Endangerment of Forest Genetic Resources
The anthropogenic influences cover a broad spectrum:
Forest Clearing and Fragmentation
Since man began utilizing natural resources, man has intervened in the forest ecosystem. Clearing of forests for agriculture has led to extensive destruction of forested land in the past. Further use of forest land for settlement, business, industry, and traffic brought further losses.
Forest Damage Related to Air Pollution
Industrialization had a further negative impact on the environment which endangered the forest. Initially, only locally restricted smoke damage was observed, but later in the 70's immissions extended over large areas which lead to leaf and needle losses and forest decline ("Waldsterben"). In Germany approximately one third of the forest stands over 60 years of age have been significantly damaged for many years.
The extent and the effects which the predicted anthropogenically caused changes in the climate might have on trees and woody shrubs, exempli gratia by global warming or by elevated UV-radiation are presently unclear. However, losses of genetic diversity can be expected.
Interference with the Water Budget
Intervention in the water budget may lead to ecosystem changes due to raising or lowering of ground-water levels. This may cause mortality of tree and woody shrub species or it may change the competitive relationship betweeen species, resulting in the displacement of species locally.
Biotic and Abiotic Damage
Extensive biotic and abiotic damaging events like insect calamities, fungal diseases and rodents, as well as damage by storms, snow or fire may lead to the loss of genetic information of locally adapted populations.
Effects of Historical Types of Forest Use
Before regulated forestry was introduced about 200 years ago, devastation of forests occurred by overcutting, forest grazing and litter use. The specific demands of the population led to selective use of certain tree species and the displacement of other tree species. Many areas have been re-afforested since the beginning of the 19th century predominantly with coniferous tree species.
Utilization of Unsuitable Reproductive Material
Forestry aims at using exclusively site-adapted and productive provenances for seeding and planting. However, one cannot exclude that, unsuitable provenances are still planted in the forest, exempli gratia by falsely marked provenances.
Effects of Improper Practices
The genetic diversity of forest stands and/or tree populations may be impaired exempli gratia by the following forest management practices by artificial regeneration using a low number of plants per hectare or by highly selective operations in stand tending and crop tree harvesting.
High game populations endanger genetic diversity by preferential browsing on the regeneration of specific tree and woody shrub species. In particular rare tree species that are endangered by browsing are often threatened in their existence.
Strictly Protected Nature Reserves / Conservation of Processes
In forests that are taken out of management, valuable rare woody plants may be threatened in their existence by the natural succession of species which are stronger competitors. If strictly protected nature reserves and/or specific conservation areas are established where such rare species still occur they may become endangered in their existence.