United States 

Forest Service 

Northeastern Forest 

Experiment Station 

Seed Fall in an 

Old-growth Northern 

Hardwood Forest 

Research Paper N E-663 

Raymond E. Graber 

William B. Leak 
Abstract 

Seed fall was measured for 11 years in a 200-year-old stand of sugar maple (Acer 

saccharurn Marsh.), yellow birch (Betula alleghaniensis Britton), and beech (Fagus 

grandifolia Ehrh.) in New Hampshire. These species accounted for 98 percent of the 

seed fall. Yellow birch had 5 good seed years, sugar maple had 3, and beech had 

none. Time of seed fall varied among species and years. Viable seed fall of yellow 

birch in good seed years began in August and continued through autumn and 

winter. Most of the viable sugar maple seed fell during a short period in October, just 

before and after leaf fall. Beech seed fall was similar, but occurred slightly later than 

sugar maple. Seed losses caused by pollination or fertilization failure, abortion, 

incomplete development, insects, small mammals, and birds varied widely among 

years, but averaged about 2/3 of the potential seed crop. Losses often were 

proportionally greater during poor seed years. 

The Authors 

RAYMOND E. GRABER, retired, served as a plant ecologist at the Northeastern 

Forest Experiment Station, Forestry Sciences Laboratory, Durham, New Hampshire. 

He graduated in forest management from the University of Washington and has 

studied forest ecology at Oregon State University and botany at the University of 

New Hampshire. 

WILLIAM B. LEAK is a research forester at Durham, New Hampshire. With B.S. and 

M.F. degrees from the State University of New York College of Forestry, he joined 

the Station in 1956 and conducts research on site evaluation, silviculture, and 

ecology of northern hardwoods. 

Manuscript received for publication 3 February 1992. 

Acknowledgment 

The authors appreciate the contributions of Donald F. Thompson, retired forestry 

technician. Don's dedicated efforts on the collection, evaluation, and recording of 

seed data were essential to the successful completion of this study. 

Northeastern Forest Experiment Station 

5 Radnor Corporate Center 

100 Matsonford Road, Suite 200 

P.O. Box 6775 

Radnor, Pennsylvania 19087-4585 

July 1992 
Introduction 

The production of seed by forest trees is a fundamental 

step in stand replacement. Most harvested stands in the 

northern hardwood forest are replaced through natural 

regeneration. Foresters try to time harvest cuts to coincide 

with good seed crops. To do this effectively, they need 

accurate and detailed information on the frequency, timing, 

size, and viability of seed crops. 

Seed crops also are of concern to wildlife managers 

interested in seed as food for birds and mammals. The 

abundance of seed from year to year has a major bearing 

on feeding habits and population levels of certain species. 

There are many gaps in our knowledge of seed production 

in the northern hardwood forest, particularly in New 

England. Much of the past research is subjective, shortterm, lacking in detail on seed viability or stand conditions, 

or derives from other regions where soils and climate differ 

from those in New England (Curtis 1959, Eyre and Zillgitt 

1953, Benzie 1959, Godman and Mattson 1975, Marquis 

1969, Grisez 1975, and Bjorkbom 1979). To fill some of 

these informational gaps, this study was designed to 

measure total seed production over an 1 1-year period, 

annual variations in seed crops, seed viability and seed 

losses in an old-growth sugar maple (Acer saccharum 

Marsh .), yellow birch (Betula alleghaniensis Britton), beech 

(Fagus grandifolia Ehrh.) stand in New Hampshire. 

Study Area 

The study was conducted in the Bowl Research Natural 

Area, White Mountain National Forest, New Hampshire. The 

stand consisted of mature sugar maple, beech, and yellow 

birch (Eyre 1980) that had been undisturbed for more than 

200 years (Fig. 1). It contained a relatively small number of 

tree species: an overstory of mature sugar maple, yellow 

birch and beech, and a well-developed understory of beech 

with a few red spruce (Picea rubens Sarg.) and striped 

maple (Acer pensylvanicum L.). 

A uniform stand of 1 ha was selected as the study plot. 

The aspect was southeasterly with an average slope of 27 

percent and an elevation of 630 m. The soil was a fine 

sandy loam till (Leak 1980) derived from granitic bedrock. 

Northern hardwoods grow well in this type of habitat (Leak 

and Riddle 1979). The plot had a basal area (trees >5 cm 

d.bl.h.) of 44.5 mtha and a seed tree (>25 cm d.b.h.) basal 

area of 34.4 mha (Table 1). Mean d.b.h. and height of 

dominant seed trees were: sugar maple, 52.1 cm and 

24.7 m; beech, 41.9 cm and 22.2 m; yellow birch, 46 cm 

and 23.8 m. 

Methods 

Twenty seed traps were distributed systematically in the 

study plot, from a random start, for the May-November 

observation periods. A modified version (Fig. 2) of 

Figure 1. -This old-growth sugar maple-yellow 

birch-beech stand has been undisturbed for 

more than 200 years. 

Bjorkbom's (1971) cylinder trap was used. The trap was a 

metal cylinder 15.3 cm diameter and 17.7 cm tall, open at 

the top with drainage holes in the bottom. A cloth liner was 

placed in the trap to ensure the capture of very small 

seeds. During windy periods, this type of trap produces an 

air stream deflection that reduces the seed catch. To 

correct this problem, a strip of metal screening was 

attached to the top of each trap. To eliminate small 

mammal depredation, a no. 2 mesh hardware cloth cover 

was placed across the top of the metal cylinder. 

Table 1 .-Stand composition (percent of basal area) by 

species and d.b.h. in the Bowl plot 

- -- 

D.b.h. Sugar maple Beech Yellow birch Red spruce 

----------------- percent basal area ...................... 

All trees 

(>5 cm) 58.1 30.1 11.1 0.7 

Seed trees 

(>25 cm) 69.4 17.2 13.4 0.0 
Figure 2. -Cylindrical seed trap as used during the 

growing season. The screen top reduced wind deflection 

during windy periods, increasing trap reliability. 

During winter, the trap construction and layout were 

modified. The number of traps was reduced to 10, placed 

at intermediate points between the locations of the summer 

traps. Instead of drainholes in the bottom, a single drain 

was drilled in the side of the cylinder, 6.4 cm above the 

bottom. A plastic spout with gauze across the inlet was 

friction-fitted into the hole. The hardwood cloth mesh cover 

and the cloth bags were removed from the cylinder. Six 

hundred ml of antifreeze (ethylene glycol) were poured into 

the trap. The trap was mounted on a pole at a height 

above the maximum snow pack. In operation, the snow 

melted as it came into contact with the antifreeze. Excess 

liquid drained out through the plastic spout. The gauze 

prevented loss of seed. These traps remained operational 

without maintenance for at least 8 weeks under conditions 

in the White Mountains. 

Seeds were collected at 2-week intervals during snow-free 

periods, and at 6- to 8-week intervals during winter. In the 

laboratory, the seeds were identified, counted, and tested 

for viability. Viability was determined by cutting and testing 

for germination during the growing season. Winter seeds 

were tested only by cutting due to the toxic effects of 

2 

ethylene glycol. Nonviable seeds were examined carefully 

to determine the cause. Bird, mammal, and insect injury 

was recognized by the unique damage. Empty seed 

denoted pollination-fertilization failure. Early seed fall of 

green, immature seeds occurred with some species. Other 

seeds were partially filled, indicating incomplete 

development due to environmental causes. 

The final measure of the effectiveness of a seed crop is 

the number of seedlings produced. Seedling emergence 

was observed on 10 randomly located circular plots (1 m2) 

from 1972 through 1980. The plots were checked for 

emergence at 2-week intervals during the growing season, 

when the seed traps were emptied. 

Results and Discussion 

Annual Seed Fall 

Yellow birch. Seed fall varied greatly during the 11 years 

of observation (Table 2). An excellent crop of 64 million 

seedsha occurred in 1974. The amount of viable seed was 

substantially lower, about 33 million (Fig. 3). Good viable 

crops of 6 to 15 million were produced in 1971, 1972, 

1977, and 1979. Medium crops of about 2 million were 

produced in 1976 and 1981. In the remaining 4 years, the 

crops were poor, such that they don't show on the chart, a 

fraction of a million viable seeds. 

Table 2.-Total seed fall (millionsha) by species and 

yeara 

Year Yellow birch Sugar maple Beech 

aMean * confidence limit, P=0.95. ' 

Seed viability of yellow birch ranged from 4 percent in the 

poor 1980 seed year to 51 percent in the excellent 1974 

year. Viability increased as the size of the seed crop 

increased (Fig. 4). In the 5 good or better years, viability 

never fell below 25 percent; in the 4 poor years, it never 

exceeded 10 percent. 

Sugar maple. Total annual seed fall ranged from 0 to 12 

million seedsha (Table 2). Good viable crops of 

approximately 3 million seedsha were produced each year 

in 1971, 1974, and 1981 (Fig. 3). Medium crops of 1-2 

million seedsha occurred in 1976, 1978, and 1979. Poor 
Beech Viable 

0.5 0 Nonviable 

n 

Yellow Birch 

71 72 73 74 75 76 77 78 79 80 81 

YEARS 

Figure 3. -Total (viable and nonviable) seed 

production by species and years. 

n Yellow Birch 

Y = 8.8+1 .45X-.013X2 s 

V 

RZ = .681 

> 

k 

1 

i 2'0 3'0 40 5b 6'0 

TOTAL SEED FALL (MILLIONS) 

h 

s Sugar Maple 

V Y =3 l+953X- 650x2 

R2= 783 c 

d 50- 

m 

I I I I Y I 

0 2 4 6 8 10 12 

TOTAL SEED FALL (MILLIONS) 

Figure 4.- Percent viable seed over total 

seed fall for yellow birch and sugar maple. 

crops of approximately 0.2 million seeds were recorded in 

1972 and 1980. Only nonviable seeds fell in 1975 and 

1977 and no seed was found in 1973. 

Viability was related to size of the seed crop (Fig. 4) and 

ranged from 0 to 48 percent. An exception was the largest 

seed crop (1971), which had the relatively low viability of 

26 percent. This low viability was the result of a severe 

outbreak of the saddled prominent (Heterocampa guttivitta 

Wikr.), a general foliage eater that consumed the seed 

pedicels and occasionally part of the samara, causing lethal 

injury to immature seeds. 

Six years of the 11 -year period produced good or medium 

crops of viable sugar maple seed and 5 years produced 

little or no seed. This is not a serious limitation since most 

successful sugar maple regeneration originates from 

advanced growth present in the understory at the time of 

ha~est. This advanced growth is replenished periodically 

during good seed years (Forcier 1975). 

Beech. Total seed fall ranged from 0 to 0.43 million seeds 

per ha (Table 2). The largest crop, 0.22 million viable 

seeds per ha in 1978 (Fig. 3), was considered a medium 

crop. Medium amounts of seed also were produced in 
Table 3.-Species shedding minor amounts of seed on the study plot in seeds 

per ha during the entire 11-year period 

Species 

No. of 

Seed fall years Nearest plant 

Total Viable Elevation Distance 

Red maple 

Acer rubrum 

Striped maple 

Acer pensylvanicum 

Mountain paper birch 

Betula cordifolia 

Paper birch 

Be tula papyrifera 

Red spruce 

Picea rubens 

Eastern hemlock 

Tsuga canadensis 

Balsam fir 

Abies balsamea 

Goldenrod 

Solidago Spp. 

Round-leaved violet 

Viola rotundifolia 

Shining club-moss 

Lycopodium lucidulum 

587 

632 

794 

587 

61 7 

61 1 

616 

Unknown 

632 

632 

151 

29 

45 1 

1 72 

53 

37 

4 1 

Unknown 

On plot 

On plot 

1971, 1974, and 1981. Poor seed crops occurred in 1973, 

1976, and 1980; and there was no viable seed in 1972, 

1975, 1977, and 1979. Seed viability, ranging from 0 to 57 

percent, was unrelated to size of crop. 

The frequency of beech seed years-4 with no seed, 3 

with poor crops, and 4 with medium crops-may be low for 

this species. There are reports of good seed years every 2- 

5 years (USDA 1974). This low production may be due to 

poor tree vigor since many of the largest beech appeared 

to have large dead branches in the crown. The cause of 

this condition could be the beech scale Nectria complex, 

which was present in the stand. Senescence could be a 

factor; but beech is a long-lived species that may survive 

300-400 years (Deen 1937). Another reason for the poor 

seed production might be the relatively high elevation of the 

plot (630 m). Beech seldom grows above 760 m in this 

area (Leak and Graber 1974). 

Minor Species. The viable seeds of the species listed in 

Table 3 represent less than 3 percent of the total viable 

seed fall (all species) during the I I-year study. Only two 

species, shining club-moss and round-leaved violet, had 

4 

mature plants present on the study plot. Seed from the 

other species came from beyond the plot boundaries. 

Possibly, one reason for the low seed viability of some 

minor species-balsam fir and red maple, for examplewas that empty or partially-filled seed is more likely to 

travel farther than filled seed. 

Seasonal Pattern of Seed Fall 

Yellow Birch. Some seed fell in every month of the year. 

A small amount of new seed fell as early as June, but no 

viable seed of the current crop fell until August. In the 5 

best seed years, viable seeds fell by mid-August. During 

the 3 medium seed years, the first viable seed fell in late 

August or early September. Seed fall in poor years 

occurred later: the first viable seed was noted in early 

September (1975), early October (1973), or as late as midNovember (1978 and 1980). Thus, the smaller the seed 

crop, the later the dispersal of viable seed. 

Three yellow birch seed years are illustrated in Fig. 5 to 

show the year-to-year variation in pattern. In 1974, 

approximately three-fourths of the viable yellow birch seed 
fell in October; in 1972 and 1977, only one-third or less fell 

by this date. At the end of November, 1974, most of the 

viable seed had been shed. The comparable figure was 88 

percent in 1972 and 57 percent in 1977. The 1977 seed 

crop was unusually late: approximately two-fifths of the 

seed fell in December and January. In good seed years, 

viability usually remained above one-third of the total 

through early winter, and then declined. 

Sugar Maple. Nearly all of the seed fell between June 

and late November regardless of crop size. This pattern 

was basically the same in a good year (1974), a medium 

year (1978), and a poor year (1972)(Fig. 5). Very little of 

the seed fall from May through August was viable. There 

were two peaks in the annual seed fall. The first occurred 

in midJune and was caused by seed abortion and insect 

attack. The June seed fall usually was much smaller than 

the October peak. A single exception was in 1979 when 

- - 

H Viable 

Nonviable 

Yellow 

Birch 

2 MJ JASONDJFMAMJ J 

MJJASONDJFMAMJJ 

Yellow Birch 

1 

n 19n 

MJJASONDJFMAMJJ 

MONTHS 

Sugar Maple 

1 972 

n 

-lLb&m MJJASONDJ 

Sugar Maple 

1974 

MJJASONDJ 

Sugar Maple 

1978 

M J J A S O N D J 

Beech 

Composite of all years 

MJJASONDJ 

Figure 5.-Average daily seed fall (viable and nonviable) by time periods, species, and selected years. 5 I 
the June seed fall was 3.71 million per ha and the October 

seed fall was 2.47. 

Generally, much of the viable sugar maple seed fell in 

October. Seed fall was particularly heavy during and just 

after leaf fall. In some years, most of the viable seed fell in 

a single 2-week period in early October: 77 and 89 percent 

of the viable crop fell during this period in 1976 and 1979, 

respectively. Few seeds fell in November, and viable seeds 

fell in December only in 1977 and 1979. 

Seed viability of sugar maple changed in a predictable way 

as the season advanced. Seed fall during June, July, and 

most of August was nonviable. Beginning in September or 

October, viability rose sharply, signaling the start of rapid 

seed fall. In good and medium seed years, viability 

averaged approximately 50 percent during this period. Peak 

viability remained for 2-4 weeks, and then dropped abruptly. 

Beech. The observations on this species are limited since 

there were no really good seed years, and only 3 medium 

years during the study. A composite graph of all seed 

years illustrates the sequence (Fig. 5). The seeds were 

shed in a pattern similar to that of sugar maple. There 

were two periods of seed fall in most years, a small 

amount in early summer (about 10 percent) and the 

remainder from late summer into early winter. The summer 

seed fall was nonviable because nearly all the seeds were 

insect infested. The first viable seeds fell in later 

September. Peak viable seed fall took place in mid-October 

to early November. The percentage of viable seeds 

increased from 14 percent in September to 83 percent in 

early November, then declined. The year-to-year variation in 

dates of seed fall was minor and did not seem related to 

size of the seed crop. 

Losses to Birds 

and Small Mammals 

Birds. The study provided estimates of bird consumption 

from feeding in the trees; there was no measure of 

consumption from ground feeding. However, little ground 

feeding was noted in the course of the study, and the data 

should represent a fairly good measure of the impact of 

birds on the seed supply. The species of birds observed 

consuming seed are listed in Table 4. 

During the 1 1-year period, birds consumed an average of 

1.1 percent of the sugar maple seed, 3.5 percent of the 

beech seed, and 16.3 percent of the yellow birch seed. The 

impact of birds on sugar maple and beech was minor, but 

the impact on yellow birch was substantial, ranging from 

none to 24.2 percent of the total seed crop. Bird consumption as a percentage of filled seed was as high as 39.8 

percent. The amount of seed eaten was correlated with the 

total yellow birch crop (Fig. 6). Birds consumed the highest 

percentage of seeds during good and excellent seed years. 

In only 1 of the 4 poor years was a measurable amount of 

seed consumed by birds. 

Table 4.-Birds observed eating tree seed in the study 

area. 

- - - - - - - 

Species consumed 

Bird species Yellow birch Sugar maple Beech 

Blue jay 

Cyanocifta cristata 

Black-capped chickadee 

Parus atricapillus X 

White-breasted nuthatch 

Sitta carolinensis 

Evening grosbeak 

Coccothraustes vespetfina 

Purple finch 

Carpodacus purpureus 

Common redpoll 

Carduelis flammea X 

Pine siskin 

Carduelis pinus X 

American goldfinch 

Carduelis tristis X 

Slate-colored junco 

Junco hyemalis X 

Yellow Birch 

Y = .317+ .809X- .008X2 

RZ = ,728 

TOTAL SEED FALL (MILLIONS) 

Figure 6.-Percent of yellow birch seed 

consumed by birds over total seed fall. 
Table 5.-Small mammals eating tree seed on the study 

area 

Species consumed 

Mammal species Yellow birch Sugar maple Beech 

Red-backed vole 

Clethrionomys gapperi X X 

Deer mouse 

Peromyscus maniculatus X X X 

VVoodland jumping mouse 

Napaeozapus insignis X X 

Eastern chipmunk 

7'amias striatus 

Red squirrel 

Tamiasciurus hudsonicus X X X 

Small Mammals. Five species of small mammals known to 

be seed predators were observed on the study plot (Table 

5,). Deer mice, chipmunks, and red squirrels were the most 

numerous and the most voracious consumers of seed. 

Seed losses were attributed to small mammals only when 

the seeds were eaten in the trees and characteristic 

fragments with tooth marks fell into a trap. No yellow birch 

seed fragments were found in the traps. The percentage of 

total seed fall destroyed was 0.5 for sugar maple and 4.7 

for beech. This arboreal feeding was done primarily by red 

squirrels and chipmunks in late summer and autumn. In 

contrast to losses to birds, the bulk of seed losses to small 

mammals, no doubt, occurs after seed fall. 

Losses to Insects 

Yellow Birch. The average annual seed loss to insects 

was 15.1 percent of the total yellow birch seed fall. The 

amount of seed consumed by insects ranged from 4.2 

percent in 1974, the best seed year, to 44.6 percent in 

1980, a poor seed year. While the actual number of seeds 

consumed was positively related to seed crop size, there 

was a trend (nonsignificant) toward greater percentages of 

consumed seed with smaller seed crop (Fig. 7). This trend 

may reflect the inability of insects to rapidly increase in 

population size to take advantage of good seed cropsespecially when preceded by a poor crop. 

Three species of insects are known to damage yellow bi~ 

seed (Baker 1972; Shigo and Yelenosky 1963; Shigo, 

personal communication). The birch seed midge 

(Oligotrophus betulae Winn.) caused only minor seed 

losses. Far more important were the seed weevil (Apion 

washii Smith) and the birch catkin moth (Epinotia 

transmissana Wik.). The larvae of these two species 

tunneled into the developing yellow birch strobili, causing 

98 percent of all losses of yellow birch seeds due to 

insects. 

Yellow Birch 

Y = 29.2-.37X+.OOO2X2 

TOTAL SEED FALL (MILLIONS) 

50 - Sugar Maple 

Y = 3.3+1.07X+4.841 (1IX) 

40 - 

R2 = ,709 

30-'I 0 

- u / I I I I I I 

0 2 4 6 8 10 12 

TOTAL SEED FALL (MIL-LIONS) 

Figure 7. -Percent of seed consumed by insects 

over total seed fall for yellow birch and sugar maple. 

Sugar Maple. As with yellow birch, there was some 

suggestion of a negative correlation-a sharp drop preceding a plateau-between percent insect damage and crop 

size (Fig. 7). Annual losses averaged 12.4 percent. Most of 

the damage was caused by unidentified lepidopterous 

larvae, which burrowed into the seeds and consumed their 

contents. 

Beech. Insect-damaged seeds were not recorded 

separately for this species before 1977. From 1977-1 981, 

34.9 percent of all beech seeds were destroyed by insects, 

ranging from 1 1 .I percent in 1981 to 90 percent in 1979. 

Most of the insect-infested seed fell during the summer. 

Larvae of the filbert worm (Melissopus latiferreanus Wlsm.) 

were identified; these bored into the seed and mined the 

interior. 

Other Causes of Nonviable Seeds 

Many seeds were not viable due to pollination or 

fertilization failures, abortion, or incomplete development. 

These nonviable seeds represented 28.1 percent, 53.8 

percent, and 27.9 percent of all yellow birch, sugar maple, 

and beech seed, respectively. 

Eighteen percent of the yellow birch seeds were empty; the 

paired ovules in the individual seeds had not developed. 

This was primarily the result of pollination or fertilization 

failure (W. Gabriel, personal communication). The primary 

cause of this failure probably was poor quality or sparse 

pollen. In years characterized by sparse flowering, seed 

production was poor and the proportion of empty seeds 

was high (Fig. 8). In the poor seed year of 1973, over half 

7 
Yellow Birch 

50 Y = 26.4- .234X+9.485 (1 .OIX) I 

I I I I I 

0 10 20 30 40 50 60 

TOTAL SEED FALL (MILLIONS) 

Figure 8.-Percent of empty yellow birch seed, 

resultina from ~ollination or fertilization failure. 

the seeds were empty; in the excellent year of 1974, only 

14.9 percent of the crop was nonviable due to empty 

seeds. 

The other important cause of nonviable yellow birch seed 

was incompletely developed or partially filled seed, which 

accounted for 10.1 percent of the total catch. The percentage of partially filled seed tended to be higher in poor seed 

years, averaging 22.2 percent, and lower in good-toexcellent years, averaging 8.9 percent. 

Sugar maple had the highest proportion of empty seeds 

YELLOW BIRCH 

18.0% 

EMPTY 

10.1 % 

PARTLY FILLED 

15.1% 

INSECTS 

16.3% 

BIRDS 

1.0% 

MISCELLANEOUS 

39.5 Ye 

VIABLE SEED FALL 

SUGAR 

(46.2 percent); the percentage did not seem related to size 

of crop. The high percent of empty seed was due primarily 

to post-zygotic abortion, which occurred in the spring soon 

after fertilization (Gabriel 1967). As a result, one seed in 

each double samara usually was empty in both good and 

poor seed years. Abortion of the remaining seed in June 

and subsequent abscission of the double samara was far 

less common, accounting for an average of only 3.5 

percent of the sugar maple seed crop. The highest June 

losses were in 1979, when 15.7 percent of the seed crop 

dropped. This loss probably was related to unusually dry 

conditions. June rainfall in 1979 was less than half that of 

normal, primarily occurring late in the month. By midJune 

of that year, newly-fallen double samaras littered the 

ground. 

For sugar maple, incomplete development or partially filled 

seed was relatively unimportant, accounting for only 4.0 

percent of the seeds. The percentage of partially filled seed 

ranged from 1.1 percent in the excellent seed year of 1974 

to 8.7 percent in the moderate year of 1978. 

Nearly all of the empty beech seed, 26.7 percent of the 

total crop, was caused by pollination or fertilization failure. 

The amount of empty beech seed was unrelated to size of 

seed crop. 

Seed Loss After Dissemination 

On the average, about one-third of the total seed fall 

reached the ground in a viable condition (Fig. 9). Only 

general observations were made on the fate of seeds after 

seed fall. No ground feeding was observed on yellow birch, 

46.2% 

EMPTY 

PARTLY FILLED 

3.5 X 

ABORTED 

12.4% 

INSECTS 

BIRDS 

SMALL MAMMALS 

7 

VIABLE SEED FALL 

BEECH 

1.2% 

PARTLY FILLED 

3.5 Ye 

BIRDS 

34.9 Ye 

INSECTS 

4.7% 

SMALL MAMMALS 

29.0% 

8.1% 

SEEDLINGS 

Figure 9.-Seed losses by cause, and final seedling production in percent of total seed fall by species. 
t,hough some small amount probably occurred. Why, then, 

was there such a low percentage of emergence (1.6 

percent) for this species? In most years, when seedling 

emergence took place, large numbers of newly germinated 

yellow birch seeds were found buried in the leaf litter, too 

deep to emerge successfully. Perhaps the main factor 

limiting emergence and initial survival of yellow birch was 

not predation, but lack of favorable microsites or niches for 

initial seedling establishment. 

With both beech and sugar maple, seed predation on the 

ground undoubtedly was significant. During the period of 

rapid seed fall in medium and good years, much viable 

seed could be seen on the forest floor. But within a week 

or two, most of the viable seed exposed on the surface of 

the forest floor had been consumed or removed by small 

mammals and, to a lesser extent, by birds. Seeds that 

escaped this feeding activity almost always were buried 

deep in the litter or humus. 

Viable Seed Biomass 

Dry weights of viable seed collected in the seed traps were 

determined for yellow birch, sugar maple, and beech. 

Sixteen seed lots were weighed for each species. The 

seeds were collected during periods of maximum seed fall 

from 1976 to 1981. Yellow birch averaged 734,888 viable 

seeds per kg. Based on this weight, the annual seed 

biomass for yellow birch ranged from 0.03 to 44.71 kg per 

ha, and averaged 9.10 kg. The average number of viable 

sugar maple seeds per kg was 12,333. Sugar maple seed 

c;rops ranged from zero to 257.58 kg per ha, averaging 

106.80 kg. The average number of beech seeds per kg 

was 3,728. The annual beech crop ranged from zero to 

57.30 kg per ha, and averaged 16.54 kg. The three species 

combined produced an average of 132.44 kg of viable seed 

per ha. 

In the best seed year, 1974, total seed fall of viable seeds 

was 44.71 kg for yellow birch, 259.60 for sugar maple, and 

28.65 for beech-a combined total of 332.96 kg per ha. In 

the poorest year, 1975, neither sugar maple nor beech 

produced viable seed and the yellow birch crop was only 

0.15 kg per ha. The extreme year-to-year fluctuation in 

seed biomass undoubtedly has a major impact on wildlife 

food supplies and population levels in the old-growth 

northern hardwood forest. 

Viable seed biomass is a measure of the resources a 

species allocates to regeneration and serves as a guide to 

its reproductive strategy. It is apparent from these data that 

seed production represents a substantial investment in 

reproductive energy that varies with species. The annual 

seedfall biomass per 10 m2 of seed-tree basal area 

averaged 19.7 kg for yellow birch, 44.7 kg for sugar maple, 

and 27.9 kg for beech. The dry weight seedfall of sugar 

maple was 60 percent greater than that of beech and 127 

percent greater than yellow birch. A possible reason for 

tlhese differences is that sugar maple is mostly dependent 

for its maintenance on seed with sufficient reserves to 

assure root penetration and survival in the undisturbed litter 

and low light levels characteristic of northern hardwood 

understory conditions. Beech, on the other hand, has less 

need for a major expenditure of energy on seed, since its 

characteristic ability to root sucker provides an alternative 

means of reproduction. Yellow birch becomes established 

on disturbed mineral soil (windthrow mounds, for example) 

and rotten logs or stumps within canopy gaps. In this case, 

the strategy appears to be the production of many seeds, 

with low food reserves, to maximize the chance that seeds 

will find a suitable regeneration niche. 

Seedling Emergence 

The emergence of newly germinated seedlings is the 

crucial test of the effectiveness of a seed crop. The 

proportion of the seed fall actually resulting in a seedling 

was low (Fig. 9). The number of yellow birch seeds 

required to produce a single seedling ranged from 22.5 to 

319.9 and averaged 62.5 over the 11 -year study period. A 

major factor affecting the required number of seeds was 

viability of the seed crop. But even more important was the 

moisture condition during the growing season, which 

favored germination and root penetration into the seedbed. 

In years when precipitation was inadequate, emergence 

was very low and the seed-to-seedling ratio was very high. 

The number of emerging seedlings was not closely 

correlated with total seed fall (r2=.20) due to this sensitivity 

to seedbed moisture. 

The mean number of sugar maple seeds per emerged 

seedling was 13.4, ranging from 8.5 to 84.2. In years of 

abundant seed fall, sugar maple produced a lower ratio of 

seeds to seedlings than in poorer seed years. In such 

abundant years, there was sufficient seed to satiate ground 

feeders, and still produce many seedlings. As a result, 

seedling emergence was positively correlated with total 

seed fall (r2=0.75). Seedbed moisture was not an important 

factor because most sugar maple emergence took place 

early in the spring when moisture was not limiting. 

The number of beech seeds per seedling was similar to 

that of sugar maple: an average of 12.3, ranging from 4.5 

to 17.4. Seed viability, ranging from 0 to 57 percent, was 

an important factor influencing the seed-to-seedling ratio. 

Although seed fall and viability were not closely related, 

total seed fall did correlate with numbers of emerging 

seedlings (r2=0.45), but viable seed fall correlated much 

better (r2=0.84). Beech seed was subject to heavy ground 

feeding, primarily by small mammals. Most of the seed that 

escaped the predators germinated in May and June. These 

seeds were deeply buried in the litter and humus and were 

little affected by the occasional mild spring droughts that 

occur in northern New England. 

Conclusions 

Results of this study show that seed production in an oldgrowth northern hardwood forest varies by species. Yellow 

birch produces more abundant seed crops at more frequent 

intervals than sugar maple or beech. For an equal amount 

of basal area, yellow birch was 26 times as prolific as 

sugar maple and 169 times as prolific as beech. Medium or 

9 
better seed years occurred in 2 of 3 years for yellow birch, 

1 of 2 years for sugar maple, and 1 of 4 years for beech. 

Seedling emergence as a percentage of total seed fall was 

much lower for yellow birch than for beech and sugar 

maple. These seed fall and emergence figures reflect 

different reproductive strategies. Yellow birch, especially in 

a closed stand, has specific seedbed requirements in terms 

of moisture and seedbed conditions, due in part to the 

small size of seed. To contact an appropriate seedbed, 

large numbers of widely distributed seeds are needed. 

Sugar maple and beech have large seeds that can tolerate 

a wide range of seedbed conditions. And, because of its 

ability to root sucker, seed production in beech is not as 

critical as for sugar maple. 

Timing of seed fall differed by species. Yellow birch seed 

was distributed over an extended period, especially when 

seed was abundant, from August through the following 

May. Most of the viable seed fell in September, October, 

and November; but, there were exceptional years when up 

to 43 percent of the viable seed fell in December and later. 

While both sugar maple and beech seed fell throughout the 

summer and autumn, the viable seedfall was mostly 

confined to September through October for sugar maple 

and October through November for beech. No viable beech 

Literature Cited 

Baker, W.L. 1972. Eastern forest insects. Misc. Pub 

1175. Washington, DC: U.S. Department of Agriculture. 

642 p. 

Benzie, J.W. 1959. Sugar maple and yellow birch seed 

dispersal from a fully stocked stand of mature northern 

hardwoods in the Upper Peninsula of Michigan. Tech. 

Note NC-561. St. Paul, MN: U.S. Department of Agriculture, 

Forest Service, North Central Forest Experiment Station. 

1 P. 

Bjorkbom, J.C. 1971. Production and germination of 

paper birch seed and its dispersal into a forest opening. Res. Pap. NE-209. Upper Darby, PA: US. Department of Agriculture, Forest Service, Northeastern Forest 

Experiment Station. 14 p.9. 14 p. [?I 

Bjorkbom, J.C. 1979. Seed production and advance 

regeneration in Allegheny hardwood forests. Res. Pap. 

NE-435. Broomall, PA: U.S. Department of Agriculture, 

Forest Service, Northeastern Forest Experiment Station. 

8 P. 

Curtis, J.T. 1959. The vegetation of Wisconqin. Madison, WI: University of Wisconsin Press. 657 p. 

Deen, J.L. 1937. Silvicultural characteristics of American trees. Philadelphia, PA: Brownell Co. 99 p 

10 

seed fell after November, and less than 1 percent of the 

viable sugar maple seed fell in December or later. 

Approximately one-third of the total seed crop reached the 

ground in a viable condition. Birds, mammals, and insects 

destroyed 14 percent of the sugar maple crop, 31 percent 

of the yellow birch crop, and 43 percent of the beech crop 

(Fig. 9). Additional predation took place after seed fall, 

especially on beech and sugar maple. The annual seed 

crop constituted a major but highly variable wildlife food 

resource. The total annual dry weight of the viable seed fall 

averaged 132 kg per ha, and ranged from less than 1 to 

more than 300 kg during the 1 I-year period. 

Empty seed was the major nonviable category for all three 

species. This condition was usually caused by pollination or 

fertilization failure in yellow birch and beech. Sugar maple 

differed in that post-zygotic abortion consistently caused 

one-half of the seeds to be empty. Incompletely developed 

or partially filled seed was prevalent in yellow birch (1 0 

percent), but not in sugar maple (4 percent) or beech (1 

percent). Sugar maple was the only species with a 

significant seed fall in June (abortion). This loss coincided 

with periods of environmental stress. 

Eyre, F.H.; Zillgitt, W.M. 1953. Partial cuttings in northern hardwoods of the Lake States. Tech. Bull. 1076. 

Washington, DC: U.S. Department of Agriculture, Forest 

Service. 124 p. 

Eyre, F.H., e. 1980. Forest cover types of the United 

States. Washington, DC: Society of American Foresters. 

148 p. 

Forcier, L.K. 1975. Reproductive strategies and the cooccurrence of climax tree species. Science 189: 

808-809. 

Gabriel, W.J. 1967. Reproductive behavior in sugar 

maple: self-compatibility, cross-compatibility, 

agamospermy, and agamocarpy. Silvae Genetica 16: 

1 65- 1 68. 

Godman, R.M.; Mattson, G.A. 1975. Seed crops and 

regeneration problems of 19 species in northeastern 

Wisconsin. Res. Pap. NC-123. St. Paul, MN: US. 

Department of Agriculture, Forest Service, North Central 

Forest Experiment Station. 5 p. 

Grisez, T.J. 1975. Flowering and seed production in 

seven hardwood species. Res. Pap. NE-315. Upper 

Darby, PA: U.S. Department of Agriculture, Forest Service, 

Northeastern Forest Experiment Station. 8 p. 
I-eak, W.B. 1980. Influence of habitat on silvicultural 

prescriptions in New England. Journal of Forestry 78: 

329-333. 

I-eak, W.B.; Graber, R.E. 1979. Forest vegetation related 

to elevation in the White Mountains of New Hampshire. 

Res. Pap. NE-299. Broomall, PA: U.S. Department of 

Agriculture, Forest Service, Northeastern Forest Experiment 

!Station. 7 p. 

I-eak, W.B.; Riddle, J.R. 1979. Why trees grow where 

they do in New Hampshire forests. NE-INF-37-79. 

Broomall, PA: U.S. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station. 26 p. 

Marquis, D.A. 1969. Silvical requirements of natural 

birch regeneration. In: Proceedings, Birch Symposium; 

1969 August 19-21; Durham, NH. Upper Darby, PA: U.S. 

Department of Agriculture, Forest Service, Northeastern 

Forest Experiment Station: 40-49. 

Shigo, A.L.; Yelenosky, G. 1963. Fungus and insect 

injury to yellow birch seeds and seedlings. Res. Pap 

NE-11. Upper Darby, PA: US. Department of Agriculture, 

Forest Service, Northeastern Forest Experiment Station. 

11 p. 
Graber, Raymond E.; Leak, William B. 1992. Seed fall in an oldgrowth 

northern hardwood forest. Res. Pap. NE-663. Radnor, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment 

Station. 11 p. 

Seed fall was measured for 11 years in a 200-year-old stand of sugar maple, 

yellow birch, and beech in New Hampshire. Yellow birch had 5 good seed 

years, sugar maple had 3, and beech had none. Viable seed fall of yellow birch 

began in August and continued through autumn and winter. Most of the viable 

sugar maple seed fell during a short period in October. Beech seed fall 

occurred slightly later than sugar maple. Seed losses caused by pollination or 

fertilization failure, abortion, incomplete development, insects, small mammals, 

and birds averaged about 213 of the total seed fall, but varied widely'among 

years. 

Keywords: beech-birch-maple, seed production, seed viability 

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