Comparative Silvics of Butternut Hybrids in Afforestation and Reforestation Plantings

Caleb E Kell, Purdue University

Abstract

Butternut (Juglans cinerea) is a tree species in the walnut family native to eastern North America. Butternut is a fast-growing, short-lived species with an average lifespan of 75 years that produces heavy crops of energy-dense nuts every 1 to 3 years starting at approximately 10 years of age. Butternut canker (Ophiognomonia clavigignenti‐juglandacearum) is an introduced fungal pathogen that has devastated butternut populations, rendering the butternut a threatened species in multiple US states and an endangered species in Canada. Hybrids between butternut and Japanese walnut (Juglans ailantifolia) display natural resistance to the butternut canker pathogen and are considered the most viable avenue for the creation of a disease-resistant butternut population. The Indiana Division of Forestry (IN-DoF) tree nursery system has sold hybrid butternut seedlings to the public since 2007. To evaluate the suitability of using butternut hybridsto restore the ecological function of the pure butternut, the performance of 21 private plantings of IN-DoF hybrid butternut stock and seven mixed-species experimental field trials containing hybrid butternut, pure butternut, black walnut (Juglans nigra) and red oak (Quercus rubra) were evaluated. In the 21 private plantings sampled, the mean tree age was seven years and the overall mean survival rate was 35% (638 seedlings were found out of 1850 planted). Damage from deer browse contributed greatly to mortality and reduced growth. Butternut trees planted in locations with low side competition assumed an open form with multiple stems, whereas butternut planted by woodland edges, in forest openings, and in other competitive environments grew in an upright form with more rapid vertical growth than open-grown trees. Butternuts planted in heavy clay soils grew poorly, but butternuts grew well in silt loams and soils with a sand or rock component with good drainage. The experimental trials, which were fenced to exclude deer, displayed the best pure and hybrid butternut performance in soils with a rock or sand component and adequate side competition. No differences of mortality, total height, timber form or merchantable height were found between pure and hybrid butternut, although hybrid butternut had faster diameter growth and a higher incidence of multi-stemmed trees than pure butternut. Black walnut had smaller diameter and total height compared to pure and hybrid butternut, but had better timber form and merchantable height compared to pure and hybrid butternut. These findings may be used to develop a series of best management practices for hybrid butternut planting and management, and support the use of hybrid butternut in butternut restoration efforts.

Degree

M.Sc.

Advisors

Jacobs, Purdue University.

Subject Area

Agronomy|Ecology|Forestry|Wood sciences

COinS