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In this new study, Bos and co-authors show that the ferns, which took advantage of the dieback of forests, themselves were subjected to stress from Hg-pollution well beyond the immediate extinction interval.

If crossed, this could lead to the rapid and irreversible dieback of the whole rainforest - potentially leading to the region becoming a significant source of CO2 emissions.

Cultural evolution among groups would tend to exacerbate resource competition and could lead to direct conflict between groups and even global human dieback.

"Because of ash dieback and the changes in climate - the crisis that we're facing - we have a very finite amount of time to do something about it," she told BBC News.

The invasive nematode is native to Japan and causes leaf deformation, dieback and mortality in infested native and ornamental beech species, officials said.