How does cutting down trees effect the earth and its enviroment ?

Answer 1

Trees convert carbon dioxide into oxygen, provide homes for numerous animal species, and fight soil erosion with their roots.

Answer 2

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RE:
How does cutting down trees effect the earth and its enviroment ?

Answer 3

This should give you a very rough point of comparison to the number of trees needed to supply oxygen for life support. It takes "17.5 trees per person" to produce oxygen to breathe but 20 trees per person to consume the CO2 exhaled according to NASA. This does not help offset other carbon emissions only what is needed to breathe.
If all we needed were trees to supply oxygen we would need 20 x 6.6 billion. or 20 x 6.6 x 10^9 = 1.3x10^11 tree just to breathe.

North American tree coverage in % forestation.

Canada has about 4,020,000 km2 of forest land.
~8 ha/inhabitant
US has 3,000,000 km2 (750x106 acres) of forest land much of it in 155 national forests containing almost 190 million acres (297,000 mi2 - 769 000 km2) of land.
http://www.unece.org/stats/trends2005/environment.htm
European countries average 44% tree coverage but this is not uniform.
Great Britian has nearly 11% forest for around 2.7 million hectares
England 7% forest cover
Scotland 15%
Wales 12%
Northern Ireland has only 6% tree coverage
http://www.chm.org.uk/library/ecosys/forest/for001.htm
Hungary 18.5%
Russia is nearly twice the combined forest coverage of Canada and US.
New Zealand 32% forest cover
http://www.cbd.int/countries/default.shtml?country=nz



http://www.nas.nasa.gov/About/Education/SpaceSettlement/Contest/Results/96/winner/seis.html
The worlds oxygen supply is primarily replaced by algae but trees do have an impact in sequestering carbon and amelioration Urban air quality.
http://www.americanforests.org/resources/urbanforests/treedeficit.php
http://www.treescleanair.org/
Tree shade even effects the urban environment by keeping the asphalt cooler so prolonging the periods between repaving.
http://findarticles.com/p/articles/mi_qa4107/is_200511/ai_n15744667/pg_6

Most importantly trees mediate our entire terrestrial climate and erosion. Deforestations impacts water runoff allowing flooding in wet seasons followed by droughts as water is no longer retained in uplands. There is a drop in humidity without leaf transpiration. This results in fewer rain bearing clouds. This will produce a feed back of decreasing rain producing greater drought. http://italy.usembassy.gov/viewer/article.asp?article=/file2002_10/alia/A2101114.htm

http://rainforests.mongabay.com/0902.htm

deforestation causes enormous disruption in habitat and mass extinction of wildlife.
http://rainforests.mongabay.com/0908.htm
http://www.springerlink.com/content/p872367kg2423832/
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VGS-47GHMW5-2&_user=10&_coverDate=12%2F31%2F2003&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=5aea9a58c199389cad60ee8f1e339205
http://www.aip.org/history/climate/Public.htm