Wind and water erosion of Sahel soils are examples of negative feedback processes. Climate is the cause of desertification. The atmosphere is the chief repository for nitrogen on the planet Earth. Denitrification occurs under aerobic conditions. Only eukaryotic bacteria carry out nitrate respiration.
Soils are alkaline in boreal regions and acidic in the tropics.
Tropical soils are highly anoxic, whereas soils from the boreal forest are aerobic. Tropical forest soils are younger than boreal forest soils. Soils from boreal forests are rich in organic matter compared to tropical forest soils. Tropical forest soils retain water, whereas water drains rapidly in soils of the boreal forest. The bird requires hardwood deciduous trees that have been cut down in order to nest.