Importance of the Grass Family - Poaceae
The grass family is the most important plant family agrictulrally, 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 (gramieae) is also one of the largest families of flowering plants with more than 650 genera and 10000 species. In Australia there are approximately 234 genera and 1320 grass pecies.
In Australia, large areas of the arid zone are dominated by hummock-forming grasses and here, grasses frequently occur in the desert as ephemerals. Alpin grasslands are a prominent feature of many mountain areas such as the kosciuszko region of south-eastern Australia.
- grasses exhibit a variety of breeding systems including cross-pollination, self-pollination, and cloning, this maintaining variability in the gene pool so that new abitats may be exploited when they become available.
-hybridsation is common between specie and this contributes to diversity. Large quantites of seed are produced by most grasses and even in adverse conditions some are set. The small, 'light' seeds (diaspores) often with hairs, hooks or awns can be dispersed by wind, water, man or animals.
-Many grasses also propagate vegetatively by the production of shoots (tillers) from basal buds or creeping stems (stolons and rhizomes, tiller can result in dense tufts, large tussocks and/or a network of shoots connected by stems just above or below ground.
- grass buds (apical meristems) are protected from fire, grazing and hooves y their low position and the cylindrical leaf bases which enclose and protect the merstematic tissue. Meristems occur at the base of each grass lea and stem internode.
Economic and Agricultural Importnce of Cereals (grass grain crops)
in the form of grains, grasses directly supply about 60% of the world's fod for human consumption including about 75% for 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 and sorghym. Rice is grown largely in the tropics and sub-tropics and is the staple diet for half of the world's population while wheat is the rpeferred food in temperate regions.
Modern breeding programs have developed the dwarf wehats and rice varieties on which the 'green revolution' has been based. Triticale (often used as a feed to livestock in temperate areas) is a recently developed 'man made' cereal crop produced by crossing wehat and rye. Cereal grain contains about 65% carbohydrate, 10% protein, 12% moisture and 5% fibre together with minerals and other substances.
Livestock and grazing
Meat is largely a product of grass crops and grasslands: 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 grass grains. Maize is one of the most important feed grains eg 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 while natural grassland has been used for grazing since animals were domesticated. Grass (eg Rye grasses Lolium spp.) were sown in the 12th century in northern Italy. The practice of pasture improvement using grass/legume mixtures or grass fertilised with nitrogen has become widespread in modern times since it results in improved animal production.
Other Grass products
About half the world's sugar is produced from Sugarcane, important byproducts of sugarcane are molasses (important dry season energy supplement for livestock) , rum and bagasse. Cane tops (leaves) are also fed to livestock. Alcoholic beverages such as beer, whisky, gin and vodka are made from a fermented cereal grain such as barley and sorghum. Fibre from grass leaves and stems is used to make paper. The dried leaves and stems of many grasses are used as thatch for house roofs (eg. thatch grass – eg. Grader grass)
Pasture Grasses & Environment
The great diversity of climate, rainfall, soil type, topography and pastoral regimes in Australia is reflected in the diversity of grass species utilised as stock fodder. Consequently, the geographic regions, which can be broadly classified into:
• monsoonal tropics,
• arid and
• temperate,
are characterised by different and usually unrelated groups of native and introduced pasture grass species.
In the monsoonal tropics with its short wet season and long rainless hot dry season, the predominant native grasses are long-lived tussockforming perennials. These grow vigorously in the wet season and provide palatable nutritious fodder. In the dry season, they become dormant and rank, and are unpalatable or only moderately palatable and low in nutritive value. The most important of the native open-range pasture grasses are species of Astrebla (Mitchell Grass), Bothriochloa and Dichanthium (Bluegrasses). These occur in extensive areas on the less infertile heavy-textured soils and cracking clay plains of northern Australia.
The wet season also produces a variety of annual and short-lived perennial grasses such as species of Iseilema (Flinders Grass), Enneapogon (Nineawn), Tragus (Small Burrgrass) and Sporobolus (Dropseed), which can be nutritious for short periods to fatten stock.
In the open rangelands of the arid and semi-arid regions, species of Triodia (Spinifex) predominate over extensive areas of infertile sandy and skeletal soils. These are tough xerophytic (drought tolerant) grasses grazed when green and in association with better-quality herbage/forbs and browse plants, but are chiefly important as drought reserves and subsistence fodder.
Burning is a regular practise in the management of rangelands in order to promote new growth and the regeneration of softer grasses, such as species of Eragrostis, and Eriachne (Wanderrie). In general, these are droughtresistant plants responding to winter and summer rainfall, and are highly suited to the arid region with its long dry periods and irregular rainfall in any season.
few species have been introduced in specific habitats of the tropical and arid regions for pasture improvement and rehabilitation purposes. Buffel Grass, is now widely naturalised as a pasture & rehabilitation plant as a result of deliberate introductions and the breeding of cultivars. Guinea grass is another valuable pasture grass. Chloris gayana (Rhodes Grass) is widely sown for fodder (& hay) due to its drought and salt tolerance, and also its stoloniferous soil-binding habit.
Some of the most important grasses of temperate and semi-arid areas in southern inland Australia include the Wallaby Grasses (Austrodanthnia), Austrostipa (southern Speargrass) and Poa (winter grass). In moist temperate regions, Lolium perenne (Perennial Ryegrass) have been naturalised or introduced are important fodder grasses. Rye grass is used too for winter feed in the subtropics eg dairy industry on Atherton Tablelands.
Avena (oats) are useful winter pasture and hay as well as a valuable cereal, Zea mays (maize) is used green or as silage for stock fodder. Similarly, Sorghum can be sown for grain, pasture, forage crop and silage.
Other important fodder grasses of temperate regions include Microlaena stipoides (Weeping Grass), Dactylis glomerata (Cocksfoot), Phalaris aquatica (Phalaris), Festuca arundinacea (Tall Fescue) and Themeda triandra (Kangaroo Grass – temperate and tropical types).
Tropical and temperate grasses: Why are they different
In general, the pasture grasses of the temperate regions are more palatable and nutritious than those of the arid and tropical areas; • this is due in part to the prevalence of better-quality soils and less severe climate. However it is also due to different biochemical pathways in the plants: The 2 types of photosynthesis that occur in plants use different enzymes, resulting in carbohydrates with either 3 or 4 carbon atoms. These plants are referred to as C3 and C4 plants. Temperate grasses and all legumes and most shrubs and broad-leafed plants (forbs) are C3 species. Generally there are more C3 grass species in southern Australia and more C4 grasses in northern tropical Australia. C4 plants are mostly tropical grasses, succulents or saltbushes of tropical or arid environments.
Rangeland plant types and their survival strategies
In Australia, our vast rangelands are characterised by low or irregular rainfall, a seasonally arid climate, infertile (sometimes saline) soils and a lack of permanent surface water. Stocking rates are low, and are determined by the availability of basic fodder and water. All rangeland plants are adapted to withstand long dry periods, and on the basis of their means of survival, they can be classified as follows:
Other grasses; Cover Grasses
This group of grasses is among the most valuable, as it fulfils the important function of preventing or reducing the loss of soil by wind and water erosion as well as providing fodder in some situations. Cover plants conserve moisture by shading soil and water surfaces, thus reducing loss to the atmosphere from evaporation. Perennials are more effective than annuals as soil binders and cover plants, due to the development of fibrous roots (as well as rhizomes) and/or their spreading mat-forming habit. Golden beard and buffel are good examples of perennial cover grasses.
Heavy-seeding annuals grasses (eg Flinders grass) also serve a useful purpose by providing a dense protective plant cover for limited periods. Brachyachne spp. (Native Couch) are pioneer species on gravelly and eroded areas.
Sandy coastal habitats are among the areas that are most susceptible to wind erosion, grazing and disturbance Hardy salt-tolerant species such as Sporobolus virginicus (Marine Couch), are successful soil stabilizers on beaches, foreshores, dunes and salt flats.
Grass Weeds
In Australian approx 374 species grasses are designated as weeds. The chief criteria applied in determining their weedy status include the plant's detrimental impact on crops, pastures and the native environment, its toxic and physically harmful effects on domestic stock, and the extent of its naturalisation. Most Australian grass weeds are accidental introductions which have become naturalised. Most of the winter and spring-growing species of southern Australia originated in temperate Europe and the Mediterranean region, while those summer-growing species which are a problem in northern Australia came mainly from Africa and tropical America.
Poisonous Grasses
The Poaceae family contains many toxic or potentially toxic species, some of which are also valuable forage crops and pasture plants. Many species have given positive tests for Cyanide/prussic acid (HCN), nitrates and some can accumulate oxalates in potentially toxic amounts.
The Importance of the Legume Family
Legumes have been gathered, cultivated, eaten and used in a multitude of ways by humans for millennia and are arguably as important as grasses in global terms. The range of uses of legumes is possibly broader than grasses. Legume products contribute enormously to the worlds economy through food (for animals and humans), pharmaceuticals, medicine, biofuels etc.
Legumes are in the Leguminosae plant family (some say the Fabaceae family) The legume family is split up into three subfamilies : 1. Fabaceae (pea type flowers) Eg. Centro, butterfly pea 2. Mimosaceae (rounded inflorescence type of flowers) Eg. Mimosa, Leucaena 3. Caesalpiniaceae (yellow open showy type of flowers) Eg. Cassia, Senna sp
Ancient cultures were aware of the ability of many legumes to improve soil, even if they did not then appreciate that this results from symbiotic nitrogen fixation. Some 40 to 60 million metric tons of nitrogen are fixed annually by agriculturally important legumes.
The natural accumulation of nitrogen in legumes has resulted in predation of legumes by a wide range of animals and insects To combat this the legume family has evolved a repertoire of chemical defences based on secondary compounds, especially alkaloids resulting in many legumes being toxic.
Grain and forage legumes are grown on approximately 180 million ha (12 – 15%) of the Earth’s arable surface and account for 27% of the world’s primary crop production Grain legumes contribute 33% of the dietary protein nitrogen needs of humans. Legumes (mainly soybeans) also contribute more than 35% of the world’s processed vegetable oil. Forage legumes provide protein, fibre and energy that have underpinned dairy and meat production for centuries. In temperate regions Lucerne/Alfalfa (Medicago sativia) is an important and highly valued forage for cattle. Other temperate pastures include eg. clovers (Trifolium spp) and vetches (Vicia spp). In the tropics; Arachis (forage peanut), Centrosema, Desmodium, Macroptilium and Stylosanthes spp are being used to improve tropical pasture systems.
The importance of legumes is based on:
• their ability to fix N in symbiosis with Rhizobium bacteria, • they are rich in protein & minerals, • they increase forage value & animal production • they enrich soil & improve other plants, • they increase the bulk & quality of pastures, • their rate of decline in quality over the season is less than grass, • mature legumes have higher digestibility & intake than grasses (legumes often have digestibilities of 70% & a crude protein (CP) of 21%, fertilized, wet season grasses may have similar digestibility but CP of about 12%), • legumes have a higher water use efficiency than grasses.
Palatability, Increaser/decreaser species and State & Transition models
Palatability varies among pasture species due to: maturity, species type, associated species, region, time of day grazed. • Palatable species are desirable species but with continuous grazing they become “decreaser” species, ie. decrease in abundance e.g. Kangaroo grass (Themeda sp)
Unpalatable/semi palatable species are undesirable and become “increaser” species ie. they increase in abundance in a grazed environment, e.g. Wire grasses (Aristida sp) and Indian couch (Bothriochloa pertusa)
Pastures in good condition contain over 50% decreaser species, Pastures in fair condition 30-50%, and Pastures in poor condition 5-30%. Very poor condition is indicated by less than 5% decreasers and over 65% increasers and unpalatable weedy invaders. Not all plants have indicator value, and some species can be decreasers in one rangeland type, but increasers in another.
State and Transition models
A tool for detecting and modelling vegetation change • Vegetation is said to be inherently unstable especially in the Australian rangelands or savannas. Changes in species composition occur over time even without grazing due to drought, flood, fire, and other natural phenomena. • A State is defined in terms of a dominant species of ground cover, vegetation structure, % ground cover, or basal area of the plants; it may also take into account the condition of the soil surface. • A Transition (or change) may be triggered by natural events (e.g. fire, drought) or by management actions (stocking rate, burning, spelling), or by a combination of these. State and transition mod
The grass family is the most important plant family agrictulrally, 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 (gramieae) is also one of the largest families of flowering plants with more than 650 genera and 10000 species. In Australia there are approximately 234 genera and 1320 grass pecies.
- Ecological importance: 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 ense 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, grasses frequently occur in the desert as ephemerals. Alpin grasslands are a prominent feature of many mountain areas such as the kosciuszko region of south-eastern Australia.
- adaptations:
- grasses exhibit a variety of breeding systems including cross-pollination, self-pollination, and cloning, this maintaining variability in the gene pool so that new abitats may be exploited when they become available.
-hybridsation is common between specie and this contributes to diversity. Large quantites of seed are produced by most grasses and even in adverse conditions some are set. The small, 'light' seeds (diaspores) often with hairs, hooks or awns can be dispersed by wind, water, man or animals.
-Many grasses also propagate vegetatively by the production of shoots (tillers) from basal buds or creeping stems (stolons and rhizomes, tiller can result in dense tufts, large tussocks and/or a network of shoots connected by stems just above or below ground.
- grass buds (apical meristems) are protected from fire, grazing and hooves y their low position and the cylindrical leaf bases which enclose and protect the merstematic tissue. Meristems occur at the base of each grass lea and stem internode.
Economic and Agricultural Importnce of Cereals (grass grain crops)
in the form of grains, grasses directly supply about 60% of the world's fod for human consumption including about 75% for 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 and sorghym. Rice is grown largely in the tropics and sub-tropics and is the staple diet for half of the world's population while wheat is the rpeferred food in temperate regions.
Modern breeding programs have developed the dwarf wehats and rice varieties on which the 'green revolution' has been based. Triticale (often used as a feed to livestock in temperate areas) is a recently developed 'man made' cereal crop produced by crossing wehat and rye. Cereal grain contains about 65% carbohydrate, 10% protein, 12% moisture and 5% fibre together with minerals and other substances.
Livestock and grazing
Meat is largely a product of grass crops and grasslands: 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 grass grains. Maize is one of the most important feed grains eg 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 while natural grassland has been used for grazing since animals were domesticated. Grass (eg Rye grasses Lolium spp.) were sown in the 12th century in northern Italy. The practice of pasture improvement using grass/legume mixtures or grass fertilised with nitrogen has become widespread in modern times since it results in improved animal production.
Other Grass products
About half the world's sugar is produced from Sugarcane, important byproducts of sugarcane are molasses (important dry season energy supplement for livestock) , rum and bagasse. Cane tops (leaves) are also fed to livestock. Alcoholic beverages such as beer, whisky, gin and vodka are made from a fermented cereal grain such as barley and sorghum. Fibre from grass leaves and stems is used to make paper. The dried leaves and stems of many grasses are used as thatch for house roofs (eg. thatch grass – eg. Grader grass)
Pasture Grasses & Environment
The great diversity of climate, rainfall, soil type, topography and pastoral regimes in Australia is reflected in the diversity of grass species utilised as stock fodder. Consequently, the geographic regions, which can be broadly classified into:
• monsoonal tropics,
• arid and
• temperate,
are characterised by different and usually unrelated groups of native and introduced pasture grass species.
In the monsoonal tropics with its short wet season and long rainless hot dry season, the predominant native grasses are long-lived tussockforming perennials. These grow vigorously in the wet season and provide palatable nutritious fodder. In the dry season, they become dormant and rank, and are unpalatable or only moderately palatable and low in nutritive value. The most important of the native open-range pasture grasses are species of Astrebla (Mitchell Grass), Bothriochloa and Dichanthium (Bluegrasses). These occur in extensive areas on the less infertile heavy-textured soils and cracking clay plains of northern Australia.
The wet season also produces a variety of annual and short-lived perennial grasses such as species of Iseilema (Flinders Grass), Enneapogon (Nineawn), Tragus (Small Burrgrass) and Sporobolus (Dropseed), which can be nutritious for short periods to fatten stock.
In the open rangelands of the arid and semi-arid regions, species of Triodia (Spinifex) predominate over extensive areas of infertile sandy and skeletal soils. These are tough xerophytic (drought tolerant) grasses grazed when green and in association with better-quality herbage/forbs and browse plants, but are chiefly important as drought reserves and subsistence fodder.
Burning is a regular practise in the management of rangelands in order to promote new growth and the regeneration of softer grasses, such as species of Eragrostis, and Eriachne (Wanderrie). In general, these are droughtresistant plants responding to winter and summer rainfall, and are highly suited to the arid region with its long dry periods and irregular rainfall in any season.
few species have been introduced in specific habitats of the tropical and arid regions for pasture improvement and rehabilitation purposes. Buffel Grass, is now widely naturalised as a pasture & rehabilitation plant as a result of deliberate introductions and the breeding of cultivars. Guinea grass is another valuable pasture grass. Chloris gayana (Rhodes Grass) is widely sown for fodder (& hay) due to its drought and salt tolerance, and also its stoloniferous soil-binding habit.
Some of the most important grasses of temperate and semi-arid areas in southern inland Australia include the Wallaby Grasses (Austrodanthnia), Austrostipa (southern Speargrass) and Poa (winter grass). In moist temperate regions, Lolium perenne (Perennial Ryegrass) have been naturalised or introduced are important fodder grasses. Rye grass is used too for winter feed in the subtropics eg dairy industry on Atherton Tablelands.
Avena (oats) are useful winter pasture and hay as well as a valuable cereal, Zea mays (maize) is used green or as silage for stock fodder. Similarly, Sorghum can be sown for grain, pasture, forage crop and silage.
Other important fodder grasses of temperate regions include Microlaena stipoides (Weeping Grass), Dactylis glomerata (Cocksfoot), Phalaris aquatica (Phalaris), Festuca arundinacea (Tall Fescue) and Themeda triandra (Kangaroo Grass – temperate and tropical types).
Tropical and temperate grasses: Why are they different
In general, the pasture grasses of the temperate regions are more palatable and nutritious than those of the arid and tropical areas; • this is due in part to the prevalence of better-quality soils and less severe climate. However it is also due to different biochemical pathways in the plants: The 2 types of photosynthesis that occur in plants use different enzymes, resulting in carbohydrates with either 3 or 4 carbon atoms. These plants are referred to as C3 and C4 plants. Temperate grasses and all legumes and most shrubs and broad-leafed plants (forbs) are C3 species. Generally there are more C3 grass species in southern Australia and more C4 grasses in northern tropical Australia. C4 plants are mostly tropical grasses, succulents or saltbushes of tropical or arid environments.
Rangeland plant types and their survival strategies
In Australia, our vast rangelands are characterised by low or irregular rainfall, a seasonally arid climate, infertile (sometimes saline) soils and a lack of permanent surface water. Stocking rates are low, and are determined by the availability of basic fodder and water. All rangeland plants are adapted to withstand long dry periods, and on the basis of their means of survival, they can be classified as follows:
- Perennial drought-resistant plants These plants usually remain in a dormant state during drought, and resume growth with the onset of favourable conditions. They are dominated by woody species (trees and shrubs), but include sclerophyllous evergreen hummock grasses, especially Triodia spp., which are shrub-like in their adaptation to drought
- Perennial drought-evading plants: Some or all of the aerial parts of the plant die when available moisture is exhausted. However, after rain, new growth (leaves or inflorescences) develops from basal and axillary buds on rhizomes and old tillers. Woody plants in this group are deciduous trees and shrubs, but the most significant component are long-lived perennial and mostly medium-sized tussock grasses such as species of Astrebla, Bothriochloa, Chloris, Chrysopogon, Dichanthium, Panicum and Sorghum.
- Short-lived drought-evading plants These plants survive long dry periods as seeds, and only grow after rain. The group comprises a large number of short grasses and forbs eg. ephemerals, annuals or short-lived perennials (biannuals). The ephemerals and annuals include numerous species in many genera such as Iseilema (Flinders grass), Tragus and Perotis (Comet Grass), which complete their life cycle in one season.
Other grasses; Cover Grasses
This group of grasses is among the most valuable, as it fulfils the important function of preventing or reducing the loss of soil by wind and water erosion as well as providing fodder in some situations. Cover plants conserve moisture by shading soil and water surfaces, thus reducing loss to the atmosphere from evaporation. Perennials are more effective than annuals as soil binders and cover plants, due to the development of fibrous roots (as well as rhizomes) and/or their spreading mat-forming habit. Golden beard and buffel are good examples of perennial cover grasses.
Heavy-seeding annuals grasses (eg Flinders grass) also serve a useful purpose by providing a dense protective plant cover for limited periods. Brachyachne spp. (Native Couch) are pioneer species on gravelly and eroded areas.
Sandy coastal habitats are among the areas that are most susceptible to wind erosion, grazing and disturbance Hardy salt-tolerant species such as Sporobolus virginicus (Marine Couch), are successful soil stabilizers on beaches, foreshores, dunes and salt flats.
Grass Weeds
In Australian approx 374 species grasses are designated as weeds. The chief criteria applied in determining their weedy status include the plant's detrimental impact on crops, pastures and the native environment, its toxic and physically harmful effects on domestic stock, and the extent of its naturalisation. Most Australian grass weeds are accidental introductions which have become naturalised. Most of the winter and spring-growing species of southern Australia originated in temperate Europe and the Mediterranean region, while those summer-growing species which are a problem in northern Australia came mainly from Africa and tropical America.
Poisonous Grasses
The Poaceae family contains many toxic or potentially toxic species, some of which are also valuable forage crops and pasture plants. Many species have given positive tests for Cyanide/prussic acid (HCN), nitrates and some can accumulate oxalates in potentially toxic amounts.
The Importance of the Legume Family
Legumes have been gathered, cultivated, eaten and used in a multitude of ways by humans for millennia and are arguably as important as grasses in global terms. The range of uses of legumes is possibly broader than grasses. Legume products contribute enormously to the worlds economy through food (for animals and humans), pharmaceuticals, medicine, biofuels etc.
Legumes are in the Leguminosae plant family (some say the Fabaceae family) The legume family is split up into three subfamilies : 1. Fabaceae (pea type flowers) Eg. Centro, butterfly pea 2. Mimosaceae (rounded inflorescence type of flowers) Eg. Mimosa, Leucaena 3. Caesalpiniaceae (yellow open showy type of flowers) Eg. Cassia, Senna sp
Ancient cultures were aware of the ability of many legumes to improve soil, even if they did not then appreciate that this results from symbiotic nitrogen fixation. Some 40 to 60 million metric tons of nitrogen are fixed annually by agriculturally important legumes.
The natural accumulation of nitrogen in legumes has resulted in predation of legumes by a wide range of animals and insects To combat this the legume family has evolved a repertoire of chemical defences based on secondary compounds, especially alkaloids resulting in many legumes being toxic.
Grain and forage legumes are grown on approximately 180 million ha (12 – 15%) of the Earth’s arable surface and account for 27% of the world’s primary crop production Grain legumes contribute 33% of the dietary protein nitrogen needs of humans. Legumes (mainly soybeans) also contribute more than 35% of the world’s processed vegetable oil. Forage legumes provide protein, fibre and energy that have underpinned dairy and meat production for centuries. In temperate regions Lucerne/Alfalfa (Medicago sativia) is an important and highly valued forage for cattle. Other temperate pastures include eg. clovers (Trifolium spp) and vetches (Vicia spp). In the tropics; Arachis (forage peanut), Centrosema, Desmodium, Macroptilium and Stylosanthes spp are being used to improve tropical pasture systems.
The importance of legumes is based on:
• their ability to fix N in symbiosis with Rhizobium bacteria, • they are rich in protein & minerals, • they increase forage value & animal production • they enrich soil & improve other plants, • they increase the bulk & quality of pastures, • their rate of decline in quality over the season is less than grass, • mature legumes have higher digestibility & intake than grasses (legumes often have digestibilities of 70% & a crude protein (CP) of 21%, fertilized, wet season grasses may have similar digestibility but CP of about 12%), • legumes have a higher water use efficiency than grasses.
Palatability, Increaser/decreaser species and State & Transition models
Palatability varies among pasture species due to: maturity, species type, associated species, region, time of day grazed. • Palatable species are desirable species but with continuous grazing they become “decreaser” species, ie. decrease in abundance e.g. Kangaroo grass (Themeda sp)
Unpalatable/semi palatable species are undesirable and become “increaser” species ie. they increase in abundance in a grazed environment, e.g. Wire grasses (Aristida sp) and Indian couch (Bothriochloa pertusa)
Pastures in good condition contain over 50% decreaser species, Pastures in fair condition 30-50%, and Pastures in poor condition 5-30%. Very poor condition is indicated by less than 5% decreasers and over 65% increasers and unpalatable weedy invaders. Not all plants have indicator value, and some species can be decreasers in one rangeland type, but increasers in another.
State and Transition models
A tool for detecting and modelling vegetation change • Vegetation is said to be inherently unstable especially in the Australian rangelands or savannas. Changes in species composition occur over time even without grazing due to drought, flood, fire, and other natural phenomena. • A State is defined in terms of a dominant species of ground cover, vegetation structure, % ground cover, or basal area of the plants; it may also take into account the condition of the soil surface. • A Transition (or change) may be triggered by natural events (e.g. fire, drought) or by management actions (stocking rate, burning, spelling), or by a combination of these. State and transition mod