The world’s grasslands fall into one of two types, including savanna and temperate grasslands. Climate plays an important role in creating each type with the grassland’s various soil types determining what plants can grow and thrive in the region. Savanna grasslands cover much of Africa as well as large areas of Australia, South America and India. Temperate grasslands are found on the plains and prairies of central North America as well as South Africa, Hungary, Argentina, Uruguay and in the former Soviet Union.
The savanna’s climate consists of a dry and a rainy season with warm or hot regions. The annual rainfall ranges from 20 to 50 inches per year. What makes the savanna unique is that the rainfall falls in a six to eight-month period, followed by a long period of drought. If the rain fell over the entire year, the savanna would appear more like a tropical forest. In October, the savanna experiences violent thunderstorms followed by strong winds, signaling the start of the drought season. The drought season often brings fires that give the savanna biodiversity.
While some savannas exist as the result of climatic conditions, other savannas, called edaphic savannas, are caused by soil conditions. Edaphic savannas occur along ridges or on hills where shallow soil exists. The soil stays porous and rapidly drains when it rains. The soil consists of a thin layer of humus created from decomposition of plant or animal matter. The humus gives vegetation the nutrients it needs to survive. Some edaphic savannas occur in valleys where clay-like soil becomes waterlogged during wet weather. While fire plays a less important role in edaphic savannas, it does leave a layer of powdery black ash that helps provide nutrients to new growth.
Temperate grasslands experience large ranges of temperatures from winter to summer with hot summers up to 100 degrees Fahrenheit and cold winters as low as -40 degrees Fahrenheit. Moderate rainfall occurs in temperate grasslands, primarily in late spring and early summer with 20 to 35 inches falling annually. Seasonal drought and fires add to the temperate grassland’s biodiversity.
The soil of the temperate grassland is deep and dark. Fertile upper layers of the soil get their nutrients from the growth and breakdown of the deep, entwined grass roots that make up much of the temperate grasslands. The decaying roots help hold the soil together so new plants gain a valuable food source to help them grow and thrive. Unfortunately, the very characteristics that make the temperate grasslands’ soil so rich are also responsible for its demise. Few prairie regions remain untouched since the soil works so well for crops and stock grazing.