Title: Goats and Soil Erosion: The Evidence
1Goats and Soil Erosion The Evidence
- Kris Dixon
- MSc World Animal Production
- Module 556 Land Husbandry in Drought Prone Areas
2The 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.)
3The 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.
4Physical 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.
5Comparisons with Other Ruminants
6Comparisons with Other Ruminants
7Comparisons 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.
8Comparisons 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.
9Impacts 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. -
10Impacts 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.
11Impacts 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.
12Approximate Static Loads Exerted by Stationary
Machinery and Animals
(Source Heady Dennis Child, 1994, p64)
13Load Bearing Capacities of Soils
(Source Heady Dennis Child, 1994, p64)
14Effects 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)
15Effects 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)
16Experimental 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)
17Feral 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.
18Shrub 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)
19Use 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.
20Socio-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
21Conclusions
- 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.
22Conclusions
- 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.
23References
- 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.
24References
- 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.