DECLINE DISEASES

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DECLINE DISEASES Reading Tex
t, Chapter 15 Hennon, P. E. and C. G. Shaw,
Jr.1997. The enigma of Yellow-Cedar decline. What
is killing these long-lived defensive trees. J.
For.95(12)4-10.
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Eucalyptus (E.viminalis, E.ovata) decline in
Derwent Valley, Tasmania over last 30 years.
Decline is most rapid where the soils are
shallow, where wind exposure is high, on
columnar rock types such as dolerite and basalt
and on northerly (sunny) and westerly (windy)
aspects. http//www.dpiwe.tas.gov.au/inter.nsf/We
bPages/EGIL-54835G?open
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Decline and dieback are used to describe a
complex of symptoms involving crown dieback, leaf
discoloration, leaf loss, reductions in leaf size
and stem radial growth, and twig and branch death
that may lead to the death of the whole tree
Symptoms of decline may be subtle, but are
persistent and progressive and usually occur over
periods ranging from 3 to 30 years. Periods of
decline may be followed by periods of recovery
which may be temporary or complete. Forest
declines usually occur over large regions and
involve single tree species. Thus the term
species decline might be a better term than
forest decline
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No principal pathogen capable of causing diseases
in healthy trees was identified in the majority
of these cases. Rather they seemed to be caused
by complex of factors. Changing climate or
unusual weather conditions have commonly been
blamed. Phytophthora root disease may be
involved.
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Some interesting and dramatic changes in tree
species populations have been identified in the
last 5000 years based on paleoecological studies
involving pollen analysis of lake sediments.
Margaret Davis of the University of Minnesota
observed a dramatic drop in eastern hemlock
pollen in eastern North America in an area from
New Hampshire to southern Connecticut an across
to upper Upper Michigan about 4500 radiocarbon
(14C) years ago (Davis 1981). Hemlock regained
its previous abundance in some areas 2000 years
later, but in other areas it never recovered to
previous levels. A number of causes for the
hemlock decline were postulated climatic change,
fire, windstorms, the impact of prehistoric
humans, and pathogens or insects.
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Important forest declines or diebacks in Europe,
North America, Australia, New Zealand, Hawaii,
South America, Africa and Asia Decline or
dieback Host(s ) Year reported
EUROPE Oak decline Quercus spp. 1739
Tannensterben Abies alba 1810 (European
silver fir decline) Waldsterben Picea
abies 1979 and hardwoods
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Declines - continued
NORTH AMERICA Alaska yellow-cedar
decline Chamaecyparis nootkatensis 1900 Ash
dieback Fraxinus spp. 1925 Pole
blight Pinus monticola 1927 Littleleaf
disease Pinus elliottii, P. taeda 1929 Birch
dieback Betula spp.
1932-35 Balsam fir decline Abies balsamae 1950
(Fir waves) Oak decline Quercus
spp. 1951 Sweet gum blight Liquidamber 1951 P
onderosa pine decline Pinus ponderosa 1950s Sugar
maple decline Acer saccharinum 1957 Red spruce
decline Picea rubens 1980s Fraser fir
decline Abies fraseri 1980s
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Declines continued THE PACIFIC, AUSTRALIA
AND NEW ZEALAND New England dieback Eucalyptus
spp. 1850s (NSW) Jarrah decline Eucalytptus
marginata 1921 (WA) Ohia decline Metrosideros
polymorpha 1970s (Hawaii) Nothofagus
dieback Nothofagus spp. 1980s (New Zealand)
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Declines continued
SOUTH
AMERICA Canopy dieback Scalesia
pedunculata Galapagos Islands 1935 Cypress
decline Austrocedrus chilensis Southwestern
Argentina 1948 Nothofagus dieback Nothofagus
antarctica Argentina (Patagonia) 1988

AFRICA Dieback of Terminalia Terminalia
ivorensis Ivory Coast and Ghana 1970s ivorensis R
ain forest dieback Newtonia buchananii, Uganda
1984 Lovoa swynnertonii and other
species Neem decline Azadirachta indica West
African Sahel 1990 Stinkwood decline Oocotea
bullata South Africa 1990
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Declines continued
ASIA Top dying of
sundri Heritiera fomes Bangladesh 1915 Cryptomer
ia japonica Cryptomeria japonica Japan 1970s decl
ine Shimagare decline Abies veitchii, A.
mariesii Japan 1976 Canopy dieback
of Calophyllum and Sri Lanka 1978 montane
forests Syzygium spp
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DECLINE DISEASE
THEORIES 1. Environmental stress and secondary
organisms theory (David Houston) 2.
Predisposing, inciting and contributing factors
theory (Wayne Sinclair, Paul Manion) 3. Climate
change or climate perturbation theory 4. Air
pollution theory 5. Ecological theory (Dieter
Mueller-Dombois)
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The Concept of Predisposing, Inciting and
Contributing Factors
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CLIMATE CHANGE OR CLIMATE PERTUBATION
THEORY Analysis of crown diebacks of red, black
and white ashes, yellow and white birch and sugar
maples in eastern Canada from 1920 to 1987
revealed they were highly episodic (Figure 15.3)
and possessed the following features a. Onset
years were abrupt and region wide, but site
influences caused local variability. b. Each
major dieback episode included a "lead" species
and 5-30 associated tree species. c. Recovery
from crown dieback also depended on local factors
and was equally as abrupt as the onset. d. Once
dieback was initiated a background or chronic
level of dieback persisted on the lead and most
associated dieback species, and e. Successive
major dieback episodes this century appear to
have become more severe in terms of species,
areal extent and mortality.
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Maple decline in NE USA and Canada
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Alaska yellow-cedar decline SE Alaska
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AIR POLLUTION THEORY Ozone Acid rain Excess
Nitrogen Deposition
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Smog in southern California forests - mostly
ozone produced by photochemical oxidation of NOx
in auto exhausts
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Ozone damage to ponderosa pine
High ozone in California (red)
Smog in LA
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Dead trees at Clingmans dome, Great Smoky
Mountains National Park (left)and Mt. Mitchell,
NC (below). Initially attributed to acid rain,
but mostly due to the Balsam woolly adelgid
Definitely unhealthy
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European Forest Decline
Waldsterben Mostly attributed to acid rain.
1987
1993
1988
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FEATURES OF WALDSTERBEN - EUROPEAN FOREST
DECLINE (1) All the important tree species were
involved, including both conifers and hardwoods,
and showing similar symptoms, not recognized
before. (2) the syndromes stood apart from
ordinary tree diseases. (3) the main symptoms
were decrease in increment, loss of foliage and
feeder roots, transparent crowns, yellowing of
foliage, premature senescence, altered branching
habit, and abnormally high seed production. (4)
rapid development - Norway spruce and pines were
expected to deteriorate so rapidly that they
would have to be cut within 3 years of showing
the first symptoms and silver fir and Norway
spruce in the Black Forest were expected to die
within 10 years. A visit to the German forests
in the mid 1980s revealed that many stands
appeared relatively healthy because dead and
dying trees had been removed. (5) the most
likely cause was a complex disease triggered by
cumulative stress from increasing air pollution
and deposition of air acid precipitation, sulfur
dioxide, nitrogen oxide and ozone. (6) Acid
deposition caused increased soil acidity
resulting in increased soil Al levels that are
toxic to fine (feeder) roots and mycorrhizae and
also depleted the soil of cations, particularly
Mg, resulting in yellowing foliage. Ozone
further damaged the foliage resulting in leaching
and further loss of Mg.
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ECOLOGICAL THEORY
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Ohia decline, Hawaii
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Based on this evidence Dieter Mueller-Dombois of
the University of Hawaii (Mueller-Dombois et al.
1983, Mueller-Dombois1992) proposed a natural
dieback theory based on four principal generic
causal factors - s (simplified forest
structure) - e (edaphically extreme sites) - p
(periodically recurring perturbations, and - b
(biotic agents).
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Another example of natural disturbance and
decline is the wave-regenerated balsam fir
forests in the mountains of the northeastern
United States, where mortality waves move through
the forest every 50-70 years (Sprugel and Bormann
1981). The waves move at a relatively uniform
pace and the forest always contains dead and
dying trees (Figure 15.8). Since consecutive
waves are only about 100 m apart, relatively
small areas can contain all phases of
disturbance. Fir waves are thought to result
from build up of rime ice during then winter on
taller trees resulting in stem breakage and waves
move in the direction of the wind. A similar
phenomenon occurs in Japan.
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Balsam fir waves Whiteface Mt., New York
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