This section is from Grasses of New South Wales (Wheeler et al., 1982).
The grass family is undoubtedly the most important plant family to mankind, agriculturally, economically and ecologically. It provides the major cereal crops and most of the grazing for wild and domestic herbivores. Grasslands are estimated to comprise about 20% of the world's vegetation. Poaceae (Gramineae) is also one of the largest families of flowering plants with more than 650 genera and about 10,000 species. It is difficult to give an exact figure for the number of generally recognised genera or species at any one time because botanists are continually at work revising genera and describing new species. Since the time of Linnaeus the family name has been Gramineae but many botanists prefer the logically derived name, Poaceae.
Grasses occur in almost every habitat around the world from the equator to the polar regions, sea level to mountain heights and aquatic to desert environments. Open situations are preferred so grasses are not common in rainforest or dense thickets. Many species grow in brackish water, salt marshes, lakes and rivers. In Australia large areas of the arid zone are dominated by hummock-forming grasses and here, as in other countries, grasses frequently occur in the desert as ephemerals. Alpine grasslands are a prominent feature of many mountain areas such as the Kosciuszko region of south-eastern Australia.
A number of characteristics, some of which are outlined below, have enabled grasses to adapt to a wide range of habitats and to spread widely. Not only do grasses as a group exhibit a variety of breeding systems including cross-pollination, self-pollination, cloning and apomixis (formation of embryos without reduction division and fertilisation) but a number can reproduce by more than one of these mechanisms. For instance some weedy species are normally apomicts and, once a suitable genotype has become established, are able to rapidly colonise a favourable environment. However they retain the ability to out-cross, thus maintaining variability in the gene pool. New habitats may then be exploited when they become available. In addition hybridisation is common between species and this contributes to diversity. Extensive hybridisation in the field makes identification of some species very difficult, for example those of the genus Lolium.
Large quantities of seed are produced by most grasses and, even if conditions are adverse, some seed is set. The small, light 'seeds' (diaspores), often with hairs, hooks or awns attached, are effectively dispersed by wind, water, man or animals. Many grasses propagate vegetatively by the production of large numbers of shoots (tillers) from basal buds or creeping stems (stolons and rhizomes). This potential for reproduction and dispersal is reflected in the fact that 13% of cosmopolitan genera belong to Poaceae although grasses comprise only 4% of the total number of flowering plant genera.
Certain other structural and functional features developed by grasses have contributed to their ecological success. A system of branching (tillering) at or near ground level results in dense tufts, often large tussocks, and/or a network of shoots connected by stems that are just above or below the ground. Buds (apical meristems) are protected from fire and from the teeth and hooves of animals not only by their position, but also by the cylindrical leaf bases which enclose and protect meristematic tissue. Intercalary meristems occur at the base of each grass leaf and stem internode. These meristems are stimulated by removal or displacement of upper leaf or stem parts. Grass leaves elongate after cutting, and shoots flattened by wind, rain or animals, are able to grow upright again. In addition basal buds are stimulated to produce new tillers by moderate cutting, grazing or fire.
These adaptations to fire, grazing or weather damage enable grasses to thrive under conditions that effectively discourage most other plants. Though only about 20% of species in a grassland may belong to the Poaceae they may make up approximately 90% of the total biomass, thus dominating the community. Grasses provide forage for herbivores that have developed in conjunction with them. The grazing animals, in their turn, contribute nutrients in the form of dung and urine and increase the rate of nutrient turnover in the ecosystem.
Grasses dominate steppe, prairie and savanna plant formations. The characteristics of grasses, already mentioned, contribute to their ability to cope with the usually seasonal and often unpredictable rainfall of grassland regions. The steppes and prairies of the temperate regions, with a rainfall of approximately 250-750 mm, are usually treeless. However, the savannas of the tropics and subtropics are characterised by scattered trees and are in areas of higher rainfall (600-1 500mm).
Grasslands are also found in areas where the climate is suitable for forest but where factors such as periodic flooding or local frosts preclude tree growth, or where man has removed the trees. It is often impossible to distinguish between natural and semi-natural grasslands because of probable continuous occupation by man and domestic animals for hundreds or thousands of years. Thus man has facilitated the spread of grass species and grassland by felling trees, maintaining large herds of domestic herbivores, and by using fire and other means of controlling regrowth. In addition, there are the large areas of grasses deliberately planted by man to feed himself and his animals and to beautify parks and gardens.
Economic and agricultural importance
In the form of cereal grains, grasses directly supply about 60% of the world's food for human consumption including about 75% of the carbohydrate and 55% of the protein. Grasses and cereal grains, converted to animal products, supply about 20% of the world's dietary protein. The principal cereals are, in order of importance, Wheat, Rice, Maize, Barley, Oats, Sorghum, Rye and several grasses usually grouped together and termed 'Millets'. Rice, grown largely in the tropics and sub-tropics is the staple diet for half of the world's population while wheat is the preferred food in temperate regions.
Archaeological investigations have demonstrated the antiquity of man's wild grass-seed gathering activities, which continue today among hunter-gatherer peoples. About 10,000 years ago there is evidence from Mesopotamia, SE Asia and Central America that people began to select and domesticate certain wild grasses that became the progenitors of modern cereals. The great variety of species and types of cereals such as Wheat, Maize and Rice, suitable for the preparation of an infinite number of foods and adapted to other uses, has resulted from a long process of selection and breeding. Modern breeding programs have developed the dwarf Mexican Wheats and IRRI Rice varieties, on which the so called 'green revolution' has been based, and the high yielding hybrid Maize. Modern Oats and Rye developed in a similar way and are thought to have originated from weeds of wheat and barley crops in the ancient Middle East with possible inclusion of wild grass genes through out-crossing. Triticale is a recently developed cereal crop produced by crossing Wheat and Rye and doubling the chromosome number of the resulting sterile hybrid, thus enabling the new plant to set seed.
Most of the world's great civilisations have been based on the cultivation of cereal crops. Barley and Wheats (Emmer and Einkorn) sustained the Egyptian, Sumerian and other Middle East civilisations. Advantages of cereals as crops include high yields for a small amount of seed and work, non-shattering inflorescence, ease of threshing, tolerance to a wide range of soil and environmental conditions, and ease of handling and storage. An average moisture content for wheat in storage would be 12%. The grain contains about 65% carbohydrate, 10% or more of protein, and 5% fibre together with minerals and other substances. This nutritious food could be stored over winter, adverse seasons, periods of warfare, and, unlike most root crops, for more than one year.
Some cereals have spread from their place of domestication to many other parts of the world where they have become adapted to new environments. Maize, a warm season crop from Central America, is now grown from the temperate regions of North America, Europe and Australia (where it is a summer crop), to the tropics of other continents. Maize is the staple cereal for much of East Africa. Sorghum, indigenous to Africa, is now a major crop in the U.S.A. and Australia. Other crops are restricted to smaller areas, for instances Teff Millet, Eragrostis tef, is used only in Ethiopia and Finger Millet, Eleusine coracana, is grown only in its homeland, Africa, and several regions of Asia.
Any disturbance of natural ecosystems, such as that practised by agriculturalists, has encouraged the evolution and proliferation of weeds; opportunistic plants capable of taking advantage of the altered conditions. In many instances the weeds are similar to the crops they infest making their eradication very difficult. Examples are wild Red Rice, Oryza rufipogon, and Barnyard Grasses, Echinochloa spp., which are a serious problem in rice paddies. Other weeds, including Red Rice and Johnson Grass, Sorghum halepense, interact with their crop relatives by hybridisation, the outcome being more vigorous and better adapted weed types. Many of the world's most persistent and troublesome weeds are grasses that are enabled to survive and spread by the activities of man.
Livestock and grazing
Meat is largely a product of grass crops and grassland: 45% of world meat production comes from ruminant animals grazing grass crops, grassland or fed cereal grain. The remaining 55%, pork and poultry meat, is produced from animals eating rations based on cereal grains. Maize is the most important feed grain making up about 60% of the total trade in feed stuffs in the U.S.A. Apart from meat, milk and eggs are important foods produced indirectly from animals fed largely on grass or cereal grain.
Though natural grassland has been used for grazing since animals were domesticated, the spread of semi-natural and sown pastures has led to a decline in the importance of natural pasturage. Grass mixtures based on Ryegrasses, Lolium spp., were sown in the 12th century in northern Italy and in northern Europe in the 16th century. The practice of pasture improvement using grass/legume mixtures or grass fertilised with nitrogen has become widespread since it results in improved animal production (though input costs increase). Leys, short term sown pastures, benefit following crops by improving soil structure, adding organic matter and increasing soil nitrogen if a legume is included in the pasture mixture. Though nitrogen fixation by legumes undoubtedly improves the nitrogen status of temperate soils, tropical grasses may make a significant contribution to soil nitrogen in tropical areas. Nitrogen fixation is known to occur in the rhizosphere of certain tropical grasses including Maize.
About half the world's sugar is produced from Sugarcane, a tropical lowland grass. Important by-products of Sugarcane are molasses, rum and bagasse. The latter is used as fuel and in the manufacture of fibre-board and paper. In Brazil, alcohol produced from cane sugar is mixed with petrol as a fuel for motor vehicles. Power alcohol produced from grain or cane is a possible renewable energy source.
Alcoholic beverages such as beer are made from a fermented cereal grain such as barley. Whisky, gin and vodka are produced by distillation of fermented grain. Cereal grains and Sugarcane are important sources of industrial starch used in the paper and plastics industries. Fibre from grass leaves and stems is used to make paper, 'esparto' being a South American grass paper (from Stipa tenacissima). Oils, distilled from the leaves of Lemon Grass, Cymbopogon citrinus, and the roots of Chrysopogon zizanioides are used in perfumery, and the leaves of Lemon Grass are an important curry ingredient.
Bamboos, which are woody grasses, are put to innumerable uses in the tropics; the most important being in building construction. Large stems are used for house frames and scaffolding while smaller stems are split and interwoven for walls and floors etc. Containers, implements and baskets are among other articles made from bamboo and the shoots and grains of some bamboos are eaten. The dried leaves and stems of many grasses are used as thatch for house roofs.
Aesthetic and other uses
Grasses are used in soil conservation and engineering to stabilise bare soil surfaces and re-vegetate disturbed areas, sand dunes and water catchments. Grass swards form the playing surface of countless sporting complexes and are used in almost every park and garden. Many grasses such as pampas grass, Cortaderia selloana, are attractive ornamental plants. Minor uses include brush bristles from Sorghum inflorescences, clarinet reeds from Arundo donax stems and even necklace beads from Coix lachryma-jobi spikelets.