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OCR for page 91
DECLINE OF RED SPRUCE IN THE NORTHERN APPALACHIANS:
DETERMINING IF AIR POLLUTION IS AN IMPORTANT FACTOR
A.H. Johnson
Department of Geology
University of Pennsylvania
Philadelphia, PA 19104
ABSTRACT
Declines are multiple stress diseases in which combinations of
abiotic and biotic stresses weaken trees, eventually causing death.
Airborne chemicals could play a role in decline diseases by
altering normal functions and enhancing natural stresses which
initiate a decline, and by causing injury which competes for
carbon with naturally-induced injuries, ultimately causing available
carbon to drop below a level critical for maintaining vital
functions. The decline of red spruce in mountain forests of the
northern Appalachians appears to have been initiated by repeated
winter damage to needles and buds from freezing or desiccation.
The spatial pattern of decline severity is associated with age, site
conditions, and the nature of the pathogens and insects which
serve as contributing stresses. Emerging research results suggest
that air pollution at ambient levels is capable of altering
resistance to winter stress in high-elevation spruce. Additional
research is needed to determine if ambient levels of airborne
chemicals serve to reduce the carbon available for defense against
and repair of the injuries caused by pathogens, drought and winter
weather.
INTRODUCTION
Recently, the unusual mortality of red spruce in high-elevation forests of New
York and New England has raised the possibility that air pollution is responsible, at
least in part, for the decline of that species. Similarly, a recent episode of unusual
mortality and symptoms in several species in central Europe has intensified the effort
to determine if airborne chemicals are important stresses contributing to "forest
decline." Some current forest problems in eastern North America and Europe are
occurring in areas subject to relatively high doses of air pollutants, but many other
declines (diseases characterized by a combination of biotic and abiotic stresses) have
occurred in places where, and at times when, air pollution is almost certainly not a
factor (e.g., Mueller-Dombois 1983~.
One useful conceptual framework divides the stresses involved in declines into
predisposing, inciting, and contributing (or secondary) stresses (Marion l 981~. Figure l
puts this concept in a simple model showing how the resources a tree has available to
repair injury and resist pathogens might change through a period of decline. During a
"decline" some trees in a population will be depleted in usable reserves to the point that
death, although possibly several years away, is inevitable (e.g., Waring 1987,
91
OCR for page 92
92
McLaughlin 1987~. Other individuals may be stressed by the inciting factors, but
recover due to lesser effects of the predisposing and secondary stresses.
1
E1 PREDISPOSING
FACT - S
~ m INcl~lNG
if STRESS
Ul ~
z . I
us E1 PREDISPOSING , |
z
al
o
AL
IN
J
ID
o
RECOVERY
9
.
~ THRESHOLD FOR
/ SY~PTO - S OF STRESS
—RESHOLD |
I pathogens ~tt~cti
DEATH
TINE ~
Figure 1. Schematic representation of energy available for defense and repair during
various phases of a decline disease. Represented are, ( 1 ) predisposing factors that
influence the vigor of an individual prior to injury, (2) a drop in reserves as repair
begins after an initiating stress, and a period of recovery or (3) decline when pathogens
or other stresses eventually become lethal.
Using Figure 1 as a guide, I have summarized the natural factors that appear to be
involved in the decline of high-elevation red spruce, suggested how air pollution might
fit into the disease complex and reviewed recent evidence suggesting that air pollution
at ambient levels may alter red spruce to a degree sufficient to promote a decline.
FACTORS RELATED TO THE OCCURRENCE AND SEVERITY OF SPRUCE DECLINE
The gradients in vegetation, soil and climate on the Adirondack, Green and White
Mountains have been summarized by many authors, and reviewed in the context of the
current decline by Johnson and McLaughlin ( 1986) and Johnson and Siccama ( 1983~.
Exposure of trees to airborne chemicals in those mountain forests is now being
characterized with considerable precision (e.g., Mohnen, this volume). Earlier estimates
have all suggested relatively high deposition of acids and heavy metals, and prolonged
exposure to acidic cloud water and elevated levels of ozone (e.g., Lovett et al. 1982,
Burgess et al. 1984, J. Panek, unpublished data on hourly ozone measurements at 1026
m at Whiteface Mt., NY). In particular, the frequent occurrence of clouds above 1000 m
and the lack of diurnal fluctuations in ozone concentrations above 1000 m make for
prolonged exposure to airborne chemicals.
OCR for page 93
93
40 -
30 -
20-
1 0 -
0
(4~
~-0~
< - = (325)
(448)
· - - 1987
O 0 1 982
-
(1 79)
-
~ (242)
1 1 ' 1
900 m 900 1049 no >1049 m
Elevation
Figure 2. Changes in percent dead red spruce over 5 years on 56 100-m transects on
Mt. Washington, NH, Mt. Mansfield, VT, and Whiteface Mt., NY. Differences are
significant in all elevational bands at P<.05 (W.L. Silver, A.H. Johnson and T.G. Siccama,
unpublished data).
Johnson and McLaughlin (1986) summarized the data from several studies which
showed that red spruce density and basal area decreased dramatically (40-80%) on five
mountains in New York and New England between the mid-1960s and early 1980s.
Surveys of mature spruce on Whiteface Mt. (NY), Mt. Mansfield (VT) and Mt.
Washington (NH) showed unusually rapid mortality between 1982 and 1987, particularly at
high elevation (Fig. 2~. The most prominent symptom in declining high-elevation
spruce has been a deterioration of the crown due to death of twigs and branches, and
recent detailed studies have shown many
important insects and diseases.
specific symptoms associated with locally
In a study of 331 permanent plots on Whiteface Mt. (NY), Battles et al. (1987)
showed the following with respect to spatial associations between forest characteristics
and the density of dead spruce:
1. More than half of the red spruce in all size classes are standing-dead in the three
1 OO-m elevational bands above 1000 m, while about 259/0 are dead in all size classes in the
three 100-m elevational bands below 1000 m.
2. The percent dead spruce is slightly greater in larger size classes than in smaller size
classes.
OCR for page 94
94
3. The percent dead spruce is greater in all size classes above 1000 m on the northwest exposure
which experiences the most severe winter winds capable of defoliating conifers.
Thus, it appears that age, elevation (representing poorer site conditions and shorter growing
seasons) and unfavorable exposure at high elevation can be considered as conditions which
predisposed the trees to greater damage from other environmental stresses.
Friedland et al. (1984) suggested that damage to foliage and buds which became visible in
early spring was probably an important ~ type of injury promoting the decline of red spruce.
Johnson et al. (1986, 1988) suggested that several consecutive years of winter damage to the
previous year's foliage and buds probably initiated and synchronized the decline across New York
and New England. The winters of the 1960s were unusually cold (Namias 1970~. Figures 3-6
show that the several years of winter damage were accompanied and followed by regionwide
reports of dead and dying spruce, a synchronized regional-scale decrease in ring width, and an
abrupt change in the long-term relationship between climate and ring width. Substantial and/or
repeated loss of new foliage from spruce growing near the top of their altitudinal range is likely
to be significant because it reduces photosynthetic biomass, removes storage tissue and energy
reserves, and judging by the production of adventitious shoots (P. Wargo, U.S. Forest Service, and
personal observations), shifts carbon allocation to the production of new shoots and needles. A
systematic study in the Adirondacks by Curry and Church (1952) and repeated observations in
western Maine (Stark, 1962-1970) and in patches of dead and dying spruce in the White Mountains
of New Hampshire (Tegethoff 1964, Wheeler 1965, Kelso 1965) indicate that severe episodes of
winter injury can kill red spruce. Thus, the repeated and severe episodes of injury to foliage and
buds two decades ago represent a likely stress which initiated and synchronized the spruce decline
and later episodes of winter injury may have served to keep the decline going.
REPORTS OF WINTER DAMAGE
south
ME east
north
ME west
NH
VT
NY
QUE
. . .
. . o
o ~ o 0 0 o.
. .. ~ o
. · -. . o
· ooo_ ~ oooo o
· ....
& , . . .
1940 1950
1960 1970 1980
i
Severe, Extensive
Figure 3. Reports of "winter drying," "winter burn," "winterkill," etc. where red foliage was
observed in spring. The tabulated incidents were generally widespread within the geographic area.
Source: Reprinted with permission of Kluwer Academic Publishers. Copyright c 1986 by D. Reidel
Publishing Company.
OCR for page 95
95
RED SPRUCE MORIALIU
NH
V]
1800 1850 1900 1950
Confirmed
O Uncertain
Spruce blindworm
· Major windstorms
Figure 4. Periods when extensive or severe red spruce mortality were recorded. Source: Reprinted
with permission of Kluwer Academic Publishers. Copyright c 1986 by D. Reidel Publishing
Company.
2.5
on
In
,_ 1.5
-
z 1.0
BY
0.5
0.O
25 RED SPRUCE MEAN RINGWIDTH CHRONOLOGIES (>800 METER ELEVATION)
um ~ Lou 1 ~ 1 920
YEARS
1940 1960 1980
Figure 5. Red spruce tree ring chronologies at 25 high-elevation sites in the Catskill, Adirondack,
Green and White Mountains. Each site is represented by two cores from 12-20 trees >10 cm dbh.
Values are raw ring widths for each year averaged for each site, then normalized to the 131-year
mean ring width. (After Johnson et al. 1988~.
OCR for page 96
96
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.]
O
.1
.2
.3
.4
.5
~,6
.7
.8
.9 .... ... ........
1944 1954 1964 ~ 1974
O Aug-Dec Model ~ Nov-July Model
Figure 6. Seven-year running correlation coefficients for actual vs. climate-predicted,
standardized ring 'widths. Open circles reflect the predictive ability of a regression
model which uses average monthly temperatures of the prior August and prior December.
This combination of temperatures was significantly correlated with ring width from
1856- 1960. Prior August ceases to be related to ring width from 1960 to 1981. Instead,
a model using prior November and current July is related to ring width. Methods are
explained by Johnson et al. (1988~.
Johnson et al. (1988), McLaughlin et al. (1987) and Cook et al. (1987) used
tree-ring analysis to show that radial growth in high-elevation red spruce across New
York and New England responded unfavorably to warm Augusts (year prior to ring
formation) and cold Decembers and Januarys (winter prior to ring formation) for the 100
years prior to 1960 when the relationship between climate and ring width changed
abruptly. While the physiological bases for those relationships are unknown, it is
interesting to note that the most severe recorded periods of red spruce mortality
occurred during periods of unfavorable summer and winter temperatures (Johnson et al.
1988, Fig. 7).
OCR for page 97
97
AUGUST (SOLID) AND DECEMBER (=D AR (3) STREW INDICES
4 .
3 .
2
x 1
O
-1
-2
3
4
it,
A
~ ,1~-- ..!
~ ~ ~ 1 ~ ~ I ~
1820 1~ 1~ 1~ 1~ 1~0 19" 19" 1980
YEARS
Figure 7. Years when unusually warm Augusts and/or unusually cold Decembers
occurred. Only monthly average temperatures that have a probability of <.05 are
included. Positive index values represent periods of stress, negative values represent
favorable periods. Solid areas are unusually cold Decembers. Methods are explained by
Johnson et al. (1988~.
Particularly notable was the spruce decline of 1871 - 1885 (Hopkins 1901 ~ which
killed an estimated 50% of the spruce in the Adirondacks, and coincided well with the
very unusual years 1871 and 1876 which had both especially warm Augusts and especially
cold December temperatures. The most recent period of spruce decline apparently
started at the end of a period of warm summers in the 1950s and at the start of a
period of unusually cold winters (see Fig. 7 and Namias 1970). From those findings, it
seems plausible that warm summer temperatures may have served as a predisposing
factor.
Several researchers have noted the occurrence of severe drought in the mid-1960s
which could serve as an initiating stress. Johnson and McLaughlin (1986) and Johnson
et al. (1988) discussed the conflicting evidence related to the possible importance of the
mid- 1960s drought. Although regionwide red spruce mortality was noted prior to severe
drought, large negative residuals from the temperature-predicted ring widths during
1965-67 suggest at least a contributing and, possibly in some areas, an initiating role.
Many of the insects and diseases which have affected red spruce historically are
present in dead and dying trees, but their occurrence varies spatially. The spruce
beetle (Dendroctonus rufiDennis Kirby) has been observed in many areas (McCreery et
al. 1987) but is rare in others, such as at Whiteface Mt. (T.C. Weidensaul, personal
communication). Armillaria mellea, the shoestring root rot fungus is present in declining
OCR for page 98
98
spruce at lower elevation, but rare at higher elevations (Carey et al. 1984~. Other fungi
(Fomes nini and CYtosoora canker) have been identified in several places over the last
two decades (e.g., Hadfield 1968~. At lower elevations, dwarf mistletoe (Arceuthobium
ousillum Peck) is associated with growth loss and mortality (McCreery et al. 1987~. The
presence of many more pests and disease organisms is expected to be confirmed by
ongoing work.
Early observers of spruce mortality at high elevation in New Hampshire and
western Maine (Kelso 1965, Wheeler 1965, Tegethoff 1964, Stark 1962) looked for, but
found no evidence of insects or fungal diseases as primary causes of the spruce
mortality they studied through repeated visits in 1962-64. They attributed the mortality
and visible decline of spruce to severe winter conditions. As in most declines, insects
and diseases appear to be serving as contributing or secondary stresses in the recent
episode of spruce decline.
To date, many of the naturally-occurring factors that have been implicated in
other declines have been shown to be temporally or spatially associated with the red
spruce decline. These are summarized in table 1.
TABLE 1.
Stresses temporally or spatially associated with the occurrence or severity of the
recent red spruce decline in the northern Appalachians and Adirondacks.
PREDISPOSING INCITING CONTRIBUTING
age
elevation (site)
winter damage insects
to foliage and buds
fungal diseases
severe exposure (drought?) winter injury
to winter winds
(warm summers?)
THE POSSIBILITY OF AIR POLLUTION INVOLVEMENT
The presence of the factors listed in Table 1 does not rule out air pollution as a
contributor to spruce decline. Figure ~ shows how air pollution could serve as a
predisposing or contributing factor by reducing reserves available to repair injuries
caused by the winter damage, drought etc. Possibly, air pollution could make trees
more susceptible to the conditions that cause the winter injury to foliage and buds.
Emerging findings (e.g., Alscher, this volume) suggest that those topics deserve
attention.
OCR for page 99
-
z
As
In
z
IL
c]
ce
lo
IL
CRITICAL T~RFCUOI n
;
air pollution damage? 1
v
THRESHOLD FOR
SYMPTOMS Of STRESS
99
Winter injury
59 -65
v
it_
Drought 65-66
or
furtt~r winter injury
; '78, '81, '84
l
v
I _o, RECOVERY
~ 'a
CAN AIR FOLIATION ENHANCE
WINTER STRESS ?
TIME - ~
DEATH
Figure S. Events that contributed to the recent spruce decline in the northern
Appalachians and possible ways in which air pollution might contribute.
Many factors contribute to a tree's ability to resist damage in winter (e.g., Weiser
1970). Davison et al. (1987) and Alscher et al. (this volume) reviewed the types of
damage plants are subject to in winter, and the ways in which air pollution might alter
resistance to those types of stress. In winter, high elevation conifers must contend
with photo-oxidation of chlorophyll (resulting in bleaching of the needles), desiccation
(thought to be caused by water loss through cuticles on bright, sunny days when water
in conducting tissues is frozen), and freezing injury (usually called "frost damage"). The
latter types of injury cause the death of needles which turn red-brown in the spring.
The exact mechanism that caused the winter damage observed in red spruce over the
past two decades is unknown, and the climatic conditions under which the injuries
occurred are, likewise, unknown. Freezing damage early in winter, desiccation on
appropriate days in mid-winter, mid-winter thaws followed by very low temperatures,
and spring frosts all have the potential to cause the damage observed.
There is evidence that air pollution might affect resistance to winter stresses.
Electron microscopy studies carried out in Finland along a gradient of air pollution
exposure showed greater alterations of cells and greater winter damage in areas of
higher pollutant exposure (Davison et al. 1987), but mechanisms or the causal agents
are not known. Since several pollutants attack constituents of cell membranes, and
since changes in cell membranes occur during the fall hardening period, Davison et al.
(1987) suggested that there is a sound theoretical basis for suspecting that air pollution
might interfere with the development of freezing resistance. Their experiments with
OCR for page 100
100
ozone fumigations (120 ppb ozone, 6 h per day for 70
days) indicated that ozone at
that dose rate was associated with increased cut~cular water loss from previous yearns
needles in one of eight clones of Norway spruce tested. Four clones showed an
increase in freezing-related damage when exposed to the ozone treatments.
Weinstein et al. (1987) and Cumming et al. (1988) and Alscher et al. (this volume)
exposed red spruce seedlings in open-top chambers to filtered air and to ozone at
ambient and twice ambient levels at Ithaca, NY. Ozone at ambient and twice ambient
levels was associated with several factors that indicated a delay in hardening. Ozone
at ambient levels was associated with increased respiration, decreased pigment
concentrations, delayed starch export or conversion, a delay in tannin accumulation, and
unusually high photosynthesis rates during the hardening period.
While there are obvious problems in extrapolating from seedlings grown under the
climatic conditions in Ithaca to mature trees growing on the mountains, it is
interesting to note that ozone exposure in the spruce-fir forest at Whiteface Mt. in the
summer of 1987 was in the ambient to twice ambient range used in the experiments
noted above. Hourly ozone concentrations averaged 47 ppb, day and night from June 1
through August 31. The maximum reading was 129 ppb, and 22% of the time, ozone
concentrations exceeded 60 ppb (J. Panek, Atmospheric Sciences Research Center,
SUNY-Albany, unpublished data). Long-term data from the summit of Whiteface
(Burgess et al. 1984) indicate that those values are representative of normal conditions.
As indicated in Figure 8, it is also important to try to determine if ambient levels
of airborne chemicals cause a decrease in the carbon available for defense and repair.
A clear record has been established with seedlings and saplings of several species that
suggests ozone at ambient levels can reduce net photosynthesis and growth without
visible symptoms (e.g., Wang et al. 1986, Skelly et al. 1983, Reich and Amundson 1985~.
Thus, there is reason to suspect that air pollution might be capable of inhibiting repair
of the winter damage sustained by red spruce during the decline. It would be useful
to have experimental evidence from mature trees in the field for the best possible
assessment.
In this regard, Vann and Johnson (1988) have begun experiments using branch
chambers for the exclusion of airborne chemicals from branches of mature red spruce.
Their preliminary results suggest improved foliage with filtered air (Fig. 9), but the
results are not sufficient at present to make judgments about productivity and carbon
reserves.
SUMMARY
The recent mortality of red spruce has components which have been commonly
associated with declines of other forest species in the northeastern U.S. Natural
factors such as age, poor sites, exposure to winter winds, and possibly climate warming
may act as predisposing factors. Repeated and severe winter damage to foliage and
buds, and possibly drought, may act as inciting factors, and insects and pathogens
appear to serve as contributing or secondary stresses. Air pollution stress might be a
contributor by enhancing the effects of the conditions leading to winter injury, or by
consuming energy reserves which might otherwise have been used to defend against
pathogens or to repair damage from winter injury or drought. The information available
at the present time suggests that ozone is the most likely pollutant for further study.
The climatic conditions and mechanisms leading to winter injury in red spruce need to
be understood in detail, and the effects of airborne chemicals on those mechanisms
OCR for page 101
101
need to be determined before a confident assessment can be made of the role played by
air pollution.
TOTAL CHLOROPHYLL CONTENT
a-' 1 1
-
~2 -
~o
At.
2~.
...
I..
..4
1.2
t.O
/
//:
~ J ~2 ~ t~: ~!~ :
"1 S 7~3 7~16 7~28
COlLECrlON OA"
"~ ~ 0~
~7 acts
· F1L~ED
1987 NEEDY DRY "IGHTS
HA l
2~:
2 ~
1~- ,
t
OA .
/~
k;/
//,/r/ my'
~ 7/OS ?~1f 7~ ~7
/
~ CI3NTIIOL + Offt'
lift ~ a/2'
· FILTERED
Figure 9. Chlorophyll content and dry weight of red spruce foliage from a control
chamber, a chamber receiving charcoal-filtered air, and an open branch. The
experimental tree was approximately 125 years old (at dbh), and growing at 1170 m on
Whiteface Mt., NY. Chambers were installed on July 3. Standard errors are calculated
from replicate twigs from one branch. Methods and operating conditions in the chambers
(temperature, PAR, relative humidity) are given by Vann and Johnson (1988~.
OCR for page 102
102
REFERENCES
Battles. I.. A.H. Johnson. T.G. Siccama. and W.L. Silver. 1987. Recent
changes in
spruce-fir forests of the New York, Vermont and New Hampshire. In: proc. of a
U.S.-German Conference on forest decline. Burlington, VT. October 19-24, 1987.
U.S. Forest Service, Broomall, PA.
Burgess, R.L., M.B. David, P.D. Manion, M.J. Mitchell, V.A. Mohnen,~ D.J. Raynal, M.
Schaedle, and E.H. White. 1984. Effects of acidic deposition on forest ecosystems
in the northeastern United States: an evaluation of current evidence. New York
State College of Environmental Science and Forestry, Syracuse, NY.
Carey, A.C., E.A. Miller, G.T. Geballe, P.M. Wargo, W.H. Smith, and T.G. Siccama. 1984.
Armillaria mellea and decline of red spruce. Plant Dis. 68:794-795.
Cook, E.R., A.H. Johnson, and T.J. Blasing. 1987. Modelling the climate effect in tree
rings for forest decline studies. Tree Phys. (3) 27-40.
Cumming, I.R., R.G. Alscher, J. Chabot, and L.H. Weinstein. 1988. Effects of ozone on
the physiology of red spruce seedlings. In: proc. of a U.S.- FRG conference on
forest secline. Burlington, VT. Oct. 1987. U.S. Forest Service, Broomall, PA (in
press).
Curry, J.R., and T.W. Church. 1952. Winter drying of conifers in the Adirondacks. J.
Forestry (50) 114- 116.
Davison, A.W., J.D. Barnes, and C.J. Renner. 1987. Interactions between air pollution
and cold stress. Proc. 2nd Internat. Symposium on Air Pollution and Plant
Metabolism. Apr. 6-9, 1987. Neuhenburg, Fed. Repub. of Germany.
Friedland, A.J., R.A. Gregory, L. Karenlampi, and A.H. Johnson. 1984. Winter damage to
foliage as a factor in red spruce decline. Can. J. Forest Res. 14:963-965.
Hadfield, J.S. 1968. Evaluation of diseases of red spruce on the Chamberlain Hill sale,
Rochester Ranger District, Green Mt. Nat. Forest. File Report A-68-S 5230.
Amherst, MA: USDA-Forest Service Northeastern Area, State and Private Forestry,
Amherst FPC Field Office.
Hopkins, A.D. 1901. Insect enemies of the spruce in the Northeast. - U.S. Dept. of
Agriculture, Div. of Entomology Bull. No.2S, new series. Pp. 15-29.
Johnson, A.H., and T.G. Siccama. 1983. Acid deposition and forest decline. Environ.
Sci. Technology. 17:294a-305a.
Johnson, A.H., and S.B. McLaughlin. 1986. The nature and timing of the deterioration of
red spruce in the northern Appalachians. Report of the Committee on Monitoring
and Trends in Acidic Deposition. National Research Council, National Academy
Press, Washington D.C. Pp. 200-230.
Johnson, A.H., A.~. Friedland, and J. Dushoff. 1986. Recent and ~ historic red spruce
mortality: evidence of climatic influence. Water Air Soil Pollut. 30:319-330.
Johnson, A.H., E.R. Cook, and T.G. Siccama. 1988. Relationshi~ps between climate and
red spruce growth and decline. Proc. Nat. Academy Sci. (in press).
OCR for page 103
103
Kelso, E.G. l 965. Memorandum 5220,2480, July 23, 1965.
Service Northern FPC Zone.
Amherst, Mass. U.S. Forest
. ,
Lovett, G.M., W.A. Reiners, and R.K. Olson. 1982. Cloud droplet deposition in subalpine
balsam fir forests: hydrological and chemical inputs. Science 218:1303-1304.
Manion, P.D. 1981. Tree Disease Concepts. Englewood Cliffs, N.J. Prentice Hall.
McCreery, L.R., M.M. Weeks, M.J. Weiss and I. Millers. 1987. Cooperative survey of red
spruce and balsam fir decline and mortality in New York, Vermont and New
Hampshire: a progress report. In: proc. Integrated Pest Management symposium
for northern forests March 24-27, 1986. Cooperative Extension Service, University
of Wisconsin, Madison.
McLaughlin, S.B. 1987. Carbon allocation as an indicator of pollutant impact on forest
trees. In Proc. of a IUFRO Conference on Woody Plant Growth In a Changing
Chemical and Physical Environment. M. Cannell and D.L. Lavander (eds.~.
Vancouver, B.C July 1987. (in press).
McLaughlin, S.B., D.J. Downing, T.J. Blasing, E.R. Cook, and H.S. Adams. 1987. An
analysis of climate and competition as contributors to the decline of red spruce in
the high elevation Appalachian forests. Oecologia 72:487-501.
Mueller-Dombois, D. 1983. Tree-group deaths in North American and Hawaiian forests: a
pathological problem or a new problem for vegetation ecology? Phytocoenologia
11:117-137.
Namias, ]. 1970. Climatic anomaly over the United States during the 1960's. Science
170:741 -743.
Reich, P.B., and R.G. Amundson. 1985. Ambient levels of ozone reduce net
photosynthesis in tree and crop species. Science 230:566-570.
Skelly, J.M., Y. Yang, B.I. Chevone, S.~. Long, J.E. Nellessen, and W.E. Winner. 1983.
Ozone concentrations and their influence on forest species in the Blue Ridge
Mountains of Virginia. In: Air Pollution and Productivity of the Forest. Pp. 143-59.
Izaak Walton League, Washington, D.C.
Stark, D. Unpublished notes on red spruce disease, mortality and winter injury
1957- 1977. State of Maine Department of Conservation, Entomology Laboratory.
Augusta.
Tegethoff, A.C. 1964. High Elevation Spruce Mortality. Memorandum 5220, September 25,
1964. Amherst Mass.: U.S. Forest Service Northern FPC Zone.
Vann, D.R., and A.H. Johnson. 1988. Design and testing of branch chambers for the
exclusion of atmospheric pollutants. In Proc. of a U.S.- FRG Conference on Forest
Decline. Burlington, VT, Oct. 1987. U.S. Forest Service, Broomall, PA (in press).
Wang, D., D.F. Karnosky, and F.H. Bormann. 1986. Effects of ambient ozone on
productivity of PODU1US tremuloides Michx. grown under field conditions. Can. J.
Forest Research. 16:47-55.
OCR for page 104
104
Waring, R.H. 1987. Characteristics of trees predisposed to die. BioScience 37: 569-575.
Weinstein, L., R.J. Kohut, and Jay S. Jacobson. 1987. Research at Boyce Thompson
Institute on the effects of ozone and acidic precipitation on red spruce. Proc.
SOth Ann. Meeting, Air Pollut. Control Assn. June 21-26, 1987, New York, NY.
Weiser, C.J. 1970. Cold resistance and injury in woody plants. Science 169:1269-1278.
Wheeler, G.S. 1965. Memorandum 2400, 5100 July 1, 1965. Laconia, NH U.S. Forest
Service Northern FPC Zone.
Representative terms from entire chapter:
ambient levels
