United States 

Department of 

Agriculture 

Forest Service 

Black Cherry Site Index Curves 

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 Northeastern Forest Experiment Station's Forestry Sciences Laboratory 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 

For many years the only available 

site index curves for black cherry 

(Prunus serotina Ehrh.) were those 

developed in 1937 by S. E. Defier,' and 

later published by the USDA Forest 

Service (Hampf 1965). These were 

harmonized curves made from height 

and age measurements taken in 

38 stands growing in south-central 

New York and northwestern Pennsylvania. These curves have been used 

extensively. 

More recently, a second set of 

black cherry site index curves was 

developed for the northern Lake 

States region (Carmean 1978). These 

are polymorphic curves made from 

stem analyses of 126 trees located on 

42 plots. These curves generally agree 

with the Defler curves below the index 

age, but show considerable departure 

above. Since the entire data set used 

to develop the Carmean curves came 

from the extreme northwestern commercial range of black cherry, it may 

not be strictly applicable to other 

geographic regions that differ in climate, soils, and in black cherry growth 

rates. 

Black cherry is one of the most 

important and most valuable eastern 

hardwoods. It is found in commercial 

quantities and attains its best growth 

and development on the Allegheny 

Plateau of western Pennsylvania and 

New York and southward throughout 

the Allegheny Mountains. Yet the 

accuracy with which existing site 

index curves describe black cherry 

heightlage relationships within this 

region remains undetermined. Therefore, the purpose of this study was to 

construct a set of black cherry site 

index curves applicable to sites on 

the Allegheny Plateau of western 

Pennsylvania and New York, and to 

compare these curves with those that 

already exist. 

'Defier, Sam E. Black cherry characteristics, germination, growth, and yield. 

Unpublished M.S. thesis. New York State 

College of Forestry; 1937. 

Procedures 

Six fully stocked Allegheny 

hardwood stands were selected for 

sampling. The sampled stands were 

even-aged second growth, about 70 

years old, free from cutting, and located on the Allegheny Plateau in 

northwestern Pennsylvania. These 

stands originated after heavy clearcutting early in the century, and now 

contain 30 to 50 percent black cherry 

in admixture with white ash (Fraxinus 

americana L.), red maple (Acer rubrum 

L.), sugar maple (Acer saccharurn 

Marsh.), and beech (Faqus grandifolia 

Ehrh.). The prevailing cool and moist 

climate of the area is characterized 

by a 120-day frost-free period and 44 

inches of well-distributed precipitation, and is typical of conditions 

where black cherry attains its best 

development. 

The six sites included soils that 

ranged in drainage from well drained 

to somewhat poorly drained, and in 

soil texture from loam to silty clay 

loam. All were residual soils, having 

developed in place from the underlaying parent material. The effective 

rooting depth was generally less than 

3 feet, being limited by a fragipan, 

perched water table, or compact 

stony layers above bedrock. Soils 

included the Cookport, Clymer, Hazelton, and Wharton series, which are 

representative and important forest 

soils in the region. Only the very 

wettest and most poorly drained soils 

where black cherry is seldom found 

and grows poorly were not sampled. 

A total of 39 sample trees growing within the six areas were felled 

and dissected. All trees were dominants or codominants that had no 

serious stem deformities, and they 

showed no evidence of suppression 

or disease. Site index at age 50 of the 

sampled trees ranged from 56 to 82 

feet. 

Felled trees were sectioned at 

5-foot intervals for their entire length. 

At each dissection point, the height 

above ground was recorded and a 

1-inch-thick disk removed for age 

determinations in the laboratory. 

Height and age data were adjusted to compensate for dissections 

not coinciding with the maximum 

height attained for a particular age, 

and for differences in the number 

of years required for seedlings to 

reach breast height. Because actual 

tree heights usually are greater than 

heights of the dissection points, 

heights were adjusted upward by 

adding half of the average annual 

height growth to the height of each 

dissection point (Carmean 1972). To 

avoid variation in the time required 

for stands to reach 4.5 feet, a constant 4 years were added to age at 

breast height to obtain total age. 

The site index curves were constructed by a technique similar to one 

described by McQuilkin (1974). First, 

regressions of the form Y = a + 

bX - cX2 were fitted to the adjusted 

height (Y) and age (X) of each sample 

tree. All regressions were significant 

(P 5 .01) and had R2 exceeding 0.99. 

From these regressions, the actual 

site index (height at age 50) and the 

corresponding heights attained at 10, 

20, 30, 40, 50, 60, 70, and 80 years 

were obtained for each of the 39 trees. 

Next, these data were used to develop 

linear regressions with site index as 

the dependent variable and height as 

the independent variable for each 

of the eight age classes. These regressions were then used to determine the tree heights at 10-year age 

intervals that predicted site indexes 

of 40, 50, 60, 70, 80, 90, and 100. Finally, these heights and ages were 

used to plot each of the 10-foot site 

index curves from 40 to 100. The 

ability of these curves to describe 

heightlage relationships was checked 

by comparing heights obtained from 

the curves with the actual heights 

attained by the original 39 trees, but 

no evaluation was made with an independent sample. 
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, secondgrowth cherry in northwestern Pennsylvania 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 between 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 

from actual heightlage patterns of 

the 39 sample trees (site index curve 

height + actual height) 

Mean Maximum Maximum 

Age departure negative positive departure departure 

Finally, the best estimates of 

site index will be obtained if breast 

height age plus 4 years is used as a 

measure of total age rather than the 

actual age since stand establishment. This will minimize the effect of 

variables, such as deer browsing, that 

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. 

To simplify the use of the site 

index curves in the field, and to eliminate the need for interpolating between the 10-foot site classes shown 

in Figure 1, the equation was used 

to produce a table of site indexes by 

2-foot heights and 2-year age classes 

(Table 3). The table can be used in lieu 

of the curves by simply picking out 

the site index that corresponds to the 

appropriate height and stand age. 

'Tabular values computed with 

the equation and given in Table 3 are 

similar but not identical to those 

obtained directly from the curves 

(Fig. 1). For example, at the index age 

of 50, tabular site indexes are about 

2 feet less than those from the curves 

at site index 50 and below, and are 

about 2 feet higher than indicated by 

the curves at site index 90 and above. 

Nevertheless, nearly all values in the 

table are within + 2 feet of the site 

indexes obtained directly from the 

curves. This is sufficient for field use. 

Discussion 

The curves developed in this 

study apply to stands that have not 

been damaged by major ice and glaze 

storms, and to those which have 

remained relatively well stocked 

throughout their life. Measurements 

from stands where extensive stem 

breakage has occurred, such as that 

associated with the glaze storms of 

1936 and 1950 (Hough 1959), will 

result in abnormally low site indexes. 

Many stands on the Allegheny Plateau 

have experienced this type of stem 

breakage, so care must be exercised 

in selecting sites that are free of such 

disturbance. 

Low estimates of site index also 

are likely if the present curves are 

applied to stands that are sparsely 

stocked, such as orchard stands and 

those that may have existed many 

years at less than 40 to 50 percent 

relative density. This will occur simply because black cherry requires 

strong lateral competition to develop 

straight boles and to maintain normal 

rates of height growth. 

Literature Cited 

Carmean, Willard H. Site index curves 

for upland oaks in the Central 

States. Forest Science. 18:109-120; 

1972. 

Carmean, Willard H. Site index curves 

for northern hardwoods in northern 

Wisconsin and upper Michigan. 

Res. Pap. NC-160. St. Paul, MN: 

U.S. Department of Agriculture, 

Forest Service, Northeastern Forest Experiment Station; 1978. 16 p. 

Hampf, Frederick E. Site index curves 

for some forest species in the eastern United States. Upper Darby, 

PA: U.S. Department of Agriculture, 

Forest Service, Eastern Region; 

1965. 34 p. 

Hough, A. F. Zoning for the manage. 

ment of black cherry on the Allegheny Plateau. Journal of Forestry. 

57~353-357; 1959. 

McQuilkin', Robert A. Site index prediction tables for black, scarlet, 

and white oaks in southeastern 

Missouri. Res. Pap. NC-108. St. 

Paul, MN: U.S. Department of Agriculture, Forest Service, North 

Central Forest Experiment Station; 

1974. 8 p. 
Table 3.-Black cherry site index estimates by 2-foot heights and 2-year ages. - -- 

Stand 

age 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 46 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 

(years) 
Auchmoody, L. R.; Rexrode, C. 0. Black cherry site index curves 

for the Allegheny Plateau. Res. Pap. NE-549. Broomall, PA: 

U.S. Department of Agriculture, Forest Service, Northeastern 

Forest Experiment Station; 1984. 5 p. 

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. 

ODC 541:561.1 

Keywords: Prunus serotina; site index curves; height growth 

a US. GOVERNMENT PRINTING OFFICE: 1984-705-0291529 

I 
Headquarters of the Northeastern Forest Experiment Station are in 

Broomall, Pa. Field laboratories are maintained at: 

Amherst, Massachusetts, in cooperation with the University of 

Massachusetts. 

0 Berea, Kentucky, in cooperation with Berea College. 

Burlington, Vermont, in cooperation with the University of 

Vermont. 

0 Delaware, Ohio. 

0 Durham, New Hampshire, in cooperation with the University of 

New Hampshire. 

0 Hamden, Connecticut, in cooperation with Yale University. 

0 Morgmtown, West Virginia, in cooperation with West Virginia 

University, Morgantown. 

Orono, Maine, in cooperation with the University of Maine, 

Orono. 

0 Parsons, West Virginia. 

0 Princeton, West Virginia. 

0 Syracuse, New York, in cooperation with the State University of 

New York College of Environmental Sciences and Forestry at 

Syracuse University, Syracuse. 

@ University Park, Pennsylvania, in cooperation with the 

Pennsylvania State University. 

0 Warren, Pennsylvania.