Presentation on theme: "Goats and Soil Erosion: The Evidence Kris Dixon MSc World Animal Production Module 556: Land Husbandry in Drought Prone Areas."— Presentation transcript:
Goats and Soil Erosion: The Evidence Kris Dixon MSc World Animal Production Module 556: Land Husbandry in Drought Prone Areas
The Domestic Goat ~ An Introduction Genus Capra, main species Capra hircus. Domestication occurred 8000 years ago around the Nile, Euphrates, Tigris and Indus rivers. Human migration led to the spread of the domesticated goat worldwide. Goats are hardy and have adapted to a wide range of climatic and ecological conditions. Goat populations have been growing at a faster rate than other ruminants. (Source: Steele, 1996.)
The Domestic Goat ~ An Introduction The world population is approximately 639 million. 41% of the total goat population is in Africa, 32% on the Indian sub-continent. Goats are cheap to purchase and are popular with poor farmers, as ownership of several goats is less risky than owning one or two cattle. They are able to survive in conditions that sheep and cattle could not, as they can utilise poor quality forage, and are more tolerant of water scarcity.
Physical Characteristics The goat is a small ruminant, weight varies between breeds and between bucks and does. Large tropical breeds may weigh up to 60kg, small dwarf breeds 25kg. Goats have a rapid reproduction rate, in good conditions females can produce their first kids at months, and thereafter every 8 months. Multiple births are common. The structure of the digestive system, and rate of passage allow goats to digest poorer quality forage than sheep or cattle. Goats are able to extract the majority of the water content of feeds, increasing their tolerance to drought.
Comparisons with Other Ruminants SpeciesNatural Feed Resources Specific Abilities Feed Intake Behaviour Impact on Environment Impact of Prolonged Exposure Goats Young lvs + sprouts of grass, shrubs + trees. Pods + Seeds Small beck, strong jaws, sensitive lips can stand on hind legs and climb. Select bark, young lvs + sprouts from standing (thorn) shrubs + trees. Eliminate young trees + shrubs Standing hay old shrubs + trees Sheep Young lvs + sprouts of grass + herbs Pods + Seeds Small beck, sensitive lips strong legs long distance runners Select young lvs + sprouts from standing vegetation. Can cover large area. Elimination of perennial grasses Standing hay annual grasses scattered shrubs + trees Cattle Young, mature + dry grasses. Straws Sensitive tongue + smell. Large beck Select palatable sp. Avoids dung patches. High intake/bite. Eliminate palatable sp. Formation of cattle tracks + open spaces Bare soil on tracks Open spaces with non palatable grass, herbs + shrubs.
Comparisons with Other Ruminants SpeciesNatural Feed Resources Specific Abilities Feed Intake Behaviour Impact on Environment Impact of Prolonged Exposure CamelYoung lvs and sprouts of shrubs +trees. Pods, young, mature + dry grass Sensitive lips + tongue, Long legs + neck. Long distance runner Select young lvs + sprouts from higher levels of trees + shrubs grazes grass can cover large distances Elimination of young + mature tree + shrubs Elimination of perennial grasses Open plains with annual grasses + remnants of old trees + shrubs EquinesYoung sprouts of grass and herbs. Standing hay Sensitive nose and smell Incisors in upper jaw Graze close to the ground Browse. Avoid patches with own faeces Elimination of palatable grass + herbs. Patches of old grass Low palatability creepers or bare soil with patches of old grass, shrubs + trees
Comparisons with Other Ruminants Goats prefer shoots and leaves to stems and a variety of available vegetation. When first turned out in the morning, goats will graze unselectively, but will become more selective during the day. Goats scatter and graze and browse individually unlike sheep which graze in groups. They can stand on their hind legs and climb some trees, reaching vegetation 1.5 – 2 metres from the ground. Goats favour grasses and legumes in rainy seasons, and trees and shrubs in the dry season. Stall fed goats may spoil and refuse a lot of the forage provided if not carefully managed.
Comparisons with Other Ruminants Cattle have a tendency to create tracks across pasture, from which the vegetation is removed, and on slopes, erosion of these tracks may lead to the formation of gullies. Sheep in particular, pull up whole plants.
Impacts of Grazing and Browsing Impacts on vegetation Plants are cut and bruised by trampling. Plants covered by disturbed soil and dung. Under heavy grazing perennial grasses often produce tillers close to the surface, increasing vegetative cover. Annual grasses will not fully develop and reproduce if heavily grazed during the growing season. The persistence of this situation can lead to complete loss of cover.
Impacts of Grazing and Browsing Where grasses form tufts, the soil between the tufts may become exposed as the younger vegetation is grazed. Broadleaved plants and shrubs may germinate in these areas, changing pasture composition. Consumption of sprouts and seedlings threatens natural regeneration. Heavy grazing creates selection pressure favouring the growth of unpalatable species. Plants are weakened and will die from excessive grazing. Soil compaction impedes rooting.
Impacts of Grazing and Browsing Heavy grazing in wetter conditions leads to lower and spreading vegetation, providing continuous surface cover. Grazing prevents litter accumulation which can impede grass re-growth and germination. Grazing delays completion of the reproductive cycle of grasses, maintaining the nutritional value of the plants.
Approximate Static Loads Exerted by Stationary Machinery and Animals Kg/cm 2 Crawler Tractor0.32 – 0.63 Sheep0.65 Wheel Tractor1.4 – 2.1 Horse or Cow1.7 Truck3.5 – 7.0 (Source: Heady & Dennis Child, 1994, p64)
Load Bearing Capacities of Soils Kg/cm 2 Organic Soils0.21 Dry Sand2.0 Wet Sand and Dry Clay4.0 Packed Gravel8.0 (Source: Heady & Dennis Child, 1994, p64)
Effects of Grazing on Soils Experiments have shown that excessive grazing in semi arid areas has a variety of impacts on soils. Reduction in depth of topsoil mainly due to compression by hooves. Higher bulk density in top cm of profile of grazed land. Lower total porosity due to the collapse of macropores and large mesopores. Increased mechanical impedance of top 10cm. Lower quantity and density of roots at top of profile. (Argentina, cattle grazing. Villamil et al, 2001)
Effects of Grazing on Soils Decrease in water retention capacity. Decrease in carbon content. Development of a “highly water repellent microstructure” Run off from bare ground, wind erosion and gully erosion on slopes. (Ecuador, intensive sheep grazing. Podwojewski et al, 2002)
Experimental Results On a five year experimental plot in Tanzania grazed with goats mature trees and shrubs survived and there was no further encroachment. Attempts in Namibia to clear shrubs from cattle pasture using goats failed to achieve this aim though further encroachment was halted. Regeneration of trees, shrubs and vegetation, integrated with goat and cattle production has been successful in Bali. (Source: LEAD, 1999)
Feral Goats Feral goats are considered a significant problem in several countries, particularly where groups are isolated in fragile environments. There are several historical examples of habitat destruction resulting from releases of goats. Eg, East Africa, Cyprus, southern Italy, St Helena, Ethiopia and Israel.
Shrub Encroachment and Soil Erosion Soil erosion has been linked with shrub encroachment. Related to bare soil patches between shrubs. Bulk density found to be higher between shrubs in shrub – steppe environment, and soil organic matter and porosity were lower than in shrub – grass or grass –steppe regions. Sediment production from shrub – steppe also found to be higher. Litter removal by run-off implicated as a mechanism whereby shrub – grass becomes shrub – steppe. (Patagonia, Parizek et al 2002)
Use of Goats in Conservation In several countries goats are now being used to halt soil erosion resulting from shrub encroachment. In California goats are being recommended as a tool to aid in the creation and maintenance of firebreaks. Goats are also being used to combat invasive exotic plant species, such as Kudzu in the American mid-west.
Socio-economic Considerations Age and gender of herder has a large impact on grazing patterns: time spent at locations, distance travelled etc. Goats are cheap to buy and keep and hence have a major role in the livelihoods of poor households Goats tend to be owned by poorer households, who have little impact on policy formation and implementation. Goats have low status in many cultures, unlike cattle, and are regarded as “a traditional, old technology”
Conclusions Human activities, for example deforestation, cultivation of marginal lands and grazing by large ruminants are significant factors in the process of degradation. As a result of their adaptability to inhospitable conditions, goats tend to be the last animals found on a degraded site. In such circumstances evidence indicates that they may impede the recovery of such areas if their grazing and browsing pressure is excessive. In other circumstances, carefully managed, goats may have a role in rehabilitation.
Conclusions Several authors have concluded that major cause of soil erosion is removal of grass cover, for which cattle are implicated, rather than the browsing of trees and shrubs. The creature most responsible for soil erosion is man. The key factor control of soil erosion in the future is human management of grazing. Goats have a critical role in the nutrition and livelihood security of poor households. Future grazing policy needs to recognise the importance of goats in poverty alleviation.
References Heady,H.F. and Dennis Child, R. (1994). Rangeland Ecology and Management. Westview Press. Parizek, B. Rostagno, C.M, and Sottini, R. (2002) Soil Erosion as affected by Shrub Encroachment in North-eastern Patagonia. Journal of Range Management, Vol. 55, No.1, January Podwojewski, P, Poulenard, J. Zambrana, T and Hofstede, R. (2002) Overgrazing effects on vegetation cover amd properties of volcanic ash soil in the paramo of Llangahua and La Esperanza (Tingurahua, Ecuador). Soil Use and Management. Vol. 18 No.1 March Peacock,C. (1996). Improving Goat Production in the Tropics. A Manual for Development Workers. Oxfam, Farm Africa.
References Steele, M. (1996). Goats. Tropical Agriculturalist Series, CTA Macmillan Villamil, M.B., Amiotti, N.B. and Peinemann, N. Soil degredation related to overgrazing in the semi-arid southern CadenaL area of Argentina. Soil Science 2001; 166: