Tamarugo belongs to the family of the Mimosaceae, Order Leguminosae. It is a little-known, autochthonous species. Neither the successive stages of its appearance nor its dispersion are known. Approximate ages of 400 years have been assigned to tamarugo trees in the Tirana area. (Muñoz, Pizarro, 1965).
Its average height is 15 metres, trunk diameter 50–80 cm, and crown diameter 15–20 m. When young, its branches are slender and angular with broad-based thorns, some 3 cm in width. The bipinnately compound leaves are short, glabrous and deciduous, with 15 pairs of 5 mm folioles. Inflorescence as a spike; perfect actinomorphic, hemaphrodite flowers; well-differentiated gamosepalous calyx and gamopetalous corolla; five fused sepals forming a hood, pubescent at the base, diminishing toward the apex; five pubescent yellow petals only in the mid-section with long fuzzy parts on the inner face; androceum with ten short or long bright-coloured stamen filaments with versatile antennae; gyneceum with long or short-style pistil; unicarpelar ovary surrounded and protected by various white fuzzy parts. The height of the stamens may exceed that of the pistil, equal it, or be only part of it. The fruit is a thick, short, peanut-shaped legume 25 mm long. The seeds are tiny, dark, compressed and separated by partitions.
Tamarugo flowers are pollinated by hymenopters such as Centrix mixta and the common bee Apis mellifera, its main pollinating agents. The peak of activity is between early September and November.
The tree grows all the year round, with peak growth from August to November, the height of the blooming season. Minimum growth period is from March to July. Acevedo (1977), nonetheless, establishes a winter recess period due to sap inactivity.
Tamarugo has a double-root system: i) tap or anchoring roots, made up of 3–4 thick roots with no branches, penetrating to depths of 7–8 m in loamy soils; ii) mass or complex of sucking roots which develop and penetrate to depths no greater than 1.50 m. Throughout their volume, sucking roots can have a moisture content of easily 40%, according to measurements made in the Refresco area in September 1966 and January 1976, on thirty-year old trees thriving in soil with a groundwater depth of 13 m. (Toro, 1967).
Tamarugo, native of the Tamarugal Pampa in the La Tirana area. Notice the height of the tree with respect to the peope at the far right-hand side of the picture. (Photo - Mario Habit)
Panoramic view of Refresco in the Salar de Pintados on the Tamarugal Pampa. Man-made tamarugo plantation established between 1964 and 1969. Visible in the foreground are sectors bordered by tamarugos functioning as windbreaks for, and marking the site of, future plantations.
Present knowledge makes it practically impossible to estimate the productive life of the tree. What is known is that it becomes productive within 7–8 years from the time it is planted, but not how many years it continues to produce - although some examples existing on the pampa suggest a very long productive life. It is felt however that the information available is sufficient to ascertain that the productive life of the tamarugo tree is long enough to justify an investment programme.
Studies were made in 1968 attempting to relate tamarugo growth to the controlled variables: age, plant spacing and groundwater depth (Instituto Forestal, 1971).
Curve graphs were constructed establishing ratios between measured parameters (total height, crown diameter) and the known variables, i.e., age and spacing. The age/height ratio of tamarugo is asymptotic, as for the first 24 years of life, it has a positive growth reaching an average height of 10 m. This growth has not increased significantly by age 40. (See graph on page 23).
Concerning the crown diameter/spacing/age of plantation ratio, the broadest diameters (averaging 12 m) were observed with spacings of 13 × 13 m at age 36. Not so the crown diameters of plantations of the same age with spacings of 6 × 6 m, where crown diameter was only 6.5 m. (See graph on page 24).
An analysis of the ratio between variations in height, groundwater depths and salinity reveals no discernible trend. Nonetheless, it cannot be definitely stated that no such relationship exists since, for all other forest species, it is an established fact that height is one of the factors most closely related to soils.
Numerous laboratory experiments using plants in a solution have demonstrated the close relationship between growth and osmotic pressure from the nutrient solution (Instituto Forestal, 1971). The relationship indicated that saline solutions, due to concentration of salt particles, act as growth inhibitors. And there is the additional factor of soil moisture tension, which can cause a drop in the absorption of water through the roots, diminishing growth or at least regulating it. Soil moisture tension in the soil profile is closely linked to groundwater table depth.
AGE/TOTAL HEIGHT RATIO - PROSOPIS TAMARUGO
AGE/CROWN DIAMETER RATIO BY SPACING: PROSOPIS TAMARUGO
AGE/FOOD PRODUCTION: PROSOPIS TAMARUGO
The growth of tamarugo's crown, source of leaves and fruit, is directly linked to increasing the initial plant spacings: 6 m × 6 m; 7 m × 7 m; 10 m × 10 m; and 13 m × 13 m. Therefore, when the rhythm of growth of the crown is known in ratio to the other variables examined, it is possible to determine how quickly a planted surface will be covered, depending on initial plantation density.
Tamarugo productivity is linked to age, plant spacing, depth and quality of groundwater, and whatever land development operations are undertaken initially. Such entomological aspects as insect pests and their control also have considerable impact on productivity.
The entire crown fructifies uniformly; as the fruit falls it scatters over the ground, more densely beneath the crown projection.
Apparently, there is no very significant variations in yield. Oyarzún (1967) reports on a controlled experiment carried out in 1957 on 19 trees, where an average yield of 2.10 kg of fruit per m2 under the crown projection was standard. In 30-year old trees, the average leaf litter and fruit per m2 of crown projection was 3.4 kg/m2 of dry matter; 18-year old trees produced an average yield of 1.8 kg/m2 of dry matter (Instituto Forestal, 1964). (See graph on page 25).
An estimated 50% of the fodder produced per m2 under the crown projection corresponds to the fruit of the tree and the remaining half to leaf litter.
The tamarugo plant has a special physiological flexibility which allows it to develop under conditions which would be lethal for other plants. The humidity provided by night mists, dew and relative humidity, is notable for its fluctuations as well as for its extent. With respect to other species, for example, it has been successfully demonstrated that an artificial mist applied to Pinus insigne sprouts during the dark period of the day/night cycle prolongs the lives of young plants by as much as 45 days, even when they have been established in dry earth.
It is known that an absorption phenomenon exists, but several researchers stress that it is probably not vital to the plant and that its function is likely to be one of provoking reduced tissue transpiration by constituting a protective layer over the leaf surface (Slatyer, 1967).
Tamarugo fruit (legume). The bottom photo shows the “fodder” from the fruit and “leaf hay”.
Tracer experiments with HHO18 on Phaseolus vulgaris revealed rapid replacement of the intercullular water by molecules of atmospheric water. This phenomenon occurred not only in the stems and leaves, but also within the tissue cells (Vartepetyan and Kursanov, 1962). This would appear to demonstrate that plants, under specific conditions, invert the flow of water from the roots to the leaves, i.e., atmospheric water is captured by the foliar surface, transmitted to the root tissues and then eliminated by difference of water potential in the molecular (diffusion) exudate. Some scientists, however, consider this exudation of water into the ground to be of small import, serving only to prolong for a short time the life of certain plants under conditions of extreme drought (Muller-Stroll, 1956; Stone et al., 1950; Kramer, 1959; Polster, 1963 and Slatyer, 1967). Despite this, research in arid and semiarid zones, as well as prior laboratory research, suggest the possibility of an accumulation of water exceeding the specific retention figure (Breazeale et al., 1950; Breazeale 1953a, 1953b; Gindel, 1966).
Experiments conducted in the Tamarugal Pampa have shown that foliar irrigation is effective in prolonging the life of tamarugo seedlings. They were treated with water marked with Tritium under laboratory conditions, as were saplings in the field. This revealed a positive transfer of atmospheric moisture accumulating in the rhizosphere, i.e. in the masses of sucker roots (Sudzuki, 1969).
The experiments of Sudzuki (1969) on foliar sprinkling of tamarugo seedlings under laboratory conditions showed that they were highly resistant to moisture deficiency and that the lowest daily weight loss was recorded for plants receiving foliar sprinkling (Table 6). This suggests that tamarugo leaves are able to use atmospheric moisture in an attempt, it would seem, to partially counteract losses from evaporation and transpiration.
TABLE 6: Average daily weight loss expressed in grams for tamarugo seedlings compared to watered pots without plants, sealed pots and basin of water
|Seedlings||Pots without seedlings||Basin of water|
|Foliar sprinkling||Ground irrigation||No irrigation||With added 100 H2O||Sealed pot||100 gr|
For both animals and tamarugo, water is the basic life element that makes the ecosystem function.
Later studies by Sudzuki focused on research on foliar absorption, the sine qua non of absorption, whether the water absorbed was capable of moving through the tissues to the roots, and whether the roots would then exude the excess water into the soil at the level of the sucking roots. At Refresco and Canchones in the Tamarugal Pampa, experimentation was carried out with tamarugo plantlets in polyethylene bags, sealed at plant neck height, and using five controls and five applications. Tritium was used as the tracer. Radioactivity selected was 4 microcuries/ml. To apply the tritium, the plants were placed under a polyethylene tarp and sprayed at night with an atomizer to the point of saturation of the mini-environment. The tarp was removed the next day and the tracer extracted the same day, using a vacuum pump with a double wall to facilitate the obtention of a vacuum. Dioxan was used as the basic and Napthelene as the secondary thinner in the radioactive solution for the determination of the amount of Tritium remaining. Specific activity was determined by using a Mark geiger counter in a Liquid Scintillation System for ten minutes.
The findings showed that tracer applications applied at night resulted in a certain amount of radioactivity in the earth around plants maintained in a Tritium-based atmosphere during the day - at least three or four daily applications of Tritium were necessary. These findings confirmed those of other scientists (Slatyer, 1967; Stone et al., 1950) as to the conditions under which foliar absorption takes place. The fact that significant radioactivity was detected (0.05%) with a single application showed that the radioisotope moved rather rapidly through the plant tissues until reaching the sucking root area. This confirms the findings of Vartepetyan and Kursanov (1962). Sudzuki's findings (1969) are summarized in Table 7, which compare the control plants with those marked with radioactive tracer.
TABLE 7: Radioactivity of aqueous extract of earth in roots of young tamarugo sprayed at night under a polyethylene tarp, as compared with control plants (Tamarugal Pampa, 1968).
|Control (c.p.m.)||B.G. (c.p.m.)||Application 4 Mc/ml (c.p.m.)|
|233||238||1 080 +|
|251||1 264 +|
+ Significant c.p.m. (counts per minute) 0.05%; control with distilled water; B.G. (natural water) Mc (microcuries).
In his summary, Sudzuki concludes that this species is able to absorb atmospheric moisture through its leaves, transmit it to the roots, and there exude it to the surrounding soil through a guttation-like process. In addition, the amount of water absorbed by the foliar vegetation is related to the time saturation humidity is reached. Peak amounts were absorbed at night. Other contributing factors were: the amount and/or velocity of water reaching the ground in inverse proportion to the size of the tree, as can be seen in Table 8.
TABLE 8: Accumulation of radioisotopes in rhizospheres of 7 to 8 year-old tamarugo plants sprayed with Tritium tracer solution day and night at Canchones and Refresco (Sudzuki, 1969)
|Application||No. sprayings in c.p.m.||BG||No. of sprayings in c.p.m.|
Pastene (1972) agrees that foliar absorption is a fact, probably so extensive in the case of tamarugo that it would permit water to accumulate in the immediate vicinity of the roots. He also raises the problem of establishing to what extent such absorption is vital to the plant. Repeating Sudzuki's experiments conducted in Santiago in 1966, Pastene substantially increased the sample in the Tamarugal Pampa itself, introducing a few methodological variations He used seedlings of different sizes for the two studies he conducted during a 55-day period. He concluded that the seedlings were able to capture atmospheric moisture, pointing out that seedlings receiving foliar sprinkling demonstrated a process of adaptation wherein the plant increased the area of its leaf surface, which was manifest in a delayed growth in stature and an increase in the number of shoots. He indicated, however, that foliar absorption capacity was not constant, being largely dependent on the extent of atmospheric humidity, soil moisture, temperature and other interacting factors. Apparently, withholding water for prolonged periods from tamarugo seedlings accelerated the process of foliar absorption on days of greatest humidity so as to get as much water as possible to store in the ground against periods of little humidity. Even more striking was the fact that exudation, or the shift of water into the ground, was sometimes so great as to exceed specific retention. See figure on following page.
Two/three-year old tamarugo in Refresco, Tamarugal Pampa. Soil moisture at different depths in percentages (Sudzuki, 1969)
The concept of xerophytism has been approached from the morphological standpoint, that is, by explaining the mechanisms whereby the plant accumulates water or prevents water losses, or evades periods of moisture deficiency. Many authors call this phenomenon resistance to drought. The physiological characteristic is explained by: i) changes in the respiratory quotient affecting the normal inhibition of starch/sugar conversion; ii) protein alterations; iii) concentration of hydrophilic colloids in the cells, causing fewer losses; iv) greater or lesser rapidity with which some plants reach the definitive point of withering; v) turgor pressure in cells implying a crucial role in cellular growth; vi) osmotic adjustment in the cellular level as a mechanism for adapting to conditions of moisture deficiency; vii) changes in the flow of energy; viii) differing potential to ionize metabolites and stabilize biomembranes to maintain cell turgor; ix) genotypic adaptation of response to the environment by species, varieties and ecotypes.
Levitt (1956) has classified plants by resistance to drought, taking two aspects into account: i) the presence of some mechanism enabling the plants to cope with critical periods; ii) the ability to increase cell metabolism capacity. Sudzuki (1975) adds a third factor: the mechanism whereby the plants are able to use the moisture contained in atmospheric humidity. This would imply a rethinking of the way in which certain plants use form and function to utilize this important source of water. Hence the term “drought resistence” or xerophytism must include the broader aspects of the forms and functions of water used by plants -- not only the way in which they retain it, but also how they obtain it.
Sukzuki's studies (1969) indicate substantial variations in the soil moisture profile. He presents the case of Refresco, where the amount of water in the rhizosphere of the sucker roots exceeded specific retention, reaching a figure of 24%, whereas specific retention was only 11.5%. This suggests a possible accumulation of water exuded from the sucker roots in excess of that needed to reach an equilibrium between the diffusion pressure deficit and the forces of soil moisture tension, as a result of which the water absorbed by the leaves would then not move from the plant tissues to the ground simply through the suction effect of the soil caused by negative gradient due to drought (which would tend to balance diffusion pressure deficit and soil moisture tension). Instead, it is now thought that some other, as yet unknown, process may intervene making possible a greater exudation of water to the soil.
Tamarugo trees three years old in the Pintados salt flat, Refresco
General view of a section of the same property in utilizable condition. Trees aged 6–7 years.
Sudzuki, Botti and Acevedo (1973) have characterized the hydric relations of tamarugo, studying degrees of potentialities of the soil/plant/atmosphere system and some aspects of the physiology of the plant which could shed more light on the process of foliar absorption. Acevedo (1977) determined that tamarugo was more active physiologically in the summer, with active sap and shoot production. In winter, on the other hand, there was apparently a recession, with no detectable movement of sap, little sprouting, and pronounced deciduous activity. It was also observed that the hydric potential of tamarugo leaves fluctuated between -15 atm and -47 atm in the summer, and between -24 and -80 atm during the winter. However, during the time the research work was being conducted (summer and winter of 1973), the atmospheric moisture potential was not such as to favour a gradient of potentials for foliar absorption.
Concerning soil moisture potential, Acevedo (1977) reports that the lowest total moisture potential of the soil around the sucker roots measured roughly -52 atm. Compared to the -32 atm moisture potential of the plant as observed in summer, this figure would probably favour a water gradient towards the soil. Relative turgor measured in the leaves showed very high percentages which remained fairly constant throughout the day, summer and winter. This would seem to indicate no moisture deficit in the tamaruao rhizosphere. As a corollary to this, it was also determined that the stomates open inversely, that is, they prefer to open during the period of darkness, at night, and are never 100% closed or open. Variations in stomate aperture are closely linked to the rate of relative humidity. The greater the humidity, the greater the percentage of open stomates, a clear phenomenon in spring and summer.
Botti (1970) described the hydric situation of the tamarugo tree, analyzing gradients of potential and certain aspects of the physiology of the plant influencing the process of moisture absorption. From his work in the Tamarugal Pampa at Canchones, he reached the following conclusions: i) moisture potential gradient is reversed, with the water moving from the atmosphere towards the soil whenever relative humidity hits or exceeds 95%; ii) a high percentage of stomates remain open during the period of luminosity, and closed during the dark period; iii) in summer, the descending sap flow lasts as long as four to eight hours at night -- the rest of the time it rises; iv) relative turgor in the leaves is very high (80–90%), and is also constant throughout the day, and all the year round. Physiological winter recession in tamarugo takes the form of pronounced deciduous activity due to the drop in sap flow and the cessation of sprouting; v) the earth in the vicinity of the active rhizosphere contains more moisture (18.8%) than nearby areas at equal depths, which contain only 1.5%.
1. Seed collecting. Producer trees are identified by their phenotypic characteristics. The fruit is picked, cleaned by machine, and ground in a stone mill set at 4 mm. Clean seed is then obtained by sieving and floating the milled product. The seed is treated with a 0.2% solution of Aldrin before storage to control insect pests. One kg contains 65 000/75 000 seeds. The seeds are treated with sulphuric acid for seven minutes to abrade the cuticile, and facilitate the exchange of gases and penetration of water through the single micropyle aperture of the seed. This causes the colloids to rehydrate and germination to begin. An alternative practice is scarification.
2. Nursery. A 2:1 mixture of soil and sheep manure is prepared in the nursery. Plastic bags 12 cm in diameter and 30 cm long, without rips or tears, are filled with the mixture and placed in carefully-levelled planting beds. These “pots” are sown with 3–5 seeds at a depth of 1.5 cm. In watering these pots, care should be taken to keep the top layer of soil, where the seeds are, moist without accumulating water in the bottom. This averts fungi infestation. Before sowing, it is advisable to treat the soil with specific fungicides, or with fumigants such as methyl bromide (CH3BR), to ward off pathogens in the early stages of germination and development of the seedlings.
Once the seeds have germinated and the seedlings emerge, they are given more water, but less frequently, thus ensuring that the downward-growing roots get enough moisture 9. It is important not to use too much water.
The seedlings remain in the nursery for 3–5 months, until they reach a height of 8–10 cm. Root development is rapid and vigorous and care must be taken to see that the roots do not rip or grow out of the plastic bag (Lanino, 1972).
3. Planting. The seedlings are planted in plots (1 km2) covering 100 ha. Planting systems used are: 10 × 10 m in square formation and 15 × 15 m in triangular.
The planting hole, some 30 cm in diameter by 40 or 50 cm deep, can be dug manually or by machine. Manually dug holes may have a greater diameter because of the process of removing the salt crust surface. Mechanically dug holes are sunk with a specially designed frontal plough Caterpillar tractor, leaving a sort of trench 80 cm wide by 1 m long at the base. With this operation, the good farm soil, or “sweet soil” is reached. The depth of the opening depends on the terrain; it is generally 80 cm in diameter, according to the depth of the saline layer, which must be penetrated completely before the planting hole is dug. When the soil is uncovered, the planting hole is dug to a depth of 30 cm and a diameter of 20 cm, either by hand or with a mechanical post hole digger.
Before planting, saturation irrigation is applied to the planting hole so as to wet it as far down as possible.
4. Irrigation. To ensure that the plants become properly established, enough water must be given to penetrate down to root level so that there is constant moisture around the roots. How many establishment irrigations are needed varies with the ground-water situation, and there will be considerable divergence as to the depth of the moisture (Lamagdelaine, 1972). An average estimate for the establishment period would be 11 waterings. The plant is established when it begins to send out new shoots. When this occurs, irrigation can be carried out every 20 days (Lanino, 1972).
One of the major items of planting costs is watering. One way to reduce the number of irrigations is to cut water losses from evaporation by stretching a plastic tarp over the hole -- another is to use drip irrigation, which makes for better water use. Carvallo (1970) compared four treatments aimed at cutting irrigation outlay: i) a sealed sack (sealing the polyethylene “pot” just at plant neck height); ii) covering the planting hole with a 40 × 40 cm polyethylene sheet 0.06 mm thick, perforated in the centre, and held down by salt blocks cut from the crust; iii) polyethylene sheet around the neck of the plant (25 × 25 cm and 0.06 mm thick) inside the planting hole and held down with dirt, with a slit for the plant to grow through; iv) drip bag for slow irrigation -- two variations: a) bag with small orifice at one end to allow water out, drop by drop; and b) wick through orifice in contact with neck of plant maintaining constant moisture but without dripping; v) control, planted under customary conditions. (See pages 39, 40, 41 and 42).
In the first three treatments, watering was done with 5-litre bags every 10, 20 and 30 days respectively, and the plastic sheets were withdrawn at 30 and 90 days. The author concluded that there was no difference among the treatments with respect to tamarugo survival, nor did he find significant differences among the watering timetables. In other words, watering could be done every 30 days. Nor were there different effects between the types of plastic sheets and between the drip and wick method of watering. Lastly, the author recommended changing the frequency of watering to every twenty days, which would mean a 50% reduction in its cost.
Forest establishment activities do not terminate with the rooting of the seedlings and the suspension of watering. The abundant growth of the basal branches and their thorns mean that they have to be pruned when the tree is 4–6 years old so as not to bar the access of livestock to the fodder.
Pruning is done by hand with a sickle. The branches are eliminated or cut to ensure that livestock have easy access to the trees. The branches are then piled up and can be used to build fences for the pasture plots.
DIAGRAM OF PLANTING HOLE
DIAGRAM OF HOW TO FIT PLASTIC SHEET AROUND NECK OF PLANT
DIAGRAM OF PLACEMENT OF PLASTIC TO FORM A ROOF
Planting tamarugo. Perforating the salt crust.
DIAGRAM OF PLACEMENT OF WATERING BAG
Pruning tamarugo to allow livestock to get under trees
Except for the Elgueta and Calderón report (1970), little reliable information is available about tamarugo's fodder-producing capacity. The one generally observed characteristic of this tree is the great individual variability of fodder production between neighbouring trees of the same age. This feature is common to all trees propagated by seeds, but is even more striking considering that variability is greater in the Tamarugal Pampa the most probable site of origin of this species (Klein, 1970).
Klein (1970) wished to determine the fruit yield without taking into consideration leaf litter. He harvested either all or part of 42 trees in sections 1 and 3 of an adult forest (Junoy), which had been planted around 1930 in square formation, spaced 20 × 20 m. One sector received an application of endosulfan and the other remained untreated. A partial harvest was made by laying 8 corrugated sheets in a circle around the trees (the sheets had an area of 1 m2). For the total harvest, the ground was swept and all material collected for later sorting. The characteristics of each tree were noted (radius, average height, number of trunks in each hole, number of stems at 1 m and their diameter, crown type, number of lower branches, type of fruit, distribution of fruit over crown and general health of tree). Samples of 100 fruits from each tree were studied in the laboratory, observing the following parameters: volume, weight and soundness. The type of damage and the agents responsible were considered, among which were the purple moth (Leptotes trigemmatus, Butler) and the fruit moth (Cryptophlebia carpophagoides, Clarke), as well as the Pampas rat.
In estimating damage, Klein took into account the enormous variability of fruit yields as related to the relatively homogeneous data on fruit distribution over the crown.
It was found that the average yield in fruit of a chemically sprayed, adult tamarugo tree was 57.361 kg, corresponding to an average yield for the crown area of 0.508 kg/m2 -- a figure much below that cited by Oyarzun (1967) and other authors.
The method used by Klein (1970), was to compare the total real weight of the harvested fruit with the estimated weight (Table 9), using nine corrugated sheets per tree to collect the fruit.
Aerial views of the forest planted by the Corporación de Fomento on the Refresco property. Tamarugal Pampa.
TABLE 9: Validity of the partial harvest method used to estimate tamarugo fruit yields
|Tree key||Total real weight of fruit harvested|
|Estimated weight of fruit|
|Difference between real and estimated figure|
|13 Z||141.48||133.50||+ 7.98|
|17 Z||63.36||65.04||- 1.48|
|19 Z||98.37||105.92||- 7.55|
|22 Z||54.33||56.96||- 2.63|
|23 Z||27.90||26.37||+ 1.53|
|26 Z||123.90||97.77||+ 26.13|
|28 Z||49.56||45.83||+ 3.63|
|30 Z||46.11||45.28||+ 0.83|
|31 Z||41.55||43.75||- 2.70|
The ratio of fruit damaged by insect pests to the weight of 100 fruits was also examined. This is given in Table 10.
TABLE 10: Ratio of damaged ripe fruit to weight (Klein, 1970)
|Tree key||Percentage of damaged fruit||Weight of 100 fruits|
|Volume of 100 fruits|
An analysis of these findings leads to the following interesting observations:
Endosulfan spraying notwithstanding, 39 out of 100 fruits were damaged, usually by fruit moths (Cryptophlebia carpophagoides).
Despite the damage done, there did not appear to be any very significant effect on fruit weight.
It should be stressed that while no direct relationship was observed to exist between insect attack and fruit weight, pests affecting the fruit caused heavy losses in the early stages of its development, at the setting of the fruit.
4. Lighter insect pest attacks were noted in a tree producing small pods.
Comparing the data obtained from the unsprayed sector, the conclusions were:
Tamarugo fruit yield is closely linked to the individual variability characteristic of the species. It is essential to determine whether this is due to forms within the species or to specific ecotypes.
Insect pest attacks influence fruit yield. For instance, in the sector receiving Endosulfan applications, a growth difference of 31.2% was observed.
Individual resistance to insect attack is not clearly appreciated. The fact that trees producing small or medium-sized fruits are less attacked does not necessarily indicate resistance to insect attack.
The data differ from those reported by Elgueta and Calderón (1970) for the year 1969, as shown in Table 11.
TABLE 11: Comparison of figures obtained by the Instituto Forestal (Elgueta and Calderón, 1970) and Klein (1970) for tamarugo fruit yield
|No. of trees observed||9||20||22|
|Collection technique||9–12 corrugated sheets 1 m2 under crown area||8 corrugated sheets 1 m2 total harvest||8 corrugated sheets 1 m2 total harvest|
|Average kg/m2 crown area||0.781||0.508||0.387|
Average fruit yield per tree (kg)
One of the most important aspects of long-term operation and management of the ecosystem is to know the plant-eating insects attacking the leaves, stems, flowers and fruits of the tamarugo tree. And it is vital to know which insects are its natural enemies and which are the native (or introduced) pollinators. The tamarugo entomological picture was reviewed by Klein and Campos (1977), who divide the insects into five groups according to the beneficial or harmful role they play: 1) leaf insects and mites; 2) insects destroying inflorescence; 3) insects attacking the fruit and seed; 4) natural pollinators, and 5) introduced pollinators. Most of the data presented here is derived from these authors.
Leptotes trigemmatus Butler (Lepidoptera: Lycaenidae) “purple moth”. It is found throughout the valleys and gorges where alfalfa is grown, in oases on the piedmont, and throughout the Tamarugal Pampa where it borders the Quillaga Valley. The principal hosts are: alfalfa (Medicago sativa); tamarugo; carob (Prosopis chilensis); “fortuna” (Prosopis strombulifera); Argentine tamarugo (Prosopis burkartii) and remata (Cressa critica). Adult insects of this species have been observed feeding on brea (Tessaria absinthioides) and eucalyptus (Eucaliptus sp.). The damage is done by the larvae, but only achieves real significance in nurseries and recently transplanted seedlings. Young, vigourous plants produce new secondary branches which usually escape a renewed attack. Damage takes the form of a circular perforation through a foliole, causing partial necrosis. Just one orifice is drilled per foliole. When its development is complete, the larva goes to pupate, preferably in the soil under the salt crust, or under the loose bark of the tree, where large numbers are found in October and November. There is a noticable drop in number as soon as the fruit begins to ripen in December. The outbreak only approaches pest proportions during the secondary flowering in winter. There is probably a massive migration of adult moths from the alfalfa fields of the mountain valleys to the Pampa as soon as Prosopis begins to sprout and bloom in September, which would explain the high initial numbers of this pest.
Among its natural enemies, there is a microhymenopter (Uscama sp.) which parasitizes the eggs to a slight extent. Once attacked, the eggs turn dark grey. The mirid Carvalho (Rhinacloa aricana - Hemiptera: Miridae) is a major predator of the numerous eggs among both newly-planted and adult tamarugo trees.
Tephrinopsis memor Dognin (Lepidoptera: Geometridae), or measuring worm. This geometrid is widely distributed throughout the Tamarugal Pampa and is particularly associated with tamarugo, though the larvae have also been observed feeding on carob. During the early stages, the larvae are greenish-yellow. They later turn dark green with bands of yellow. At the last larval stage, the worm is 2.4 cm long and feeds voraciously on inflorescences -- where it does most of its damage -- and leaves of both tamarugo and carob. A natural enemy in some forests is the Polystes wasp, which preys upon the most developed larvae.
Leaf “gluer” is an unidentified microlepidopter, widely distributed throughout northwestern Argentina among Prosopis alba and P. nigra in the phytogeographic zone known as El Monte. It is widely distributed among tamarugo and carobs in the Pampa. At the height of its development, the larva measures 3.8 mm and is 2.8 mm wide. It is yellowish-orange in colour and moves its body by contorting it. It can cause intensive defoliation, especially in young trees.
Hemiberlesia rapax (Comst.) (Homoptera: Diaspididae). This scaly insect is found from Arica to Llanquihue; it is a diaspid which attacks trunks and branches, but is not very important economically. Various endoparasites prey on it.
Heteropysylla texana (Craw.) (Homoptera: Psyllidae). This insect is occasionally found in tamarugo inflorescences and foliage, but causes only slight damage. It does cause a serious problem of defoliation and galls on the smaller branches of the carob tree, but the worst damage is abortion of the flowers, withering at the apex of growth, and abundant secretion of sugar.
Aphis sp. (Homoptera: Aphididae). This insect is known as the tamarugo louse. A dark coffee colour, it attacks the young shoots of the plant. Major damage is done only in nurseries in spring. The pest is kept under control by its predators (Crysopa sp. and syrphids) and by an unidentified parasite.
Cecidomid (Diptera: Cecidomydae). Species unidentified. It is found throughout the Great Northern area in association with Prosopis. It is also to be found in northwestern Argentina in association with plants of the same genus. The eggs are orangish, 0.12 mm wide and 0.8 mm long, with a smooth, shiny chorion. At the last stage, the larva is 1.3 mm long. The adults have a very delicate appearance. The male is dark coffee to black in colour, while the female ranges from orange to deep red. As soon as the eggs hatch, the larvae insert their bucal apparatus into a particular spot on the leaf tissue, from which they do not move until the last larval stage, when they drop off to pupate in the soil. Damage takes the form of a pale green circle on the chlorotic shoot where the larva has inserted itself. The result is defoliation, varying in intensity by season. This species also attacks carob, where it produces heavy defoliation, particularly in the summer months (especially January).
Two microhymenopters, Platygaster luctuosa (Hymenoptera: Platygasteridae) and Diglyplus sp. (Hymenoptera: Eulophidae), prey on the larval and pupate stages of this cecidomydae. In October and November, other natural enemies such as Crysopa sp. prey upon this pest at different stages of its larval development.
Eriophyes tamarugae (Wilson). (Acarina: Eriophydae). Tamarugo blistering. This pest is found in association with tamarugo throughout the salt flats of the Tamarugal Pampa. The eryophid female measures 180–220 microns long by 48 microns wide (Wilson, 1968). Damage is mostly evident in the foliage of seedlings in nurseries and in adult trees. Once attacked, the foliole curls up, thickens and distorts with abnormal growth. The colour gradually goes from yellow to dark coffee until the leaf falls to the ground. Natural control of this pest is exercised by certain neuropters of the Hemerobidae family. But the most important natural enemy is the mite Agistemus collyerae González (Acarina : Stigmaeidae). It is found in the folded leaf feeding on the adult eryophid.
Ithome sp. (Lepidoptera: Walshiidae). “Flower moth”. It is widely distributed throughout the Tamarugal Pampa in all areas where tamarugo and Prosopis burkartii thrive. But it has not been found to affect carob inflorescences.
The adult is a velvety greyish-black. At rest, it measures up to 5.3 mm long by 1.3 mm wide. The rather cylindrical eggs are roughly 0.38 mm long and 0.15 mm wide. At birth, the larvae are small (1 mm long) and whitish, with a dark coffee-coloured cephalic capsule. Larvae at the last larval stages measure 5.3 mm long and turn yellowish with ochre-coloured dorsal spots. The pupa is yellowish, turning to dark coffee colour when the adult is ready to emerge. It measures 2.5 – 3.8 mm long by 0.8 mm wide at mid-section. The female lays its eggs in tamarugo buds at a depth of 0.5 mm. The eggs seem to require a high-humidity environment to develop normally. No eggs have been found in open flowers. The newborn larva prefers to feed on the base of the pistil and secondly on the stamen. As the larva develops, it moves from one bud to the next by drilling a tiny tunnel through to the adjacent bud. Sometimes, nine to twenty flower buds are found glued together. The rachis is destroyed by galleries which prevent the sap from circulating, after which withering appears and the tiny flowers fall, even though there is no apparent damage. During the peak blooming period, damage is estimated at 20–40% of all blooms. No natural enemy has been found for this pest.
Leptotes trigemmatus Butler. In its earliest stages, the larva perforates the bud or open flower, introducing the head and prothorax into the petals. This pest eats the whole inside of unopened buds and destroys the pistil base (the ovaries) of open inflorescences. The flower may be completely destroyed.
Tephrinopsis memor Dognin (Lepidoptera: Geometridae). Damage is found in the open flowers. The style, stigma, stamens and petal tips are especially subject to attack. 30–50% of the upper part of the petal may be eaten, which generally involves more than half the inflorescence. Attacks occur when blooming is well advanced.
Franihiniella rodeos Moult. (Thysanoptera: Tripidae). “Tamarugo thrips”. This pest appears in large numbers during inflorescence, especially once the buds open. The damage is done to the petal tips, which exhibit withering and necrosis. Despite the large quantities of this pest found from September onward, no estimate has been made of the damage it causes.
Crytophlebia carpophagoides Clarke (Lepidoptera: Olethreutidae) “Fruit moth”. Found throughout the Tamarugal Pampa, Lluta Valley and Azapa Valley. The adult is a pale grey moth with metallic or black spots on the upper surface of the hind wings, very much like the apple moth. It is 10–11 mm long with a wing expansion of 25–26 mm. The larva is white, with a black cephalic capsule which turns to coffee colour. The newly hatched larva bores into the fruit where it consumes the seed. It emerges through a characteristic orifice of irregular shape to move on to the next fruit. When its larval development is complete, it migrates to more sheltered areas, usually under the loose bark of the tree. The adults begin to appear at the end of September. The largest numbers are in October, dropping in November/December. The greatest damage is done to little-developed fruit, where the raceme may be destroyed. Trials by Klein and Campos (1977) showed damage rates of as much as 17.4% of the fruit. Peak damage is estimated at 30%.
Natural enemies at the dormant stage are various parasites of the order Hymenoptera: Dibrachys cavus Walker, Bracon hebetor Say and Periossocentrus sp. An estimated 25–30% of the dormant larvae of the fruit moth are thought to be destroyed by this form of control.
Leptotes trigemmatus Butler (Lepidoptera). This pest also attacks the fruit of the tamarugo, especially during the early stages of development, causing the fruit to fall. Growth is usually halted in the fruit attacked, which turns dark green, dehydrates and finally falls.
Scutobruchus gastoi Kingsolver (Coleoptera: Bruchidae) "Tamarugo worm". This worm species is endemic in the Tamarugal Pampa. The adults measure 2.2 mm long. Upon emergence from the ripe pods, they leave orifices roughly 1 mm in diameter, very similar to those left by the purple moth. Last-generation worms winter in the windfall fruit, emerging in large numbers during the next blooming period.
Despite the fact that tamarugo has anemophilous pollinization, entomophilous participation seems to be important for obtaining proper fructification.
Given the large quantities of nectar-rich flowers, the development of apiculture seems possible, but there are climatic limations to this, as well as limitations imposed by the blooming season and the absence of other meliferous flowers (Klein and Campos, 1977; Rolando, 1974).
The “solitary bee”, Centrix mixta Friese, plays the most important role in pollinating tamarugo as well as the other Prosopis species. This bee builds its nest in the saline soil, making a solid cemented tunnel. The adults begin to appear around mid–August, coinciding with the flowering period for tamarugo, chañares (Gourliea decorticans) and oasis citrus. They cease activity when blooming time is over at the end of November. By the second flowering in the winter, they are gone.
Trials were conducted with the domestic bee, Apis mellifera, for the purpose of upgrading pollinization and obtaining additional income. The ecological adaptation of the species was excellent and the quality (colour and flavour) and quantity of the honey such as to presage the development of bee-keeping.
Nonetheless, the fact that flowering is concentrated in a three-month period entails the need for artificial feeding of the hives although, with proper management and transfer to the Andean foothill valleys, this requirement could be offset by only the cost of moving the bees.
Cadahia (1970) presents a biological timetable of the major pests attacking tamarugo during the growing season, the damage done by the pests (percentage of losses), and the most advisable time to apply treatments. (Table 12).
The three species considered of major importance are the “flower moth”, the “purple moth” and the “fruit moth”. The first two produce various generations during the critical period, but it is believed that Cyrptophlebia carpophagoides Clark produces only one generation. This is because its larvae have been observed after the last larval stage to go into a stage of diapause which lasts until the beginning of the next period. Major damage is done to inflorescences by the flower moth and the purple moth. According to León (1974), the figure may be as high as 52%.
León (1974) conducted trials in the northern part of the Salar de Pintados comparing emulsifiable and powdered insecticide preparations. The point was to ascertain their degree of effectiveness in controlling the three major insect pests attacking tamarugo. The conclusions were that a 4% solution of Endosulfan was statistically superior, producing the highest percentage of sound fruit, though similar yields were obtained with Endosulfan 35% E. Powdered insecticides were also recommended, as dusting was found to be ten times quicker than using emulsions.
Earlier experiments by Klein (1969) show that the best treatments were with Endosulfan E.C. 0.07% active ingredient, and Endosulfan W.P. 0.5% active ingredient, with a significant increase of 45.1 and 100%, respectively. He also studied potential tamarugo fruit yield apart from pest impact. The plants were sprayed at sprouting, blooming and fruit formation with Endosulfan W.P. 0.5% active ingredient and mythl parathion 0.43% active ingredient. The first pesticide was applied on 12 February, 6 November and 26 November; and the second on 10 December, once the departure of the pollinator Centrix mixta was assured. The findings indicate a 210 kg and 427 kg increase for two trees. The two methods of application compared were crop dusting from the air and on the ground with Endosulfan Emulsianate 5% active ingredient in diesel oil. Ground treatments were 100% as compared to 30% with aerial spraying, which also affected the bee, Centrix mixta.
TABLE 12: Biological studies of the major plagues affecting tamarugo during growing season, percentage of fruit losses and recommended date for applying control treatments (Cadahia, 1970)
|Legend:||\\\\||vulnerable fruit production periods|
|a||adults||lp||larvae in diapause|
|e||eggs||ps||pupae in soil|
|l||larvae||maximum adult population|
This vast stretch of desert, with its single basic flora relationship, is a very poor area from the plant and flora standpoint. There is no specific association of flora because the plants incidentally found are some of the most xerophytic of all the region. Nor is it possible to discern a true relationship between man and plant.
Sometimes, every open areas with a few shrubs and perennial grasses are found tracing the course of underground streams flowing beneath apparently dry riverbeds. These riverbeds may or may not have surface runoff during the random rainy years. The subsoil is usually slightly more moist in these areas than in the rest of the desert.
The present plant community is relatively homogenous, being made up of a very few species, with greater variability where the groundwater table is closer to the surface. The following species are found in association with tamarugo: Prosopis strombulifera (Lam) Benth, known as “fortuna”; Prosopis burkartii Muñoz, the Argentine tamarugo; Tessaria absinthioides DC, brea; Distichilis spicita “salt grass”; Cressa cretica L., retama; Atriplex spp., “pillaya”; Euphorbia tarapacana Phil. and Tagetea minuta L. Prosopis Chilensis or carob, is also found in the area, but was probably introduced (León, 1974). Atriplex, Chenopodium and Distichlis species are only found in small areas bordering salt flats, where they thrive on sandy promentories sculpted by wind erosion.
The habitat and ecological niches of the fauna associated with these plant formations constitute their territory for food or prey. The ecological limiting factor is definitely water, which largely regulates the distribution and type of fauna co-existing in this environment. This factor has confined wildlife to certain specific sectors, which has led to indiscriminate hunting by men, resulting in the extermination of many species of interest to man, and the reduction of other fauna populations to the point where they are clearly endangered species (IREN, 1976).
Aridity severely limits the development of relatively large numbers of animals. Despite this, where running or underground water is available, or where there is dense ground fog, open forests develop with tree species providing food and protection for the primary consumers of the ecosystem (IREN, 1976).
1. Scaly reptiles
Phrynosaura reichei. Known as a lizard of very low population density, it inhabits an adverse environment with little water, its only source of food being wind-borne insects. It spends most of the day under the salt crust to avoid excessive dessication.
Tropidurus tarapacensis. This reptile, known as the “desert lizard”, is found in highly specific environments (tamarugo ecosystem) or in more dynamic areas such as the railway stations of small rural towns.
2. Mammals (carnivores)
Dusicyon culpaeus, known as the “culpeo”. This is a northern jackal, abundant from the coast to the altiplano, and nocturnal by nature. It ranges over great distances in search of small fauna for food.
Dusicyon griseus domeikoanus, known as the “chilla”. Rarely seen in the Tamarugo area, it is more frequently found in the valleys.
Galicitis cuya or “Quique”. This is a small weasel, diurnal by nature, which crosses its territory with its family in file formation. It preys principally on rats, mice and small birds. It is the animal most characteristic to the Tamarugal Pampa, to which it is ecologically well suited.
Ctenomys robustus, known as the “tuco-tuco”, is highly adapted to living underground. It feeds on roots and insects. A supranasal membrance allows it to close its nostrils. It also has small, strong, chisel-shaped teeth for digging deep into the ground.
Phyllotis darwini repestris, known as the “lauchón” in the Tamarugal Pampa, it lives together with another related small rodent, Akodon andinus dolichonix. It is found everywhere in Chile and eats insect larvae and plant wastes.
A review of the literature on wildlife of the Tamarugal Pampa suggests that fauna have become less widely dispersed and fewer in number, due to unrestrained human intervention in the form of hunting, persecution and the introduction of domestic herbivores (IREN, 1976).
Birdlife is less rich than other vertebrate species, and much poorer than insect species. It is particularly scarce in the Tamarugal Pampa because its existence depends on the availability of drinking water (Donoso, 1967).
Four-year old P. tamarugo competing with native Atriplex atacamensis in the San Pedro de Atacama salt flat. March, 1978.
9 Essential to inoculate when not in situ.