United States Department of Black Cherry Site Index Curves Agriculture Forest Service for the Allegheny Plateau Northeastern.-.~- Forest Experiment Station Research Paper L. R. Auchmoody N E-549 C. 0.Rexrode The Authors L. R. Auchmoody is a principal soil scientist at the North- eastern Forest Experiment Station's Forestry Sciences Labora- tory at Warren, Pennsylvania. Before his retirement, C. 0.Rexrode was a research forest entomologist at the Northeastern Station's Forestry Sciences Laboratory at Delaware, Ohio. Manuscript received for publication 1 May 1984. Abstract Black cherry site index curves were developed for the Allegheny Plateau in northwestern Pennsylvania. They show for this region that height rises less sharply prior to the index age and is maintained for a longer period thereafter than described by existing curves. An equation to predict site index from height and age is furnished to allow the use of these curves in computer processing. For field use, a table of site indexes by 2-foot heights and 2-year ages is provided. Introduction Procedures For many years the only available Six fully stocked Allegheny 1-inch-thickdisk removed for age site index curves for black cherry hardwood stands were selected for determinations in the laboratory. (Prunus serotina Ehrh.) were those sampling. The sampled stands were developed in 1937 by S. E. Defier,' and even-aged second growth, about 70 Height and age data were ad- later published by the USDA Forest years old, free from cutting, and lo- justed to compensate for dissections Service (Hampf 1965). These were cated on the Allegheny Plateau in not coinciding with the maximum harmonized curves made from height northwestern Pennsylvania. These height attained for a particular age, and age measurements taken in stands originated after heavy clear- and for differences in the number 38 stands growing in south-central cutting early in the century, and now of years required for seedlings to New York and northwestern Pennsyl- contain 30 to 50 percent black cherry reach breast height. Because actual vania. These curves have been used in admixture with white ash (Fraxinus tree heights usually are greater than extensively. americana L.), red maple (Acer rubrum heights of the dissection points, L.), sugar maple (Acer saccharurn heights were adjusted upward by More recently, a second set of Marsh.), and beech (Faqus grandifolia adding half of the average annual black cherry site index curves was Ehrh.). The prevailing cool and moist height growth to the height of each developed for the northern Lake climate of the area is characterized dissection point (Carmean 1972). To States region (Carmean 1978). These by a 120-day frost-free period and 44 avoid variation in the time required are polymorphic curves made from inches of well-distributed precipita- for stands to reach 4.5 feet, a con- stem analyses of 126 trees located on tion, and is typical of conditions stant 4 years were added to age at 42 plots. These curves generally agree where black cherry attains its best breast height to obtain total age. with the Defler curves below the index development. age, but show considerable departure The site index curves were con- above. Since the entire data set used The six sites included soils that structed by a technique similar to one to develop the Carmean curves came ranged in drainage from well drained described by McQuilkin (1974). First, from the extreme northwestern com- to somewhat poorly drained, and in regressions of the form Y = a + mercial range of black cherry, it may soil texture from loam to silty clay bX - cX2 were fitted to the adjusted not be strictly applicable to other loam. All were residual soils, having height (Y) and age (X) of each sample geographic regions that differ in cli- developed in place from the under- tree. All regressions were significant mate, soils, and in black cherry growth laying parent material. The effective (P 5 .01) and had R2 exceeding 0.99. rates. rooting depth was generally less than From these regressions, the actual 3 feet, being limited by a fragipan, site index (height at age 50) and the Black cherry is one of the most perched water table, or compact corresponding heights attained at 10, important and most valuable eastern stony layers above bedrock. Soils 20, 30, 40, 50, 60, 70, and 80 years hardwoods. It is found in commercial included the Cookport, Clymer, Hazel- were obtained for each of the 39 trees. quantities and attains its best growth ton, and Wharton series, which are Next, these data were used to develop and development on the Allegheny representative and important forest linear regressions with site index as Plateau of western Pennsylvania and soils in the region. Only the very the dependent variable and height as New York and southward throughout wettest and most poorly drained soils the independent variable for each the Allegheny Mountains. Yet the where black cherry is seldom found of the eight age classes. These re- accuracy with which existing site and grows poorly were not sampled. gressions were then used to deter- index curves describe black cherry mine the tree heights at 10-year age heightlage relationships within this A total of 39 sample trees grow- intervals that predicted site indexes region remains undetermined. There- ing within the six areas were felled of 40, 50, 60, 70, 80, 90, and 100. Fi- fore, the purpose of this study was to and dissected. All trees were domi- nally, these heights and ages were construct a set of black cherry site nants or codominants that had no used to plot each of the 10-foot site index curves applicable to sites on serious stem deformities, and they index curves from 40 to 100. The the Allegheny Plateau of western showed no evidence of suppression ability of these curves to describe Pennsylvania and New York, and to or disease. Site index at age 50 of the heightlage relationships was checked compare these curves with those that sampled trees ranged from 56 to 82 by comparing heights obtained from already exist. feet. the curves with the actual heights attained by the original 39 trees, but 'Defier, Sam E. Black cherry character- Felled trees were sectioned at no evaluation was made with an inde- istics, germination, growth, and yield. 5-foot intervals for their entire length. pendent sample. Unpublished M.S. thesis. New York State At each dissection point, the height College of Forestry; 1937. above ground was recorded and a Results The black cherry site index curves derived in this study are given in Figure 1. They show substantially different heightlage patterns than described in the original curves by Deflerl and by the curves developed for the Lake States by Carmean (1978). In both sets of existing curves, height rises sharply before the index age and then falls off quickly after the age of 50 years. By contrast, second- growth cherry in northwestern Penn- sylvania has slower early growth and more sustained height growth after the index age. These differences in curve form mean that using the other curves locally will result in lower than actual site indexes for stands be- tween the ages of 20 and 50 years, and higher than actual site indexes in stands older than 50 years. These deviations are large, underestimating by as much as 15 to 16 site index points in very young stands (age 20) to overestimates of 10 to 15 site index points at age 80 (Table 1). The new curves appear to closely track black cherry heightlage patterns in this area, as evidenced by small mean departures between the original 39 sample trees and the composite site index curves (Table 2). Though the accuracy of the curves has not been verified with independent data, we nevertheless believe that the curves can be used with confidence since the sample trees used for their development and the sites upon which the sample trees grew were highly representatim of the region. To enable the use of the curves with electronic data processing, an equation was developed to predict site index from height and age. The equation is: Site Index = 71.558 + 1.437(height) - 2.353(age) + 0.016(ageZ) - 0.007(height x age) Each of the four variables are significant (P 5 .01). The equation has an R2 of 0.993 and a standard error of estimate equal to 1.78 feet. Figure 1.-Black cherry site index curves for the Allegheny Plateau. Four years should be added to breast-height age to obtain total age. Dashed lines are beyond observed data. Table 2.-Departure of the new site index curves Finally, the best estimates of from actual heightlage patterns of site index will be obtained if breast the 39 sample trees (site index curve height age plus 4 years is used as a height + actual height) measure of total age rather than the actual age since stand establish- Mean Maximum Maximum ment. This will minimize the effect of Age departure negative positive variables, such as deer browsing, that departure departure are not site related but that have a major impact on early height growth. The use of actual age, such as that determined from stand records or low stumps, will result in lower than actual site indexes where it has taken more than 4 years for the stand to reach breast height. Literature Cited Carmean, Willard H. Site index curves for upland oaks in the Central Discussion States. Forest Science. 18:109-120; 1972. To simplify the use of the site The curves developed in this index curves in the field, and to elim- study apply to stands that have not Carmean, Willard H.