Dave Taylor's African Safari: Abiotic Factors of the Serengeti-Mara Ecosystem - Volcanoes

Abiotic Factors of the Serengeti-Mara Ecosystem
Volcanoes
Page 8

Is the Great Rift Valley really an abiotic factor? Yes. In places, the cliffs of the rift valley have isolated animal populations so that they developed new species. This is especially true in the case of Madagascar Island where a family of primitive primates were isolated from the competition of more highly developed monkeys and apes. Without this separation we would not have lemurs to study and enjoy today.

More important to the Serengeti-Mara ecosystem are the numbers of volcanoes that line the rift valley on both sides. Without the presence of these towering giants spewing forth lava and ash, this ecosystem would not have existed or endured.

Three Types of Volcanoes

Volcanoes may be active, dormant or extinct. The last volcanic eruption in this area was in 1983 when Ol Doinyo Lengai erupted spewing ash once again on the plains. This was its fifteenth eruption since geologists began recording such things in this region in 1880. Ol Doinyo Lengai lies at the northeastern limit of the Serengeti Plains in Tanzania. It is the only active volcano in the ecosystem. It is 2740 meters (8990 feet) above sea level.

Some, like Kenya’s Mount Longonot (altitude 2 775 meters / 9,104 feet) and Tanzania’s Mount Kilimanjaro (altitude 5 896 meters / 19,343 feet) are considered dormant and may yet come back to life.

A third category is those that are extinct. Ngorongoro (2 200 meters / 7,218 feet) and Mount Kenya (5 200 meters / 17,060 feet) are examples of these.

Equally important to the formation of this ecosystem are volcanoes that lie to the west of the Serengeti-Mara. These volcanoes did not lay down much lava or ash within the region but, nonetheless, helped create the conditions that allow for great herds of animals to exist here.

The Virungas of Eastern Zaire consist of several active and extinct volcanoes. The resulting towering mountain range is high enough that it forces moisture-laden winds blowing inland from the Atlantic to drop their water on the western slopes. Had these mountains not existed, it is likely that the Serengeti-Mara ecosystem would be much wetter than it is today and that a forest would have covered the land.

How the Ngorongoro Area Was Formed

Lava and Ash

The lava that poured forth from the many volcanoes surrounding the Serengeti-Mara region built up the land. In places, the lava floes are two or three thousand meters thick (1.2 to 1.9 miles). These floes raised the surface of the land, covering the original granite rock, that was itself created from cooling magma.

By raising the elevation of the land, the lava formations caused a cooler climate than one would normally expect to find so close to the Equator. Lava also contains nutrients that, as the lava erodes, enrich the soil.

Equally important to the ecology here is another product of volcanic activity. In some regions, the volcanoes threw out cubic tons of ash.

The crocodile in the photograph (at right) is lying on a bed of ancient lava. The bank behind the reptile is made up of volcanic ash. The Mara River has eroded through the ash until it reached the lava flow.

Concrete Ash and Animal Hooves

In places, this ash was so fine that when it dried after a rainstorm it became as hard as concrete. Tree roots were unable to penetrate it and could not grow there. Grasses, however, with their shallow root systems, could survive here and even prosper. The herds of migrating wildebeest and zebra, as well as other plains game, actually help the grass too. Their droppings enrich the soil and their hooves break up the concrete-ash into a thin layer of soil. The short grass plains of the Serengeti are a good example of this interaction between ash, hoof and dropping.

As in any area this large, there are great differences in soils.

Soils on the eastern plains are shallow, highly saline and alkaline due to the recent falls of volcanic ash. They become deeper and less alkaline to the north. Some of these chemicals are important to health of the grazing animals and they will move from one location to another to seek out the chemicals they need.

In other places, a slight increase in altitude increases the amount of rainfall and taller grasses may be found. The pounding of rain breaks up soils and the greater volume of dead grass creates a soil mix that favors scrub brush or even trees. As a result, the plains are a mixture of scrub forest, acacia dominated savanna, forests and grasslands. Each area houses its own wildlife community.

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