Why are there virtually no large forested ecosystems in countries like Egypt, Qatar, Israel, Saudi Arabia, Yemen and Somalia like there are in most European countries and in certain parts of eastern and western United States. Certain parts of China, most of Japan, New Zealand and some parts of southern Argentina are also heavily forested.
Only because you cast the question this way. There is no other reason. National borders are arbitrated by human events, like migration and war. Borders between forests and deserts are arbitrated by natural events, like subsidence and climate change. The result is therefore arbitrary.
Too hot and dry, is the main reason. Not enough rainfall to support plant growth to any great extent, and that which does grow (in the Sahara, at least) is overgrazed by herds of animals (particularly goats). The land is marginal for any kind of plant-growth, infertile and way overstocked for its capacity to cope. During the Ice Age, the weather patterns that are now over Europe were pushed down over North Africa, which made the entire region a lot wetter. This allowed the human populations of that time to exploit the desert far more fully than is possible nowdays.
pluto2 Rainfall, as Xylene has mentioned. Ofcourse you have to consider that deforestation is a major historical factor in why there are no trees in some of the places you mentioned. There is actually alot of research in attempting to explain why trees and grass co-exist in savanaas (rather than one outcompeting one another) and it is these savannas which "act" as the transition from desert to forest in many places. Consider figure 1 in the below link http://researchspace.csir.co.za/dspace/bitstream/10204/2072/3/sankaran_2005.pdf They reported on 854 sites from across Africa and show a clear correlation between MAP (mean annual precipitation) and the % of wood cover in an area. As you can see, under 200mm MAP, woody cover (trees) is zero and it increases with increasing MAP.
There are many reasons, some climatic, some human. http://www.voanews.com/learningengl...-Trees-To-Help-Save-Their-Land-121510649.html
because Chinese Government is not stopping,Chinese government only care about economy but they have no issues with the destroyed Nature.
Can be historical too, for example in north Africa, like Tunisia, it used to have alot of forests, almost all covered in forests, but threw histroy, all that changed for economic reasons (agricultural and industrual reasons). Like in the Roman era in north africa, when north Africa became "the feeder" of Rome, it produces alot of food needs of the Roman empire, the forests were butched, also for wood.
