and southern Sweden, in order to provide tools for an easy estimation of standing biomass of poplar stands. Diameter and height measurements of 167 trees were included: 117 for calibration and 50 for validation. The constructed diameter-height equations were developed using a mixed-effect modelling approach to address the variations among sites of the plantations and obtain a flexible tool capable of providing locally calibrated estimates. Different models with various structures and stand variables, such as mean diameter and age, were tested. The best model presented R (2) values of 0.87 and 0.96, for the fixed and mixed model parts, respectively. Thus, it appears to be capable of providing useful estimates of heights of poplar stands from measurements of stem diameters in sample plots, thereby facilitating the planning and management of Swedish poplar plantations as future energy feedstock.