<story><title>Why Leaves Really Fall Off Trees</title><url>http://www.npr.org/templates/story/story.php?storyId=114288700</url></story><parent_chain></parent_chain><comment><author>tokenadult</author><text>There is interesting science behind deciduous trees losing their leaves.&lt;p&gt;&lt;a href=&quot;http://treephys.oxfordjournals.org/content/18/8-9/537.full.pdf&quot; rel=&quot;nofollow&quot;&gt;http://treephys.oxfordjournals.org/content/18/8-9/537.full.p...&lt;/a&gt;&lt;p&gt;Deciduous trees have an important role in urban environments.&lt;p&gt;&lt;a href=&quot;http://www.sustland.umn.edu/maint/trees.html&quot; rel=&quot;nofollow&quot;&gt;http://www.sustland.umn.edu/maint/trees.html&lt;/a&gt;&lt;p&gt;&lt;a href=&quot;http://extension.usu.edu/forestry/HomeTown/Energy_TreesandEnergy.htm&quot; rel=&quot;nofollow&quot;&gt;http://extension.usu.edu/forestry/HomeTown/Energy_TreesandEn...&lt;/a&gt;&lt;p&gt;This link caught my eye because the source was National Public Radio in the United States, in the northern temperate zone (Northern Hemisphere). As I expected, the original date of the article was October (2009). At this time of year (April 2011), deciduous tree leaves are mostly falling only in the Southern Hemisphere.</text></comment>
<story><title>Why Leaves Really Fall Off Trees</title><url>http://www.npr.org/templates/story/story.php?storyId=114288700</url></story><parent_chain></parent_chain><comment><author>guygurari</author><text>&lt;i&gt;If trees kept their leaves permanently they wouldn&apos;t have to grow new ones&lt;/i&gt;&lt;p&gt;If leaves were kept indefinitely they&apos;d also have to deal with damage, wear and tear and so on. Biological systems often seem to prefer replacing over repairing damaged parts, which is perhaps another reason why leaves are replaced. For instance our skin is constantly being replaced, so injured pieces are discarded instead of repaired.</text></comment>