Establishment and growth of trees in arid region is very slow due to
hostile environmental conditions such as, low and uncertain
rainfall, extremes of temperature, high evapotranspiration, strong
winds, loose sandy soils which are prone to wind erosion and are
infertile having poor moisture holding capacity. The problem is
further compounded by very large population of animals and human
being which impede the growth of plantations by overbrowsing and
felling. Obviously, forestry in such regions could be promoted only
with species which not only thrive under these constraints, but are
fast growing. Acacia tortilis is an important tree of arid
region of many African and Asian countries, where its natural
plantations are in abundance. It was introduced in Indian desert in
1958 from Israel and has been found a very promising species. It is
particularly suitable for sand dune stabilization. The species,
locally known as ‘Israeli babul’ has made Indian desert its natural
home during last three decades.
Acacia tortilis, is native of Sudan,
Ethiopia, Yemen, Somalia, part of Kenya, Tanzania, Arabia and Southern
Israel. It is usually a medium size tree of 4 to 12 m height, sometimes a
shrub or bush 1.5-18 m high, occasionally of 21 m. Bark on trunk usually
rough and fissured, grey to black brown. Crown usually flat and spreading
(parasol type) but sometimes (especially in sub sp. raddiana)
rounded. Young branchlets densely to sparsely pubescent or glabrous to
subglabrous. Spines paired; some short and hooked, up to about 5 mm long,
others long straight, slender, whitish, 1.2-8(-10) cm long, never enlarged
or inflated. Petiole usually with a gland. Pinnae 2-10, occasionally to 14
pairs on a short rachis up to 2 (-4) cm long, usually glandular between the
top 1-3 and lowest 1-2 pairs of pinnae. Leaflets 6-20 pairs per pinna,
glabrous to densely pubescent, 0.5-2.5(-6) mm long, 0.2-1(-1.5) mm wide.
Flowers white or yellowish-white, scented, in round fluffy heads 0.5-1.1 cm
in diameter, on axillary peduncles 0.4-2.5 cm long. Pods variable
indehiscent or slowly dehiscent, contorted or spirally twisted, very rarely
and abnormally (Kenya) pods straight or nearly so, glabrous, pubescent or
tomentellous, rarely with spreading hairs. Seeds oblique or parallel to long
axis of pods.
In general, A. tortilis, a member of family
Mimosoideae is very distinctive and easily recognized with the
characteristics mixture of long straight spines and shorter hooked ones
combined with spirally twisted or contorted crown has given it the popular
name of Umbrella Urorn; however the foliage is smaller than in many acacias,
and the whitish flowers in small round heads are also characteristic, though
this is a feature shared with other Acacia species. Under Indian arid
conditions this species starts flowering and fruiting at 3 years of age.
Flower buds appear in the first week of May and fruit setting commences from
mid July. Fruits ripen during the period November to February. On an
average, annually a tree yields 4 to 6 kg seeds at 6 to 8 years of age.
Seeds of this species which are light brown in colour resemble those of
Acacia nilotica sub sp. indica (babool) in size and the weight is
approximately 85 g/1000 seeds.
General Distribution
Widespread in Africa, from South Africa northwards to Algeria and Egypt,
extending in Asia to Israel and southern Arabia. A. tortilis is
cultivated in India (sub sp. raddiana) and Pakistan.
In India, plantations of Acacia tortilis occur in the districts of
Barmer, Bikaner, Jaisalmer, Sri-Ganganagar, Jodhpur, Pali, Seekar, Churu,
Jhunjhunu, Nagaur, etc. in western Rajasthan. It is also being planted in
arid zones of Gujarat, Haryana, Punjab, Tamil Nadu, Andhra Pradesh and
Karnataka. It is prominent on sand dunes of arid regions where it has good
growth. In western Rajasthan, roadside plantations are predominantly of
Acacia tortilis. In IGNP, stage I area there are old plantations of
Acacia tortilis which have attained very good growth. Block plantations
of Acacia tortilis have been raised in desert districts of western
Rajasthan to meet fuel and fodder demands. Acacia tortilis has been
planted in silvipastoral systems along with Lasiurus sindicus and
Cenchrus ciliaris in arid regions. It also occurs on farm lands as
boundary plantations. In Sudan it is found in the northern region where
rainfall is 200 mm or below. In the drier parts, it is confined to water
receiving sites, and is characteristic of erosion runnels in desert
lay-gravel. The sub species raddiana was noted growing in fossil
black clays and on rocky cliffs (Kordofan, Sudan), on deep sands (Abeche,
Chad), on eroded ‘reds’ (Tin el Hasan, Morocco) and in red ferruginous soils
on iron pans north of Kano, Nigeria. In Botswana, Acacia tortilis
occurs in floodplain grasslands, parklands and tree savanna. In Somalia,
Acacia tortilis occurs in wide range of soils which include saline and
gypseous. In Abu Dhabi, it is generally confined to the heavy soils in the
valley flats. In West Africa, occurrence of Acacia tortilis sp.
raddiana, extends from Senegal to the Red sea and across the Sahara to
Tunisia. The southern limit of the main distribution runs from Saint Louis
in Senegal eastward to south of Lake Chad, a line which corresponds to the
500 isohyet and marks the edge of Sahel. In Wadi El-miyah, Acacia
tortilis sp. raddiana occurs as a dominant of vegetation
community type II, along with Pergularia tomentosa, Panicum
turgidum and Capparis decidua. In Egyptian desert (tributary
wadis in eastern part) Acacia tortilis dominates in association with
Leptadenia pyrotechnica, Maervacrassifolia and
Solenostemma argel. In the middle and southern regions, the associates
are Aerva persica, Cassia senna, Colocynthis vulgaris, Salsola baryosma,
Balanites aegyptiaca and Morettia philaena.
A. tortilis is widely occurring and variable species within which four
sub species are recognized. Their geographical ranges are generally
distinctive, though there is some overlap in sub species tortilis and
sub species raddiana. The sub species are separated by the presence
or absence of pubescence on the pods, their width and differences in the
pubescence of the branchlet. The shape of the crown is distinctive is sub
species raddiana.
Distribution of Sub Species
Acacia tortilis
subspecies
tortilis
Synonyms – Mimosa
tortilis Forsk
Sub species tortilis occurs in Somalia,
Ethiopia, Sudan northwards to Egypt and Israel extending to the Yemen, Arab
Republic, P.D.R. Yemen, Oman, Saudi Arabia, Abu-Dhabi and Qatar.
Acacia tortilis
sub species raddiana (Savi) Benan var. raddiana
Synonyms - A. raddiana
Savi A. fasciculate
Guill & Perr. non H. B.K. A.tortilis
var. lenticellosa Chiov. A.tortilis
forma raddiana (Savi) Roberty
Tree 1.2-10m high, with more or less rounded crown. Young branchlet and
leaves glabrous or
subglabrous. Pods 6-9 mm
wide, glabrous glandulae.
Sub species raddiana var. raddiana occurs in northern Africa
from the Senegal eastward to the Sudan,
Somalia and Kenya. Its
status (native or introduced) in Kenya is uncertain. It also extends through
Egypt to Israel, Jordan
and Saudi Arabia. It is widely planted in Indian arid zones, the maximum
coverage being in western
Rajasthan.
Acacia tortilis sub
species raddiana var. pubescens A. Chev.
Synonyms - A. fasciculata
var. pubescens (A. Chev.). A. tortilis var. pubescens Aylmer ex. Burtt Davy.
A.raddiana
var. pubescens (A. Chev.) A.F. Hill.
Similar to var. raddiana but young branchlets shortly more or less
pubescent and pods appressed –
puberulous.
The var.
pubescens has been found in Mali, Algeria and Sudan. It will be noted
that the features
differentiating
var. pubescens from var. raddiana are those that might be
expected from hybridization
between sub species
raddiana and sub species tortilis.
Trees in Israel “intermediate in some
characters between A. raddiana and A. tortilis” considered
hybrids. Similar
trees were described as “tortilis (raddiana X spirocarpa)”
in Tunisia near Bou Hedma. It
was considered that
the distinctions between spirocarpa and raddiana were not
clear, though it was
suggested (without
reasons) that raddiana might be better reinstated as a species.
The considerations such as these, together
with the occurrence of glabrous pods in sub species
heteracantha
that raddiana has been placed sub species of Acacia tortilis.
Acacia tortilis sub
species spirocarpa (Hochst ex. A Rich) Brenan var. spirocarpa
Synonyms - A. spirocarpa Hochst ex.
A. Rich
A. petersiana Bolle.
A.spirocarpa
var. major Schweinf.
A. spirocarpa forma pubescens Terracc probably
A.pappii
Gandoger
A.tortilis
forma spirocarpa (Hochst ex. A. Rich) Roberty.
Sub species Spirocarpa var. spirocarpa is restricted to
eastern Africa, occurring in the Sudan, Ethiopia,
Somalia, Uganda, Kenya
Tanzania, Malawi, Mozambique, Zimbabwe and Botswana.
Acacia tortilis
sub species spirocarpa var. crinita Chiov. The var. crinita
has been found in Somalia,
Kenya and Tanzania.
Some specimen at the Royal Botanic Gardens,
Kew from the Yemen Arab Republic are very similar to var.
crinita in their
densely spreading hairy pods, but the pods lack glands. The evidence is
insufficient for a
certain opinion but it is
possible that these specimens are sub species tortilis showing long
hair on pods
to var. crinita.
Acacia tortilis
sub species heteracantha (Burch) Brenan
Synonyms - A.
heteracantha Burch.
A.litakunensis
Burch.
A.spirocarpoides
Engl.
A. maras Engl.
The sub species heteracantha occurs in
Southern Angola, Namibia/S.W. Africa, Botswana, Zimbabwe, Mozambique, South
Africa and Swaziland.
The occurrence of occasional intermediates
between sub species heteracantha and sub species spirocarpa
was observed but the vast majority of specimens can be placed without
difficulty in one or the other sub species.
Acacia tortilis is the most
important species for sand dune stabilization. It plays a paramount role in
Indian desert for wind erosion control. Shelter belts of Acacia tortilis
are raised along roads, railway tracks and farms. It yields good fuel wood,
leaves are lopped for fodder and fruits also form good fodder for the
livestock. Twigs, branches and thorns are used as fencing materials. Bigger
branches are used as poles for erecting fence around farms and plantations.
Wood Properties
Annual rings are observable in Acacia
tortilis plantations in Africa (Senegal and Niger) but they are very
irregular. The negative growth characteristics are diffuse porosity, banded
parenchyma, false or disjointed rings, discontinuous rings and indistinct
boundaries. Xylem vessels in Acacia tortilis are mostly solitary, but
they also occur in radially, diagonally and even tangentially oriented
multiples (2 to 4 vessels in multiples). The perforations were transverse or
oblique or simple. Inter vascular pitting was predominantly alternate with
linear apertures. Tyloses were not encountered, but the vessels had gummy
deposits. Wood parenchyma was paratracheal of the aliform confluent type and
formed narrow concentric bands with large starch grains in the cells. The
broader bands of A. raddiana were the only difference that readily
distinguished the two species. A frequently occurring feature was long
vertical columns of cells containing rhomboidal crystals. These were most
abundant in wood that was differentiated during weak cambial activity.
Strength properties of the species are given in the following table.
Property
Condition
Value
Specific gravity Green 0.66
Oven
dry 0.69
Weight Green 1164 kg/m3 at 76.3 per cent
Oven
dry 769 kg/m3 at 12 per cent
moisture content
Fibre
stress Green 335
kg/cm2
At elastic
limit dry 461 kg/cm2
Static bending Modulus of rupture green 608 kg/cm2 dry 806 kg/cm2
Modulus of elasticity
green 58000 kg/cm2
dry 71900 kg/cm2
Work to elastic limit
green 0.133 kg/cm2 dry 0.199 kg/cm2
Impact bending Izod value of
work green 160 kg/cm
Absorbed dry 105 kg/cm
Compression Parallel to green 344 kg/cm2
dry 416 kg/cm2
Perpendicular to grain green 90 kg/cm2
dry 70 kg/cm2
Surface hardness Radial green 615 kg
dry 638 kg
Tangential green 614 kg
dry 578 kg
Shear parallel to grain
Radial green 114.2kg/cm2 dry 160 kg/cm2
Tangential green 133.1 kg/cm2 dry 122.0 kg/cm2
Fuel
There is fuel wood deficit situation in arid zones of Rajasthan,
Gujarat, Harayana and other states. In Rajasthan the gap between the demand
and supply is of the order of 1.65 m tones per annum. This calls for
enhancing fuelwood yield. Acacia tortilis is a very good source of
fuelwood, because of its fast growing habit and excellent coppicing
behaviour. In Indian arid regions, it is the most important species planted
on panchayat lands under ‘village fuel wood plantation’ scheme. On a
panchayat land in Seekar district, Acacia tortilis planted for fuel
wood was severly lopped leaving only the main stem and main branches. The
plantation shows very good sprouting of new foliage. Acacia tortilis
is found to be one of the 35 species chosen as particularly suitable for
fuelwood in hot arid areas of Africa and middle east. Its dense ‘red hard
wood has high calorific value of 4400 K cal/kg making superior firewood and
charcoal. The tree starts giving fuel wood at the age of 8 to 10 years at
the rate of 50 kg/tree. Close planting at 3m x 3m yielded 54 tonnes/ha of
fuel wood at 12th year of planting at Jodhpur. Acacia tortilis
was found to be one of the commoner species for charcoal making in west
Africa.
Fodder
Increase in livestock population and dwindling
fodder resources of western Rajasthan leaves vast gap in demand and supply
of fodder. This chronic deficiency of fodder needs to be corrected by
stepping up fodder production from tree based land use system.
Acacia tortilis is one of the important
sources of fodder for cattle in western India. West Africa, Somalia,
Ethiopia, Sudan etc. Foliage and fruits of Acacia tortilis are
important browse. A ten year old tree yields about 4 to 6 kg dry leaf and 10
to 12 kg pods per year. The foliage of Acacia tortilis is very much
liked by sheep, goat, camel, cows and wildlife. The leaves are fed green as
well as dry. The green foliage is fed during February to May. Whereas to
store dry leaves, they are collected in the month of October. Fruits are
preferred for stall fed animals. Like leaves, fruits are also collected and
stored dry. However, the pods should be grinded and fed to make it more
nutritious.
Leaves and pods of Acacia tortilis have
been reported to be rich in proteins and other nutrients at par with
Acacia nilotica, another important fodder species of semi-arid region.
Crude protein and digestibility coefficient of Acacia tortilis has
been reported to be 18% and 46.2%, respectively. Nutrient contents in the
leaves have been reported to be, total N 14-18%, digestible N 11-12%, P
0.15-0.18% and net energy 5.552-6.212 mega joules/kg of dry matter. Pods of
Acacia tortilis contain protein 18.8%, fat 2.4%, carbohydrate 46.2,
minerals 5.1% and crude fibre 20.1%. Nutrient contents of the pods were,
total N 14-18%; digestible N 9.8-14%; P 0.20-0.28%, net energy 4.141-5.522
mega jules/kg dry matter and digestible N per forage unit, 118-160 g.
Work under Indian conditions has shown that
leaves of Acacia tortilis contain about 14.6% protein, 36% cell wall
constituents, 10% hemi-cellulose, 25.9% acid detergent fibre and16.2
cellulose. These contents are at part with fodder from other tree species of
arid region. More over water content of the fresh leaves of Acacia
tortilis is about 60% which is helpful in partially meeting the water
requirement of animals in this water deficit region of Thar desert. Some
chemical ingredients interfere the digestion of fodder when fed to animals.
They are present in lower proportion (within permissible limits), such as
tannin 6.4% lignin 9.7% and cutin 0.4%.
Environmental
Conservation/Amelioration
Sand movement is the spectacular feature of
arid region which besides causing environmental hazards, pose serious
problem such as siltation of canals and wells, engulfing the agricultural
fields damaging crops, blocking railway and road transport, etc. Sand dune
stabilization is the most important way of controlling wind eroded sand.
Acacia tortilis has been found to be the most suitable and excellent
species for planting on unstabilized sand dunes. Along roads and railways
tracks and agricultural farms, it forms very effective shelterbelts. When
raised with Albizia lebbeck as central row, Acacia tortilis
reduced the wind velocity by 50 per cent upto the distance of twice the
height of reduced the wind velocity by 50 per cent upto the distance of
twice the height of shelterbelt, influencing the soil erosion and nutrient
loss which were reduced to half. With the heavy biotic pressure, tree cover
of Oran lands (‘Dev Vans’), Gochars (grazing lands) and catchment areas have
vanished, adversely affecting the microclimate of the surrounding habitats
and influencing the water collection in the reservoirs which are the main
source of drinking water for near by villages. The afforestation activities
to regenerate such degraded common property land resources by Governmental
and non-governmental agencies, include Acacia tortilis as an
important plantation species. It’s plantation on hill slopes and ravines
prevents soil erosion from these sites and checks the siltation of water
reservoirs.
Other Uses
The thicker branches of Acacia tortilis
are used as poles for erecting fencing. It’s wood is used as small timber in
house construction and making agricultural implements. Roots of Acacia
tortilis are made into spear shaft in Senegal, stems into fish spears at
Lake chad and flexible roots are used for nomadic huts by the Fulani. The
bark is used as vermifuge and as a dusting powder for skin diseases in
Guinea.
Acacia tortilis has been
found to provide a source of surplus honey in Botsvana, Oman and Yemen. The
honey yield is estimated at 2-3 kg per colony per season. Acacia tortilis
is useful in treating several ailments in African countries. In Egypt,
Libya, Tunisia, Algeria and Morocco, gum of Acacia tortilis is used
to treat ocular infections, jaundice and pulmonary diseases. The dried
powdered bark is used as a disinfectant in healing wounds, and the seeds are
taken asan antidiarrhoeic. In Somalia, the stem bark is used in treatment
against asthma. In Oman, young shoots of Acacia tortilis are used for
treating mastitis. In Senegal, the bark which contains a high concentration
of tannin is used as an anthelmintic. Its powder is used for treating skin
disorders. Spear shafts are made from roots.
Acacia tortilis
is a plantation species in arid and semi arid regions of India. There are no
natural stands of Acacia tortilis in India. In western Rajasthan,
there are older plantations of 25 to 30 years. Natural regeneration has not
been significant in these plantations. Various reasons for lack of natural
regeneration in Acacia tortilis are as follows:
Its seed coat is very hard and under the arid land
conditions, where top soil dries rapidly, seeds fail to
germinate owing to lack of sufficient moisture.
In older plantations where canopy closure has taken place,
like one in Jati Bhandu (Jodhpur forest
division), fallen seed fail to germinate due to inadequate solar
radiations and unfavourable temperature
conditions. Lower proportion of established seedlings was
observed under canopies compared with open areas.
Studies conducted in controlled environmental
condition by varying the photon flux density
(PFD), showed that biomass of seedlings declined with
decreasing PFD.
The plantations in arid region are largely accessible to
grazing by animals. Whatever little number of seeds
germinate, the young seedlings are browsed by
animals which have large population in Indian arid zone.
The seeds which are left in excreta of animals,
grazing in Acacia tortilis plantations and eating their pods,
give rise to good germination. But such tender
seedlings are either trampled or browsed by animals or they
wilt in dry hot environment of arid regions. On
sand dunes such seedlings are buried by moving sand. The
influence of browsing in natural stands of
Acacia tortilis in Tanzania was found
alarming. When browsed by
giraffe, it took 36 years to reach 5.75 m height
whereas, in absence of browsing this height was attained
in 13 years.
Acacia tortilis has been found to be a good coppicer.
Coppice shoots of 2 year old trees were reported to
have mean height of 384 cm. To attain this mean
height of 2 year old coppice shoots, seedlings initially
transplanted took 4 years. Each stump produced on
an average 3 to 4 coppice shoots and 100 per cent
shoot emergence was recorded from the felled
trees of 12 year old plantation. In a coppicing trial the multi
stemmed Acacia tortilis didn’t produce
adventitious shoots if left uncut, but cutting some or all of the
stems resulted in sprouting from the cut stumps
.Shots vigour and numbers per stump were not influenced
by stem diameter or height, but both increased
with the number of stems cut. All aspects of shoot
development were adversely affected if the trees
were in poor health, and the number of trees producing
shoots showed a marked decline on poor sites.
Indeed, plantations of Acacia tortilis in India are largely on
poor sites which may be the cause of its not so
good coppicing in field conditions. The time of cutting
also affects the coppice growth. Studies in Sudan
indicated that Acacia tortilis of less than 25 cm
diameter coppiced if cut before the rain.
Site selection for
raising nursery plays an important role in raising the seedlings. The
location of nursery should be near the area where plantation is proposed to
be undertaken. It will reduce the damage of seedlings and avoid dislocation
during transportation over long distances and also cut down the expense of
transport. The site should be near the metal road to facilitate easy
transport of seedlings. Good quality water should be available in plenty for
irrigation. Supply of labour should be adequate in the area. The site should
be free from insect and disease hazards and from harmful fungi and
nematodes. The nursery site should be level and should not be prone to
flooding during monsoon. It should be protected against the wind by raising
shelter trees and an exposure which is excessively hot in afternoon should
be avoided.
Seed Collection and
Storage
Seed should be collected from a tree which is matured,
healthy and has good growth. Seeds should be collected from the right kind
of provenance of selected seed production area. Under Indian arid
conditions, flower buds appear in the first week of May and fruit setting
commences from mid July in Acacia tortilis. Fruits ripen from mid
November to end of February. Seeds should be collected at right maturity
time. Maturity of seeds is usually indicated by the cracking of dark
coloured pods containing seeds that are hard coated and dark in colour.
Collection of green Acacia seeds has been advocated as a means of arresting
severe bruchid attack and avoiding the need for presowing treatment. Two
simple field tests used in combination can be employed to judge the degree
of maturity of ‘green’ crops:
take a sample of pods and
leave them to dry in the sun for a day or so. If seed remains swollen in the
pod
and is turning dark in colour, it is
usually sufficiently mature to collect. If, on the other hand, the seed
loses moisture and contracts it would be
unwise to collect it.
Make transverse cuts
through several seeds. The embryo should be firm and swollen whilst the seed
coat
should not collapse when cut.
These
seeds need to be stored safely with proper measures like fumigation,
dusting, cold storage, etc. until it is required for sowing. Acacia
tortilis seeds retain their viability for many years and present few
storage problems by virtue of their hard seed coat which restricts moisture
exchange and loss of stored reserves through respiration. Generally it is
advised to store them dry, in moisture-proof airtight containers. Glass or
plastic bottles and tin containers are suitable. They should be as full as
possible to reduce the amount of included air. Treating with insecticidal
powder (Phostoxin used in Israel malathion, pyrethrin and benezene
hexachloride based insecticides) and fumigation (carbon disulphide) will
protect the seeds against insect pests. A new method known as preservation
by carbon dioxide exchange is being advocated by the Division of Forest
Research, CSIRO, which is cheap and easy. The seeds remain viable for a
period 7-8 years under protected conditions.
Sowing
Seeds of Acacia tortilis have hard seed coat which
is impervious to water which causes seed dormancy and the germination may
extend over months or years. To ensure a high germination percentage which
is rapid and uniform, pre-sowing treatment is necessary. The successful
treatments are of two major classes.
Wet
Use of boiling or hot water, acids, organic solvents and
alcohols.
Dry
Use of dry heat, microwave energy, impaction, percussion,
and manual or mechanical scarification.
Several studies on seed treatment indicate that maximum
germination in shortest time could be achieved by soaking the seeds in
concentrated sulphuric acid. The time of treatment varied from 20 to 60
minutes depending upon seed size and age.
Use of suitable potting mixture is essential for raising
healthy seedling stock. To raise nursery stock of Acacia tortilis in
arid region, practice in vogue is to mix sand, clay soil and farmyard manure
in 1:1:1 ratio. Mixing of only 20% tank silt + 6% FYM was found to nearly
double the height (from 21 cm in pure sand to 39 cm) of Acacia tortilis
seedlings. The potting mixture is filled in polythene bags of about 20-30 cm
length and 5-8 cm width. Perforations are made in the bottom of the bags to
facilitate better drainage.
Treated seeds are sown directly into polythene containers
at about 1 to 2 cm depth. Two seeds are usually sown in each container and
surplus germinant picked out to empty ones. Sowing is generally done in the
month of February. Seedlings from these sowing attain, on an average, 30 to
40 cm height by early July. Now they are ready for transplant.
Regular supply of good water is essential for good
germination and healthy growth of seedlings. Nutrient concentration has no
effect on germination and radicle length. In case of non-availability of
good water, the waters of EC 4 to 6 m mhos/cm and SAR upto 15 can be used
for Acacia tortilis. No fertilization is required for nursery plants
of Acacia tortilis. Watering should be given every day either by
sprinklers or garden canes. Weeds from nursery bags should be removed.
Acacia tortilis is mainly raised from seeds.
Vegetative propagation tried indicates that rooting ability of leafy 2-node
cutting of Acacia tortilis was good in the summer, though, there were
large clonal variations.
Acacia tortilis is suitable
for deep sandy soils of arid region. It was particularly found a suitable
species for
sand dunes and sandy plains. It is also being planted
on degraded sites such as shallow soils of low fertility,
low hills, ravines etc. It thrives well in extremely
arid climate of less than 200 mm rainfall and, extreme
temperatures of as high as 500C and as low
as 00C. Western Rajasthan has
virtually become its natural
habitat.
Plantations of Acacia tortilis are raised as block
plantations, road side or canal side plantations in rows and
as shelterbelts along farm boundaries. The plantations
are primarily raised from nursery grown seedlings.
Acacia tortilis could be raised by seed sowing
also. Site preparation for planting Acacia tortilis will vary
depending upon soil and topographic conditions. They
are discussed in following lines.
Sand
Dunes
To raise Acacia tortilis on
sand dunes, the site is to be prepared as follows. Protect the planting site
by
erecting suitable barbedwire fencing before planting.
Erect micro-wind breaks (about 2’ height) of locally
available shrubs or other plant material at 5 m spacing
across the prevailing wind direction in parallel strips
or in checker boards design at 5 m x 5 m spacing. The
material used for micro-wind breaks is usually the
shrubs of Aerva psuedotomentosa or Crotolaria
burhia. In the first year of planting seeds of Lasiurus
sindicus may be sown along the strips to obtain
live fencing. This is completed by the mid of June. With
the onset of monsoon, pits of size 60 cm x 60 cm x 60
cm are dug at 5 m x 5 m spacing and seedlings are
planted. The pit soil is refilled after mixing farmyard
manure.
Deep
Sandy Soils
Pits of size 50cm x 50cm x 50cm are dug before commencement
of rains. At the time of planting
weathered soil along with farm yard manure is refilled.
It is advisable to make saucer shaped depressions
around each tree immediately after planting for better
harvest of rain water. Saucers of 1.5 m diameter
have been found very effective in conserving rain water
and better tree growth in arid regions.
Shallow Sandy Loam Soils Overlying Hard Calcareous Pan
The hard pan on such sites
hinders root growth and consequently the tree establishment. Therefore,
deeper pits of size 90 cm deep and 60 cm diameter
are dug and refilled with a mixture of weathered soil
and farm yard manure in equal proportion.
Thereafter, saucers of 1.5 m diameter are prepared around each
tree.
Rocky and Semi Rocky Terrain with Scattered Soil Pockets
Wherever soil pockets or
accumulations of soil exist, pits of 45 cm x 45 cm are dug. Half the soil is
refilled
and remaining half is made into crescent shape
ridge of 15 cm high across the local slopes to harvest the
runoff. Wherever slope is more, slanted trench
ridge system of planting is very effective. For raising
Acacia tortilis on ravine lands trench and
pit method of soil working is suggested.
Acacia tortilis
plantations are raised as block plantations as well as row plantations in
the form of shelter belts along roads, canals, farms etc. In block
plantations espacement is 3m x 3m on sandy plains, 5m x 5m on sand dunes and
at 3m x 3m interval in shelterbelt plantations. In agroforestry and
silvipastoral system different spacings have been tried. It was plantedat 4m
x 4m spacing when intercropped with sorghum, pigeon pea and castor. In a
silvipastural system with Cenchrus ciliaris as the inter crop,
Acacia tortilis, at 5m x 10m spacing, produced the maximum biomass.
In arid regions, planting at a suitable depth (deeper
planting) helps faster establishment of trees. Higher survival of deep
planted seedlings of Acacia tortilis was reported. The seedlings
raised in 30 cm deep tubes survived better than those raised in 18 cm deep
tubes.
Acacia tortilis, though grows on poor sites and has
low maintenance requirement, responds to better management of moisture and
nutrients. Under rainfed conditions use of moisture harvesting and
conservation practices such as micro-catchment approach, mulching, weeding,
etc. are essential for better establishment and growth of trees. It was
reported that circular water catchments in combination with application of
pond sediment and farmyard manure caused significantly better growth of
trees. Run off collection by making inter row slopes of 20 per cent or
bigger saucers of 1.5 m diameter have been found to increase tree growth
dramatically in Indian arid region. Petroleum mulches have been found
beneficial in raising Acacia tortilis on sand dunes in Iran. Rainfall in arid
region is highly uncertain. Sometimes there are long dry spells resulting in
heavy mortality of seedlings in the year of establishment. Therefore,
supplemental waterings, are essential for the first two years. Three to four
waterings per year are beneficial. It requires repeated waterings in first
year of establishment. Acacia tortilis could be raised by irrigation
with saline water of EC 4 to 6 m mhos/cm and SAR upto 15. In very adverse
conditions like Lakhara Velara area of Kachchh in Gujarat (sea salinity
coupled with aridity), use of drip irrigation is done in the simple form
.Fertilizer application is not advised in Acacia tortilis plantations
in arid regions. Fertilizer application under moisture stress conditions has
detrimental effect on tree growth. However, when watering is ensured, trees
may respond to fertilizer applications. It was reported that P is the most
limiting nutrient in Savanna because of the strong translocation from the
leaves to the twigs before leaf abscission.
Use of biofertilizers has tremendous potential in Acacia
tortilis. The Acacia tortilis could be inoculated with fast
growing strains of rhizobia. Seedlings of Acacia tortilis were found
to develop rhizobial nodules 8 nodules/plant were observed when Acacia
tortilis seedlings were inoculated with native rhizobia. Use of VA
mycorrhizal fungus Glomus mosseae increased the seedling weight of
Acacia tortilis by 170%. Root weight was also increased, and the
indication was that mycorrhizae enhanced the drought tolerance.
Moisture plays a very crucial role in arid zone forestry.
Six to eight weeks after planting, weeds are usually
large enough to compete for water with the newly planted seedlings. It is
therefore advisable to start weeding
about 6 to 8 weeks after planting by using a hoe. In this operation weeds
are dug out by roots. If necessary it
is advised to go for second hoeing preferably before the weeds produce seeds
so as to eradicate weeds from
the area. Hoeing helps in preventing moisture loss through cracks formed
especially in heavy soils where
aeration is also improved. Weeding some times also helps avoiding the danger
of fire.
Thinning
Trees need space, both for their crows and roots. They
compete for root space soon after planted, first with
weeds, later with the trees planted near them. The roots of the remaining
trees spread further and can secure
a larger supply of water and mineral nutrients, if some of the near by trees
are removed. Density of the
planting and the rate of thinning depends on the quality of site, rainfall
and the extent and method of
cultivation.
Pruning
Acacia tortilis
is recommended to be lopped once a year for sustained production. The
guidelines include not
to lope tree of less than 2m or branches with a diameter greater than 7.5
cm, only lopping mature leaves, and
always leaving the top third of the tree unlopped. The influence of pruning
on the growth of Acacia tortilis was
studied in N. Transvaal (South Africa). Trees were tolerant of pruning and
increased in size when all current
season’s shoots were removed. Shoot production increased after winter
pruning and decreased after summer
pruning.
Numerous insect pests and diseases attack Acacia
tortilis right from seed collection to plantation stage. Some important
insects pests and their control measures are being described here.
Pests of Seeds
Four main groups of insects feed upon the seeds of
Acacia tortilis in arid and semi-arid zones. These are Coleoptera
(beetles), Hemiptera (plant Bugs) Lepidoptera (moth and butterflies) and
Hymenoptera (phytophagus wasps). The Coleoptera (beetles) is the most
important group of insects causing damage.
The larvae stage of Coleoptera, Lepidoptera and Hymenoptera
cause damage by boring into the seed from an egg laid on the pod or in the
pod tissue. Hemiptera (plant bugs) feed externally in the larvae and adult
stages by inserting sucking mouth parts into pod tissue.
The Bruchidae beetles exert tremendous influence on the
leguminous trees in tropics. Bruchidae are small insects. They are
oval-shaped but appear slightly truncated at both ends. Most species have
large compound eyes with a deep U-shaped cleft opening towards the front.
The antennae arise from this cleft. Most bruchids have flattened scale like
hairs covering the thorax and elytra.
Majority of bruchid species infesting the tree, lay eggs on
the surface of the developing pods. Egg development takes 5-10 days from ovi-position.
The larva’s first priority on emergence is to gain access to the seed.
Larvae first form a tunnel within the seed and then enlarge this to make a
cell. During the period of growth, which may take 3-4 weeks or as many
months, depending on prevailing climatic conditions, the larvae moult 4
times and then pupate. Before this happens preparation is made for the
emergence of the adults. The area of the cell nearest to the out-side is
cleared and enlarged and only a thin layer of testa is left which forms a
circular window of semi-translucent material. On emergence the adults bite
their way out leaving circular holes.
Control Measures
Preventive Measures The trees selected for seed
production can have individual branches covered with sleaves or pollination
bags made from woven glass fibre material to
exclude the pest species.
Chemical Control Insecticides like Endosulphan and
Tetrachlorvinphos are effective against bruchids.
Biological Control Some parasites and predators can
be successfully used to control the bruchids. Parasites attack on egg,
larvae and pupal stages.
Egg Parasitoids
Bruchid eggs, because of their position on the
out side of a pod, are easily located by parasitoids. Uscana
sumifumipennis has been reported be a group
of egg parasitoids associated with bruchids.
Predators
Bruchids fall to complete their life cycle in
presence of mites (Acarina) of the genus Pymotes. They feed
on egg, larvae pupae and adults of bruchids.
Pymotis boylei is most probably the species which attacks on
bruchids.
Pests of Trees
Julodis sp. is the important pest of adult
trees which causes severe defoliation.
Acacia tortilis is also susceptible to root
knot nematode species, Meloidogune javanica and M. incognita.
Eriophyids cause gall formation on the leaflets and
pinnules and in place of axillary buds. An out growth is
created due to hyperplasia.
Powder pest beetles (Sinoxylonanale
and Sinoxylon crassum) are the most important pests of timber
which reduce felled timber to dust in weeks.
These beetles can be effectively controlled by applying
1.5% linolane/endosulphan water emulsion on
timbers.
The insect pests of Acacia tortilis and their nature
of damage are given in the table below.
Arid region has menacing population of rodents causing
heavy damage to the plantations by debarking and slicing of stem and roots.
Trunks of Acacia tortilis have been observed to be completely sliced
by rodents. The important rodent species involved are Gerbillus gleadowi
and Meriones hurrianae. Losses to the tune of 4.5-10 per cent in a
period of two months have been reported in Acacia tortilis
plantations in Nagaur district. To control rodent attack on plantations
following measures should be undertaken. The active burrow should be checked
and prebaiting (one kg bajra grain and 30 g groundnut/sesame oil) is
suggested for two days. On the fifth day, 2 per cent zinc phosphide should
be added to the bait (1 kg pearlmillet + 20 g vegetable oil + 20 g zinc
phosphide) and rolled deep into the active burrows at the rate of 6 g per
burrow. After 8-10 days of operation, Bromadiolone (0.005 per cent) ready to
use loose bait or wax cakes should be rolled deep in the freshly opened
burrows for managing the residual population of rodents.
Diseases
A number of pathogens attack Acacia tortilis right
from seedling stage to established plantations and also during storage of
seeds. Diseases such as seed rot, wilt and collar rot attack seedlings of
Acacia tortilis. Tip dying of growing shoots is encountered both in
nursery and in young plantations. Old plantations of Acacia tortilis
were found to suffer from ganoderma root rot, heart rot (Fomes sp.) and die
back in Pushkar (Ajmer)
and in other localities. Various diseases of Acacia tortilis and
their control measures are discussed.
Seed Rot
Seed rot commonly occurs in storage when immature or cracked
seeds are stored in high moisture conditions. The genera belonging to fungi
imperfecti i.e. Aspergillus niger, A. flavus, Penicillium
sp. and Alternaria sp. attack the cracked areas of seed and cause rot
which spoils the seed in storage. Treatment with mercury based fungicides
i.e., Emisan -6 @ 0.1% or Captan @ 0.2% was found effective in checking the
fungal infection during storage. Keeping moisture free conditions and
isolation of damaged seeds, reduce the chances of infection.
Tip Dying
Tip dying incited by Botrydiplodia theobromae causes dying
of young shoots in nurseries and in young plantations of Acacia tortilis.
The pathogen in fact acts as a secondary invader after attack of tip borer.
Combination of fungicide and insecticide (Blitox @ 2% + Metasystox @ 0.05%)
applied as foliar spray controls the disease.
Fusarium Wilt
Yellowing and early defoliation of leaves are the characteristic symptoms of
fusarium wilt followed by death of seedlings. Water logging and high
moisture conditions favour the infection of wilt in nursery plants. Avoiding
water logging conditions and soil drenching with Bavistin @ 0.1% or Dithane
Z-78 @ 2% prevent the disease infection.
Collar Rot
Macrophomina phaseolina, the casual organism of collar rot infects young
seedlings of Acacia tortilis. Hot and dry climatic conditions favour
the occurrence of disease. Soil drenching with Bavistin (0.1%) or Dithane
M-45 (0.2%) controls the disease attack.
Ganoderma Root Rot
Ganoderma root rot which is caused by Ganoderma lucidum attacks old
plantations of Acacia tortilis. The disease occurs throughout
Rajasthan and Gujrat. The old infected stumps and roots act as source of
infection. Spread of disease takes place through root to root contact. Hot
and dry climate favours the spread of disease. The disease can be minimized
by avoiding pure plantations and raisisng resistant provenances.
Heart Rot
Heart rot is caused by Fomes sp. It is a wound parasite
which enters through the mechanically damaged branches or hole made by the
borers. Sporophores are perennial and dark to light brown in colour. The
disease can be minimized by avoiding untimely lopping and mechanical injury.
Die Back
Die back caused by Irpex flavus, attack on the broken
branches in Acacia tortilis plantations. Light yellow coloured,
sessile fruiting bodies of fungus are generally observed in the lower
surface of the branch. Disease can be managed by pruning of infected
portions and applying Chaubattia paste.
Bark Canker
Bark canker caused by Botryodiplodia theobromae, has been
reported on old plantations at Pushkar, Ajmer. Sun scorch causes splitting of bark and then the fungus
enters through these cracked portions and spoils sap wood. Sometimes attack
of borer and termites is also reported.
Leaf Rust
Leaf rust caused by Ravenelia acaciae is characterized by early
defoliation in nurseries and young plantations. The disease can be
controlled by spray of copper based fungicides at monthly intervals.
Acacia tortilis
has been found to be the fast growing species in arid conditions. However,
its growth varies depending on site conditions and management practices.
Three year old plantation of Acacia tortilis at Jodhpur attained mean
ht of 4.5m and collar diameter 12.3 cm at 3 year of age. However, on a
shallow sandy loam soil overlying a hard calcareous pan at Pali, they were
only 1.6 m tall and had 4.1 cm collar diameter. Growth studies at different
site conditions in Indian arid zone indicated that Acacia tortilis
registered a mean annual increment of 61, 56.1, 44, 57.5 and 55.5 cm on deep
sandy soils, shifting sand dunes, rocky and semi rocky refractory sites,
sandy loam shallow soils overlying hard calcareous pan beneath, respectively
(shown in the table). Mean annual height and D.B.H. increments of Acacia
tortilis were reported to be 78 cm and 1.1 cm, respectively, over 8
years at Jodhpur.
At 10 years of age Acacia tortilis attained a height of 641 cm and
D.B.H. 14.1 cm which increased to 785 cm and 20 cm, respectively at 14
years of age. Trees raised from transplanted seedlings exhibited better
growth than by sowing. Height of 5 year old trees under two situations was
312 cm and 182 cm, respectively. At a site having 350 mm rainfall in
Pakistan, Acacia tortilis attained a height of 3.1 m at 3 year of
age.
When raised as shelterbelt at Jodhpur,
Acacia tortilis attained a height more than six metres after seven
years of planting.
In Indira Gandhi Nahar Project area of Indian desert,
Acacia tortilis raised on sand dunes with limited irrigation at 3m x 3m
spacing attained a height of 3.60m and G.B.H. 10cm at 3 years of age. The
M.A.I. of 6 m3/ha was reported.
Performance of Acacia tortilis under different site
conditions in arid region (Western
Rajasthan).
Location
Mean Soil type
Age of Mean
Survival
Annual Rainfall
plantation growth
(percent)
(mm)
(years) (cm) (Ht.)
(DBH.)
Jodhpur 320
Deep sandy soil 9
599 13.2
100
Pali 440
Shallow sandy loam 9 547
10.8 98
overlying hard calcareous
pan
below 22 cm
Kailana 320 Rocky
site with scattered 6 304
7.5 100
(Jodhpur distt.)
soil pockets
Beriganga 320
Semi Rocky site with 5 320
8.0 100
(Jodhpur distt.)
accumulation of
transported soil
In an average plantation, on a 10 year rotation, the yield per tree was
estimated to be 80-100 kg fuel, 100 kg fodder, and 20-25 kg of thorny twigs
and branches for fencing. Fuel yield per hectare after 10 years is estimated
to be 30 tonnes or an average of 3 tonnes/ha/year. Higher yields upto 5
tonnes per hectare could be obtained by planting at closer spacings and in
good soils or with higher moisture.
Full grown tree of Acacia tortilis gives, on
average, 10-12 kg leaf and 4-6 kg pod yield in western Rajasthan. In
Harayana, about 15 to 20 kg of green fodder has been reported from Acacia
tortilis. Acacia tortilis yields small wood which is used for fence
posts and for small implements. The bole and branch wood production of 363.6
kg per tree (93.14 t/ha) under wider tree spacing has been reported.
Comparative studies on economics of planting different tree
species in western Rajasthan, indicate that on a 10 year felling cycle,
Acacia tortilis proved to be most economic with a net cost benefit ratio
of 29% per hectare, whereas the other species had negative cost benefit
ratio. A cost benefit ratio of 1:2 from 10 year rotation of Acacia
tortilis planted at 5m x 5m spacing at Jodhpur was reported.
Planting Acacia tortilis in a silvipastoral system
has been found more remunerative than its pure plantation. Estimates of
total revenue from fuel wood and fodder over the 7 year period showed that a
combination of trees (5 x 10 m spacing) with grass (Cenchrus ciliaris)
produced greater income than trees or grasses alone.
Establishment and growth of trees in arid region is very slow due to
hostile environmental conditions such as, low and uncertain
rainfall, extremes of temperature, high evapotranspiration, strong
winds, loose sandy soils which are prone to wind erosion and are
infertile having poor moisture holding capacity. The problem is
further compounded by very large population of animals and human
being which impede the growth of plantations by overbrowsing and
felling. Obviously, forestry in such regions could be promoted only
with species which not only thrive under these constraints, but are
fast growing. Acacia tortilis is an important tree of arid
region of many African and Asian countries, where its natural
plantations are in abundance. It was introduced in Indian desert in
1958 from Israel and has been found a very promising species. It is
particularly suitable for sand dune stabilization. The species,
locally known as ‘Israeli babul’ has made Indian desert its natural
home during last three decades.
