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OCR for page 200
6
The Nature and Timing
of the Deterioration of
Red Spruce in the
Northern Appalachian Mountains
Arthur H. Johnson and Samuel B. McLaughlin
INTRODUCTION
Over the past decade, researchers have postulated a
number of possible effects of environmental pollutants on
forest ecosystems. Theoretical and experimental inves-
tigations have shown that acidic substances might affect
many aspects of plant and forest function. In addition,
some researchers are now beginning to study how acidic
substances interact with other pollutants and natural
stresses to affect forest ecosystems. Thus, there is a
reasonable amount of evidence suggesting how acid depo-
sition might affect forests, but to date no studies have
shown the postulated effects to be present in the field.
The finding of widespread mortality of red spruce
(Picea rubens Sarg.) in the northern Appalachians (Siccama
et al. 1982, Johnson and Siccama 1983, Carey et al. 1984,
Foster and Reiners 1983, Scott et al. 1984) sparked
research and speculation about whether acid deposition is
a cause. Because of the lack of documented mechanisms,
only circumstantial evidence supports claims that acid
rain has caused damage to spruce in eastern North America.
The suspicion that atmospheric deposition may play a role
in the decline of red spruce is supported mainly by the
facts that large-scale changes in the forest have taken
place in high-elevation areas receiving airborne heavy
metals and acidic substances at rates that appear to be
greater than those experienced by almost all other
forested areas in North America and that no obvious
natural cause has been documented.
Red spruce have died in uncharacteristic numbers near
the top of their elevational range where they are subject
to extreme climatic conditions as well as to pollutant
input. We find evidence that the current episode of
200
OCR for page 201
201
mortality could have been caused by climatic changes and
that there are other possible natural contributors that
remain unevaluated at the present time. To some extent,
understanding the nature and timing of this forest
disturbance puts constraints on the range of natural and
anthropogenic factors that might be involved, but there
is no way now to determine rigorously whether the
deposited materials are assimilated benignly by the
forest or if the airborne pollutants have altered life-
sustaining processes enough to cause significant
mortality.
HIGH-ELEVATION CONIFEROUS FORESTS OF THE APPALACHIANS
Researchers have long studied the zones of vegetation
types that exist on the mountains of the eastern United
States where forest composition varies along an
attitudinal gradient. Subalpine stands dominated by fir
and/or spruce occur from tree line down to 750 m in the
White Mountains (New Hampshire), 850 m in the Green
Mountains (Vermont), and 900 m in the Adirondack Mountains
(New York). To the south, spruce-fir forests continue as
patches on the highest peaks of the Appalachians. The
lower boundary varies from about 1060 m in the Catskill
Mountains (New York) to 1525 m in the Great Smoky
Mountains (Siccama 1974, Costing and Billings i951).
Gradients in flora and environmental conditions in the
eastern montane forests have been describer by numerous
investigators (i.e., Foster and Reiners 1983, Siccama
1974, Myers and Bormann 1963, Harries 1966, Adams et al.
1920, Holway et al. 1969, Scott and Holway 1969, McIntosh
and Hurley 1964, Whittaker 1956). Figure 6.1 summarizes
attitudinal gradients on Camels Hump (Vermont), a site
that has figured prominently in recent research. In the
Green Mountains (Vermont), sugar maple is the most
important canopy species (by density and basal area)
below 750 m, and balsam fir is most important above 850
m. A rather narrow transition zone lies between. Red
spruce is a minor species in the hardwood forest (<750
m) and above 1150 m. It is most important in stands of
the transition and lower boreal zones (760 to 1150 m).
Vegetation patterns are similar, but somewhat more
complex, in the Catskill, Adirondack, and White mountains
because they are irregular massifs rather than linear
ridges like the Green Mountains (Siccama 1974, Holway et
al. 1969, McIntosh and Hurley 1964).
OCR for page 202
202
a
100 ~
J
>
UJ
z 50
cr
o
cat
5
4
b
j / \.
1-~
oL
c
ELEVATION (m)
-?
i_
3 1 1 1 1 1
40
I
20
1 _
O _
I I I I I ~
600 800 1000 1200 600 800 1000 1200
ELEVATION (m)
d
103 60
1 o2 ~
-
1 ~ ~ 50
1 Do ~6
1
10-1
_ ,~.
600 800 1000 1200 600 800 1000 1200
ELEVATION (m)
ELEVATION (m)
FIGURE 6.1 Altitudinal gradients in tree species and
environmental characteristics at Camels Hump, Vermont.
Curves are based on measurements at 11 elevations (except
Figure 6.1(d)) by Siccama (1974) in 1964-1966. (a)
Species importance value (based on basal area, density,
and frequency) for sugar maple (Acer saccharum Marsh)
(SM); yellow birch (Betula alleghaniensis Britt.) (YB);
beech (Fagus grandifolia Ehrh.) (B); red spruce (Picea
rubens Sara.) (S.: balsam fir (Abies balsamea (L.) Mill)
(F); white birch (Betula papyrifera var cordifolia
(Marsh) Regel) (WB). (b) Basal area of all live woody
species of >2-cm dbh. (c) Soil pH (H2O) and
exchangeable calcium (NH4OAC extraction) in the B
horizon. (d) Growing season throughfall collected by
three to five rain gauges under the canopy at seven
elevations. Amounts were measured weekly during the
ice-free period during 1964-1966. (e) Maximum and
minimum air temperature under the canopy. (f) Average
number of frost-free days during 1964-1966.
OCR for page 203
203
e
40
20
O
to
-20
~0
maximum __
_
minimum
, 1 1 1 1 1 ~
600 800 1000 1200
E LEVATION (m )
FIGURE 6.1 (continued).
160
140
120
100
80
60
f
-
1 1 1
-
600 800 1000 1200
ELEVATION (m)
In addition to the elevational gradients, patterns of
vegetation are influenced by natural disturbance and
disturbance caused by human activity. Logging, fire,
landslides, and windthrow have affected the composition
and structure of the coniferous forests that have been
studied in relation to red spruce decline.
There is evidence that red spruce was a much more
important component of the coniferous and hardwood
forests of the northern Appalachians prior to the period
of extensive timber harvesting in the late 1800s and
early l900s (Siccama 1971). Extensive harvesting of red
spruce coupled with unfavorable conditions for regen-
eration after harvesting are generally thought to be the
main reasons (Pielke 1979).
DEPOSITION OF ACIDIC SUBSTANCES AND HEAVY METALS
IN NORTHERN APPALACHIAN FORESTS
The reasons that cause many to suspect pollutant stress
as a factor contributing to mortality in red spruce are
the following: (1) Pollutant deposition in subalpine
forests appears to be very high relative to deposition in
nearly all other extensive forested areas of North
America. (2) The pollutants in sufficient doses are
probably capable of altering many of the life-sustaining
processes key to maintaining forests. (3) There have
been no obvious natural causes offered to explain the
observed mortality. m e following factors hinder a
satisfactory scientific assessment of the role of
atmospheric deposition: (1) The variety of pollutants
and their delivery rates are not defined precisely. (2)
OCR for page 204
204
Testing the impact of the array of known pollutants on
the many life-sustaining processes is a complicated
task. (3) Any change caused by pollutant substances is
superimposed upon naturally occurring changes that alter
forest composition, structure, and function, making it
difficult to distinguish between natural and anthro-
pogenic effects.
The subalpine coniferous forests of the northern
Appalachians are above cloud base for considerable
portions of the year. The estimates of the duration of
cloud cover vary from approximately 200 h/yr at 600 m in
the Green Mountains to about 40 percent of the year at
1220 m in the White Mountains (Siccama 1974, Lovett et
al. 1982). Cloud moisture tends to be much more acidic
than precipitation, with average H+ concentration
during the growing season reported to be 288 + 193
umol/L (Lovett et al. 1982). Based on a model of cloud
droplet capture and on measurements of the chemistry of
10 cloud events, Lovett et al. (1982) estimated cloud
water inputs of major ions to a subalpine balsam fir
forest at 1220 m on Mount Moosilauke (New Hampshire) to
be considerably greater than bulk precipitation inputs
(Table 6.1). Excluding dry deposition, the deposition of
acidic substances (H+, NH4, Sod , Nod) in the
subalpine balsam fir forest is estimated to be three to
six times greater than in the lower lying hardwood forest
TABLE 6.1 Annual Deposition in Bulk Precipitation to a Northern Hardwood
Forest at Hubbard Brook, New Hampshire, Compared with Estimated Annual
Deposition by Bulk Precipitation and Cloud Droplet Capture in a Subalpine
Balsam Fir Stand on Mt. Moosilauke, New Hampshire
Hubbard Brook
(Northern Hardwood Forest)
( 1963- 1974)
(kg ha- ~ yr- l)a
Mt. Moosilauke
(Subalpine Balsam Fir)
(1980-1981)
(kg ha- ' yin ~ )b
Bulk Bulk Cloud
Ion Precipitation Precipitation Water Sum
H+ 1.0 1.5 2.4 3.9
NH4+ 2.9 4.2 16.3 20.5
Na+ 1.6 1.7 5.8 7.5
K+ 0.9 2.1 3.3 5.4
SO2- 38.4 64.8 137.9 202.7
NO3 19.7 23.4 101.5 124.9
a Date from Likens et al. (1977).
bOata from Lovett et al. (1982).
OCR for page 205
205
TABLE 6.2 Mean (x), Standard Deviation (s), and Number (n) of Samples for
ionic Concentrations in Bulk Precipitation at the Huntington Forest, Newcomb,
New York
Bulk Precipitation (1leq/L)
Ion x s n
NO3 31 22 67
SO2- 66 37 66
H+ 88 56 64
K+ 6 15 70
Ca2+ 13 19 70
Mg2+ 5 9 70
Na+ 4 8 70
NOTE: Elevation of forest approximately 500 m.
SOURCE: Mollitor and Raynal (1983) in Burgess et al. (1984).
at nearby Hubbard Brook, New Hampshire (Likens et al.
1977). Values for major ion deposition at high elevation
in the northern Green Mountains estimated from rime ice
chemistry, cloud chemistry, and droplet capture by
artificial collectors (Scherbatskoy and Bliss 1984) are
in rather close agreement with the estimates of Lovett et
al. (1982). The estimates of acid deposition at high
elevation exceed by severalfold the values calculated
from low-elevation data collected by the major monitoring
networks (see Chapter 5), but it is clear that the
cloud-water input estimates are subject to uncertainty
owing to the small number of samples, the variability in
cloud chemistry, and the difficulties associated with
determining cloud-water capture by the forest canopy.
Roman and Raynal (1980) have reported recent
alterations in patterns of tree rings of red spruce in
mixed conifer/hardwood stands in the Huntington Forest
(Adirondack Mountains). Precipitation in that area had a
mean H+ ion concentration of 88 + 56 ~mol/L;
overall precipitation chemistry is presented in Table 6.2.
As in the case of lake sediments (see Chapter 9), lead
has been shown to be a useful indicator of atmospheric
deposition to forest soils (Reiners et al. 1975, Siccama
et al. 1980, Johnson et al. 1982, Friedland et al.
1984a,b). High concentrations of lead have been observed
in the subalpine forest floor in New England (Reiners et
al. 1975, Johnson et al. 1982, Friedland et al. 1984 a,b,
Hanson 1980). The amount of lead in the forest floor
increases with elevation (Figure 6.2)--amounts at 1000 m
OCR for page 206
206
_ 2.5
E
-
O 2.0
o
J
LL
'A 1 5
A:
o
I
1~ 1.0
Z
6
UJ
~ 0.5
t
|Mean + S.E.
(n=5)
P< 0.01
0 500 1000 1500
ELEVATION (m)
FIGURE 6.2 Altitudinal gradient of lead in the forest
floor (Oi + Oe + Oa horizons) for 5 random samples
collected at 27 sites in Massachusetts, Vermont, and New
Hampshire. After Johnson et al. (1982).
are approximately three to four times higher than those
at S00 m. A similar elevational trend in the concentra-
tions and amount of lead in the forest floor was observed
at Camels Hump (Table 6.3), but no trends in the concen-
trations of other metals were noted (Friedland et al.
1984a). Lead concentration in the forest floor at Camels
Hump peaks in the Oe horizon (2 to 8 cm beneath the
surface), reaching a mean of 302 + 14 agog (Friedland
et al. 1984b). Between 1966 and 1981, lead concentrations
in the forest floor at Camels Hump increased by 57
percent in the northern hardwood (548 to 731 m), 124
percent in the transition (762 to 853 m), and 95 percent
in the boreal (883 to 158 m) zones (Friedland et al.
1984a). Copper and zinc concentrations also increased at
somewhat lower rates during the 15-year period.
Converting the 15-year increases in metal concentra-
tions to annual rates, Friedland et al. (1984a) determined
that the increased concentrations of lead, copper, and
zinc in the forest floor were about equal to regional
OCR for page 207
207
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OCR for page 208
208
estimates of atmospheric deposition of those metals
(Groet 1976, Siccama et al. 1980, Smith and Siccama 1981,
Scherbatskoy and Bliss 1984). These data are consistent
with the contention that subalpine coniferous forests
receive considerably higher rates of atmospheric depo-
sition than the adjacent lower-altitude hardwood forests.
To date, the estimates of atmospheric inputs are
imprecise because there are few data from short periods
of record that show large variations in chemical compost
tion. Largely because of the effect of cloud-droplet
interception, the subalpine coniferous forests apparently
receive acidic substances and heavy metals at rates that
appear to be greater than the rates in neighboring low-
elevation forests. With the exception of areas near
large sources of sulfur or metal emissions no other
forests in eastern North America receive trace metals and
-
acidic substances at rates as great as those estimated
for subalpine coniferous forests of Vermont and New
Hampshire. There is, however, little reliable evidence
that we can use to assess whether we should expect
chronic effects on biota resulting from the past and
current atmospheric inputs of acidic substances.
CHARACTERISTICS OF RED SPRUCE
IN HIGH-ELEVATION CONIFEROUS FORESTS
Red spruce are abundant in cool, soloist climates of the
high elevations of the southern and northern Appalachians,
in coastal regions from Maine to Nova Scotia, and in
interior areas of southern Quebec, northern Vermont,
northern New Hampshire, Maine, New Brunswick, and Nova
Scotia; in the montane forests, sites with a high capacity
to hold moisture are particularly favorable (McIntosh and
Hurley 1964). Red spruce older than 300 years are common
in the northern Appalachians (Siccama 1974, Burgess et
al. 1984), and tree ring patterns indicate that some
individual trees remain suppressed beneath the canopy for
80 years or more, attesting to the shade tolerance of the
species. These characteristics allow it to be competitive
in high-elevation forests with its more vigorous but
shorter-lived competitors, balsam fir and white birch.
At present, red spruce in the understory or in the
canopy may show symptoms of disease or injury in the
montane forests of New York, Vermont, and New Hampshire
(Johnson and Siccama 1983, Burgess et al. 1984, Friedland
et al. 1984c). One set of symptoms is common to all of
OCR for page 209
209
the northern Appalachian sites discussed below.
Trees show needle discoloration and death, crown
thinning, an altered branching pattern, and the eventual
death of branches and individuals. Friedland et al.
(1984c) observed that in all size classes browning of the
newest needles was widespread after the winters of 1980-
1981 and 1983-1984. They suggest that the most coupon
observation of foliar loss--that it is most noticeable at
the outer tips of the branches--might be accounted for by
repeated winter damage to new foliage. Typically (but
not uniformly) the crowns of mature, declining red spruce
appear to die back from the top down and from the outside
inward (Johnson and Siccama 1983), and severely declining
trees generally have five or fewer year classes of
needles.
Studies in the northern Appalachians of root fungi
indicate the presence of pathogens that play a secondary
role. Early studies (Hadfield 1968, Mook and Eno 1956)
found infection by Cytospora kunzii, Fomes pint, and
Armillaria mellea. These studies also noted the absence
of insects or pathogens that might be a primary cause of
disease. A recent study of 288 red spruce in hardwood,
transition, and boreal stands in the White, Green,
Adirondack, and Catskill mountains showed that declining
spruce were infected with Armillaria mellea (Carey et al
1984). Armillaria infected approximately 4 percent of
the severely declining trees in the boreal zone, 25
-
percent in the transition forests, and approximately 45
percent in the hardwood zone, indicating that Armillaria
is an agent related to deteriorating red spruce. But
owing to its absence in many declining trees it is not
the main cause of deterioration.
Decline, Disease, and Injury
.
Burgess et al. (1984) have offered an important
perspective on the current status of red spruce in the
northern Appalachians. Most commonly, "decline" has been
the term used to describe the current deterioration of
red spruce (e.g., Johnson and Siccama 1983, Carey et al.
1984, Siccama et al. 1982, Scott et al. 1984). Declines
differ from most diseases in that they are not the result
of a single causal agent. Manion (1981) has suggested a
model for declines whereby three categories of stress may
act to produce mortality. Environmental factors (e.g.,
poor site quality, airborne pollutants, nutrient defici-
OCR for page 210
210
encies) may predispose a tree to greater than normal
damage from a short-term initiating stress (i.e.,
drought, frost damage, insect defoliation, severe air
pollution event), which is followed by contributing
stresses, which are often lethal attacks from biotic
agents (e.g., root pathogens, bark beetles). Because
there are several possible stress factors in each of the
three categories, declines can be very difficult to
resolve into their components. Historically, several
tree declines dating back to the 1930s have been
documented in North America (Marion 1981, Houston 1981,
Mueller-Dombois 1983), often without satisfactory reso-
lution of the causes. Many incidence s of decline show a
strong relationship to drought conditions (Burgess et al.
1984, Houston 1981), with several other factors presumably
determining the ultimate fate of the affected trees,
since not all droughts trigger declines. It is also
important to note that widespread and synchronized
episodes of canopy diebacks are occurring and have
occurred in areas not subject to high levels of air
pollution (e.g., Hawaii, Mueller-Dombois 1983).
The characteristic of slowly advancing dieback in red
spruce (defined here as loss of foliage and branch death)
and the presence of secondary pathogens are consistent
with the concept of decline. On the other hand, declines
are most commonly associated with mature trees (Marion
1981), and the observation of mortality and symptoms in
smaller size classes is unlike most other known declines
(Burgess et al. 1984). The observation of needle damage
and dieback in red spruce in many size classes indicates
that injury (short-term effects of a stress) may be
involved at some stage in spruce deterioration. There is
no evidence to date that red spruce are deteriorating
solely because of a biotic disease (defined here as a
long-term interaction of a host with a pathogen), but the
understanding of biotic agents associated with deteri-
orating red spruce is incomplete because no systematic
studies of the occurrence of pathogens have been reported.
Changes in Red Spruce Populations
Johnson and Siccama (1983) reported on the status of
red spruce crown dieback in northern hardwood, transition,
and boreal stands in the Appalachians. Methods and data
from that survey are given in Appendix A and Figure 6.3.
The percentage of spruce that are dead or in an advanced
OCR for page 220
220
Multiple-regression analyses of red spruce chronologies
from old-growth, high-elevation stands in Maine (Conkey
1979) and in New York (Cook 1985) indicate that spruce
ring width is related to temperature, particularly in the
winter and spring. Cook analyzed an old-growth red
spruce chronology from a stand at Lake Arnold in the High
Peaks region of the Adirondacks. Models based on average
monthly temperatures provided a good fit (adj r 2 =
0.436 to 0.481) to annual index values for the
calibration period 1890-1950 (Figure 6.11). The models
predicted index values reasonably well from 1951 to
1967. After 1967, ring width was considerably less than
predicted by the models, suggesting that the trees were
responding to factors other than, or in addition to,
temperature (Figure 6.11).
1.6
1.4
1.0
0.e
0.6
1.2 ALN A IDA ~ ~ ~ ~
~v~1
7vV~ ~ 7Y'V
Actual
Estimated
0.4 ~ . .
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980
YEARS
FIGURE 6.11 Actual and estimated red spruce tree ring
indices at Lake Arnold in the Adirondack Mountains
(elevation 1150 m) based on a temperature response
model. The model was developed using mean daily
temperatures for the Northern Plateau Climatic Division
of New York. The model was calibrated using the
1890-1950 period, and model predictions run from 1951 to
1976. The dark line is the actual indice record, the
light line is the estimated indice record. The climate
model was Index = -0.261 Jp - 0.300 Ap + 0.180 Op + 0.202
Np + 0.291 Dp + 0.155 Mc + 0.209 Sc. R2 = 0.502;
R:dj = 0.436, OF = 53. (Jp, previous July
temperature; A, August; N. November; D, December; Mc,
current flay temperature; S. September). (From Cook
1985). The number of rings at breast height ranger from
142 to 297, with most in the range 200 to 250.
OCR for page 221
221
Conkey (1979, 1984a,b, 1985) showed an abrupt and
sustained change in red spruce maximum latewood density
in high-elevation, old-growth red spruce in Maine after
1962 that she tentatively attributed to the effects of
shortened growing seasons caused by a series of cool
spring temperatures. The interpretation of latewood-
density chronologies is a promising new tool in assessing
the response of trees to their environment, but it is
difficult to tell at present what factors are most
important in determining density patterns. Conkey's
findings are another signal of changes in tree ring
properties probably related to temperature beginning in
the 1960s.
The tree ring evidence is consistent with the
contention that red spruce have been deteriorating for
approximately 20 to 25 years and that the deterioration
was probably synchronous across the northern Appalachians.
One acceptable interpretation of the available evidence
is that, sometime around 1960-1965, the balance of stand
conditions and environmental factors stressed red spruce
beyond its ability to recover completely and that a
decline ensued. Another is that continual or increasing
stress to which red spruce is particularly susceptible
has caused widespread injury, mortality, and collapse of
the canopy in high-elevation stands. We are unaware of
any clear evidence that balsam fir are deteriorating
except as a secondary consequence of gap formation and
the attendant increase in microclimatic stress (i.ee,
increased susceptibility to wind and winter damage).
Tree ring records for balsam fir generally do not show
the abrupt change in the 1960s (Figures 6.8 to 6.10)
observed in red spruce except at the front of naturally
occurring fir waves at elevations above the spruce-fir
zone (Marchand 1984).
SUMMARY OF POSS IBLE CAUSES
Dieback symptoms are most pronounced above 900 m,
which is an environment subject to natural stresses such
as wind, cold winter temperatures, and nutrient-poor
soils and to high levels of pollutants such as acidic and
heavy metal deposition. Sorting out the factors that
have actually contributed to the large-scale deterioration
of red spruce is complicated by the lack of information
on pathogens, the range of known natural stresses and
potential pollution-related stress factors, the background
OCR for page 222
222
of mortality caused by normal stand dynamics, and the
secondary effects of stand destabilization. The breakup
of the high-elevation stands in some areas appears to
have proceeded as a positive-feedback system--the gaps
increase climatic stress and susceptibility to wind, then
blowdown enlarges the disturbance patches and exposes
more trees. It appears that the breakup of the deteri-
orating stands was triggered by rather extensive mortality
in spruce, and the observation that red spruce in all
size classes now show the development and progression of
dieback argues that at least some of the factors causing
spruce mortality are still operating. Although the for-
mation of disturbance patches (particularly by windthrow)
is an important determinant of vegetative patterns, the
synchronized spruce mortality across a broad region, and
mortality in all size classes, are different from the
disturbance phenomena currently recognized as contributing
to present-day vegetative patterns is subalpine spurce-fir
forests (Foster and Reiners 1982). Of interest in a
historical context are reports of widespread mortality in
red spruce between 1871 and 1890 in eastern North America
(Hopkins 1891, 1901). These suggest that large-scale
mortality in red spruce populations can be unrelated to
pollutant deposition. The episodes summarized by Hopkins
(1891, 1901) occurred at roughly the same time in West
Virginia, New York, Vermont, New Hampshire, Maine, and
New Brunswick and were tentatively attributed to a spruce
beetle (called Dendroctonous piceaperda by Hopkins (1901))
-
acting as a secondary agent following some other stress.
A rigorous investigation of the nature, extent, and
symptoms of previous episodes of spurce mortality might
provide useful information for comparison with the recent
conditions of spruce decline.
In evaluating the possible causes of the current red
spruce deterioration we recognize the following pos-
sibilities at the present time. Further research and
evaluation of each is warranted
.
1. Stand dynamics resulting from aging or
successional characteristics.
2. Drought.
3. Biotic disease.
Repeated or severe winter damage due to climatic
change.
5. Pollutant effects.
6. Combinations of pollutant and natural stresses.
OCR for page 223
223
Considering the available data, aging or competitive
pressures seem unlikely to be primary factors causing
mortality of red spruce because the observed patterns
argue against them:
widespread and synchronous mortality;
mortality in all age classes; mortality in stands of
widely differing basal area, age, composition; and
disturbance history. Although most of the deteriorating
northern stands are multiaged and contain old spruce
(more than 200 years old), few have basal area values
characteristic of virgin, old-growth spruce stands,
reported to be 45 to 69 m2/ha in New Hampshire and 41
to 59 m'/ha in Maine (Foster and
Some stands (see Figure 6.10)
in the late nineteenth and early
some extent the regrowth of some
the late 1800s may have resulted
Reiners 1983).
were subject to logging
twentieth centuries. To
stands after cutting in
in critical competitive
pressure and sharply decreasing ring width by 1960 (Meyer
1929). On the other hand, other stands show no signs of
release caused by logging or other major disturbance
(e.g., Figure 6.8) but show the same share rina widen
decrease over the past 20 years.
_ _ ~ _ _ , _ _
The subalpine forest on
the west side of Mount Washington is a virgin forest, and
it shows dieback, mortality, and decreased ring width in
the same way as the rest of the high-elevation sites.
(See also Foster and Reiners 1983.) The deterioration of
stands harvested intensively less than a century ago
argues against the contention that the observed dead
spruce result only from the breakup of old-growth stands.
Mortality in all size and age classes and in stands with
different disturbance histories argues against the idea
of "cohort senescence" (mortality of an even-aged canopy)
that has been applied to other synchronous episodes of
canopy tree death (Mueller-Dombois 1983). However, the
previous episode of regionwide spruce mortality and
periods of logging could have served as synchronizing
events that led to a mu~tiaged cohort, which grew into a
highly competitive situation by 1960.
Widespread drought in the northeastern United States
in the mid-1960s (see Chapter 3) was prolonged and severe
(Cook and Jacoby 1977), and as droughts are often
associated with declines of other species (Marion 1981,
Houston 1981, Burgess et al. 1984) the 1960s drought has
been proposed as a possible cause of the current spruce
deterioration (Kelso 1965, Tegethoff 1964, Hadfield 1968,
Siccama 1974, Johnson and Siccama 1983). However, it is
difficult to assess the extent of drought stress in
high-elevation forests. Examination of Palmer Drought
OCR for page 224
224
Severity Index values (which are, at best, a modest
representation of high-elevation drought) shows that the
peak drought years were 1964 and 1965 (Johnson and
Siccama 1983). The data of Siccama (1974), reproduced in
Figure 6.1(d), provide direct evidence that it was not
dry in absolute terms at Camels Hump and that growing
season precipitation amounts increased substantially at
higher elevation. Even though 60 cm of warm season
precipitation might be a critically low amount for trees
adapted to higher precipitation, the increase in
precipitation with increasing elevation argues against
drought as a principal cause of deterioration, since the
degree of deterioration increases at higher elevation.
The persistence of dieback symptoms in smaller size
classes (Friedland et al. 1984c) also argues against a
drought 20 years past being a principal cause of the
continuing deterioration. Finally, the observations of
patches of dead and dying spruce in 1962 (Kelso 1965,
Tegethoff 1964, Wheeler 1965) indicate that some mortality
was occurring before the period of most-intense drought.
Based on the reported observations of the past 20
years it appears unlikely that red spruce are deteri-
orating because of a biotic agent. Although no primary
pathogens nave been reported, no systematic studies have
been conducted so this possibility cannot be confidently
rejected at present, and its definitive evaluation awaits
further research.
More likely as a key factor in spruce decline was a
second climatic anomaly that occurred during the 1960 s
and that could have had a region-wide, adverse influence
on red spruce. In Chapter 3 we have described the
occurrence of anonamously cold winters across the eastern
United States from 1962 to 1971 (e.g., Namias 1970), and
several observations suggest that such an occurrence
could be of primary importance. Multiple regression
analyses of tree ring chronologies (Cook 1985, Conkey
1979) suggest an adverse effect of cold winter tempera-
tures and cool spring temperatures on annual ring width,
although no physiological connection has been established.
Numerous reports of severe winter damage, particularly
during the past 20 years, suggest that red spruce is
susceptible to damage from winter conditions, particularly
after mid-winter thaw (Curry and Church 1952, Pomerleau
1962, Friedland et al. 1984c, Burgess et al. 1984).
Early observers of the recent deterioration of spruce in
New Hampshire observed severe winter damage in stands
with dying spruce and suggested that severe winter
OCR for page 225
225
29
27
25
F 2
19
17
_ N EW ENG LAN D
1 889-90
AVG DEC-FEB TEMPS (1888-89 - 1976-77)
15
13
Q.~R R7
. nor
1 904-05
1 933-34
1 976-77
~ _ _
~ ~ ~ ~ 1917-18 ~ ~ ~ ~ I I I
1888 1896 11904 1912 1920 1928 1936 1944 1952 1960 1968 1976
1900
YEAR
FIGURE 6.12 Trend in winter temperatures in New England
(after Diaz and Quayle 1978). The smoothed curve is a
third-order polynomial least squares fit.
conditions may have contributed to the mortality (Kelso
1965, Wheeler 1965, Tegethoff 1964). Trends in New
England winter temperatures (Diaz and Quayle 1978) show
that the past 25 years have been characterized by a trend
toward colder winters (Figure 6.12). Diaz and Namias
(1983) and Conkey (1985) have shown evidence of cool
spring temperatures and shortened growing seasons in the
1960s and 1970s. The effects of cool springs and cold
winters may be of particular importance to spruce growing
near the top of its elevational range where the growing
season length may be marginal under average conditions.
Acidic substances, heavy metals, and gaseous pollutants
alone or in combination could alter life-maintaining
processes in forests. Whether they can do so to the
extent necessary to cause the mortality reported in the
above discussion cannot be rigorously evaluated. There
is no indication now that acidic deposition is an
OCR for page 226
226
important factor in the red spruce decline. Ring width
anomalies occur in the 1960s in areas of relatively low
acidic deposition (Roman and Raynal 1980) and in higher
elevation studies where deposition is higher, and where
trees are in contact with acidic cloud water for a sub-
stantial part of the year. The abrupt and synchronous
changes in ring width and wood density patterns across
such a wide area seem more likely to be related to
climate than to air pollution. Acid deposition or other
airborne chemicals might play a role in predisposing the
trees to the factors that are injurious, and when those
factors are clearly defined, the role of airborne
chemicals can be better assessed.
Testing hypotheses involving interactions of natural
and pollution stress will eventually be warranted since
it may be difficult to reconstruct the effect of climatic
anomalies or biotic disease in a way that will show that
those factors alone could have triggered the recent
deterioration. Finally, refined procedures for tree ring
analysis may provide useful insights on the involvement
of climate.
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Representative terms from entire chapter:
ring width
