Structure of black walnut (Juglans nigra L.) stands on sandy soils in Hungary

Understanding the various processes and relationships that take place in forest ecosystems is generally possible only through long-term observations. This is especially true of the biological production of forests, through the in-depth exploration of their structure. In Hungary the black walnut (Juglans nigra L.) is one of the most valuable exotic tree species, mainly because of its very valuable wood, with fine tissues and unique colour, for furniture industry. Generally, the species is established by manual seeding, and can also be regenerated well by coppice shoots, but not by natural seeding. Black walnut regularly produces seeds from the age of 25-30 years and its rotation age is 70-80 years. It is also used outside forests due to the very decorative stem and crown shapes. In this paper, out of the stand structure factors, the relationships between age and height (r2 = 0.7205), age and diameter (r2 = 0.7719), age and number of stems per ha (r2 = 0.3485) as well as between diameter and number of stems per ha (r2 = 0.4595), all considered important for cultivation technology, were examined (based on the data collected in 34 black walnut stands, age of 7 to 67 years). We also analysed the diameter distributions in two black walnut stands with tending operations, reporting them as a case study. Its future role may be increased mainly on sandy soils of better quality, therefore the more accurate exploration of the structure of black walnut stands growing under such conditions can be considered as gap-filling.