Conditions that promote karst development are well-jointed, dense limestone near the surface; a moderate to heavy rainfall; and good groundwater circulation. Limestone (calcium carbonate) dissolves relatively easily in slightly acidic water, which occurs widely in nature.
Crowther said first he had to figure out how many trees are on Earth and that number was far more than anyone expected: 3.04 trillion trees, according to a study published Wednesday in the journal Nature. 14 Photos Trees Around The World.
The number of trees per acre is called tree density and it has been increased from before. Though in many European orchards the number of trees per acre is set at 5,000 trees or more, in the US the apple tree density starts at 450-485 trees per acre with a maximum of 1,100 trees/acre.