National Forestry Research Institute
Saltillo Coah, Mexico
It has been estimated that the planet Earth is close to 4.6 billion years old. During the first 4 billion years Earth was practically a desert, in the strict sense of the word, because it consisted exclusively of inorganic matter. Besides, with the lack of atmosphere, solar energy did not find in its path molecules that would absorb, in part, the ultraviolet rays, causing them to entirely bear upon the earth's surface, thus hindering the formation of living creatures.
Only after 800 million years, and for the first time, the simplest form of celular organization, the Blue-Green Algae, appeared in the seas, an organism capable of achieving the process known as photosynthesis, activity with which oxygen was first produced and which, very rapidly, became the vital element for animal life.
This apparently insignificant fact become an important event, for with the elaboration of oxygen, ozone was also produced, an element whose function is to stop the sun's ultraviolet rays and to generate better conditions for the development of more complex living creatures. These initially settled by the shores of continents and progressed inland by degrees.
During this millenary period, in which the above described process was accomplished, different forms of life appeared and —in order to survive in a changing atmosphere— they had to evolve. One of the greatest inventions of nature, chlorophyll, dates from this period.
As yet, it has not been possible to establish the time in which the first vascular plants appeared and created the green pigmentation on Earth; nevertheless, it is believed that they started to occur at the end of the Silurian Age, approximately 400 million years ago. With the appearance of vascular plants, the massive formation of different types of forest took place, reaching its peak during the Carboniferous Age.
In addition to atmospheric instability and diversity in the adaptation mechanisms of life forms, both plant and animal, the conformation of continents was changing; their configuration has not always been the same, as they underwent important displacements before reaching their present outline (Figures 1, 2, 3, and 4). Almost simultaneously, and as a consequence of the above, deserts appeared and to date, they are located in sites that seem capricious; yet, evidence points to an intimate relation in their distribution with the separation of continents.
For all these reasons the regions rich in vegetation receded upon the formation and expansion of new arid zones; this is how the present deserts made their appearence. Now, these unfold throughout the course of two bands passing over the Tropics of Cancer and Capricorn, between 15° and 35° latitude in both hemispheres and in some cases, as in Argentina and Asia, reaching up to 55° (Figure 5).
|Figure 1.||Architecture of the Continents 180,000,000 years ago||Figure 2.||Architecture of the continents 125,000,000 years ago|
|Figure 3.||Architecture of the continents 55,000,000 years ago||Figure 4.||Present shape of the continents.|
The causes that originated the existence of deserts on Earth are so varied that it would be complicated to offer a satisfactory analysis in this regard; nonetheless, the common denominator in the presence of deserts lies, fundamentally, in the dynamics of the atmosphere's general circulation and in the peculiarities observed in the geomorphology of the terrestrial globe. In the first case, the degree of incidence of solar radiation and the combined effect of Earth's rotation make the Equator receive a greater quantity of radiation, a fact tending to heat the air masses, thus forming a pattern of atmospheric circulation of the meridional type; also, the planet's rotation produces areas of latitudinal winds that raise, cool and condense the heated air in the Equator, causing it to discharge its entire humidity in the tropical area, thus creating the two great belts of high atmospheric pressure, located in latitudes close to 30°.
As regards deserts at greater latitudes, in turn, they are located in the Southern Hemisphere, in the Chilean-Argentinean Patagonia; these desertic regions originated due to geographic conditions, for they are distant from the sea, at considerable altitudes, and because they are surrounded by mountainous configurations serving as topographic barriers that prevent the passage of humid winds and create an absence of rain in their midst.
This is known as “orographic shadow”, and it is produced when the winds collide with the mountain massif; getting cooler upon ascending, they discharge their entire moisture on the windward slopes. When these masses of air become dry winds, they descend through the leeward slopes and, upon reaching the arid valleys, they disappear, thus depriving them of humidity and generating the deserts (Figure 6).
Figure 5. DESERTS OF THE WORLD
Efforts have been made to explain the location of the desert belts on the base of the 23° 27' inclination of Earth's axis; correspondingly, the propitious angle of inclination concentrates the radiated energy in these areas with the obvious result of greater elevation in temperature and the development of arid conditions (Figure 7).
Arid and semiarid regions in the planet exceed 64 million km2 in area, representing 43% of the continental total land and 14% of Earth's total area. Deserts are distributed in five great regions, as follows:
NORTHERN REGION OF AFRICA-EURASIA
Here are located the Sahara desert, the deserts and steppes of the Soviet Union, China and Mongolia, and the deserts of Somalia-Chalbi, in Eastern Africa, as well as other arid and semi-arid areas extending towards the west, through the Arabic peninsula, the Persian Gulf, Pakistan and India; further north, we find some in the coastal areas of the Mediterranean region and in Iran.
SOUTH AMERICAN REGION
This corresponds to a strip distributed along the western coast, and an area in the oriental Andean portion, stretching out to the extreme south of the continent.
Formation of the orographic shadow
The 23° 27' slant angle of the Earth axis propitiates concentration of radial energy on the desert belts.
SOUTH AFRICAN REGION
This region is formed, basically, by the coastal deserts of Namib, Karroo and Kalahari.
It is formed by the great Sandy Desert and the Victoria Desert.
NORTH AMERICAN REGION
Located in the United States of America and in the Mexican Republic, it entails five subregions as follows: the Sonoran desert, the Mojave, La Gran Cuenca (The Great Basin), and the Baja California area.
Due to the great number of biotic and abiotic factors involved, it is difficult to establish with precision the borders of the arid and semi-arid zones by their characteristics in climate, vegetation, geology, etc. This has given way to numerous classifications, based on some of the already mentioned aspects. Also, in trying to uniform criteria, a series of proposals have been made, among which the following may be mentioned:
The Austrian meteorologist, Wladimir Koppen, defines deserts as regions in which evaporation is, at least, twice as high as rainfall. Le Houérou, in turn, considers them as areas receiving less than 100 mm of yearly rainfall; and semi-arid, those in which rain does not exceed 400 mm per year.
In Mexico, Martinez and Maldonado published a paper in 1975 in which they analyze the different physical and biological factors involved, correlating them to define the arid zones as those in which rainfall is below 350 mm per year, with an irregular distribution during the vegetative cycle, where the average temperature lies between 15° and 25°C, and with a seven-month drought and less than 70% forest cover, where xerophilous species are dominant.
They also define the semi-arid zones as those in which the annual rainfall varies from 350 to 600 mm, with an annual average temperature of 18° to 22° C, and with 6 to 8 months of drought. Their forest cover exceeds 70% and the dominant vegetation consists, basically, of different types of shrubs and grasses.
One of the regions having the above mentioned characteristics is part of the desert in the North American region, which cuts into Mexico in the subregions of the Chihuahuan Desert. This desert is located in the north central portion of the country, between the Eastern Sierra Madre, the Neovolcanic Mountain Range and the Western Sierra Madre.
The Sonoran Desert is located between the Western Sierra Madre and the coast of the Sea of Cortes. The Baja California desert, a coastal arid zone, also known as “Desierto de Neblinas” (Foggy Desert) is located in the Baja California peninsula, formed by the west winds and cooled by the oceanic currents that bathe the Pacific shore (Figure 8).
The great altitudinal oscillation of the Mexican Republic, its location at both sides of the Tropic of Cancer and the influence it receives from the ocean due to the narrowness of its continental mass, are factors that gave rise to this climatic diversity. Therefore, the forest cover in Mexico is very complex, as in this territory one finds practically all the great biomes of the world that have been classified as tropical forests, temperate forests, shrubs and grasslands, not to mention different plant communities such as high altitude plateaus, aquatic and halophilous vegetation, etc. (Figure 9). The causes of this diversity are due not only to the geomorphologic and climatic conditions mentioned above, but also because Mexican territory presents meridional South American vegetation as well as boreal North American and Eurasian, and some unique biomes, probably indigenous to Mexico.
The management of the forest cover in Mexico was started twenty thousand or more years ago, when man, as hunter and gatherer, lived in close relationship with nature and the success he derived form his activities depended largely on his ability to distinguish the vegetal species that were useful; during the last millenia, life for the Mexican inhabitants was based on agriculture; they were not intimately dependent on forests, shrub or grassland. During that long period of time, generation after generation transmitted a host of information, by word of mouth, regarding the dynamics of vegetation, their relation to climate and soil, but above all else, their usefulness.
At first, a certain ecological equilibrium was maintained between man and nature because he only extracted what was necessary to survive; imbalance developed gradually, when great demand for construction material in the mining activities started during the colonization; agriculture, cattle breeding and forest activities also increased notoriously. Not only was the regional ecology disturbed during this period, but also much floristic knowledge was lost, as regards the uses and employment of innumerable species, which, according to the chroniclers, were used differently by native groups.
Figure 8. Deserts of Mexico
Figure 9. Vegetational groups of Mexico.
Scientific development in modern times has required more exact information regarding the natural resources in the forest cover; and the detailed study of communities has enabled the identification of different biomes, the real indicators of diverse environmental conditions.
Basing on the structure of vegetation, determined by these concepts, it has been possible to delimit 27 types of vegetation in the tropical and sub-tropical zones in Mexico, covering 24% of the country's total area; it has also been possible to identify 18 types of forest in the temperate and cold zones, representing 21% of the Mexican terrytory's total land. The remaining 55% is covered by the characteristic vegetation found in arid and semi-arid zones, 45% of which are shrubs and 10% grasslands.
In these types of arid zone vegetation the flora is quite varied, with more than 2,200 species belonging to, at least, 60 genus in 122 families. In terms of their abundance, the most important are: Compositae, Leguminosae, Graminae, Cactaceae and Liliaceae, species that have helped man meet certain necessities and have aided him to thrive in this region. Man managed them with ability and differently; firstly, he divided them according to their usefulness and then grouped them in arboreal, fodder, industrial, medicinal, nourishing and ornamental species; later, he directed his endeavours to their domestication and cultivation.
At present, the arboreal species supply fuel and construction material; they are used in the timber industry, in arts and crafts, as tanning agents and in the manufacture of tools, to mention but a few.
In arid zones, the fodder species form the nourishment basis for breeding cattle, thus maintaining the equilibrium in animal life in these regions; due to their importance, we must stress the existence of grasslands and fodder shrubs.
Because these species produce fiber, wax, rubber, saponin, oil, alcohol, hormones, antirusts, fungicides, etc., they have found use in industry.
The medicinal species have contributed to Mexican pharmacology after several products have been synthesized to cure problems related to cardiovascular, digestive, tract, diuretic, antibiotic, renal, anti-scorbutic, astringents, anti-rheumatic and dermathologic ailments.
The nourishing species have helped in the nutrition of man with fruits, flowers, stems, leaves, roots, and/or seeds; it is also important to mention the ornamental species, which have provided man with relaxation and recreation and because of their beauty, the group of the agaves and Cactaceae are remarkable.
From the physionomic and utilization point of view, the forest cover of the regions with an arid or semi-arid climate is so variable that for descriptive effects it is grouped under the collective label of shrubs and grassland.
Shrubs cover 45% of the national territory and are considered as plant communities of the shrub-like type, proper to arid zones; in the Sonoran Desert shrubs are distributed through the coastal plain and in the low mountains in the state of Sonora. In the Baja California Desert, it occupies the greater part of the peninsula, excepting the Juárez, San Pedro Mártir and La Laguna Sierras and the southern portion of its territory. In the Chihuahuan Desert, shrubs are distributed in the high Mexican plateau, encompassing the northern regions of the country (in the states of Chihuahua, Coahuila, Nuevo León, Tamaulipas, San Luis Potosí, Zacatecas ans Aguascalientes) up to the states of Guanajuato, Jalisco, Hidalgo and Mexico; it reaches further south in a narrow strip that penetrates Puebla and reaches Oaxaca.
The forest cover in this type of vegetation, as compared to other plant communities in the country, is probably the least affected by human activities because the ecological characteristics are not favorable to the development of intensive agriculture or cattle breeding; but there are notable exceptions in the irrigated zones, with a highly sophisticated agriculture that harvests from garden produce and fruit trees to cotton, wheat, sorghum and soybean. Of course, there are no traces left of the native vegetation in these small areas. Non irrigated agriculture is frequently practiced where a moisture holding capability exists, in the best soils and in regions where aridity is less prominent; the traditional crops are corn, barley, oats and beans. At present, and with the advantage of the technology developed through research, ecocultures of gramineous prairies, fodder shrubs, maguey, prickly fruit cactus, oregano, damiana, jojoba, etc., are carried out.
There is a more generalized use of shrubs in cattle breeding, activity which is now practiced in an extensive scale, and the goat is the animal species more common there because not only does it need small quantities of water to survive, but it is also particularly well adapted to the vegetational characteristics of shrubs; cattle, horses, sheep, mules, fighting bulls and rodeo animals are also raised in these regions.
The impact caused by cattle breeding in the shrub forest cover is a gradual disappearance of desirable species and the appearance of invading ones; because of this, there are great extensions of arid zones in Mexico with overgrazing. Nevertheless, there are areas where summer grazing is practiced, considerably elevating production and productivity of the soil.
Contrary to what happens in regions with good ecological characteristics, man in the desert is bent on obtaining maximum benefit from the natural vegetation that surround him; hence, many plant species have traditionally been used for the building of homes, the erection of fences, as fuel or for nourishment. Yet only a few species are exploted intensively because their products, having industrial qualities, are marketed and commercialized in the country and abroad.
It is important to mention the following species in this bracket (Table 1):
USE OF MAIN INDUSTRIAL SPECIES FOUND IN ARID ZONES
|Species||Common Name||Obtained Product||Uses|
|Euphorbia antisyphylitica||Candelilla wax||High quality wax||Cosmetics, paints, records, matches, paper containers, electronics, lubricants, insulators, etc.|
|Agave lecheguilla||Lechuguilla||Hard Fiber||Manufacture of brushes, sacks and cords|
|Parthenium argentatum||Guayule||Natural Rubber||Manufacture of tires.|
|Yucca camerosana||Spanish bayonet||Fiber||Used in cords and in the manufacture of sacks|
|Yucca filifera||Soaptree yucca||Natural source of hormones, oil, fiber||Pharmaceutical industry in the preparation of steroid hormones (manufacture of contraceptives) to obtain paper from trunks. 20% oil content.|
|Cucurbita foetidissima||Buffalo gourd||Oil||33% oil content|
|Ungnadia speciosa||Monilla||Oil||67% oil content|
|Lophophora williamsii||Peyotl||Mescaline and alcaloids||Preparation of beverages and as fungicide agent.|
|Fluorencia cernua||Tarbush, Blackbush||Planovoids||Compounds extracted from its leaves have fungicide activity|
|Acacia berlandieri||Guajillo||Alcaloids||Compounds with great fungicide activity are extracted from the flower.|
|Larrea tridentata||Creosote Bush||Resins, norhydroguayaretic||Antirust in food industry; for the preparation of fats and varnishes, phenolic type fungicide|
|Simmondsia chinensis||Jojoba, Goatnot, Cofee Berry||Liquid wax||Waxes, oils, cosmetics, lubricants and as a substitute for sperm whale oil.|
Candelilla wax (Euphorbia antisyphilitica). This species is distributed over an area close to 14 million ha; high quality generic wax is obtained from the stem.
Lechuguilla (Agave lecheguilla). This species provides a hard fiber used in the manufacture of brushes, sacks and cords; it is commonly associated with Euphorbia antisyphilitica and is distributed over approximately 11 million ha.
Guayule (Parthenium argentatum), with a similar range, has been a source of natural rubber and has been exploited since 1906. It covers more that 9 million ha.
Spanish bayonet (Yucca carnerosana) is distributed over an area close to 11 million ha, and from its tender leaves fiber used in ropes and the manufacture of sacks is obtained.
Soaptree yucca (Yucca filifera) is distributed in an area close to 9 million ha. This species provides a natural source of hormones and is notable for its quantity of sarsaponenin.
There are also other types of palms in the Sabal, Washingtonia and Brahea genera used in arts and crafts and in the manufacture of hats.
Creosote bush (Larrea tridentata) contains resins used as base in paints and in the manufacture of fats and varnishes as well as phenolic type fungicides; it is also important for its protein content, apt for animal consumption.
The seed of the jojoba, Goat-not, Coffee berry (Simmondsia chinensis) produces a liquid wax of multiple uses, but it is mainly used as a substitute for whale oil.
Palo mauto (Lysiloma divaricata) produces tannins which are very useful in the leather industry.
Orchilla (Rosella spp.) is a lichen used as raw material in the dying industry.
The management of the forest cover where these industrial species are found has been traditional and to date it is still practiced in many regions of the country; as examples we can mention Euphorbia antisyphilitica and Parthenium argentatum, normally uprooted; hence, their natural growth has been greatly hindered. The management of Agave lecheguilla, Yucca filifera and Simmondsia chinensis has been performed at two levels: in natural environments, and by simply cutting off the fruit, establishing the inaccessibility of domestic animals and eliminating the competition from other species.
Important factors in their management are the timing and the method used for harvesting the fruit. Lysiloma divaricata, Rosella spp. and Larrea tridentata have been managed in the traditional manner and only their stems are used for extracting their components (tannins, boiler compound and dyes).
In the group of medicinal plants (Table 2) the following are outstanding: ocotillo (Fouquiera splendens), chaparro prieto ((Acacia rigidula) cenizo (Leucophyllum texanum), damiana (Turnera difusa), txoloache (Datura stramonium), anacahuita (Cordia boissieri), farry duster Calliandra eriophylla) tarbrush, blackbrush (Flourencia cernua), guayacán (Porliería angustifolia) and different species of the genus Rhus.
MEDICINAL SPECIES IN ARID ZONES
|Fouquieria splendens||Albarda or ocotillo||Anti-cough|
|Acacia rigidula||Chaparro prieto||Brew, gastric disorders.|
|Leucophyllum texanum||Cenizo||Brew, gastric disorders.|
|Euphorbia antisyphilitica||Candelilla wax||Catartic, venereal diseases|
|Turnera difusa||Damiana||Aphrodisiac, brew, tranquilizer|
|Datura stramonium||Toloache||Hallucinogen, anorexic, anti-scorbutic, anti-inflamatory, anti-neuralgic.|
|Cordia boissieri||Anacahuita||Used as stimulant and expectorant.|
|Acacia farnesiana||Sweet acacia||Anti-dysenteric, anti-spasmodic, antituberculosis, astringent.|
|Calliandra eriophyla||Furry duster||Invigorator|
|Fluorencia cernua||Tarbush, blackbrush||Expectorant|
|Porlieria angustifolia||Guayacán||Anti-rheumatic, dïaphoretic, emmenagogic, venereal diseases, vascular stimulant.|
|Larrea tridentata||Creosote bush||Anti-rheumatic, gall-stones, kidney stones, dermatitis, dysuria, hepatitis.|
|Lippia spp.||Oregano||Food spice|
|Castela texana||Chaparro amargoso||Brew, gastric disorders (ulcers).|
The management of these species is basically limited to the gathering of the vegetative parts used for medicinal purposes; for example, the flower in Cordia boissieri is used; the leaves, in Flourencia cernua; the stems, in Porlieria angustifolia and the tender seeds, in the genus Rhus; yet there is no specific methodology in their management.
Ornamental plants form another useful group in these same areas, and it is common to find different species of agaves and Cactaceae, charming locals and foreigners alike for their beauty. They are exploited in their natural environment and are also cultivated commercially (Table 3).
These plants, as well as those mentioned above are simply gathered by the inhabitants of arid zones for their commercialization in urban centers; occasionally, they are exported.
In Mexico arid zones the exploitation of some arboreal species is frequent, as happens with the following: willows (Chilopsis linearis) and the palo de arco (Tecoma stans), used in the manufacture of furniture and tool handles; barreta (Helietta parvifolia) and palo zorrillo (Cassia emarginata), very appreciated for building fences; the wood of the mesquite (Prosopis spp.) is used to make staves, to obtain coal, firewood, hulk staves for small boats, fence post, shoe and furniture blocks; the palo fierro (Olneyda tesota) is used in buildings and as arts and crafts material, etc. (Table 4).
The traditional management of these species is almost limited to the gathering of logs and branches; the areas with species providing fuelwood are highly plundered near population centers.
LIST OF THE MAIN ORNAMENTAL SPECIES IN ARID ZONES
|Agave americana||Agaves, maguey|
|Yucca filifera||Soaptree yucca|
|Ferocactus pringley||Barrel cactus|
|Echinocactus viznaga||Barrel cactus|
|Echinocereus pectinatus||Biznaga arcoiris|
|Astrophytum capricorne||Birrete de obispo|
USES OF MAIN ARID ZONE TREE SPECIES
|Chilopsis linearis||Willow||Manufacture of tool handles, hoes and furniture|
|Helieta parvifolia||Barreta||Very useful in the installation of fences|
|Prosopis spp.||Mesquite||Its wood is used in the manufacture of staves, fences, as building material and fuel.|
|Fouquieria splendens||Ocotillo||Building material and fuel|
|Opuntia imbricata||Coyonoxtle||Building material.|
|Yucca filifera||Soaptree yucca||Building material and fuel.|
|Cassia emarginata||Palo zorrillo||Fence building|
|Tecoma stans||Palo arco||Home building and furniture|
|Olneya tesota||Palo fierro||Furniture, building and arts and crafts.|
As to the nourishing species, there is a great variety and the most frequently used are; the tepari bean, some Cactaceae in the preparation of sweets or liquors, entailing most of the species in the Dasylirion and Agave crops; oregano, used as a spice; chile piquin (Capsicum bacatum), damiana, sage and other spices used as brews; also used are the fruits of different types of Yucca; bulbs and seeds contribute to the nourishment of the arid-zone inhabitants. It is necessary to underline the importance of the nopal plants (Opuntia spp.) because the tender cladodes are eaten as a fresh vegetable and the fruit is sweet to the taste.
As has been stated before, shrubs have been more generally used for cattle breeding; therefore it is convenient to mention that they not only produce abundant fodder from forage shrubs, but also from grasses. Important among shrub species are: the saltbush (Atriplex canescens), saladillo (Atriplex acanthocarpa), guayacan (Porlieria angustifolia), blue palo verde (Cercidium floridium), vara dulce (Eysenhardita polystachya), ramoncillo (Dalea tuberculata), as well as different Opuntia species and many other shrubs (Table 6).
ARID ZONE NOURISHING SPECIES
|Lippia spp.||Oregano||Spice in foods.|
|Dasylirion spp.||Sotol||Liquor is obtained for the elaboration of alcoholic beverages.|
|Agave spp.||Maguey||Elaboration of alcoholic beverages.|
|Capsicum bacatum||Chile piquin||Spice|
|Turnera diffusa||Damiana||Prepared in a brew as a tranquilizer and as a liquor.|
|Opuntia spp||Nopal||The tender cladodes and the fruit are used in the human diet|
|Yucca filifera||Soaptree yucca||The fruit or pulp is used to make jellies and jams, as human nourishment.|
USE OF SOME FODDER SPECIES FOUND IN ARID ZONES
|Cerdicium floridium||Blue palo verde|
|Eysendhardtia polystachya||Vara dulce|
|Albizzia occidentalis||Palo escopeta|
Arid zone cattle breeding in Mexico is of the extensive type, and because of the ecological characteristics of these regions the fodder species already mentioned are important in the nourishment of cattle, mainly during the dry season; bearing this in mind, the management of range lands is carried out by rotation, where the management of grasses and shrub-like vegetation is combined with the management of cattle.
The vegetation group of grasslands, together with the shrubs already described, are distributed in arid zones and, for descriptive reasons, are grouped in grasslands clusters and halophytic formations.
The grasslands with clusters cover some 2.5 million ha, and they are formed by mediumsized and fascicled gramineous plants. The most characteristic species in this plant community are: Bouteloua curtipendula and Bouteloua uniflora, as well as different species of Stipa, Muhlenbergia, Aristida and other genera.
The halophilus grasslands, formed by medium-sized gramineous plants with a height of 30 to 40 cm, are resistant to salt concentrations in the soil and are found in an area of over 1 million ha; the most representative are; Sporobolus airoides, Hilaria mutica, Hilaria jamessii, Sporobolus phyramidatus, Sporobolus cryptanuus, etc.
From the economic point of view, grasslands are very important in these zones because they are particularly befitting to the breeding of cattle in these regions; nevertheless, in most cases, they are not used to full advantage and in may areas evidence exists of excess grazing, thus diminishing the forest cover to a critical level and, logically, exposing the soil to the effects of erosion.
The experience obtained by means of investigation in the handling of the forest cover in arid zones produces the following data:
Guayule (Parthenium argentatum). The management of this species is carried out by performing 40% cuts in relation to its height. This permits a constant production in the natural environment; besides, it makes, it easier for the seeds in the soil to sprout. It is also an aid in seedling development.
The results obtained through investigation in the management of the candelilla wax (Euphorbia antisyphilitica) recommend partial cuts in the plant so as to ensure its regeneration. Cuts have to be performed after winter and before the first rains.
The optimal management of the nopal plant is obtained by pruning 30% of it biomass.
As regards the lechuguilla (Agave lecheguilla), it is advisable to collect the shoots found facing north, thus obtaining greater production and better quality fiber.
The tarbush, blackbush (Fluorencia cernua) and oregano (Lippia spp.) cover areas in the north of the country. It is recommended to cut the plants up to 40% of their biomass.
Bearing in mind that cattle breeding is the most disturbing agent to influence forest cover in arid zones, it is advisable to determine this activity in agreement with the summer pasture coefficient, the establishment of conservation practices for the hydrologic basin, the correction of gullies, the planting of shrubs with fodder qualities and sowing of indigenous as well as introduced grasses.
As has been explained, one sees that the natural balance in arid zone ecosystems in Mexico has been greatly unsettled due to human activities, mainly because of the fragmentary practices of the traditional models of management; nevertheless, when one analyzes ecological characteristics and research findings one does not recognize borders between the practices performed in agriculture, livestock raising and/or forestry, hence it is evident that the forest cover in arid zones presents viable alternatives for the integral use of its resources, but bearing in mind that technical management should insure the permanence of the natural environment; more importantly, the fact that a multiple use management model can increase production and productivity in these plant communities must stress it consideration by renewable natural resource managers.
Undoubtedly, when we hear the word desert we imagine a vast expanse of sand where no vestiges of life can be seen; yet the truth is quite different, because within the flora that shapes the desert cover there exist numerous species and varieties which, in different times through history, have been used advantageously and have constituted the generating basis of economical resources for arid zone dwellers.
Precisely because there is great variety in the characteristics of Mexican arid zones and in the species that thrive in them, it is necessary to increase present production by managing these resources in a totally correlated way and to reach an integral rural development. In this manner not only economic resources are generated, but also the preservation of wild fauna, and consequently that of man himself, will be guarantied.
|SPECIES||ENGLISH COMMON NAME||SPANISH COMMON NAME|
|Larrea tridentata||Creosote bush||Gobernadora|
|Fluorencia cernua||Tarbush, Blackbush||Hojasén|
|Cercidium floridium||Blue palo verde||Palo verde|
|Olneya tesota||Ironwood||Palo Adán|
|Prosopis juliflora var. glandulosa||Mesquite||Mezquite|
|Atriplex canescens||Saltbrush||Costila de vaca|
|Calliandra eriophylla||Farry duster||Calderona|
|Chilopsis linearis||Desert willow||Mimbre|
|Ferocactus pringlei||Barrel cactus||Biznaga colorada|
|Cucurbita foetidissima||Buffalo gourd||Calabacilla loca|
|Datura stramonium||Jimson weed||Toloache|
|Euphorbia antisyphilitica||Candelilla wax||Candelilla|
|Yucca carnerosana||Spanish bayonet||Palma samandoca|
|Yucca filifera||Soaptree yucca||Palma china|
|Simmondsia chinensis||Jojoba, Goat-Not Coffee berry||Jojoba|
|Acacia rigidula||Chaparro prieto|
|Acacia farnesiana||Sweet acacia||Huizache|
|Castela texana||Chaparro amargoso|
|Agave americana||Agaves, Maguey||Maguey americano|
|Echinocactus viznaga||Barrel cactus||Biznaga burra|
|Echinocereus pectinatus||Biznaga arcoiris|
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The agriculture at Region I, Tarapacá, in a sea-mountain transect, can be defined as coastal valley agriculture, pampa agriculture, Andean foothill agriculture and Andean high plateau agriculture. The prevailing characteristic for this activity in Region I is that of being the typical agriculture of extreme aridity, inserted at the Atacama Desert, one of the most arid in the world, and depending completely on artificial irrigation, on account of the fact that rainfall at the coastal valleys and pampas is negligible. Only in the Andean foothills and high plateau does rainfall reach about 200 mm annually, concentrated in the months of January and February. In the high plateau, during these months, there are snowfalls which insure water availability for the rest of the year. Nevertheless, every few years drought periods occur which affect all kinds of agriculture, from sea to mountain.
The Institute of Agronomy (IDEA) of the Tarapacá University is located at the Azapa Campus, 12 km from the city of Arica and at 250 m altitude. It is an academic unit primarily geared to agricultural research.
AIMS OF THE AGRONOMY INSTITUTE (IDEA) OF THE TARAPACA UNIVERSITY
Areas of the Institute
The Institute of Agronomy (IDEA) has organized its academic work around three areas of the agricultural sciences, according to the human, economic and physical infrastructure resources currently available to it.
These areas generate, either individually or combined, the research and extension activities undertaken. They also contribute with teaching at the Faculties of the University.
Plant Protection Area
This area is engaged in the study and solution of the main sanitary problems of the crops, with the purpose of obtaining good quality and well-presented products so as to compete advantageously in domestic and international markets.
The specialized departments in this Area are: Entomology, Nematology, Phytopatology and Weed Control.
At the present time, Entomology and Nematology are permanently operational, while phytopatology is partly active.
Natural Resource Area
Its purpose is to study the soil and water resources with a view to their rational utilization, taking into consideration the conditions encountered in arid and extremely arid zones, typical of this region. Among the most relevant aspects are the constant concern with the irrigation problems, given the scantiness of the resource, and the permanent interest in good utilization of the soils.
This Area is planned to include specialization in soils, irrigation and fertilization. Presently, the irrigation and fertilization problems are being dealt with.
Plant Production Area
It conducts research on the management problems of crop and fruit species and strains characteristic of arid and desertic zones. Furthermore, it is engaged in the introduction and evaluation of germplasm, with the purpose of offering alternatives for the crops of the region.
The areas of specialization considered here are: horticulture, fruit production, fodder plants and agricultural crops and economy.
The activities currently under way are those related to horticulture, fruit production and agricultural economy.
The projects of the Institute are oriented towards research, extension and education, in this order of priorities, in accordance with the functions assigned to it by the DFL 150 of the Ministry of Public Education, the Act which created the Tarapacá University and its academic structures.
To meet the objectives set forth by the Institute, the following research activities are presently being conducted:
The extension activities carried out by the Institute are structured on the basis of extension courses, field days, speeches, exhibits, seminars, symposia and organization of congresses and round tables on specific subjects.
The extension courses offered periodically by the Institute are:
Another extension activity organized every two years by the Institute are the National Olive Days, having organized the first ever of such events in 1981.
Every year it organizes the agricultural and institutional exhibit at the Altiplanic Regional Fair (FERAL), in the Parinacota Province.
In joint agreements with agriculture-related national institutions, it conducts agricultural extension and technology transference programs, through demonstration crops, field days, extension brochures, training courses for the local farmers, speeches and educational itinerant photographic exhibits, primarily at the mountain area of the Parinacota Province.
The teaching activity of the Institute consists of the dictation of optional courses on general formation for the various careers offered by the Tarapacá University.
The academic personnel of the Institute participate as leader professors for degree works of students from this University and from other institutions of agricultural and livestock education of the country.
The Institute of Agronomy (IDEA) has four experimental plots: two at the Azapa valley (14 ha in total) and two at the Lluta Valley (76 ha in total), with a combined physical area of 90 ha.
The laboratories and administration compound are located at plot No. 27 of the Azapa valley, km 12.5, Colonia Juan Noé Crevani. 1,200 sq m of buildings in this property house the crop, soil, irrigation, nematology, entomology and phytopathology laboratories. There is also a library specialized in agriculture.
Each laboratory has regional collections, among which stand out the entomological collection, with over 60,000 individuals labelled; the massive and permanent collection of phytoparasite nematodes; the collection of plants native to the region and a phytopathological herbarium.
The Germplasm Bank is another major item which the Institute maintains for the crop genetic improvement works in the region.
A microcomputer was recently incorporated to start a Regional Agriculture Data Bank, complemented with the general computing capacity of the University.
IDESIA is a periodical publication intended for the diffusion of the scientific works of the academic personnel in the Institute and from other scientists from the University, or from other institutions who wish to publish articles dealing with the agricultural situation of the Atacama Desert. Five volumes of this review have already been published, and distributed throughout the world.
The technical bulletins are another source of information prepared by academic personnel of the Institute, with 35 issues already released.
There are also miscellaneous publications and Extension Leaflets for the local farmers.
The catalog with the publications of the Institute in available upon request.
The Publications Office has exchange arrangements with the main libraries in the world, through museums, universities, governmental libraries and public and private experiment stations.
INSTITUTIONS COLLABORATING WITH THE INSTITUTE OF AGRONOMY (IDEA)
A number of both foreign and local institutions contribute to the various activities of the Institute.
ACADEMIC PROJECTION OF THE INSTITUTE OF AGRONOMY OF THE TARAPACA UNIVERSITY
The Institute of Agronomy of the Tarapacá University has defined its academic projection around basic and applied research on the desert agro-silvo-cultural ecosystems in Region I.
Due to the complexity of the problems encountered in these ecosystems, their systematic study requires the contribution of various agricultural disciplines and of other fields of knowledge. In this regard, the Institute of Agronomy of the Tarapacá University needs a number of researchers in its various subject areas to foster the exchange of ideas on, or approaches to, the complex realities of this Region.
The development objectives of the Institute of Agronomy of the Tarapacá University and the present staff envisage some specific areas which will necessarily have to be incorporated in the medium term, so as to meet the research needs in Food Technology, Cameloid Stock Raising, Plant Production in Semi-Controlled Environments, Phytopathology, Virology and Agricultural Mechanization.
With this critical mass of researchers, it will be possible to enlarge the research activities towards the typical desert areas with extreme aridity conditions, which are presently only tangentially approached.
Concurrently, the Institute is carrying out a post-graduate program for its staff, with the aim of counting, at the end of this decade, on at least one Ph. D. per area, so as to become a leading institution at the regional —and, perhaps, national— level in the research on extreme arid regions.
This academic unit of the Tarapacá University, in its medium to long term development plans, contemplates the inclusion of post-graduate courses on desert agriculture, once the academic post-graduate stage abroad is completed and cooperation agreements are materialized with national and foreign universities, and international development organizations. This academic activity, oriented towards the post-graduate improvement, would make it possible to offer the more than 20 years of experience in research presently available at this Institute.
The growth planned in this direction requires the improvement and expansion of the present facilities, equipment and laboratories to insure the achievements proposed. We hope to count, in this regard, with the continued support and cooperation of the authorities of our University.
Last, the Institute of Agronomy of the Tarapacá University wishes to submit to this Round Table, the idea of establishing, at the Tarapacá University, a Center for the Studies of Desert Zones of the Southern Cone of America and, in particular, of the Atacama Desert, where the researchers from Chilean and foreign universities —and from other organizations devoted to the study of these areas of extreme aridity— can contribute with their knowledge.