The species composition of forests is simplified, food-chains of particular groups of organisms are broken and regulatory functions of forest biocenoses cease. Direct effects of forest damages due to strong grazing by insects, fires or wind is immediately visible. In fact, they do not determine the actual aftermath of these phenomena. Indirect effects last for decades and can show up in forms of changes that are not easy to attribute to the actual, primary reasons. This is why it is very hard to diagnose the health condition of forests.
Some forests are dangeorously thin.
The decrease in the number of trees per unit of forest area resulting from the dieback of the weakest trees causes the reduction of tree crown density. Almost half of the forests have low crown density. There are even cases of large breaks in the crowns. This means that there is no protective ceiling of tree crowns, which exposes the interior of the forest to many external influences. The thinning of tree stands leads to fundamental changes in the basic physical parameters of the forest environment.