No. 122 

1961 

YELLOW BIRCH GROWS BETTER IN 

MIXED-WOOD STANDS THAN IN NORTHERN 

HARDWOOD OLD-GROWTH STANDS 

Yellow birch, the most valuable timber tree in the northern hardwood 

forest, is losing ground in northern New England. Birch dieback in the 

late 1930s and 1940s killed millions of board-feet of yellow birch. Meanwhile, the demand for yellow birch veneer ahd lumber has increased by 

leaps and bounds. So industries that depend upon yellow birch are having 

increasing difficulties in finding adequate supplies of raw material. 

The prospects for a better supply situation in New England during 

the next few decades are not good. Practically all tracts of any size that 

once had good stands of yellow birch have been cut over. Future supplies 

must come mainly from trees that came in after logging or trees that 

were too small to cut when the tract was logged, and thus will be much 

affected by yellow birch growth rates in second-growth and cutover oldgrowth stands. Knowledge of the sites and conditions where yellow 

birch grows best would enable us to favor the species on those sites and, 

to some degree, improve the supply situation in the future. 

Records from permanent cruise plots, which were laid out on the 

Bartlett Experimental Forest in New Hampshire soon after its establishment in 1931, provide comparative performance data for yellow birch 

on sites occupied by typical northern hardwood and by mixed hardwoodsoftwood stands. Records on growth and mortality from plots in these 

two stand types over an &year period after the initial cruise are summarized in this report. For the purposes of this study, only those early 

8-year records were suitable because many of the mixed-wood plots were 

not retallied after 1939-40. 
Historical 

The study plots were all in old-growth stands. These stands had been 

cut over in the 1880s and 1890s-many of them twice, first for softwoods and, a little later, for the better hardwoods-but they had never 

been clear-cut. As far as we know, cuttings in the different forest types 

were all at about the same intensity. 

Possibly the mixed hardwood-softwood stands were cut somewhat 

heavier than the true northern hardwoods because of the demand for 

softwoods at that time. However, since we have no definite knowledge 

of comparative intensities of cuttings, it is assumed that post-cutfing 

conditions on the mixed-wood and northern hardwood sites were roughly 

similar, and that the cuttings did not affect the residual birches 'much 

differently on one class of site than the other. 

In general, the stands left after the cuttings consisted of large trees 

that either were defective or of low-value species, together with many 

stems of varying quality in the pole and small sawtimber sizes. And, in 

general, no management practices were applied. The residual stands 

where the plots for this study were located remained unmanaged up to 

and through the 8-year period on which this report is based. 

The Study 

Fifteen permanent %-acre cruise plots in unmanaged mixed-wood 

stands, and 50 such plots in unmanaged northern hardwood stands provided the basic data for this study. The mixed-wood sites were moist 

areas along brooks or in swales; northern hardwood sites were mostly 

well-drained slopes and ridges. Trees on the plots were measured at the 

time of establishment in 1931 or 1932, and remeasured 8 years later. 

At the beginning of the study, average basal area of the mixed-wood 

stands was 127 square feet per acre, of which about half was in eastern 

hemlock and red spruce, and half in red maple, yellow birch, beech, and 

Table 1.--Initial percentage of basal area in yellow birch by cover type 

Initial total 

basal area 

per acre 

Cover 

type 

square Percent Percent - 

- feet 

Northern hardwood 17 48 2 7 14 11 104 

Mixed-wood 17 31 29 27 13 12 7 

Initial 

proportion of 

yellow birch 

Percentage distribution of 

yellow birch basal area 

. 

5-1W 11-15% 16-20% 21+% 
other hardwoods. Average basal area of the northern hardwood stands 

was 104 square feet per acre, nearly all of which was in hardwoods; 

only a few scattered hemlocks and spruces grew on the plots. In both 

types, yellow birch comprised 17 percent of the basal area, and distributions of the birch by size groups fell into somewhat similar patterns 

(table 1). The higher percentages of the basal area in larger trees in 

the mixed-wood reflects faster growth rates of the birch on those sites. 

Table 2.--Annual accretion1 and mortality, in percentage of basal area, 

by species and type (trees larger than 4.5 inches d.b.h.) 

'~ccretion is growth in basal area (expressed here as a percentage of initial basal area) on trees 

that were larger than 4.5 inches d.b.h. at the time of the first masurement. Growth on trees that died 

b 

Cover 

type 

a during the period is not included. 

Comparisons of the 8-year growth between species and types are 

expressed below in terms of accretion rates (see table 2). Since yellow 

birch always shows relatively little ingrowth because of its intermediate 

tolerance, accretion-which does not include ingrowth-was considered 

the best measure for comparing this species with its more tolerant 

neighbors. 

The annual accretion rate of yellow birch over the 8-year period was 

2.1 percent in the mixed-wood, as compared to 1.7 percent in the northern 

hardwood type. On mixed-wood sites, yellow birch grew as fast or faster 

than three common associates-beech, red maple, and eastern hemlock. 

On northern hardwood sites, it ranked last among these associates, partly 

because it grew more slowly there, and partly because the other species 

grew better on these sites (table 2). 

Average annual yellow birch mortality, in percent of basal area, was 

only 0.5 percent on the mixed-wood sites; on the northern hardwood 

sites, it was 1.3 percent-more than 2% times as much. In general, birch 

mortality compared favorably with that of other species on mixed-wood 

sites, but considerably exceeded that of other species on northern hardNorthern hardwood 2.1 0.6 1.7 1.3 2.6 0.1 2.6 0.1 

Mixed-wood 1.6 .6 2.1 .5 2.1 .5 1.7 .1 

wood sites (table 2) . 

Beech Eastern hemlock 

Accretion Accret ion 

Mortality 

Mortality 

Yellow birch 

Accre- ' MortalRed maple 

t ion 

Accret ion itY 

Mortality 
Discussion 

Since this study was restricted to one small locality, conclusions drawn 

from it must be somewhat tentative. The data definitely do indicate, however, that in old-growth stands yellow birch grows appreciably faster, 

and suffers appreciably less mortality, on sites occupied by mixed-woods 

than on those occupied by true northern hardwoods. 

There is abundant evidence from other Bartlett studies1 that yellow 

birch in northern hardwood stands grows comparatively slowly-in fact, 

that it generally is the slowest growing component of such stands on 

typical northern hardwood sites. So far as can be determined from our 

data, better performance by the birch on mixed-wood sites holds true 

for trees of all sizes beyond the sapling stages. And although we do not 

have direct supporting evidence, it may reasonably be assumed to hold 

true for trees of all ages, and for second growth as well as old growth. 

The better performance of yellow birch in mixed-wood than in northern 

hardwood stands is viewed primarily as an effect of site, although associated species possibly exert some influence. The specific factors responsible for the differences in growth and mortality have not been determined; this is a subject meriting further study. 

The results reported above have practical significance: Because of the 

dwindling supply of yellow birch timber, some real effort will be required 

to provide for the future demands of industry. So, although northern 

hardwood stands have been a major source of yellow birch timber in 

the past, the slow growth and high mortality of the species on typical 

northern hardwood sites means that these sites are not the best ones for 

growing birch under management. Our findings indicate that one opportunity for increasing production of yellow birch lies in management practices that favor the species on the moist mixed-wood sites where it 

apparently grows best. 

-WILLIAM B. LEAK 

Research Forester, Laconia Research Center 

Northeastern Forest Experiment Station 

Forest Service, U. S. Dept. Agriculture 

Laconia, N. H. 

lFilip, Stanley M., Marquis, David A., and Leak, William B. Development of old-growth 

northern hardwoods on the Bartlett Experimental Forest-a 22 year record. Northeast. Forest 

Expt. Sta., Sta. Paper 135. 7 pp., illus. 1960. 

Gilbert, Adrian M., Wilson, Robert W., Jr., and Hutnik, Russell J. Growth behavior of 

northern hardwoods after a partial cutting. Jour. Forestry 53 : 488-492, 1955. 

Wilson, Robert W., Jr. How secondgrowth northern hardwoods develop after thinning. 

Northeast. Forest Expt. Sta., Sta. Paper 62. 12 pp., illus. 1953. 

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