Effects of coppice thinning on growth and yield of Emory oak sprouts in southeastern Arizona

Emory oak (Quercus Emoryi) is a dominant tree species in San Rafael Valley in southeastern Arizona. However, basic information about the effects of coppice thinning on the growth and yield of this species is lacking. Thus, objectives of the study were to measure the effects of coppice thinning on Emory oak survivor growth, ingrowth, and mortality, which are the basic components of a growth budget. This study determined gross growth, net growth, and yield estimates. In addition, this study evaluated the mean annual growth (MAG) values in relation to the biological rotation age of Emory oak in southeastern Arizona.

Coppice thinning treatments were applied to sprouts of different ages. Height and diameter at root collar measurements were taken immediately after thinning and again 5 years later. Sprouts were classified into 5 age groups, 4 stump diameters, and 3 level of coppice thinnings and an unthinned control. The interactions of these treatments and their effect on growth and yield were analyzed.

Stump diameters did not significantly affect the growth components, growth estimates, or yield estimates. The number of residual sprouts significantly affected the growth components, growth estimates, and yield estimates. Survivor growth, gross growth, net growth, and yield were lowest for 1 residual sprout, except for net growth of 8-year-old sprouts. There were no significant differences in net growth between the different coppice thinning treatments. At age 8-year-old sprouts, the mean annual growth of individual sprouts increased as the number of residual sprouts per stump reduced. Based on this relationship, it is recommended that 1 residual sprout be left when thinning sprouts. Age of sprouts significantly affected growth. There was an increase in the mortality of the control sprouts in the 6th year. Based on those results, it is recommended that thinning be conducted in the 5th year of the sprout's growth.

Proper timing of thinning can reduce the rotation age of Emory oak sprouts, if the rotation is based on achievement of a specified diameter. To draw firm conclusions about the effects of thinning on shortening the rotation age, the study measurement needs to be continued into the future.