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 "grasslands forest biotic" 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.
In order to understand why trees are unable to successfully encroach on grasslands, we need to consider both abiotic (non-living) factors and biotic (living) factors.
Abiotic factors are environmental conditions that can affect the growth and survival of trees in grasslands. Two possible ways that abiotic factors prevent trees from taking over are:
1. Fire: Grasslands are prone to regular wildfires, which are usually started by lightning strikes or human activities. These fires clear out any tree saplings and promote the growth of grasses, which are better adapted to survive and recover from fire. The heat from the fire also helps to break down the woody material of trees, making it easier for grasses to dominate the landscape.
2. Soil Moisture: Grasslands often have well-drained soils with low moisture content, which can limit the growth of trees. Many tree species require higher moisture levels to establish and grow successfully. The drier soils of grasslands may not provide enough water for tree roots to access, limiting their ability to compete with grasses.
Biotic factors refer to the interactions between different organisms in an ecosystem. Two possible biotic ways that prevent trees from taking over are:
1. Grazing: Grasslands are often home to large herbivores such as bison, deer, and pronghorn. These animals feed on the grasses, keeping them short and preventing the growth of tree seedlings. Their constant grazing pressure creates a competitive advantage for grasses, as they are better adapted to withstand grazing and can quickly regrow from the base.
2. Competition for light: The dense, clumped growth form of grasses allows them to effectively compete with trees for sunlight. Grasses can efficiently capture and utilize the available light, leaving little to reach the ground and inhibit the germination and growth of tree seedlings. The dominance of grasses shades out potential tree saplings, preventing their establishment.
By considering these abiotic and biotic factors, we can understand why trees are unable to take over grasslands completely and why grasslands persist as natural ecosystems.