Shut Off That Engine!

G-01 Air Pollution as a Factor Affecting Global Forest Health

Industrial growth has inevitably led to the emission of toxic gases into our atmosphere. When they exceed certain limits or concentrations, these gases are catastrophic and can turn deadly towards the very systems that sustain our survival. Like many ecosystems, forests can easily become a target.

Source: Dan Aamlid, Norwegian Forest and Landscape Institute,
Source: Dan Aamlid, Norwegian Forest and Landscape Institute,

In this technical session, Borys Tkacz from the United States set the stage by providing an overview on the state of the health of forests in the country. A great deal of his presentation emphasized forest-related threats, especially mortality and other forms of destruction that pests unleash on forests. He underscored the role of forest fires, monitored using time-series MODIS imagery, as well as ozone pollution which will, among other effects, result in dramatic shifts and decline in lichen communities.

Modeling and simulation examples that many of the European presenters alluded to highlighted a worrisome trend regarding the impact of certain types of pollutants and nutrient loads to different forest ecosystems. For example, an illustration from Austria showed the effects of acid rain, especially on the soil pH, which would inevitably affect forest lands. The Lithuanian example emphasized that air pollution and acid deposition were some of the main factors driving tree crown defoliation. So was a case that Andrzej Bytnerowicz of the U.S. laid out for the Carpathian forests in Eastern Europe. These experiences formed the basis for what Martin Lawrence from Germany referred to as “clean air politics” in Europe, where policy makers are using such scientific findings to craft legislation that targets sustainable forest management, carbon sequestration, and climate change.

As if the American and European examples were not perturbing enough, Shuirong Wu shared even more frightening simulations that showed significantly higher critical load exceedances, especially in Northeast and Southeast of China. These regions are some of the main industrial areas of Mainland China so it’s expected that air pollution would be among their main issues, but probably no one in the audience expected to hear that air pollution here could be close to two times that of some European countries (Norway and the Czech Republic, for example)! These are sobering statistics that could have weighty implications for forest management in China and neighboring countries since, as we all know, air pollution and many other environmental ramifications do not respect territorial borders.

A very fascinating talk was given by Steven McNulty while presenting on the interactions of climate change and acid load exceedance in the southern United States. What was so captivating about his work was the synergy that he so vividly showed existed among acid load, southern pine beetle, and drought and high temperatures. These linkages resulted in the resiliency of seemingly unhealthy tree,s while those that appeared healthy crumbled under the weight of these interactions, hence his famous phrase, “the rise of mediocre trees.”

While most of these findings might not come as surprises, they nevertheless give us a fresh bone to contend with: some of us might ask ourselves what we could do as responsible citizens to minimize our carbon footprints, and in the process contribute, in our own small ways, towards promoting healthy trees and healthy forests.


Written by: Humphrey Kalibo

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