Impacts of intensive management on black walnut (Juglans nigra L.) growth and bole quality at mid-rotation

High value hardwood species, such as black walnut (Juglans nigra L.), are increasingly planted and intensively managed in the hopes of profitably producing high quality logs. Success or failure of silvicultural practices used to establish these plantations are commonly judged on the basis of early diameter growth response. However, it is generally not known whether treatments judged to be successful when the stand is young translate into mid- and late-rotation bole quality and, ultimately, log value. This study revisits a 35-yr-old experimental black walnut plantation in south-central Illinois (black walnut site index(50) = 23 m), to evaluate how initial planting density, interplanting with nitrogen-fixing black alder (Alnus glutinosa [L.] Gaertn.), postestablishment weed control, and time of thinning impacted the productivity and bole quality at mid-rotation. Postestablishment weed control conducted at age 6-7 yr did not impact walnut diameter at age 35, but incidence of frost cracks and grade defects in the butt log (lower 2.44 m) were 100% and 30% greater, respectively, on trees receiving the weed control treatment. Time of first thinning of the alder affected walnut quality in the upper log (second 2.44 m log). The higher planting density of walnut and alder reduced the number of defects by 31% in the upper log, but at the expense of stem diameter growth. At a walnut planting density of 7.9 x 7.9 m, interplanting black alder impacted neither walnut diameter growth nor bole quality. The early thinning treatment increased the number of defects on the upper log, but not the butt log. These results suggest that intensive management can have a complex and enduring impact on black walnut plantation growth and development, and elucidate the need for long-term assessment of silvicultural treatments where bole quality is an important component of stand value.