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.
1 According to the last forest inventory, there are almost 247 billion trees over 1 inch in diameter in the U.S. 2  The average tree in an urban/city area has a life expectancy of only 8 years. 3  The tallest tree in the country is a Coast Redwood growing in northern California's Redwood National Park.