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Abiotic Diseases

Here we consider a variety of diseases caused by non-living (abiotic) agents. Included are some cases that might be characterized as injury.

Air Pollutants


Several flourine compounds are produced during smelting (high temperature treatment of ore to purify minerals), particularly when producing aluminum.


Hydrogen and carbon, like CH3CH2CH2- etc. Maybe some double bonds, some oxygen here and there, etc. These result from incomplete burning of fuels during combustion. If someone's car needs a tuneup badly, it smells and puts out visible smoke. Much of that is hydrocarbons.


Produced during combustion of fuel that contains sulfur impurities. Mostly occurs in coal, but also oil. That is why there is a distinction between high-sulfur and low-sulfur coal. Many heavy industries release large amounts of SO2. Electrical plants, smelters.

A big coal-burning power plant, with two generators, can burn 650 tons of coal per hour at each generator. If that is 2% sulfur, that can generate 65 tons of SO2 per hour, also NOx.


Produced during any kind of combustion under heat and pressure. The N comes not necessarily from the fuel but from the air, which is needed of course to provide O2 for combustion. So automobiles, factories, electrical generating plants, etc. all produce NOx. NOx can also come from the soil. NOx themselves are not very toxic, but they react in the atmosphere to make toxins.


ozone formulaThis is a secondary pollutant. Several primary pollutants, under the influence of ultraviolet light, make it. The chemistry is more complex than given here. Don't worry about the full equation, but you should know what pollutants are involved in making O3. Additional sources are stratosphere, lightning, forests. The stratosphere is a separate pool of ozone that is beneficial because, ironically, it actually protects us from ultraviolet light!


PAN formulaPeroxy-acetyl nitrates - also a secondary pollutant formed from action of UV light on precursors in smog. An example is CH3COO2NO2.

Acid precipitation

Another secondary pollutant in a sense. SO2 and NOx combine with water and oxidize to form various acids, primarily sulfuric and nitric acids. Although pure water has pH 7, water equilibrated with unpolluted air has pH 5.6 (CO2 dissolves, making carbonic acid). Rain more acidic than that is considered to be "acid rain." Rain in many parts of the world is pH 4-4.5. Rain with pH below 2 has been recorded (more acidic than lemon juice). Actually it gets deposited in forests in other forms than rain, so the immission is often called "acid deposition."

Photochemical smog

Visible pollution containing the secondary pollutants O3 and PAN and the associated primary pollutants.


include ozone, NOx and PAN

Effects on Plants

We could try to distinguish between injury and disease, injury being damage from a brief exposure at a particular point in time; disease being damage resulting from exposure over a longer period. That distinction is pointless in this case, so we won't worry about it. Let's consider it all disease.

Another distinction we might make is between acute symptoms: exposure over a period of time leads to, among other things, more or less obvious symptoms, usually on the leaves. Finally, there is the situation where there may be growth loss or other subtle symptoms that may be difficult to detect, much less diagnose.

A note on concentrations. In the U.S., it is the practice to express pollutant concentrations in ppm or ppb (parts per million or billion). This drives scientists in other parts of the world nuts, and they are right. The units refer to parts of volume, although it is not clear and could just as easily be weight, which is much different.


Hardwoods: marginal chlorosis --> necrosis. Conifers: tip burn/necrosis.

Various aluminum plants and other chemical plants that release flourides have severe mortality and damage around them. In North America, most are in the West. Areas of severe mortality are as large as 2000 acres, and damage can be up to 50 sq. miles. Flouride analyses of leaves support the conclusion that flouride is the responsible pollutant.

Hardwoods: mottling, flecking, stippling. Color can be purplish or white. Can coalesce, leading to bleaching of portions of the leaf. Conifers: chlorotic mottling, stunting, maybe tip necrosis. Symptoms of oxidant injury are not uncommon, especially on understory plants and especially late in the summer.

Although we cannot know for sure, it is thought that natural levels may be about 10-20 ppb. It is pretty common to see levels of 40 ppb in many parts of the country. It is thought that 55-85 ppb is about the threshold for forest growth impact. 80 ppb causes visible symptoms on eastern white pine (or less, depending on exposure time). Levels up to 400 ppb have been recorded in the San Bernardino Mountains of California!

White ash, aspen, ponderosa pine and eastern white pine are sensitive.

not really pathogenic at normal levels?
Hardwoods: silvering/bronzing of underside, rare. Damage to trees in nature is not known.
Hardwoods: interveinal chlorosis and necrosis. Conifers: chlorotic spots and bands, brown tips.

"Clean" air probably has less than 1 ppb. On Whiteface Mtn. in New York, 1-3 ppb are usually recorded. EPA Air Quality Standard, average annual maximum is 31 ppb. Levels in acute problem areas, close to the source, are 500+ ppb.

Case studies

Smelters and SO2 - Sudbury Ontario

Three large nickel and copper smelters have discharged 2-3000 tons of SO2 per day. Result: no vegetation over 25,000 acres, stunted vegetation over 36,000 acres, and loss of white pine over 720 sq. mi. They closed one of the smelters in 1972 and put the worlds largest smokestack on another - 1,250 feet high. This has been done in many areas, so we don't get the acute damage as often. This is a classic case that led to the phrase, "Dilution is the solution to pollution." There has been erosion and acidity, devastating lakes and streams. Elevated nickel and copper remains in the soil up to 30 miles away. Another example is Copper Basin in Tennessee, and various smelters, generating plants, etc. in the West. Generally, conifers are most sensitive to SO2.


Erzgebirge on the border of Czechoslovakia and eastern Germany - SO2

(Under development)


San Bernardino Mountains - O3

The San Gabriel and San Bernardino Mtns. lie about 50 miles east of Los Angeles. They present a barrier to the eastward movement of air, and inversions are frequent. Ponderosa pine gets chlorotic mottling, stunted needles and needle retention reduced to 2 years. Trees become susceptible to bark beetles and annosum root rot. Growth impact on ponderosa pine is dramatic:

low pollution, 1910-1940 - 0.5 cm/yr radial growth
hi pollution, 1941-1971 - 0.3 cm/yr

Forests there are changing as a result, less pine.


Waldsterben and Northeastern U.S. Forest Decline (Prelude to Decline Topic)

(Under development)



This is a complex subject, and one should not rush to judgement. Some people have their minds made up one way or the other about whether pollutants are causing forest damage in region-wide situations where there are no symptoms. If you develop an opinion on the question, I advise you to do it based on an independent evaluation of the facts. Even in the hallowed halls of academia, there are those that will try to push their opinions on you. Study the issue, find your own facts, and think for yourself.


Other Abiotic Diseases


Usually, and preferably, the term frost damage is restricted to damage due to subfreezing temperatures during the growing season, or while the tree is not dormant. This can be after bud break, due to a late spring frost. Spring frost damage is fairly common. Young tender shoots droop and go dark, then fall off. The damage is soon difficult to detect.

Less commonly, frost may occur prior to hardening off of shoots and buds, due to an early autumn frost. An early winter in central Alaska led to an unusual situation where the winter came while green leaves were still on the deciduous trees. Leaves persisted through the winter and into the following summer. Apparently buds were not completely set so it probably led to some shoot damage.

Winter Injury

Damage due to low temperature during winter dormancy is a separate phenomenon, though related. It may actually be two phenomena. In one scenario, which may be called winter freezing, warm weather during dormancy induces partial deacclimation. If it is followed by a rapid and large drop in temperature, there may be freezing damage to shoots and/or buds. Repeated cycles of extreme temperature fluctuation make such trees much more susceptible to such injury. The result is reddening and browning of foliage in the spring (evergreens) and dieback of shoot tips.

In some cases, bark injury results. This is especially common after solar exposure heats up the bark, which then freezes. This is called sunscald, but may be better called winter sunscald to distinguish it from heat injury to the bark from the sun in summer, which is probably much less common.

Water - Not enough

Can be a chronic problem for trees that can be characterized as a disease. Acute symptoms include wilting, but over time slower growth, then twig and branch dieback can be major symptoms. Often, weak secondary pathogens can be involved in killing back twigs and branches of drought-stressed trees.

Moisture stress of trees is a function not only of precipitation, but also soil properties. For most plants, a soil with balanced particle sizes and lots of organic matter is ideal, partly because of moisture. The finer particles and organic matter increase the moisture-holding capacity of the soil. Soil that is high in sand and low in clay and organic matter could lead to drought stress right after soil drains.

Water - Too much

The other extreme is just as bad. Actually, the problem is insufficient O2. And just like not enough water, there can really be two causes: excessive rainfall or flooding, and soil structure that impedes drainage. Just as a sandy soil drains too quickly, holding little moisture, a soil high in clay (often called "heavy" soil) tends to have poor drainage and limited air spaces. Rootlet mortality and attack by oomycetes are common consequences. Soil compaction and hardpans have a similar effect. Trees that do well in wetlands usually tolerate low-O2 environments and consequently do well in cities, where pavement and compaction reduce soil aeration. The U.S. Forest Service has online info on flooding and its effects on trees.

Nutrient Deficiency

This is a big topic. In quasi-natural forests, deficiency symptoms are not normally seen, although growth can be increased by fertilization. Deficiency symptoms can be seen on occasion in ornamentals and off-site plantations.

Symptoms vary with the tree species, and can be complicated by combinations of nutrients. Worse, the symptoms are rarely diagnostic, meaning the symptoms are non-specific and, considered alone, do not usually allow a reliable diagnosis. Without vast experience with particular cultivars in a particular area, extensive analyses may be necessary to confirm a diagnosis.

Still, there are some generalities that are useful and practical to keep in mind. Here are some facts about two nutrients as examples:


Here we are primarily talking about deicing salt. There are several other situations where salt can damage plants though: some areas have saline soils, or slightly saline irrigation water that can accumulate in the soil. Coastal areas can have salt spray that affects the local plant communities. In those situations problems can arise, particularly in plants out of their native range or when unusual conditions spread salt out of it's usual area. For instance, hurricanes can cause plant damage up to 10 miles inland, not just by breakage but by salt injury to foliage.

Salt affects plants via two routes: through the soil, and as salt spray.

Deicing salt via soil

Areas below road grade, usually quite close to road, especially where tree's roots are all in low area with limited drainage. Symptoms: leaf scorch, premature defoliation, dieback, can contribute to death. Can see in red pine in the Adirondacks. Sugar maple is susceptible. Mechanisms: osmotic concentration in soil too high, roots can't obtain enough water. Na may replace cations like Ca and K in soil, creating deficiency. Na also raises pH, making iron unavailable. Na also degrades soil texture.

Deicing salt via salt spray

Up to 50 meters of highway, especially downwind. Exposed plants collect the most droplets so get the most damage. Symptoms: needles brown at the tips, drop early. Hardwoods- buds die, twigs die back --> brooms. Mechanisms: Cl- toxicity seems to be the big problem, accumulates at tips and margin. Kills tissue, impairs cold hardiness. Tolerant plants limit accumulation.

Chronic Wind Stress

In some areas of the world, forests at high elevations experience very strong and frequent winds. In the mountains of New England and in Japan, the tree line is thought to be determined largely by wind rather than other ecological determinants such as growing season. There are apparently several mechanisms:

At the highest forested elevations, this mortality is organized into waves that progress slowly up the mountain. The forests there are fir and the phenomenon is called "fir waves." At lower elevations, in spruce-fir forests, the mortality is less organized and scattered around.

Girdling Roots

Sometimes roots develop in an unfortunate position, choking off other roots or the base of the stem as they develop. This is especially common on planted seedlings. It is made more likely by growing of seedlings in containers or close cultivation of the soil.


Lightning causes significant damage to forest and shade trees. In one study, it was considered responsible for 1/3 of mortality in a ponderosa pine stand. It causes mortality of tops, branches or whole trees, creates large wounds for decay, and often leads to a slow death. The current usually goes down near the cambium, but may go along outer surface for a portion of the distance (discontinuous damage).

Look for long strips of bark and outer sapwood blown off the surface. It may look like the tree exploded afterwards. It follows the grain of wood, often spiral. Usually one can see that it goes all the way to soil, may even blow soil off roots.

Funny picture “Tree diseases? Cool!”

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Last modified 27 May, 2007