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| Various species of grass growing together in a grassland area. |
Grass has been around for 30 million years. There are 9 700
species of grass of which 967 occur in Southern Africa with 329 endemic
species. [1]
This makes grass the fourth largest plant family on earth. From a day-to-day
perspective the importance of grass to humans is often underestimated. One
needs only to think what they ate for breakfast this morning or dinner last night and you
will realise that grass is an important part of every meal. Rice, oats, maize,
wheat, barley, rye, sugar and more are all grasses and are an important
cornerstone of daily diets. Even the
animals that we eat are dependent on grass, therefore we are indirectly getting
the energy they have converted from the grass. The role of grass in the energy
cycle and nutrient cycle is extremely important.
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| Due to the low growth parts of the plant, grass is able to withstand fire, drought and grazing. Using these destructive forces to gain advantage over other plants growing around it. |
Of the grasses the most important in terms of contemporary
human culture is the grass we know as wheat. Wheat, a prime agitator of the
Neolithic revolution, was first cultivated in the Fertile Crescent at least 10
500 years ago. This ultimately resulted in the success of humans over other
species. Wheat enabled humans to spread out and sustainably increase their
population densities into Europe and Asia and eventually the entire world. The
domestication of grass also led to the domestication of livestock and this
further contributed to the success of humans. [2]
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| Grassland scene consisting of a few types of grass. There are grasses filling all the niches in the grassland ecosystem. Some are bushy, some grow low to the ground, while some form dense stands. |
Today grass is widely cultivated due to human activity.
Sugar, maize, rice and wheat are the most commonly cultivated grasses globally.
The amount of land that is under the cultivation of these grasses is enormous.
The environmental impact and socioeconomic implications of the widespread
cultivation of grasses is significant and very interesting to think about. From
an ecological perspective it is clear that globally biodiversity is
negatively affected because of these crops.
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| These burnt out trees are testament to a past fire. These trees were over five years old. No longer saplings, yet they succumbed to the flames. |
From the perspective of the grasses however, their success
is really astounding. They have, in a sense, managed to use humans to spread
globally and colonize land that they would never naturally be able spread to.
They managed this trick by offering a high-energy sugar in exchange for
worldwide cultivation. The relationships of these grasses to humans can be seen
as one of obligate mutualism. Humans would not be able to continue the way they
currently live without these grasses and the grasses, such as wheat, rice, maize etc., as they currently exist
would not be able to survive without people.
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| This Aloe will survive the fire damage, its point of growth is well protected by its fleshy leaves and compressed growth form. The Acacia saplings that grow around this aloe have burnt and most will not survive. |
Despite getting some help from people, grasses have done
very well for themselves. They have been around for about 30 million years. The
origin of grass must have been humble: a small plant adapted for dry conditions
competing with other desert scrub plants. Over time more species appeared and
began to compete with and replace dry woodland areas. About four million years
ago grass had begun to produce savanna. [3] Today
approximately 40 percent of the earth’s terrestrial surface is covered by
grass. The success of grass has to do with the co-evolution of grazing animals,
the resistance to frost and the ability of grass to use fire to its advantage
as well as the ability of grass to be drought resistant.
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| Even on rocky hills like this, over time grass will replace the woody plants. |
The growing points of grass are low on the plant and these
are often below the ground. With other plants, the growth points are above
ground and susceptible to fire damage as well as frost damage. Over time fires
and frost will eliminate the small trees and shrubs and favour the grasses as
dominant on the landscape. Within any grassland system there will be many other
plants that are not grasses that are adapted for the hostile conditions of
growth created by the grassy cover.
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| Euphorbia clavarioides is a herbaceous plant adapted to grassland areas. |
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| Xerophyta retinervis, this is another plant adapted to grassy areas. The stem is fire resistant and can survive sustained drought and spells of frost. |
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| Some trees are specifically adapted to grassland areas. This Cussonia paniculata has deeply fissured and corky bark. This offers it some resistance to fires and cold. The other trees in the photograph may have survived the fire, but they too will eventually be replaced by grass. |
Africa, because of the large areas of grassland and associated
savanna is home to 75 different bovids and of these 72 are antelope. This is an
incredible diversity. These animals came into existence about 25 million years
ago which is well within the era of grass. Even though not all antelope are
grazers, they are just an example of the kind of diversity that a rich food
source can sustain.
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| The Blue Duiker, Cephalophus monticola, one of the smallest antelope. This is a forest species which browses on fallen fruit and leaves. Even though it is not a grazer this species indicates the diversity which has been enhanced by grass. |
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| The Eland, Tragelaphus oryx, is the largest antelope. This animal which can way up to 940kg is a major consumer of grass. Even though they do browse, grass makes up a substantial portion of their diet. |
Grasslands
store far less carbon than forests in actual plant material, but grassland
soils are usually far richer in carbon than forest soils, so grasses
effectively remove carbon from the atmosphere and store it in soils. This may
in part be due to frequent fires, which produce copious charcoal that is not
easily decomposed by bacteria and becomes incorporated into the soil. […]
Grasslands are much lighter in colour than woodland and they reflect a greater
proportion of solar radiation into space, contributing to cooling. The air over
grasslands is generally much drier than over woodland because trees tap
deep-water sources and pump the water into the atmosphere by transpiration.
Water vapour is a powerful greenhouse gas, so more grassland means drier, and
thus cooler air. (The Story of Earth and
Life. Struik: Cape Town. Page 261.)
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| This grassland scene captured in the Suikerbosrand Nature Reserve clearly shows how much lighter grassland is compared to woodland. Note how shrubs and trees are limited to protected areas. |
The rise of grasslands led to a decline in forests and many
animals had to adapt to this change. Grazers emerged and colonized the
grasslands and carnivores followed. Human evolution was also significantly
affected by the domination of grass plants. Paleoanthropology generally accepts
that the ancestors of modern humans left the forests to become savanna
creatures, and that this move from forests to the grassy plains was what
resulted in bipedalism. [4]
Grass has been an important factor for
the emergence of the human being. It played a role in the primordial past when
hominids were still finding their legs and it played a major role in the
development of modern culture through the early beginnings in the Neolithic
period. It has also produced partner animals on which we are reliant and which
have also helped humans rise to the point where we now find ourselves. On a
global scale, grass may be responsible for cooling our planet and keeping the
temperatures at an optimal level. Without grass, humans would not have
developed, as the forests would not have receded forcing our distant ancestors
to colonize the open areas.
Our culture and biology is so closely
tied to grass that the global colonization of the human animal would not have
been possible without the domestication of specific species of grass. One thing
however is for certain, when humans are long gone, grass will continue to
quietly grow and be a powerful source of energy driving biological diversity
and sustaining a multitude of organisms.
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| This harvester termite, Hodotermes, is a major grazer of grassland. Insect consumption of grass is greater than that of mammalian consumption in natural areas. These termites diets consist of 94% of grass and they can consume 1-3 metric tons of forage per hectare per year. |
[1]
van Oudtshoorn, F. 2012. Guide to
Grasses of southern Africa. Briza: Pretoria. Page 10.
[2]
For a more detailed and very stimulating discussion of the role of wheat in
human culture see Jared Diamond’s book Guns,
Germs and Steel.
[3]
McCarthy, T and Rubidge, B. 2005. The Story of Earth and Life. Struik: Cape
Town. Page 261.
[4]
Anyone can try a simple experiment to see that advantages of bipedalism first
hand. Next time you are in a grassland environment, when surrounded by long
grass, go down on your hands and feet and see how different the environment is
from down there. The adaption of standing on ones rear feet provides security
as well as a vantage point from which one can see the surrounding environment,
thus contributing to the success of the species.
