Nonlinear height–diameter models for three woody, understory species in a temperate oak forest in Hungary

Information about the diameter and the height of woody species is fundamental to developing growth and yield models in forest stands. Ten nonlinear height–diameter functions were fitted and evaluated for the site. The dataset consisted of 957 selected individuals of three dominant woody species (Acer campestre L., Acer tataricum L., and Cornus mas L.) and represented a wide range of woody species sizes. Changes in these equations following dieback of oak canopies were analysed. Residual standard error (RSE) results of the two-parameter functions showed that the “Wykoff et al. 1982” and “Bates and Watts 1980 – Ratkowsky 1990” functions had lower RSE values in 1972. After oak decline the “Larson 1986” and “Bates and Watts 1980–Ratkowsky 1990” functions had lower values. The RSE data for the three-parameter functions showed that the “Pearl and Reed 1920” function had fitted RSE values at the start of the long-term study. After the canopy decline function, the “Ratkowsky 1990” function RSE value was lowest for A. campestre and C. mas. “Pearl and Reed 1920” was the best-fitted function for A. tataricum. Height – diameter equations increase our knowledge about the growth of these species, which will enable us to improve management planning in oak forests.