Goats and Soil Erosion: The Evidence

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Goats and Soil Erosion The Evidence

• Kris Dixon
• MSc World Animal Production
• Module 556 Land Husbandry in Drought Prone Areas

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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.)

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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.

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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 15 - 18 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.

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Comparisons with Other Ruminants
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Comparisons with Other Ruminants
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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.

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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.

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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.

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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.

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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.

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Approximate Static Loads Exerted by Stationary
Machinery and Animals
(Source Heady Dennis Child, 1994, p64)
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Load Bearing Capacities of Soils
(Source Heady Dennis Child, 1994, p64)
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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)
  

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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)

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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)

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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.

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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)

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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.

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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

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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.

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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.

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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 2002.
• 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 2002.
• Peacock,C. (1996). Improving Goat Production in
  the Tropics. A Manual for Development Workers.
  Oxfam, Farm Africa.

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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 166441-452.