How does deforestation affect biogeochemical cycles?
Deforestation affects biogeochemical cycling mainly by disrupting the water cycle, causing water to be lost more rapidly from the ecosystem and with it important elements and nutrients.
The biggest effect deforestation has on the biogeochemical cycles of a given area occurs via the disruption of the water cycle. Streams and rivers carry water away from the landscape and to the sea. Trees and other plants retain water by sucking it up from the ground and returning it to the atmosphere above through a process known as evapotranspiration.
Because water is an excellent solvent, elements like nitrogen and phosphorus and ions like calcium are all easily transported by water. When deforestation occurs water is no longer captured by the trees and all of the important ions and molecules are exported from the system by streams and rivers.
Some of the consequences include a loss of base cations from the soil, making them acidic - a harsh environment for biota. The loss of ammonium, nitrate and phosphate - important nutrients for growth - can lead to oligotrophic conditions. Increased water flow through the soil leads to erosion, which can remove organic materials that serve as food to soil organisms. Of course, without trees there is a loss of habitat and food resources needed by organisms that themselves influence biogeochemical cycling through their activities.
An excellent way to learn more about this particular topic is to review the research done at Hubbard Brook Experimental Forest in New Hampshire (http://www.hubbardbrook.org/). They were the first to quantify the changes due to deforestation.