Soil
and Water
Conservation
Through
Vegetative
Measures
Introduction
The fragile upland areas in the
Cordillera Region have been always subjected to various land uses
due to increasing population. The presence of understocked vegetation
and the continuous intervention of man, many parts of the region
have become very prone to erosion.
Geological erosion is the type
of erosion that is taking place in the uplands aside from human
interference and these are contributing to massive soil movement.
Soil erosion results to the sedimentation
of creeks, rivers, and other water bodies, which eventually leads
to frequent flooding of the lowland areas during rainy days. Other
effect may include unproductive farmlands, reduced supply of potable
water, silting of reservoirs, and destruction of personal properties.
To be able to solve these problems, soil and water conservation
(SWC) technologies be necessarily applied in the uplands.
One effective SWC measure is the
use of vegetation. Vegetative cover protects the soil from possible
erosion. It holds the soil in place while absorbing the great
impact of rain. Using vegetation as a method to control soil erosion
has been found effective and economical (Weildelt 1975).
However, the effectiveness of the
vegetative cover structures depend on the density of the vegetation
planted including composition, species used and site condition.
Advantage of areas with vegetative cover
Erosion rate in areas with forest
vegetation is practically zero. Trees and plants, including dead
leaves, decayed branches and other forest litters are effective
in controlling soil movement during heavy rains. They also provide
better soil structure, increase infiltration and water-holding
capacity.
Some distinct and unique features
of vegetation as ground protective cover are:
1. A dense vegetation prevents raindrops from striking the ground
directly.
2. The vegetation will constantly add organic matter/humus that
increases the soil's water holding capacity.
3. Decayed roots of plants create numerous small holes in the
ground which will serve as miniature reservoirs of water.
4. Roots of living plants hold the soil in place and prevent it
from being washed away.
5. Tree vegetation will serve as fuel, post, timber, and scenic
green landscape.
6. Trees, plants and other vegetation can control sheet and rill
erosions. They can be planted to stabilize gullies, streambanks
or road banks.
The use of vegetation, however,
as a soil stabilizer has its own limitation on very steep slopes,
where only solid structures can provide the desired protection
and stability.
Suitable plants for erosion control
Local plant species growing vigorously
in the locality should be used. Other species which are suitable
for planting in specific sites and have the desired characteristics
to control erosion could be used.
In general, practically all plants
can be used as vegetative cover. When used for erosion control
purposes, these plants should meet one of the following requirements:
1. They can grow on degraded and
eroded sites;
2. Their roots can grow rapidly, while their vegetative parts
can form dense and spreading canopy/crown to provide immediate
protection to the area;
3. They possess deep and wide root system for good anchorage of
the subsoil. However, a plant species having a dense shallow root
system can also be used because of the "matting effect;"
4. They can be easily established by cuttings, stumps, or bare
root seedlings;
5. They can produce a large volume of litter to help improve the
soil;
6. They can withstand the physical stress of falling stones and
landslides; and
7. They can withstand or survive brush fires.
There are some plants recommended
for soil erosion control, these are:
a. Trees
b. Shrubs
c. Vines
d. Grasses
Some of the common vegetative SWC
measures in the uplands
a. Fascines
b. Hedgerows
c. Bench brush layers
Trees
Trees are the most common and widely
distributed plants on earth. They are primarily recommended for
gully areas. They produce heavy, deep and broad spreading root
systems that bind soil particles together. Litter from trees when
decayed into humus absorb large quantities of rainfall and will
later on be stored and drained through the sponge-like cover without
unnecessarily eroding the ground surface soil. Trees also permit
the growth of other vegetation underneath such as weeds, greases,
shrubs, vines or brushes. These are also effective soil stabilizer
and can hold water and gradually release it into streams or other
drainage outlets. Lastly, trees can be established more easily
at cheaper cost, and are more effective protection cover on gully
areas than other vegetation.
Consider the following tree species
for vegetative cover in erodible areas:
1. Alder or Alnus (Alnus maritime)
2. Madre de cacao or kakawate (Gliricidia sepium)
3. Paper mulberry (Broussonetia luzoniensis)
4. Tibig (Fucus nota)
5. Benguet Pine (Pinus kesiya)
6. Kamachile (Pithecolobium dulce)
7. Mangium (Acacia mangium)
8. Guava (Psidium guajava)
9. Murray red gum (Eucalyptus camaldulensis)
10. Calliandra (Calliandra callothyrsus)
11. Anchoan dilaw (Cassia spectabilis)
12. Akleng parang (Albizzia procera)
13. Rain tree (Samanea saman)
14. Giant ipil-ipil (Leucaena leococphala)
15. Acacia (Acacia auriculiformis)
Shrubs
Shrubs can be used to control soil
erosion. They can also be used as supplement to more valuable
plants that are scarce in the area. Shrubs can be underplanted
with trees.
The following shrub species can
be used to control soil erosion:
1. Baho-baho (Lantana camara)
2. Lisak or wisak (Nauclea spp.)
3. Sunflower (Helianthus riparia)
4. Dumanay (Homonoia riparia)
5. Maguey (Agave cantala)
6. Binatang Hambog (Malvaviscus grandiflora)
7. Dama de noche (Centrum nocturnum)
Vines
Vines are used chiefly in gullies
within pasture areas and in other places where protection alone
is desired. The same preparation of the ground for tree planting
is necessary for setting vines.
Some of these are the following:
- Kudzu (Pueraria thumbergiana)
- Centrosema (Centrosema pubescens)
- Punkinggan
- Lespedeza cuneata
- Stylosanthes
spp.
Grasses
Grasses can supplement tree planting
for erosion control on gully areas. They can be established by
sowing the seeds or planting of cutting, stolons, stubbles, etc.
In sowing seeds of greases, slope surface should not be smoothened
to minimize soil erosion and to keep the seeds from being washed
away. Pits/holes should be spaced about 600 mm apart along the
contour and staggered, afterwhich seeds shall be sown and covered.
If stolons or cuttings are used,
they should be firmed very well into the soil. Bermuda grass is
one of the most effective grasses to plant in gullies to control
soil erosion. It rapidly develops a strong root system.
The recommended grasses to be planted
are:
1. Bermuda grass (Cynodon dactylon)
2. Kikuyo (Pennisetum clandestinum)
3. Kawayan tinik (Bambusa spinosa)
4. Japanese bamboo or fishing rod bamboo
5. Paspalum conjugatum
6. Napier
Fascines
Fascines are bundles of long and
dense brushwoods of varying lengths. For slope stabilization,
length of fascine should not exceed three (3) meters otherwise,
they would become too heavy to handle (the weight of a fascine
with a length of 1 m and 25 cm diameter is 13 to 14 kg.).
Hedgerows
Hedgerows are vegetative strips
planted across a hillside/mountainside. It is used to slow down
rainwater runoff and deposit. This is a good method for dividing
hillsides into smaller sections so that overland flow/surface
runoff from heavy rainfall cannot build up enough speed thus controlling
the possible occurrence of soil erosion.
Bench Brush Layers
This involves the construction
of benches, a 30 degrees cut, slightly inclining towards the slope
of about 1-meter in width. Branches and cuttings are overlaid
in a netted manner.
Source: ERDS-CAR-DENR, 1994. Soil
and water conservation through vegetative measures, Technology
Transfer Tips, Vol.1. Baguio City.
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