Prosopis sp. include medium-sized shrubs and trees of wide diameter, some as high as 20 metres, with trunks of more than one metre in diameter. Most species have thorny branches. The leaves, as in many legume trees, are compound, being made up of numerous, feathery-looking, small leaves. The flowers are small and usually found bunched in spherical or elongated heads.
Though Prosopis sp. also grow near water, some are found in areas so dry that few other plants can survive there. Prosopis can survive and even thrive in soils of high salinity and low fertility. The species usually need a yearly rainfall minimum of 250 mm, but some can adapt to areas where the mean annual rainfall is as low as 75 mm or less. They can easily withstand long periods of drought while still producing abundant pods.
The pods of Prosopis are among the oldest foods used by prehistoric man in the Western Hemisphere, constituting, up to the present time, a source of proteins and carbohydrates for many North and South American desert dwellers. The pods grow on small stems forming racemes or bunches of up to twelve pods. These are usually 3 – 20 cm long, twisted into spiral form, and containing a number of yellow seeds embedded in a sweet or dry pulp.
When ripe, the pods fall to the ground. Unlike other legume seeds, they do not open as they dry, so that neither the pulp nor the seed is lost. Livestock can be maintained on pods from Prosopis forests in Hawaii, Peru, Chile and Argentina. The pods can also be gathered and stored for later use. The food value is comparable to that of barley or maize.1
Mimosaceae: Trees or shrubs, very rarely herbs; leaves usually bipinnate, rarely single-pinnate; flowers hermaphrodite, small, spicate, racemose or capitate, actinomorphic, 3–6 usually 5-merous; calix tubular, valvate, 5-lobed or toothed; petals valvate, connate into a short tube, mostly hypogynous; stamens equal in number to the sepals or more numerous or indefinite, free or monodelphous; anthers small, 2-locular, opening lengthwise, often with deciduous gland at the apex; ovary superior; fruit a legume; seeds with scanty or no endosperm.
Most common species (in Chile):
Acacia caven (Mol.) Hook. & Arn: espino, espino maulino, churque, churco, quiringa (fruit) (Figure CXXXVII);
Prosopis chilensis (Mol.) Stuntz: algarrobo, algarrobo dulce, algarrobo de caballo (Figure CXXXV);
Prosopis fruticosa Mayen: algarroba;
Prosopis tamarugo Phil.: tamarugo;
Prosopis strombulifera (L) Benth: fortuna, espinillo, retortón;
Calliandra chilensis Benth: espino rojo;
Prosopis alpataco Phil.: alpataco (Figure CXXXVI).
| 1 | Stamens numerous, that is, more than 10 per flower. | |||
| 2 | Staminate filaments free from each other, sometimes slightly adherent, forming various small groups | Acacia | ||
| 2 | Inferior staminal filaments fused in a more or less long tube (stamens monodelphous) | |||
| 3 | Elastically dehiscent valves which separate from the apex downward, bending without twisting; pod gradually narrowing toward the base, with thick edges | Calliandra | ||
| 3 | Valves not elastically dehiscent, remaining straight; valves abruptly narrowing toward the base, with finer sutures | Albizzia | ||
| 1 | Stamens 10, that is twice as many as the petals; filaments free from each other; leaves bipinnate | Prosopis | ||
| Fruit | ||||
| Corola actinomorphic, small, the stamens considerably longer than the corola; flowers in dense spikes. | ||||
| Stipules spine-shaped, straight, divergent, often large, fused at the base and slightly decurrent, located outward from the buds or foliar facicles of the axils; axilary spines lacking; leaves bipinnate | Prosopis tamarugo | |||
There are 44 known species of Prosopis. Three are aggressive weeds invading sub-tropical grasslands, and six, featured in this chapter, can produce fodder and usable wood in areas where other trees fail for want of rain or poor soils. Several other species of potential value are presently used in their natural state in very local instances.
Prosopis sp. are usually found on poor soils but they also thrive in fine sand or rocky soils. Some species have a high salt tolerance and also contain nitrogen-fixing nodules in their roots which maintain plant growth in nitrogen-poor soils.
The plants grow easily from seed and regenerate from root suckers or runners, so the survival rate is surprisingly high. The plant has a considerable network of secondary roots, as well as tap roots which, to seek out groundwater, often penetrate to depths of 10 m and sometimes 20 m.
In addition to being attractive to livestock, Prosopis sp. also attract bees. The nectar of Prosopis flowers produces a fine-flavoured honey.
Prosopis wood is generally fibrous and irregular (excepting that produced on plantations). The colour ranges from chalk-yellow to fire-red. The wood polishes very nicely, and has been compared to walnut, rosewood and mahogany. It can be used for fine parquet floors, furniture and cabinet-making. It has a long life in contact with the ground, and is therefore much used for fence posts. The first pavement blocks used in the streets of San Antonio, Texas, were made from Prosopis wood. And the principal avenues of Buenos Aires in Argentina are paved with Prosopis blocks over sand and lightly tarred, producing a surface that is smooth, durable and noise-abosrbing. But its major use is as fuelwood. It was formerly used to fire locomotives and industrial boilers and to power mining operations. It is still used today in rural areas for cooking and heating. It has a high calorific value, producing high-quality charcoal and little ash.
Some Prosopis species are excellent for checking erosion, for fixing the shape of coastal dunes, for windbreaks and for reforesting uncultivated lands, as in India, for instance, where erosion is causing the Rajputana (Thar) Desert to encroach in the direction of New Delhi.
The most important Prosopis weeds are Prosopis glandulosa Torrey, a native of northern Mexico and the American southwest; Prosopis ruscifolia, a native of the Gran Chaco from eastern Bolivia and Paraguay to the north-central part of Argentina; and Prosopis juliflora, a native of Central America and the West Indies.
In Argentina 3, Prosopis grows naturally over most of the country. It thrives in areas with a mean annual temperature above 12°C. Where rainfall is concerned, the species covers vast areas between isohyets 300–500 mm. These are plants of the plains, mesas and foothills, where semi-arid climates prevail. The carobs, Prosopis alba and Prosopis nigra, usually prefer clay soils and groundwater within reach of their deep roots.
Shrub species such as Prosopis ferox, P. alpataco, 4 P. argentina and P. denudans are dominant in very dry conditions. P. argentina and P. alpataco are true, semi-desert psamophytes, usually growing in very sandy soils. Prosopis ruscifolia grows in brackish soils. Prosopis sp. are not tall plants. The tallest is probably P. ferox in the Humahuaca Valley. In the relatively rainy northeast, they grow in high, dry fields.
The sugary fruits favour propagation by animals and insects. Indeed, most Prosopis species are propagated by animals which eat their fruit. Prosopis species growing on steppes or plains, unlike the forest or wet jungle species, need no protection at the juvenile stage. As soon as they germinate, they flourish at ground level in competition with shrubs and grasses.
From the standpoint of floral biology, they are classified as protogine entomophytes. Though the flowers are not showy, they do bear nectar and attract a great many bees and other hymenopters.
Most Prosopis are gregarious species, tending to form pure associations or else be the dominant species in the xerophytic forest.
The genus has various uses, as have been described. In Argentina, its uses can be classified as follows:
Wood, fuelwood, charcoal. The most important species in this connection are Prosopis chilensis, P. alba, P. nigra, P. flexuosa, P. caldenia, P. algarobilla, P. ruscifolia, P. kuntzei and P. torquata. The wood is used to manufacture furniture, frames, railroad ties, carts, posts, barrels, vats, paving blocks, floors, pulleys, moulds, etc. The very hard wood of P. kuntzei, as well as providing good firewood, is used for making bows and cabinets. P. algarrobilla fence posts are long lasting and have been used since early times. In addition, this species provides excellent fuelwood.
The “caldén” can also be used for parquet floors, in which case the wood must be cut when green, and dried.
Mimosaceae. Prosopis alpataco. a) branch with flowers (x 2/3); b) single flower (x); c) antler (x); d) pistil (x). Pisano, E. & Bravo R., No. 852. Original F. Sudzuki.
Fodder. For livestock, the greatest nutritional value is found in the fruit -- the foliage is less utilized and only when very green.
The indehiscent, internally articulated fruit is a transformed pod, with a mesocarp of varying fibrosity and pulpiness. The composition of the fruit varies according to species and variety.
Food. Carob fruit is also used in the human diet, though this habit persists only in rural areas. Today, as yesterday, the indigenous peoples of these areas, particularly the Chaco and Formosa, find the carob a valuable resource to use in a number of ways:
Patay. This is a very sweet, floury paste obtained by grinding the dried, ripe pods in a mortar and packing the milled product in special jars. When oven-dried, the paste keeps well and can be stored.
Honey. The concentrated infusion made from the fruit makes a rather pleasant-tasting honey.
Anapa. A sweet, refreshing drink prepared by simply grinding the pods in a mortar and adding water.
Aloja. An alcoholic drink obtained by fermenting the must from P. alba and P. chilensis.
Coffee. The fruit of Prosopis nigra and other species is used as a coffee substitute, much as Ceratonia siliqua is used in Europe.
Alcohol. Ethyl alcohol is prepared by fermenting and distilling the sugared extract from the pods.
Tannins and chinchona. The bark, sawdust and fruit of various species are used locally for tanning purposes.
Gum. This is of very minor use. P. nigra exudes gum which is used as a substitute for arabica gum in food, pharmaceuticals and industry.
Medicinal substances. Various species of Prosopis are used in folk medicine for eye afflictions. Some herbal shops in Buenos Aires sell P. strombulifera fruit, which is said to soothe toothache. Leaves and shoots of P. ruscifolia are used to treat eye inflammations.
Dyeing. Cotton is dyed a deep chestnut brown with carob root. The active principle is carobic acid which, when oxidized, gives perfect hues of black, dark grey, chestnut and other tints to wool, cotton and silk.
In the foreground, two algarrobos (Prosopis chilensis Mol.) growing spontaneously near Canchones, Pampa del Tamarugo. Tamarugos in the background.
To sum up at the close of this chapter, the following six Prosopis species deserve special attention:
Prosopis affinis Sprengel. This is a thorny, subtropical tree with a flat crown which grows to heights of two to eight metres. It branches irregularly, and has a short trunk with diameters of up to 60 cms. It grows naturally in great numbers on the Paraguayan savannah, in eastern Argentina, Western Uruguay and southeastern portion of the Rio Grande do Sul of Brazil. When cut at eight- to ten-year cycles, it can produce valuable yields not only of food, but also of wood for posts.
Prosopis alba Grisebach. This round-crowned tree grows 5 to 15 metres high, with a straight trunk as much as one metre in diameter. It is very important in the subtropical plains of Argentina, Uruguay and Paraguay, southern Bolivia, and northern Chile and Peru, where it grows naturally in semi-arid zones of 250–500 mm mean annual rainfall. It is cultivated to a certain extent. It is useful for windbreaks and to plant alongside roads, just as it is useful for fodder, lumber, and reforesting dry and saline soils.
Prosopis Chilensis (Molina) Stuntz corr. Burkart 5. This round-crowned tree is native to Peru, Bolivia, central and northern Chile, and northeastern Argentina. It is found at elevations of up to 2 900 metres, and is of importance as a producer of wood, fuelwood, fodder and food.
Prosopis nigra (Grisebach) Hieronymus. A round-crowned tree growing to heights of four to ten metres. It produces wood (lumber) for the Gran Chaco Desert and grows naturally in southern Bolivia, Argentina, Paraguay and western Uruguay. It is widely used to manufacture furniture and barrels, for fuelwood, fodder and in the human diet.
Prosopis pallida (Humoldt and Bonpland ex Willdenow) H.B.K. This tree grows to heights of 8 to 20 metres but is shrubby in poor soils. It is native to the driest areas of Peru, Colombia and Ecuador, especially along the coast. It is also a naturalized citizen of Hawaii and Puerto Rico. It is of great value in arid environments as a producer of lumber, fuelwood and fodder.
Prosopis tamarugo F. Philippi, which species is discussed in greater detail below.
Mimosaceae. Prosopis chilensis. a) branch with flowers (x ⅔); b) single flower (x); c) antler and parts of filament (x); d) pistil (x). Pisano, E., No. 703. Original F. Sudzuki.
Great Northern Chile is composed of the First Region with 58 072 km2 and the Second Region with 125 306 km2. Its typical features are desert landscape, broad range in day-to-night temperature, abundant mineral resources and scant agricultural land.
There are three structural ecological units: the Andean cordillera, the coastal range, and the depression lying between the two mountain ranges. Their origin lies in the various tectonic movements and shifting of the Upper Tertiary. The Quaternary period gave rise to intense volcanic activity with three characteristic upheavels culminating in the sharp rise of the western Andes above the Chilean and Bolivian plains. This severe-featured, arid landscape is crossed by rare surface flaws. North of Pisagua (19oS), a few rivers manage to bear their waters to the sea. Though the land is arid today, the entire region is cut by deep, dry, alluvial gorges. The face of the landscape has been molded throughout by the past action of water. The sector bears a network of dead watercourses, mute witnesses to the wet climate and heavier rainfall prevalent at the outset of the Quaternery period.
Agricultural activitities throughout this vast zone are minimal and scattered, dependent for their existence on the availability of water and its quality. For this reason, farm crops are confined mainly to the neighbourhood of a few brooks and oases.
The natural grasslands of the altiplano, located at an average altitude of 4 200 m, constitute another resource. The resources of the altoplano are virtually unused and consist mostly in the extensive raising of sheep and Camelidae americana (CORFO, 1970).
The Tamarugal Pampa 6, which owes its name to Prosopis tamarugo, is a plain stretching from 90° 33' to 21° 50' south. The plain slopes at a rate of 1% to 2% from east to west, and varies in elevation from 300 to 1 200 metres (Billinghurst, 1893). O'Brien's map, mentioned by Bermúdez (1975), is an important historical document. It measures 0.96 × 1.29 m and is dated 14 August 1765, City of Tarapacá. The map covers an area ranging roughly from 19° 35' southward towards the city of Matilla, at 20° 32' S. To give a quick, purely visual impression of the map, it sketches a setting, and not without artistic merit, wherein the profiles of the coastal and Andean mountain ranges clearly emerge, and between them, running north to south, the depression of the central desert area is plainly seen.
LOCATION OF THE TAMARUGAL PAMPA
Destruction of the natural tamarugo forest.
Area near Canchones: axe felling of a tamarugo over 40 years old.
In local dialect, the Tamarugal Pampa is known as the “Tangled Forest” (Tarapacá), though today this somewhat poetic designation has ironic overtones. The characteristic face of this land is desert and salt. The old chronicles describe the area as densely covered with tamarugo trees, but most of these were felled at the turn of the last century to supply fuel for local mining operations.
At present, the most extensive natural group of trees is found around La Tirana (northernmost side of the Salar de Pintados), covering an area of roughly 100 hectares. Doubtless, the original dimensions of the Tirana natural forest were much greater. In fact, recent excavations have unearthed semi-fossilized trunks over a wide area.
The present-day plant community is very homogenous, being made up of a few species, which become more varied where the groundwater table lies closer to the surface. This water originates in the mountain ranges where it rains in the summer and from whence underground flow recharges the groundwater system. Most of the inflow to the Tamarugal Pampa groundwater system spends itself naturally, mainly in evaporation from the ground and evapotranspiration from plants. As the water moves from north to south it picks up salt (especially the upper layers). This is why the best quality water for human and farm use nonetheless contains 500 – 1 000 ppm dissolved solids.
Some by-products of northern Chile's aridity are the serious problems of unemployment, the concentration of capital in mining operations, minimal industrial development and almost non-existent, unprogressive agriculture, spread over small sectors. All of these present an immense obstacle to the social, economic and cultural development of the population.
The "Corporación de Fomento de la Producción de Chile (CORFO) (Chilean Corporation for the Promotion of Production), through its National Livestock Development Programme (1961–1970) tried to approach the problem of the development of the northern areas in a different way - a way which might be called “desert economics”, or making use of those special natural features of desert regions which are difficult to alter. The main idea was to transform the desert into an ecosystem where agro-forestry would predominate an attractive hypothesis no doubt, from the standpoint of harmonious social and economic development.
Despite an initial lack of scientific evidence to support this hypothesis, CORFO was able to demonstrate that it was possible to develop sheep-raising systems in an inhospital desert environment.
The stock-raising experiment achieved the target set by the Director of the National Livestock Development Programme of Chile 7, who led a programme directed towards ensuring stable and permanent stock resources. The livestock experiments were launched in 1964, after a series of preliminary studies and research (Kretschmer, 1964).
An ecosystem as specific as that of the Tamarugal Pampa dictated that a cautious path of action be followed in the projection of this programme.
Desert ecosystems have distinctive peculiarities. They lie outside the conventional conception of pastures as regards their potential capacity as fodder resource producers. Some specialists have therefore defined pastures as those ecosystems where the major resource is plant tissues directly utilizable by domestic animals. This is a very general definition. In this plant community, the only limiting factor is the capacity to produce plant tissue in a form compatible with harvesting by herbivores. If this definition is accepted, then even forests and scrub used by wild game animals and/or domestic livestock can be classified as pasture (Contreras et al., 1978).
For the purposes of this study, the tamarugo ecosystem, restored by man to the Tamarugal Pampa, will be considered as pasture producing mainly tamarugo leaves and fruit which fall to the ground and are eaten by livestock.
Up to 1966, research was carried out exclusively on aspects of animal production: determining which breeds of sheep and goats were suitable under conditions where the sole feed was based on the area's only resource, and seeing that normal production and fertility indices were unaffected by this.8
In 1967, forestry studies were undertaken to define better systems of planting and multiplying trees from seed. Other basic aspects of plant physiology were studied with a view to finding out more about how the foliar systems of tamarugo absorb moisture from the air.
The tentative conclusions reached after five years of this work can be summarized as follows:
The tamarugo tree, native of the First Region, is easy to propogate, providing the proper techniques are used (CORFO, 1970; Lanino, 1972).
The most suitable soils for afforestation at low planting cost are those where the groundwater level lies at depths of 2 – 10 m, making possible a brief, initial period of irrigation.
Tamarugo grows in ground covered by a salt crust, varying in thickness from 10 cm to 60 cm. It also adapts to, and grows in, soils without a salt cover, whether clay or sandy soils. It is, in any case, a highly salttolerant species once the stage of tap-root development has been reached.
Forested salt flats and soils evaporate less water than unforested areas. Evaporation measurements showed the mean annual evaporation rate within the forest to be 309 m3/ha, whereas outside, it was 1 590 m3/ha.
Tamarugo has a highly specific physiology. Under conditions of pronounced atmospheric humidity (above 80%), the plant absorbs water through its foliar system, transports it along the root system, and deposits it in the microrhizosphere, where it is reasorbed as water (Sudzuki, 1969). This trait explains why the tamarugo tree thrives in areas where groundwater lies forty or more metres deep and where there is no contact between it and the root system of the plant.
Tamarugo produces highly palatable fodder suitable for small stock such as goats and sheep, as well as for such larger stock as cattle and horses.
There are three types of fodder: the fruit (a legume); the leaves, which can be browsed off the tree where accessible; and what falls from the tree and accumulates beneath its shade (Tables 1 to 4).
The nutritive value of tamarugo is good in that it contains approximately 5% crude digestible protein and as much as 55% digestible nutrients. Carbohydrate and fibre content are adequate, and there is enough fat to prevent lipid deficiencies in the diets of goats and sheep.
The carrying capacity of a fully productive hectare of land planted with tamarugo (normally a fifteen-year old plantation) exceeds that of natural grasslands. Table 4 projects the theoretical carrying capacity, by age, of one hectare of tamarugo plantation.
The species and breeds adapting best to the Tamarugal Pampa ecosystem are Angora goats and Karakul, Suffolk Down and Australian Merino sheep. Table 5 shows the yields found by comparative studies.
Water troughs and freshly-sheared sheep in a tamarugo forest suitable for grazing
TABLE 1: Percentage breakdown of tamarugo fruit from four samples (Lanino, 1966)
| Components or Variables | S a m p l e s | |||
| 1 | 2 | 3 | 4 | |
| % | ||||
| Dry matter | 91.5 | 93.0 | 96.7 | 98.4 |
| Crude protein | 11.9 | 13.3 | 11.5 | 13.3 |
| Crude fibre | 28.8 | 31.7 | 32.5 | 34.2 |
| Ether extract | 1.6 | 2.3 | 1.7 | 1.4 |
| Ash | 6.1 | 5.4 | 4.4 | 6.4 |
| Free nitrogen extract | 51.4 | 47.3 | 49.9 | 44.8 |
TABLE 2: Percentage breakdown of tamarugo fruit digestibility from three samples (Latrille and García, 1968, and Lanino, 1966)
| Digestible Components | S a m p l e s | ||
| 1 | 2 | 3 | |
| % | |||
| Protein | 4.92 | 7.65 | 6.32 |
| Crude fibre | 12.06 | 12.47 | 16.26 |
| Ether extract | 1.20 | 1.46 | 0.84 |
| Free nitrogen extract | 24.70 | 22.53 | 36.89 |
| Total digestible nutrients | 44.38 | 45.95 | 61.38 |
TABLE 3: Projected annual yield of tamarugo fruit and leaves by age and ground area covered: yield estimated per tree and per hectare
| Age in years | Area covered (m2) | Fruit and leaves (yield per tree) (kg) | Fruit and leaves* (yield per ha) (kg) |
| 5 | 12 | - | - |
| 10 | 33 | 79.20 | 4 356 |
| 15 | 50 | 120.00 | 6 600 |
| 20 | 67 | 160.80 | 8 844 |
| 25 | 84 | 201.60 | 11 088 |
| 30 | 100 | 240.00 | 13 200 |
| 35 | 113 | 271.20 | 14 916 |
| 40 | 125 | 300.00 | 16 500 |
TABLE 4: Theoretical carrying capacity of a tamarugo plantation by age (in sheep per hectare)
| Age of tamarugo (years) | Breeder sheep per hectare |
| 1–6 | Without pasture |
| 7 | 0.5 |
| 8 | 1.0 |
| 9 | 1.5 |
| 10 | 3.0 |
| 11 | 4.0 |
| 12 | 5.0 |
| 13 | 6.0 |
| 14 | 8.0 |
| 15 | 10.0 |
| 16 | 10.0 |
TABLE 5: Comparative yields in wool from three sheep breeds and one breed of goat, lamb weight at 120–130 days, and head count at branding, as observed in a tamarugo forest (Refresco)
| Species and breed | Wool yield * (kg) | Head count at branding | Meat yield (lamb weight) at 120–130 days (kg) |
| Australian Merino | 4.0 | 60 | 18 |
| Suffolk Down | 2.5 | 90 | 32 |
| Karakul | 1.8 | 75 | 29 |
| Angora goat | 3.5 * | 120 | 18 |
1 Tropical Legumes: Resources for the Future. National Academy of Sciences, Washington, D.C., 1979.
2 Muñoz Pizarro, Carlos. Sinopsis de la Flora Chilena.
4 See figure on page 5 (Sinopsis de la flora chilean, Muńoz Pizarro, C).
5 See figure on following page.
6 Climate, geomorphology, soils and hydrology are discussed in greater detail in Part IV.
