In the 1980s, the forest damage caused by air pollution led to rethinking the choice of tree species and in particular gave the spruce and fir fewer prospects. In the meantime, the air quality and hence the future prospects for the fir have again improved. The fir is therefore again being cultivated as a silvicultural option and for distribution of risk.
At the same time, research of the forest ecosystem revealed the major importance of deciduous trees for forest soils. Deciduous trees are therefore a central element of ecologically compatible forestry.
By contrast, some tree species are afflicted by wide-ranging diseases. Those affected for decades now are elms, and ash trees in recent years. Therefore scientists and foresters look for tree species that can adapt to climate change or thrive under the anticipated circumstances, those that bind lots of carbon dioxide from the atmosphere and form species-rich ecosystems.