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Title: Goats and Soil Erosion: The Evidence


1
Goats and Soil Erosion The Evidence
  • Kris Dixon
  • MSc World Animal Production
  • Module 556 Land Husbandry in Drought Prone Areas

2
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.)

3
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.

4
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.

5
Comparisons with Other Ruminants
6
Comparisons with Other Ruminants
7
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.

8
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.

9
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.

10
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.

11
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.

12
Approximate Static Loads Exerted by Stationary
Machinery and Animals
(Source Heady Dennis Child, 1994, p64)
13
Load Bearing Capacities of Soils
(Source Heady Dennis Child, 1994, p64)
14
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)

15
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)

16
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)

17
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.

18
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)

19
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.

20
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

21
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.

22
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.

23
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.

24
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.
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