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Research being undertaken in the Atacama desert of Chile on the Tamarugo tree, Prosopis Tamarugo Phil*

A.G. Robertson


References


The Acatama, the driest desert in the world, occupies the central region of northern Chile and southern Peru. It receives no rainfall because the high Andes block any flow of moist air from the east, and the very cold Humboldt current that runs north along the Pacific Coast produces insufficient evaporation to permit rain clouds to be formed in on-shore breezes. The Atacama is devoid of vegetation, but rich in scenic beauty and mineral deposits.

One of the many phenomena of this truly remarkable wilderness is the artificial establishment of forests of the Tamarugo tree (Prosopia tamarugo, Phil), in conditions that might ordinarily be considered impossible. The Tamarugo is a native of northern Chile and grows naturally in watercourses at the foot of the Andes, these small streams being occasionally fed by melting snow and sporadic mountain rainfall. At less frequent intervals, the flow is sufficient to carry into some of the large salt lakes of the Atacama.

The Chilean Government, through its semi-private agricultural research organisation (SACOR) has established an experimental station (Fundo Refresco) in the middle of the large salt lake, Salar de Pintados, one of the four occurring in a large plain in the Atacama known as "la Pampa del Tamarugal". La Pampa del Tamarugal lies between latitudes 19°30'S and 22°15'S, at an altitude of 1100 metres, and it has an area of 1 250 000 hectares. Fundo Refresco, eighty km south-east of the city of Iquique, was established to increase artificially the sparse natural Tamarugo groves, to assess their potential for grazing by sheep, the ultimate aim being to supply the important northern industrial cities of Iquique and Arica with cheap meat. At present, meat is trucked over 2 000 km from southern-central Chile. Fundo Refresco has 15 000 ha of Tamarugo forest 7 000 ha being fenced off into 100 ha blocks. This fenced area now holds 12 000 head of stock, 10 000 of which are sheep, the rest being goats and cattle. There is one full-time agronomist employed in research, a manager, and about fifty workmen.

The climate of la Pampa del Tamarugal corresponds to a temperate desert, mean daily temperatures being moderate, even though there are occasions when the daily temperature variation is up to 40°C. From May to September there are strong and frequent periods of cold weather, especially at night, while the intense heat of summer is mediated by cool afternoon Pacific Ocean breezes. It never rains, and although relative humidity is generally low, there are always some nights throughout the year, particularly in summer, when it is between 80-100%.

The soils of Fundo Refresco, located on the dry Salar de Pintados, have a cap of salt varying from 0.3 - 1 m thick. This hard, rough cap is composed principally of chlorides and sulphates of sodium. The soil beneath is a combination of the two types to be found in la Pampa del Tamarugal; the deep, coarse, excessively drained, sedimentary soils of the Big Piedmont fans that originate in the foothills of the Andes and the fine clays and limes with saline stratas and capping that originate from the coast. The result is an alkaline soil of good moisture-retaining capacity, and a ground water table of from two to fourteen metres.

The vegetation of the la Pampa del Tamarugal is very restricted, the principal species being Prosopis tamarugo. There also exists the closely related Prosopis chilensis (also known as Algarogo chilensis). Two native maltbushes are associated with the Prosopis spp., Atriplex atacamensis Phil. and A. desertorum, (neither of which are grazed by stock), Tessaria absinthoides, a Distichlis sp. and two Baccharis spp.

Prosopis Tamarugo, a legume, reaches its maximum height of ten metres at thirty years of age. It commonly has three main trunks and three very deep tap roots. Depending on the density of planting, the foliage diameter is up to twelve metres. Leaves are tiny, pinnate and clustered between the hard, sharp four-centimetre spines that grow regularly along the thinner branches. These thinner branches frequently sucker from the lower trunk area and also hang down to ground level from all over the spreading main branches making the zone under the foliage almost impenetrable in the unpruned tree. The Tamarugo has a longevity of about 400 years.

Prosopis chilensis is a slightly smaller tree of similar appearance, save that it is much clearer of low and hanging thin branches, and they have fewer and smaller spines. Although the Tamarugo draws most of its moisture requirements from deep ground water supplies (which vary from 1 000 - 3 500 p.m. salts in la Pampa del Tamarugal) it also has the incredible capacity of absorbing significant quantities of moisture from the air, through the leaves, which is translocated to upper soil levels for later use. This "reverse transpiration" only takes place during those nights of the year when the desert air has a relative humidity of greater than eighty per cent. The phenomenon occurs most often in summer.

The production of fruit and leaves from the Tamarugo is considerable. The first fruiting generally occurs when the tree attains ten years of age. Flowering takes place twice a year in June/July and September/October, although only the later flowering produces fruits which are matured and shed in December/February. Production of fallen fruits and leaves is directly proportional to the age of the tree and to the density of planting, the latter factor largely determining the diameter of foliage projection. Total annual production stabilizes after the tree attains thirty years of age and does not appear to be affected by ground-water salinity.

Table 1 shows the average annual production of fallen fruits and leaves taken from 204 P. tamarugo trees growing in a variety of forest densities.

Table 1. Annual Tamarugo production.

Age (years)

Average annual production (kg/tree)

Average annual production (kg/m2 foliage projection)

10

  25

0.75

15

  57

1.00

20

  96

1.20

25

138

1.30

30

170

1.40

35

190

1.40

Typically, fruit and leaves each make up about 50% of the total dropped annually by the Tamarugo.

Table 2 is an analysis of the nutritional value of the mature fallen fruit, seeds and leaves of P. tamarugo.

Table 2. Nutritional value of Tamarugo fruits, seeds, leaves.

Nutrient Measure

Fruit (seed in pod)

Seeds

Leaves

Dry matter

91

93

88

Crude protein

11

  9.0

  9.0

Digestible protein

  6.0

  1.3

Fat extract

  1.5

  8.7

  1.8

Calcium

10

  0.3

  5.5

Phosphorus

  0.1

  1.4

  0.1

Total digestible

     

Nutrients

60

23

Research at Fundo Refresco into optimum plantation densities of P. tamarugo is at pesent inconclusive, except to narrow the range to between 204 trees/ha. (7 × 7m) and 68 trees/ha. (12 × 12 m). Preliminary work on foreign production tends to favour dense plantations; however, little is known of the management required for dense Tamarugo forest, and economic analyses and grazing studies have not been completed. Recent plantations established in la Pampa del Tamarugal are at a density of 100 trees/ha. (10 × 10 m).

Table 3 shows the average expected foliage projection, and annual production from P. Tamarugo at different ages and densities of plantation. It also gives the estimated maximum potential carrying capacity of the different types of P. Tamarugo forest assuming an annual consumption of 800 kg dry fallen forage per adult dry sheep.

Table 3. Annual Tamarugo production

Age (yrs)

Plantation spacing (metres)

Density (trees/ha)

Foliage projection (m2/ha)

Annual forage production (kg/ha)

Maximum carrying capacity (sheep/ha/ year)

10

13 × 13

  60

2 200

  1 800

  2.2

20

13 × 13

  60

5 200

  6 200

  7.8

30

13 × 13

  60

7 100

  9 900

12

40

13 × 13

  60

7 800

10 900

14

10

10 × 10

100

2 800

  2 200

  2.8

20

10 × 10

100

6 900

  8 300

10

30

10 × 10

100

8 100

11 300

14

10

   7 × 7

204

5 500

  5 000

  6.2

20

   7 × 7

204

8 500

11 000

14

30

   7 × 7

204

8 700

13 000

16

The values used for annual forage production come from measurements made with small samples, and these estimates of foliage projection assume a circular projection to the ground, these being calculated from measurements of average foliage diameter. Experiments at Fundo Refresco with caged adult sheep fed a ration of 60% fruits and 40% demonstrated a daily intake of 2 - 2.5 kg dry forage, or some 800 kg per year. There are no field experiments to confirm that sheep do consume a diet of such proportions and their ration did not take account of the grazing taken by sheep from fresh Tamarugo leaves. However, it must be noted that field observations verify that almost all the sheep's diet is taken from fallen fruits and leaves.

It is not completely naive to estimate the potential carrying capacity of Tamarugo forest by assuming that all the fallen forage can be retrieved by sheep, as the hard salt cap makes this possible if not entirely probable. Trampling does not affect the tough fruits.

Little is known of the quantitative effects of forage loss and spoilage by insect attack, leaf trampling, and excreta contamination of forage. These factors and errors inherent in the assumptions used above must be significant, for preliminary investigations suggest carrying capacities approximately half those estimated in summer. The fruit of P. Tamarugo are fat, exceptionally tough, crescent-shaped pods of about 5 cm long, while those of P. chilensis are wide, flattened straight pods of up to 15 cm. The small brown seeds have their coats broken by brief immersion in sulphuric acid followed by cultivation in plastic tubes of moist soil. At three months of age, when the young trees are some twenty to thirty cm tall, they are planted in the bottom of holes, which are themselves sixty to eighty cm deep and eighty cm in diameter. These large holes are necessary on the Salar de Pintados to remove enough of the thick salt cap to expose the soil underneath. The young Tamarugos are planted in their plastic tubes to encourage the growth of tap roots. The six litres of water applied to the trees at planting has been found to be sufficient to sustain them during establishment, but not enough to develop the young roots, the latter being a significant problem in Tamarugo establishment.

Present grazing investigations involve sheep, goats and cattle of which the former are, to date, the most successful. The four breeds of sheep at Fundo Refresco are Karakul, Suffolk Down, Merino Precoz and Australian Merino.

The Karakul originating from Eurasia, is a fine, strong, meat-producing sheep with coarse, short, black wool. Its outstanding physical characteristic is an enormous thick flattened tail which is used for fat storage. The meat of the Karakul is reputed to have highly acceptable flavour and contains little fat. The wool is of no value but the skin of the lamb has excellent commercial prospects for fabrication into winter fashion garments. In 1977, twenty pedigree Karakul rams were imported from Australia. The Merino Precoz is the result of the cross between French Merino and German Merino, two popular dual-purpose breeds from central Chile where they are used primarily for meat production.

The Australian Merinos at Fundo Refresco were producing the poorest weight gains of any of the breeds. However, the specimens being used were of extremely poor quality, being very thin and tiny, and results obtained from the present animals should be not taken as a guide to the potential of the breed. However it must be said that the Australian Merino probably does not fulfill the primary objective of SACOR at Fundo Refresco, that being firstly cheap meat production, wool being of minor consideration. The most successful animal, in terms of growth rate, has been the Karakul Merino Precoz. Growth rates are good, but unfortunately cannot be presented here. The pure Karakul and Merino Precoz also produce well. Suffolk Down performance has been satisfactory.

There are some 400 Angora goats at Fundo Refresco and preliminary results are promising if goat meat production is the aim, for no investigation is being undertaken of mohair yields.

The cattle sighted at Fundo Refresco were Herefords with some Santo Gertrudis Hereford calves. The Hereford calves showed very poor growth while the few results from cattle grazing are preliminary and inconclusive.

All indications at present point to sheep being the most productive animal to graze Tamarugo forest. The management of Tamarugo forest is not easy and certainly not completely understood, particularly as regards dense planting.

The principal problem of Tamarugo management is the clearing of low and hanging branches to allow sheep free access to graze fallen fruits and leaves. The pruning is a painful and tedious task. A Chilean labourer usually completely prunes forty trees per day, although there are trials in progress to test the effectiveness of clearing only sufficient branches to permit a sheep entry under the canopy. (The one big advantage P. chilensis has over P. Tamarugo is that its trunk and main foliage are much cleaner of low thin branches and it has fewer, smaller spines. However, it is said to be a more irregular producer of forage). At Fundo Refresco the pruned branches are piled together to make very effective internal fencing.

The second problem is the annual predation on mature seeds by the larvae of an indigenous butterfly. At the end of autumn it is apparently rare to find a Tamarugo seed pod that has an intact seed complement. This annual predation must considerably deplete the nutrition available to the sheep.

Other problems include the necessity to establish colonies of beehives in the forest to ensure the maximum fruiting as natural pollination levels are low. Rats, which live in burrows in the salt cap, also cause damage, eating the bark of the young trees. Problems of sheep management relate principally to the penetration of the long Tamarugo spines into the feet and eyes of stock. Constant vigilance of the flock is needed, as lameness is a regular problem. The rough salt cap of Salar de Pintados has many deep narrow holes in which sheep occasionally catch and break their feet and the feet of the sheep need constant clipping. The salt cap is poisondis to stock and blocks of pure salt are laid out for sheep. The salt blocks are consumed avidly. Vitamin A is deficient in a Tamarugo diet and each sheep is given 1.5 million units in two or three injections per year. One further problem of management is that effective grazing cannot be commenced in the year of first fruiting. Tamarugo forest establishment in Chile costs about 1 000 Chilean pesos ($ Aust. 29) per hectare. This cost includes planting, stock water supplies, fencing and other incidentals. About 70% of this total cost is consumed by manual labour, and the basic pay of a farm labourer at Fundo Refresco is approximately $ Aust. 16 per week with board and keep.

The introduction of the Tamarugo tree to the arid zone of Australia appears to have good prospects in those areas that can fulfil the specialized environmental needs and that can be justified economically, because it has a high carrying capacity, very few maintenance requirements and is long lived.

The prospect of whole farms becoming Tamarugo grazing enterprises seems unlikely and one sees the greatest value of the tree arising from strategic plantations being used as drought reserves, as sources of summer nutrition or in raising the productivity of salt-affected lands and salt lakes. It must be noted however that there can be considerable difficulty in switching inexperienced sheep from the grazing of pasture to the foraging of dry fruits and leaves on the ground.

Further information regarding the research of Fundo Refresco can be obtained from either: Ing. Pedro Joustra, Sociedad Agricola CORFO Ltd, Matias Cousina 64, 3°, Santiago, Chile, or Ing. Manuel Montt, Fundo HRefresco, Casilla 2245, Equipe, Chile.

References

Elgueta S., Hernan y Calderson S. Sergio (1971). `Estudio del Tamarugo como productor de alimiento por ganado lanar en la Pampa de Tamarugal'. Santiago, Institute Forestal, Informe Technico no. 38, pp. 36.

Sudzuke H. Fusa (1969). `Absorcion foliar de humedad atmosferica en Tamarugo, Prosopis tamarugo Phil'. Maipu, Universidad de Chile, Boletin Tecnico no. 30 pp. 23.

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