The Jizera Mountains (Jizerské hory) are a part of the Black Triangle, which, in the past, was one of Europe's most polluted regions. Situated on the Czech–Polish border, these mountains were heavily affected by extreme SO₂ and NO_x loads emitted from coal power plants in the piedmont. During the 1970s and 1980s, the upper plateau of the Jizera Mountains experienced substantial forest decline due to air pollution. Dying stands were felled on more than 12,000 ha. Modernization of the energy industry after 1989 has led to a significant reduction in air pollution in the Black Triangle. Therefore, replanting the clear-cut areas in the Jizera Mountains became possible during the 1990s, and a new generation of forests has covered the upper plateau of the mountains. However, these even-aged, mainly spruce stands urgently need to be diversified in terms of age, structure, and species composition. This is not an easy task due to extreme microclimate, acidified soils, and damage to plants by rodents and deer. In 2007, a project aimed at the diversification of local ecosystems was initiated. The project is based on a system of diversification centers and corridors containing a species admixture (broadleaf trees and silver fir), which is protected from game, to form a web that enriches the age and spatial structure of forests on the upper plateau and complements their species composition. Initially, these centers and corridors were placed in more sheltered and accessible places and planted with the standard planting stock in combination with large-sized transplants (<100 cm). Through silvicultural measures, the web became successively denser and expanded to sites with less environmental protection. Supportive measures like initial fertilization of plantations and the biochemical amelioration of depleted soils have also been implemented.