Transcript Goats and Soil Erosion: The Evidence

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 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.
Comparisons with Other Ruminants
Species
Natural Feed
Resources
Specific
Abilities
Feed Intake
Behaviour
Impact on
Impact of
Environment 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 +
Small beck,
sprouts of grass + sensitive lips
herbs Pods +
strong legs
Seeds
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
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.
Sensitive
tongue +
smell. Large
beck
Comparisons with Other Ruminants
Species
Natural Feed
Resources
Specific
Abilities
Feed Intake
Behaviour
Impact on
Impact of
Environment Prolonged
Exposure
Camel
Young 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
Equines
Young 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
Crawler Tractor
Sheep
Wheel Tractor
Horse or Cow
Truck
Kg/cm2
0.32 – 0.63
0.65
1.4 – 2.1
1.7
3.5 – 7.0
(Source: Heady & Dennis Child, 1994, p64)
Load Bearing Capacities of Soils
Kg/cm2
Organic Soils
0.21
Dry Sand
2.0
Wet Sand and Dry Clay
4.0
Packed Gravel
8.0
(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
•
Journal of Range Management, Vol. 55, No.1, January 2002.
Podwojewski, P, Poulenard, J. Zambrana, T and Hofstede, R. (2002)
•
•
affected by Shrub Encroachment in North-eastern Patagonia.
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.
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; 166:441-452.