development of canopy stratification during early succession in northern hardwoods
TRANSCRIPT
Forest Ecology and Management, 4 (1982) 41--51 41 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
D E V E L O P M E N T O F C A N O P Y S T R A T I F I C A T I O N D U R I N G E A R L Y S U C C E S S I O N IN N O R T H E R N H A R D W O O D S
SUSAN H. BICKNELL
Forestry Department, Humboldt State University, Arcata, CA 95521 (U.S.A.)
(Accepted 15 April 1981)
ABSTRACT
Bicknell, S.H., 1982. Development of canopy stratification during early succession in northern hardwoods. Forest Ecol. Manage., 4: 41--51.
Canopy development on a 6-year-old strip cut was analyzed by measuring the heights to terminal buds and bud scale scars of the tallest individuals of each species present on 50 plots of radius 6 m. Phenology of height growth was monitored during the following growing season. Pin cherry (Prunus pensylvania L.), an intolerant short-lived tree, had the fastest growth rate and was on the average the tallest Species from the second to the sixth year Of regrowth. Although advance regeneration of sugar maple (Acer saccharum Marsh.) and beech (Fagus grandifoloa Ehrh.) were the tallest trees during the first growing season, their slower growth rate insured that they would not keep up with the pin cherry. Trembling aspen (Populus tremuloides Michx.), striped maple (Acer pensylvanicum L.) and yellow birch (Betula alleghaniensis Britt.) occupied an intermediate position in the canopy by the end of the sixth growing season, and showed relatively greater annual height increment than beech or sugar maple° Height growth phenology differed slightly for each species. Beech, ash (Fraxinus americana L.) and sugar maple commenced growth early, grew rapidly and set buds all by 1 August (beech by 15 June). Yellow birch, pin cherry and trembling aspen started growing as early as the others, grew more slowly at first but then grew for a longer period of time. Striped maple seemed to be somewhat intermediate. Growth phenology and growth rate are related to the tolerance and growth form type (e.g. determinate or indeterminate) of the species. The most tolerant species tend to be determinate in growth form, have slower growth rates and complete height growth earlier. The in- tolerant species tend to be indeterminate, have a faster growth rate and continue to grow for a longer period. These may be mechanisms by which many species can grow together and avoid adverse effects such as suppression.
INTRODUCTION
The s i lv icu l tu re and r e q u i r e m e n t s o f t he i m p o r t a n t species o f n o r t h e r n h a r d w o o d s in t he N o r t h e a s t o f t he U n i t e d S t a t e s is well k n o w n (Wilson and Jensen , 1954; Leak a n d Wilson, 1958 ; Marquis , 1965 ; B j o r k b o m , 1967 ,
42
1972; Marquis et al., 1969; Leak and Solomon, 1975). Prescriptions for the natural regeneration of this forest type under many different conditions have been made (Marquis, 1967; Leak et al., 1969).
The influence of the intolerant trees, especially the weedy ones, and the shrubby successional plants is much less well understood (Bicknell, 1979). Two views have been presented. One states that the weedy trees (partic- ularly pin cherry, (Prunus pensylvaniea L.), aspen (Populus trernuloides Michx.), striped maple (Acer pensylvanicum L.) and mountain maple (Acer spicaturn Lain.)) appear to have no harmful long-term effects on the tolerant crop trees, and may in fact have the beneficial effect of re- ducing the density of undesirable understory sapling stems (Longwood, 1951). The other view is that overabundant growth of weedy shrubs and trees can retard regeneration of desirable species by as much as 10 years (Wilson and Jensen, 1954). Marquis (1965) states that weeding (removal of pin cherry and striped maple stems competing with birch) of birch regeneration favored the birches at least temporarily, but the long-term effects of weeding could not be predicted. Both of these views are prob- ably equally valid under different conditions, including the amount and size of the opening made by cutting, the presence or absence of advance regeneration, and the availability of seed of both tolerant and intolerant crop tree species.
When individual species are grown in pure stands, we need not be con- cerned with their relative rate of growth compared to other species (except perhaps from an economic point of view). Our concern naturally turns to matters of spacing and stocking, or compet i t ion among individ- uals of the same species. But natural regeneration systems are typically multi-species. In these systems we must consider the relative growth rates of each species we are interested in growing, as well as their tolerance characteristics. A greater understanding of the successional patterns during early regeneration and the influence of the weedy shrubs and trees on the crop trees is necessary for the early silvicultural t rea tment of regeneration. Pre-commercial weeding operations may represent a significant investment and need to be used only when based on sound knowledge about the ecological benefits to the crop trees.
SITE DESCRIPTION
This study was conducted in the Hubbard Brook Experimental Forest (HBEF) located in the White Mountains of New Hampshire. The history, geology, topography, climate, soils, vegetation and fauna of the HBEF have been described in detail (Johnson et al., 1968; Bormann et al., 1970; Siccama et al., 1970; Likens, 1971; Federer, 1973; Sturges et al., 1974; Whittaker et al., 1974) and these descriptions are summarized in Likens et al. (1977).
43
The HBEF occupies the 3,076 ha watershed of the Hubbard Brook (elevation 229--1,015 m). Its climate is humid continental with sbort cool summers and long cold winters. Mean air temperature is 19°C in July and -9°C in January. Soil frost is infrequent as a result of continuous winter snow pack. The well-drained, acid (pH 4.5), sandy loam softs (spodosols or haplorthods) average about 0.5 m in depth, and are derived from s toney till. The till, as well as the bedrock, is derived from highly meta- morphosed sedimentary rocks and granitic rocks. The HBEF is forested with second growth northern hardwoods dominated by beech (Fagus grandifolia Ehrh.), sugar maple (Acer saccharum Marsh.), and yellow birch (Betula aUeghaniensis Britt.). Associated species are white ash (Fraxinus americana L.), red maple (Acer rubrum L.), hemlock (Tsuga canadensis (L.) Cart.), balsam fir (Abies balsamea (L.) Mill.), and red spruce (Picea rubens Sarg.). The forest was logged in 1910--1919, and except for ex- perimental manipulations has been undisturbed since. There is no evidence of fire (Bormann and Likens, 1979).
This s tudy was instituted on one of the moni tored watersheds at the HBEF (Watershed 4 or W-4). W-4 (area 36 ha) is on a south--southeasterly facing slope of 10--15 °. In 1969, W-4 was surveyed into 49 east--west strips each 25 m wide, for a progressive strip cut exper iment (Hornbeck et al., 1975). With the exception of a buffer of trees left standing along the stream channel, the entire watershed was clearcut over the next 6 years. One third of the strips were cut in 1970, one third in 1972 and the last third in 1974. All trees and snags larger than 2.5 cm d.b.h, were felled and the commercially utilizeable wood was transported off the watershed. Canopy height was about 20 m before cutting.
METHODS
During the sixth year of revegetation (1976) the relative growth rotes of the dominant species were assessed (Bormann and Likens, 1979; Bicknell, 1979). Utilizing three 6-year-old strips, transects were laid out parallel to and in the center of the strips. Stakes were placed at 10 m intervals and used as the center point for 3 m radius plots. Within each plot, the tallest tree of each species present was selected, including two of a species if in- dividuals of both seedling and sprout origin were present. The tallest tree was selected rather than averaging the height of all the trees of that species present because the 6 -year-old forest is ex t remely dense and contains many individuals.which will never reach the canopy (Bicknell, 1979). The tallest trees represent those most likely to survive. Furthermore, a single tree 6 m tall dominates an area approximately equal to the 3 m radius plot employed (28 m:). For each tree selected, crown class was designated, diameter at breast height and diameter at 10 cm were measured and the age was determined by counting bud scale scars. The tree was cut down at the base and age determined again by count ing the rings. Annua l height
TA
BL
E I
Mea
n he
ight
s (c
m)
± S
.D.
of
sapl
ings
of
sele
cted
spe
cies
gro
win
g o
n a
sit
e cl
ear
cut
in 1
97
0--
19
71
. D
ata
incl
ud
e h
eig
ht
bef
ore
th
e cu
t an
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um
ula
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ht
for
6 ye
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succ
eed
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th
e cu
t.
Spe
cies
(N
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Mea
n
(ori
gin)
sa
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hei
gh
t
19
70
1
97
1
19
72
1
97
3
19
74
1
97
5
19
76
Ac
er
sacc
ha
rum
(61
) s
18
±3
3
49
±3
9
98
±5
1
14
2±
55
1
98
±6
8
23
4±
79
2
86
±8
8
Ad
van
ce g
row
th(2
6)
42
±3
9
68
±4
7
11
7±
57
1
57
±5
9
21
8±
68
2
52
±8
0
30
5±
91
P
ost
-cu
t g
row
th(3
5)
0±0
35
±2
4
84
±4
0
13
0±
49
1
82
±6
3
22
1±
75
2
72
±8
2
See
dlin
gs4(
49)
18
±3
9
42
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9
89
±4
9
12
9±
50
1
81
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0
21
5±
70
2
65
±7
9
Stu
mp
sp
rou
ts(l
l)
14
±2
6
73
±3
0
13
0+
39
1
90
±4
2
26
1±
63
3
12
±6
6
37
1+
67
Ac
er
pen
sylv
an
icu
m3
( 5
1)
s 13
±21
6
0±
36
A
dv
ance
gro
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(20
) 3
4±
20
8
5±
30
P
ost
-cu
t g
row
th(3
1)
0±0
43
±3
0
12
5±
45
2
01
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0
26
1±
65
3
08
±6
2
36
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69
1
48
±3
9
22
7±
43
2
97
±5
5
34
6±
45
4
05
±4
8
10
9±
41
1
84
±4
6
23
8±
60
2
83
±5
9
33
8±
68
Ac
ers
p~
a~
m(2
1)
s 2
1±
24
56
±38
1
10
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0
15
7±
55
2
06
±6
9
24
1±
73
2
90
±7
9
Ad
van
ce g
row
th(1
4)
32±
23
73±
36
13
0±
46
1
77
±5
3
23
2±
63
2
68
±6
7
31
9±
74
P
osb
cut
gro
wth
(7)
0±0
22
±1
2
69
±2
6
11
5±
30
1
53
±4
7
18
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51
2
29
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9
Bet
ula
all
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ien
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(50
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3±12
30
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8
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1
52
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3
Ad
van
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) 32
±26
8
9±
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1
53
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20
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46
P
ost
-cu
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th(4
5)
0±0
24
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8
74
±3
8
14
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51
21
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63
2
73
±7
1
34
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85
2
50
±7
0
31
3±
62
3
82
±9
0
20
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61
2
69
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1
33
5±
84
Fag
us g
ran
dif
oli
a(5
3) 5
69
-+59
9
3±
65
12
2-+
67
149-
+66
1
87
26
5
225-
+72
26
7-+
76
Ad
van
ce g
row
th(4
6)
79-+
57
103-
+65
13
1-+
67
15
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65
1
97
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6
237-
+70
2
97
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2
Po
st-c
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gro
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(7)
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28
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1
59±
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89-+
21
12
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31
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40
18
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53
R
oo
t sp
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) 34
-+40
6
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36
94
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1
21
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144-
+81
19
3-+
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223-
+71
S
tum
p s
pro
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(3)
0-+0
25
±12
5
7±
16
8
5-+
7
125-
+14
1
69
±2
5
208-
+43
S
eedi
ings
(43)
7
9±
58
1
03
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7
13
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69
15
8-+
67
197-
+68
23
5-+
72
27
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74
Fra
xin
us
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eric
an
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2) 5
7±
16
35
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86-+
55
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66
2
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9
24
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88
29
9-+
105
Ad
van
ce g
row
th(l
l)
34-+
18
77-+
38
13
3±
57
1
88
±5
9
247-
+67
28
4-+
67
33
6±
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3
Po
st-c
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gro
wth
(41
) 0-
+0
23-+
17
73
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7
13
4±
63
19
0-+
78
233-
+86
28
9-+
103
See
diin
gs4(
49)
8-+
16
35-+
33
86-+
54
144-
+62
20
2-+
72
240-
+84
2
94
±1
01
S
tum
p s
pro
uts
(2)
0±0
44-+
19
129-
+60
23
8-+
41
31
3±
54
37
9-+
59
46
1±
69
Po
pu
lus
trem
ulo
ides
2(1
5) 5
0±
0 18
±21
8
8±
41
Pru
nus
pens
ylva
nica
2( 5
0 )5
0±
0
52±
30
16
6±
63
2
37
~7
4
31
1±
10
6
37
0±
11
3
15
1±
60
2
89
±8
0
41
9±
10
6
51
6±
10
9
61
3¢
10
6
1All
ind
ivid
ual
s o
f th
is s
peci
es w
ere
seed
ling
s. N
o ro
ot
spro
uts
or
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ere
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ivid
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f th
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spec
ies
wer
e se
edli
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ori
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atin
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fter
th
e cu
t, e
ven
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P.
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3Onl
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ensy
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. T
hey
are
rep
ort
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og
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ith
the
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ecau
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4A f
ew i
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s w
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orm
bec
ause
of
the
dif
ficu
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f d
eter
min
ing
th
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stat
us
in t
he
fiel
d.
SThe
mea
n o
f al
l tr
ees
of
this
spe
cies
mea
sure
d.
Th
is m
ay e
xce
ed 5
0 b
ecau
se m
ore
th
an o
ne
tree
of
each
spe
cies
may
hav
e b
een
mea
sure
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er p
lot
wh
en b
oth
sp
rou
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d s
eed
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ivid
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s w
ere
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un
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c~
46
growth for the 6 previous years was measured using bud scale scars, A total of 50 plots comprising 353 trees were completed in this manner.
At intervals of 2 weeks during the summer of 1977, two to six saplings of each of the species noted in Fig. 3 were visited and note made con- ceming the length of the terminal twig, initiation of bud break and bud set and termination of twig growth. All of these saplings were growing in the open (unshaded by any other plants) on W-4 at the HBEF. Ob- servations began 1 May and continued until about 1 September. A final visit was made on 20 October.
RESULTS AND DISCUSSION
Table I presents heights for eight species measured on W-4. Three of the species listed in the table are depicted in Fig. 1 to show clearly the relative height of these species as the canopy develops during the first 6 years of regrowth. Pin cherry is the fastest growing species followed by sugar maple stump sprouts. The slowest growing species is beech, which
E
f - O~
7 "
C 0
f Sugar Maple (sprouts}
~p
6 0 | 1 2 3 4 5 6 CUT
Years of regrowth
Fi~ 1. Relative height of three major species revegetating W-4. Fastest growing is pin cherry, next fastest of all species is sugar maple stump sprouts. The slowest growing species of all is beech. All other species (see Table I) would fall between sugar maple stump sprouts and beech.
started with the tallest individuals from advance regeneration and ended with the shortest. As can be seen from Table II, all of the species had a mean age very near or greater than 6 years old, the age of the cut. This indicates clearly that all of these species were present at the beginning of this succession or immediately thereafter. Consequently, all species were subjected to the same open, low competition environment during
TABLE II
Diameters and ages of saplings growing on a six year-old cu t s tr ip on W-4
47
Species Mean d.b.h. Mean diameter Mean age (cm±SD) at 10 cm (years ± SD)
(cm ± SD)
Sugar maple 1.5 ± 1.4 2.3 ± 1.3 8.1 + 4.3 S t r iped maple 2.0 + 0.8 3.6 + 1.5 6 . 9 + 1.8 Moun ta in maple 1.4 ± 0.8 2.6 ± 1.3 7.4 ± 1.S Yel low birch 1.6 ± 0.8 2.5 ± 1.3 6.6 ± 3.4 Beech 1.5 ± 1.3 3.0 ± 1.8 11.5 ± 5.9 White ash 1.6 ± 1.0 2.6 ± 1.3 6.2 ± 0.9 Trembl ing aspen 1.9 ± 1.0 2.6 ± 1.3 5.7 + 0.5 Pin che r ry 4.8 ± 1.5 6.4 ± 1.8 6.0 ± 0.0
the first growing season. The difference in growth thus reflects differences in capacity to utilize the environment rather than differences in environ- ment. After the first 2 years, the canopy differentiates and different species may be influenced by the particular environment of their canopy stratum. Whatever the cause, differences in the growth rates continue during the 6 years examined. This results in rapid differentiation of the canopy into a pin cherry layer which is super-dominant over a less well defined layer where stump sprouts and intolerant trees (birches and aspen) are the tallest and tolerants like beech and sugar maple saplings are the shortest.
Annual height increment for five species of saplings is shown in Fig. 2.
140,
E 120, u
100, .=
i_ 80,
~- 60,
c 40, r- I
20,
o Pin cherry
i rembling aspen YellOw birch
~ Z ~ 2 § L s CUT
Years of regrowth
Fig. 2. Annua l he ight i n c r e m e n t o f five species of saplings revegeta t ing W-4.
48
Annual height increment fluctuates for all species, but not in the same way. For example, during the third growing season, the height increment for pin cherry, yellow birch and aspen was greater than it was the year before. For sugar maple and beech, the height increment for the third season was less than that of the second. In the fourth growing season, when sugar maple and beech increments increased, the pin cherry, yellow birch and aspen increments all decreased. These growth patterns may be related to the adaptations of determinate and indeterminate growth forms (Marks, 1975). The three indeterminate species, pin cherry, aspen and yellow birch, continue twig elongation (height growth) as long as conditions are favorable during the growing season. Determinate species, sugar maple and beech, produce all the leaf primordia which will be available for the next growing season during the current growing season (Zimmerman and Brown, 1974; Bormann and Likens, 1979). Consequently, increased height growth as a response to favorable environmental conditions would not be evident until the following growing season.
The length of twig extension measured at 2-week intervals was expressed as a percent of the total twig extension and presented in Fig. 3. All species had initiated growth by May 15 and all had set buds by the October visit. Bud break was complete by May 1 for all species except white ash. Bud set occurred very early for beech {June 15). For ash it was about July 15 and for sugar maple it was August 1.
Beech, ash and sugar maple all have a flush of growth quite early in the spring while yellow birch, pin cherry and trembling aspen continue ex- tension throughout the growing season. Striped maple seemed to be inter- mediate, with twig extension lasting longer than the first three species, but terminating before the indeterminate group.
The shape of the bar of each species in Fig. 3 is indicative of the pro- portion of twig extension completed by a particular date. Beech extension occurred almost all at once resulting in a bar which was wide almost from the beginning. In contrast, the bar for pin cherry is increasing in width gradually throughout its length indicating that pin cherry's rate of twig extension was nearly constant through the growing season. The trembling aspen saplings observed accomplished about half the total twig extension after August 1. These results agree very well with those of another study by Marks {1975), with the exception that the trembling aspen in Mark's study completed most of its twig extension much earlier than that oi> served here.
There seems to be a relationship between the timing of twig extension, the shade tolerance characteristics of the species, and the adaptation to determinate or indeterminate growth form (Bormann and Likens, 1979). The species which are determinate and are tolerant (or intermediate) com- plete twig extension considerably earlier than those which are indeter- minate and intolerant of shade. It is advantageous for species which are
49
I 0
t -
it
b t~
3
F,k~pc h
0 o
Ash
~x~or Maole
Y ~ l l n ~ R } r r h
Tremblina Asoen
May1 Moy15June1 June15Julyl July15Augl Aug15 S~¢Octl
Fig. 3. Period of terminal twig elongation for seven species of saplings on W-4. Wavy line terminating a bar indicates variability between individuals as to date of bud set.
determinate like beech to put out leaves all at one time early in the growing season. This insures a short period of exposure to nearly full sun before other species have put out many leaves. It also insures that each leaf will be productive for the longest possible time. An alternative strategy used by the indeterminate species insures the largest number of leaves that can be produced under the current environmental conditions, but each leaf is not necessarily in production for a maximum length of time.
The pattern of seasonal canopy development begins with the tolerant species putting out the most leaves first. These species are probably in subdominant positions in the canopy, and they are shaded progressively more as the taller intolerant species put out leaves gradually. This is not only a description of the pattern of canopy development, but also the suggestion of a mechanism by which slower growing tolerant species survive beneath dense canopies of fast growing species.
50
SUMMARY AND CONCLUSIONS
The intolerant species, pin cherry, formed a super~anopy very early during revegetation and stump sprouts of sugar maple shared dominance with pin cherry for a short time. By year three, pin cherry was clearly the single dominant. Saplings of advance growth of beech and sugar maple which were initially the tallest plants on the cut resided in the lowest stratum of the canopy at the end of the sixth growing season. Even in completely open conditions, their capacity for height growth did not approach that of pin cherry or of the maple stump sprouts. Trembling aspen, striped maple and yellow birch occupied an intermediate position in the canopy by the end of the sixth growing season. The seasonal timing of growth in terms of twig ex- tension was shown to be related to the tolerance characteristics of the species and to their adaptation to determinate or indeterminate growth form. These are mechanisms by which many species can grow together and avoid adverse effects such as suppression from the other species. Early com- pletion of twig extension and the delayed-type response of a determinate growth from in tolerant species (e.g. beech) are mechanisms by which they may avoid suppression from other faster growing intolerant species (e.g. pin cherry).
REFERENCES
Bicknell, S.H., 1979. Pattern and Process of Plant Succession in a Revegetating Northern Hardwood Ecosystem. Doctoral thesis. Yale University.
Bjorkbom, J.C. 1967. Seedbed preparation methods for paper birch. USDA Forest Service Research Paper NE-79.
Bjorkbom, J.C., 1967. Seedbed preparation methods for paper birch. USDA Forest paper birch. USDA Forest Service Research Paper NE-238.
Bormann, F.H. and Likens, G.E., 1979. Pattern and Process in a Forested Ecosystem. Springer-Verlag, New York, 253 pp.
Bormann, F.H., Siccama, T.G., Likens, G.E. and Whittaker, R.H., 1970. The Hubbard Brook Ecosystem Study: Composition and dynamics of the tree stratum. Ecol. Monogr., 40:373--388.
Federer, C.A., 1973. Annual cycles of soil and water temperatures at Hubbard Brook. USDA Forest Service Research Note NE-167, UpperDarby, PA, 7 pp.
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