The contribution of particulate matter to forest decline

Bonn University: Air pollution is related to forest decline and also appears to attack the protecting wax on tree leaves and needles. Bonn University scientists have now discovered a responsible mechanism: particulate matter salt compounds that become deliquescent because of humidity and form a wick-like structure that removes water from leaves and promotes dehydration. These results are published in “Environmental Pollution”.

Nature conservationists call it “lingering illness”, and the latest report on the North-Rhine Westphalian forest conditions confirms ongoing damage. Bonn University scientists have now shown that salt deposits on leaves may decrease the drought tolerance of trees, thereby contributing to forest decline. “Our study reveals that so-called wax degradation on pine needles may develop from deposited particulate matter”, says Dr. Jürgen Burkhardt from the Institute of Crop Science and Resource Conservation. Wax helps to protect leaves and needles from water loss.

It has long been known that air pollutants accelerate wax ageing and that “wax degradation” is closely related to forest damage. “Wax degradation was addressed by many studies in the 1980s and 90s, but sound explanations for both the degradation mechanism and the high correlation with forest damage have yet been missing”, Dr. Burkhardt reports. Previous approaches assumed chemical reactions for wax degradation, whereas the present study reveals physical reasons. “The deposition of hygroscopic salts is capable of decreasing the drought tolerance of trees”, co-author Shyam Pariyar says.

...Recently, regional forest damage has been reported in the western USA and other parts of the world. A relationship with increasing climate change-type drought has been proposed, but the newly discovered mechanism involving particulate matter might contribute to the regional forest damage. “Particularly because air concentrations of hygroscopic particles have largely increased within the last decades”, says Dr. Burkhardt...

A foggy forest near the northern Rhine, shot by Thomas Klein-Hitpaß (Rototom), Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license