Vital Forest Graphics

of gaseous pollutants through the sto- mata – the area where damage is often first apparent. The symptoms vary according to species and pollutants. The vulnerability of trees and forests to other pests, such as invasions by bark beetle, can also increase as a result of chemical pollution. Diagnosis of problems affecting trees can be complicated by the pres- ence of similar symptoms caused by other stresses besides air pollutants. For example forests and trees quickly react to drought, with discoloration, loss of foliage and die back ultimately leading to tree mortality. As the fre- quency of climate change induced drought is expected to increase in some areas, the health of more forests is likely to be at risk. In the 1980s, acidic deposition – commonly termed acid rain – was considered to be a threat to ecosystems in Europe and North America. Exten- sive surveys indicated the condition of forests across these regions was rapidly deteriorating. Although air quality in Europe has improved considerably over the years, trees are still under stress (MCPFE 2007). More recently, ozone – formed through the interaction of nitro- gen oxides, volatile organic carbons (VOCs) and sunlight – has emerged as a significant problem in many regions. With its characteristic symptoms, such as purplish-brown stippling on the upper surfaces of leaves, ozone damage is particularly associated with forests near large urban sites such as Mexico City and Los Angeles. Trees and forests have also been affected in many other regions, including much of south- central Europe, and damage is some- times associated with the highly toxic peroxyacetyl nitrate (PAN). Unlike sulphur dioxide, sourced mainly from large scale operations such as coal-fired power stations, nitro- gen oxides are emitted from multiple sources, with vehicle exhausts a big fac-

tor. Such emissions – which can also adversely impact on trees and forests – are more difficult to control. Some of the earliest and most detailed studies of the effect of air pollution on forests were conducted around actual sources of pollution, such as smelters (Kozlov and Barcan 2000). The studies showed pollution levels were severe enough to kill all trees and vegetation in the vicinity. Such deserts – devoid of all nature – still surround several smelters in Rus- sia. As soils are usually heavily polluted by a range of chemicals, any clean-up is extremely difficult. While the type of direct injury to forests seen near smelters in North America and in lignite-burning areas of eastern Europe is unlikely to con- tinue for much longer due to tighter emission regulations, air pollution- related damage to trees – much of it

in the form of ozone – is likely to per- sist in these areas into the foreseeable future. Outside these regions, particu- larly in Asia and South America, dam- age caused by air pollution seems likely to increase. Recent brown cloud One of today’s most urgent and wide- spread air pollution problems is the smog that extends over much of China, with both urban and rural air quality often extremely poor. At times vis- ibility over a wide area is less than 100 metres with a thick pall of smog cloud- ing the sky. The impact of smog on vegetation in China is not well-known, though it is clear widespread damage is being done to trees, forests and other vegeta- tion around sites of particularly high pollution. A similar situation pertains in India.

The Kola Peninsula under threat from deadly emissions

5VY^LNPHU :LH

NORWAY

)HYLU[Z :LH

Kirkenes

Kirkenes

NORWAY

FINLAND

Nikel

Nikel

Murmansk

RUSSIA

/`WVN`TUPH WO`ZVKLZ and 7HYTLSPH VSP]HJLH coverage 0% 3% 20%

Monchegorsk

FINLAND

>OP[L :LH

RUSSIA

SWEDEN

0

120 40 80 160 km

SO 2 air concentration ( › g/m 3 )

5VY^LNPHU :LH

Forest death area Inner visible damage zone Outer visible damage zone Inner non-visible damage zone Outer non-visible damage zone

)HYLU[Z :LH

10 20 40 60

NORWAY

2 4 6

Murmansk

Nikel

Monchegorsk

SWEDEN

>OP[L :LH

FINLAND

Source: AMAP 1998.

RUSSIA

VITAL FOREST GRAPHICS 51