Question

Even without human intervention of farming, trees always try to encroach on the prairies, yet they are never able to successfully, completely do so. this is why there are naturally occurring grasslands (meadows, pairies, savannas). what are two good ways the prairie's abiotic factors might prevent trees from taking over and two good biotic ways.


Since this is not my area of expertise, I searched Google under the key words "<I>grasslands forest biotic</I>" to get these possible sources:

http://www.ksr.ku.edu/libres/Mammals_of_Kansas/regions.html
http://www.fire.uni-freiburg.de/iffn/country/in/in_7.htm
(Broken Link Removed)
http://www.answers.com/topic/biome
http://sev.lternet.edu/index.php?module=ContentExpress&func=display&ceid=34

I hope this helps. Thanks for asking.