No. 125 

1961 

AGE-SIZE RELATIONSHIPS IN 

ALL-AGED NORTHERN HARDWOODS 

During the summer of 1960, a series of clearcuttings in small patches 

were made in an old-growth stand of northern hardwoods on the Bartlett 

Experimental Forest, Bartlett, New Hampshire. This provided an opportunity to observe the variation in ages of a wide range of trees of different 

sites and species. The annual rings of over 100 stumps were counted in 

this stand of typical all-aged, old-growth birch, beech, and maplewhich 

has been untouched by loggers since some light cutting took place late 

in the 19th century. 

Sampling the stumps was on a casual, "let's-take-a-look" basis and was 

not randomized; instead annual rings were counted as the loggers felled 

the tree. Many stumps-particularly those of yellow birch-had rings 

that were extremely difficult to count in the field, so they were by-passed. 

White ash, hemlock, and beech had the easiest rings to count. Almost 

50 percent of the stumps counted were beech; fewer stump counts were 

obtained for sugar maple, red maple, and hemlock-in that order.' 

The resulting data, biased though they were because of sampling inadequacies, brought to light a large variation in ages between trees of 47 

the same diameter. And if the stumps with rings too difficult to count* 

had been included, this variation would conceivably have been greater. 

The extent or magnitude of the variation in ages within d.b.h. classes 

is illustrated graphically in figure 1. The 14-inch d.b.h. class had -the - - 

lFor some early work of this type on hemlock and sugar maple in Michigan see: Gates, 

F. C., and Nichols, G. E. Relation between age and diameter in trees of the primeval northern 

hardwood forest. Jour. Forestry 28: 395, 1930. 
8EEcn 

X SUGAR MAPLE 

0 RED MAPLE 

greatest variation in ages, with a range of 115 years between the oldest 

and the youngest tree; and the 16-inch class had a range of 100 years 

between extremes. Beech alone had a range in age of 74 years for the 

8-inch class and 91 years for the 14-inch class. And the samples were 

fairly evenly distributed throughout the extremes. Vertical lines on the 

graph are merely to emphasize the extent of age variation within d.b.h. 

classes. 
The hemlocks, a common associate of northern hardwoods, were the 

oldest trees recorded, with ages of 205, 214, and 305 years for three 

17-inch trees nione. Hemlock was not included in the plotted data because 

the extreme age of the samples exaggerated the range of ages. 

Intolerant species such as yellow birch, paper birch, and white ash 

did not vary so greatly in age as did the tolerants, the largest spread 

being 26 years for both the 17- and 18-inch d.b.h. classes. This smaller 

variation would be expected, considering the relatively short life-span of 

these species and their inability to withstand shade. 

Of course, the age variation within size classes in these all-aged stands 

is due to differences in individual tree growth rates. These differences 

are in turn brought about mainly by suppression of the tolerant trees to 

various degrees, differences in site characteristics, and perhaps genetic 

differences. Early cuttings in the Bartlett stands played a part in increasing 

this variation by releasing trees from competition and creating openings 

favorable for the establishment of young, thrifty reproduction. TO a much 

lesser extent, natural catastrophe such as windfall and normal stand 

mortality accomplished similar results. Thus these stands are a complex 

mixture of sizes and ages, with a wide range of ages for any particular 

size. 

Aside from being somewhat interesting, the data collected at Bartlett 

emphasize several important questions pertaining to the single-tree selection system, which is widely used in the management of all-aged northern 

hardwoods. For example, can relative age be estimated from the external 

characteristics of a tree? How is age related to vigor? Will a 70-year-old 

8-inch tree respond to release in the same manner as a 90-year-old 8-inch 

tree? Are there differences between the insect and disease resistance of 

such trees? What are the relative sprouting capabilities? 

These are only a few of the many questions which need to be answered 

before we can competently manage northern hardwood stands that have 

age variations within size classes as great as shown in this study. 

-BARTON M. BLUM 

Research Forester, Laconia Research Center 

Northeastern Forest Experiment Station 

Forest Service, U. S. Dept. Agriculture 

Laconia, New Hampshire