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Reductions in photosynthetic rate and capacity have been described for a
number of tree species; experiments have shown that as little as 16 per cent
decrease in current ozone levels could result in a 40 per cent reduction in
productivity in the Loblolly pine. Similar effects are reported for
jackpine, spruce, sycamore, birch and ash, although effects are normally more
severe in conifers than in deciduous species. The potential for worldwide
woodland and forest damage is clear.
Plants from alpine and high latitude environments, and those most exposed in
other regions, are among the most UV-resistant species. Nevertheless,
recent evidence suggests that even these species suffer reduced
productivity under the already significantly enhanced levels of UV-B.
In addition, adverse physiological and developmental effects may well be
brought about by UV- B indirectly through alterations to the production and
concentrations of plant hormones and other growth regulators. It is
thought that, in many cases, UV-B simply acts as an additional stress to
plants already challenged by, for example, drought, soil contamination or
disease. Under such circumstances enhanced UV-exposure could tip the balance
against survival.
Even less is known about the impacts of UV-B radiation on land animals than is
known for plants. Impacts are likely both through direct exposure
of sensitive areas of the body and indirectly through effects on food
species further down the food chain. Again, as for aquatic organisms,
juveniles will be among the most sensitive and least protected individuals.
In mature animals, the principle target of UV-damage is uncovered skin.
Exposure to excessive UV-B can lead to skin burning, changes in
pigmentation and in vitamin D- synthesis, with increased risks of skin
cancers, eye conditions and suppression of the immune system over the
longer-term. Juveniles are especially vulnerable. Damage to juveniles before
their protective barriers (body hair, shells, skin pigmentation) are fully
developed will likely kill the individual before it reaches maturity. Few wild
animals, especially those which are prey, are able to overcome a childhood
weakness.
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WHEN A TREE BURNS IN THE FOREST, WHO WILL SEE IT?
If a tree falls in the forest, will anyone hear it? If a tree burns under the
searing rays of UV-B radiation, will anyone see it? And will anyone notice
the slow alteration of terrestrial ecosystems before it is too late to stop
the burning from going deeper?
The global depletion of the ozone layer is increasing the rain of UV-B
radiation on forests from the equator to the subpolar regions. This radiation
has many impacts, some of them subtle and indirect, on all forest ecosystems.
Even small increases in the amount of UV-B, especially in the shorter
wavelengths, will reduce the growth of many plants, change plant internal
chemistry, influence plant and animal life cycles, affect the decomposition
of ground litter, and even alter the air flowing through the forest. Such
impacts will change the distribution of species within a particular
ecosystem, and these changes will cascade to other levels of the food chain.
This burning will not leave a charred stump as do the forest fires quickly
raging through many of the forests today. Instead the burning will be slow,
internal damage visible to the casual observer only as curled needles or
subtle changes in leaf colour.
The burning rays of UV-B radiation will first affect those trees most directly
exposed to it: the crowns of the tallest trees, trees growing at the edges of
clearings and rivers and seedlings in clear-cut zones. But they will also
penetrate deeper as time goes on to the lower layers of the forest canopy
until ultimately reaching the soil. There, UV-B will influence the production
of the soil itself through alterations in soil chemistry and impacts on the
lives of the soil biota, microbes, fungi, plants and invertebrates which
transform forest litter to a nutrient-rich humus capable of sustaining many
forms of life.
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THE LONELY DEATH OF
PENGUIN CHICKS - SCIENCE FICTION OR SCIENTIFICALLY PLAUSIBLE SCENARIO?
In
January 1995, the mass starvation of penguin chicks in three widely separate
regions of Antarctica was reported by Australian scientists. Some penguin
parents were observed as far as 200 km offshore desperately searching for
food for their young.
The young birds fed krill, a small shrimp-like crustacean which has
mysteriously disappeared in recent years in many Antarctic waters. Scientists
do not believe that harvesting of the krill could account for the decline,
but they are mystified as to the cause of disappearance.
Should they be? Krill feed on the normally abundant crop of phytoplankton which
bloom in Antarctic waters every spring. These blooms occur under the
ever-growing Antarctic Ozone Hole which permits high levels of deadly UV-B
rays to penetrate into the ocean water. Scientists from around the world have
spent many recent years under the Antarctic Ozone Hole observing the UV-B
damage to the spring phytoplankton bloom.
Studies suggest that UV-B radiation kills only certain species of phytoplankton
and causes others to clump together for protection. The surviving
phytoplankton may thus be too large to be eaten by krill and so the krill die.
The death of large quantities of krill leads to pressures on the remaining
krill from predatory fish, seals, whales and birds. This could lead to a
collapse of the krill communities near the penguin rookeries forcing parent
birds to search far out to sea for food for themselves and their young.
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