The process of Forest Fragmentation that is affecting the whole world return back to many causes that could natural or human-induced.
A. Natural Causes:
These natural causes have minimum effect regarding forest fragmentation but can still contribute on the long time-scale. These include:
1. Wild Fires:
Wild fires cause the loss of wide areas of forests and consequently results in isolating some patches from the others. However, the effects of fire is a minor effect regarding fragmentation and it’s more considered in regard of forest destruction since these fires do not create much patches but rather destroy entire portions of the forest.
Figure 1. Forest fires (http://wrel.com/wordpress/wp-content/uploads/2011/02/forest-fires_bWGjw_691.jpg)
2. Climate change:
Changing climate is one of the important causes of forest fragmentation especially in tropical and subtropical rain forests that spread over large areas. The changing climate conditions and the variation of climate amongst different geographic location causes the formation of ecological islands that differ from their surroundings creating separate patches.
Figure 2.Climatic Isolation (http://www.ew.govt.nz/PageFiles/1910/report1.jpg)
3. Geological causes:
The geological modifications that have encountered the plant earth during its evolution have resulted in isolating certain areas causing fragmentation and this can be manifested by geographical islands.
Figure 3. Geographic Isolation (http://mm04.nasaimages.org/MediaManager/srvr?mediafile=/Size4/nasaNAS-10-NA/85430/sanmiguel_ast_2005149_lrg.jpg)
B. Human-Induced Casuses:
1. Urbanization:
Urbanization is one of the most important causes of forest fragmentation. As cities and villages develop, large-scale destruction of forests occurred to set ground for human colonization and city expansion. This resulted in destroying big areas of the forest while retaining small patches for decoration and entertainment; consequently, forest fragmentation occurs.
Figure 4. Urbanization and forest fragmentation (http://img3.photographersdirect.com/img/12941/wm/pd1890204.jpg)
Another effect of urbanization is the road networks where the development of roads to connect distant locations by passing through forests resulted in forming forest patches separated by these roads, and this kind of separation have strong negative effect on the ecology of the forest even if the separation is by an 8 meter road.
Figure 5. Forest roads (http://gearheads.in/images/imported/2011/02/82.jpg)
2. Agriculture:
Another critical cause of forest fragmentation is agriculture where large areas of forests are replaced worldwide by agricultural land and consequently few patches of trees remain between these lands. This is an important consequence of the worldwide food demand that requires massive agricultural land.
Figure 6. Agriculture in Forests (http://www.treehugger.com/20100225-amazon-industrial-farm.jpg)
3. Lumber:
Cutting trees for lumber that started early in history has played and is still playing an important role in decreasing forest areas and keeping only small patches that don’t have the ability to regenerate.
Figure 7. Fragmentation by Cutting trees (http://www.bigwideworld.org/wp-content/uploads/2009/11/habitat.jpg)
4. Pollution:
Even if minimal with respect to other human-induce causes, pollution still have part in the process of forest fragmentation by causing the destruction of habitats near urban places and keeping place for only very small niches that can provide good life conditions for forest maintenance.
