08-09-2003 - Biodiversity

sagar: Author=’David Clark’ program=’3869′ video=”San Andreas gif courtesy of http://pubs.usgs.go v/gip/earthq1/._DB:_ This is Earth and Sky with a question from a listener. “Why don’t tree branches grow perfectly straight toward the sun?”

_JB:_ It might seem as if, for tree branches, the higher and closer to the sun, the better. Branches support a tree’s network of leaves that catch sunlight. And trees in the wild need sunlight for photosynthesis – it’s how they generate their energy. A branch will grow to give the most leaves the most light – and that might mean that some branches will grow sideways – and away from the leaf “pack”.

_DB:_ There’re other factors that affect the way branches grow. Gravity constantly pulls them toward Earth. And branch growth is affected by wind. Part of the trade-off any tree has to make is between gathering light, staying stable in the wind, and succeeding against nearby competitors. So when branches grow crookedly, they are a living record of the tree’s overall survival strategy.

_JB:_ Trees have sensors that detect light and gravity. From the moment a tree begins its life, it knows which end is up. A tree will generally attempt to grow toward the light and away from the pull of gravity. But, as a tree gets older, its branches tend to grow more outward than upward – that’s so the tree can cast a wider net to catch the light of the sun.

_DB:_ Thanks today to the “U.S. Forest Service”:http://www.fs.fed.us/ and to the “National Fish and Wildlife Foundation”:http://www.nfwf.org/, supporting the conservation of native fish, wildlife, plants, and their habitats. We’re Block and Byrd for Earth and Sky.

Written by EarthSky