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Riparian Ecosystems in : Current Status and Future Direction 1

Miguel Caballero Deloya 2

An increasing population dependent on subsistence agriculture threatens the future of Mexico's ext~nsive riparian ecosystems. If these strategic ecosystems are to survive to provide goods and services for future generations, both the Meltican government and society :is a whole must be involved in an effort to: (1) evaluate present conditions, including causes of habitat destruction; and (2) generate specific legislation to establish reforestation programs and protective measure~.

INTRODUCTION TYPES OF MEXICAN RIPARIAN ECOSYST~MS

Mexico is a nation covered by numerous The remarkable variation in climate, altitude, mountain ranges. The most important are: Western and soils, has provided for a notable diversity of Sierra Madre, Eje Neovolcanico, Eastern Sierra riparian habitats in Mexico. For the purposes of Madre, and Southern Sierra Madre. Many other this discussion, only three major types are smaller mountain systems are scattered over the considered: arid-land, high-altitude, and Mexican geography. Several peaks have elevations tropical riparian ecosystems. above 4,000 m (12,000 ft). Arid-Land Riparian Ecosystems Such a wide orographic diversity has favored the existence of abundant riparian ecosystems. From a broad perspective, Mexico is an arid According to Tamayo (1962) there are 172 major nation. The Mexican National Forest Inventory water courses in Mexico. Half of them (86) flow provides an estimate of 67.44 million hectares of to the Pacific Ocean. In all of them, an average arid and semi-arid lands in the country volume of 375 billion cubic meters of water flow (Subsecretaria Forestal. 1984. p. 13). yearly. In addition to the Pacific Ocean, the two other major drainage systems are the Atlantic In arid regions, riparian ecosystems are Ocean and the Interior 8asin. usually distinct from other habitats. Rivers and water deposits are mostly seasonal, but water It is worth mentioning that the Mexican availability in riparian ecosystems is higher. In nat ional , the "ahuehuet e" ( these conditions, vegetation is more abundant as a mucronatum) is characteristically the most response to more favorable growing conditions. widespread community component of riparian Shreve and Wiggens (1964) report for the Gulf of habitats of subtropical and te1nperate climates. California coastal lands, along the Baja California Peninsula, a denser vegetation on the Despite their abundance, riparian habitats water courses. Principal species include Prosopis have received limited attention. Political,' juliflora var. torreyana, Prosopis palmeri; Olneya financial, and scientific efforts have been directed to those ecosystems which exert the greatest effect on rural community development, those which impact most on agricultural and forage production nationwide, or those which occupy the greatest amount of land.

In the following pages, a brief discussion is presented on the nature and characteristics of the Mexican riparian habitats, the most important problems they face, and what their perspectives are for the coming years. lpaper presented at the symposium, Riparian Ecosystems and Their Management: Reconciling Conflicting Uses, April 16-18, 1985, Tucson, • Arizona.

2Director General, National Institute of Forestry Investigations, Secretary of Agriculture Fig. l.--Amacuzac river, in the dry lands of alld Water Resources, Mexico City, Mexico. Guerrero State.

9 tesota; Cercidium floridum, Hymenoclea pentalepis, The high precipitation characteristic of and .!1aplopappus sonorensis, among others. these regions is responsible for the existence of several important rivers. Those rivers and their Coyle and Roberts (1975) include the tributaries concentrate large numbers of riparian following species as characteristic of riparian ecosystems. Tropical riparian systems contrast habitats in Baja California: Anemopsis with those of arid and high-altitude regions. The californica, Arundo donax, Platanus racemosa, majority of the rivers in tropical Mexico have a Juncus sp., P~ £remOntii, Salix laevigata, continuous water flow throughout the year, even Salix chilensis, Typha sp., WashInitonia filifera, though the amount of flow varies seasonally. This and Washingtonia robUSt a. characteristic, plus the fact the tropical habitats occur at low elevations (usually below 500 m) create special conditions that determine In the Chihuahuan desert, Salix chilensis and the amount and type of vegetation. Some of the some species of the genus Populus are frequent most widely distributed species in these types of along permanent river courses. Along ephemeral ecosystems are: Ficus spp. ("amates"), water courses, Schinus molle ("pirul"), Chilopsis Lonchocarpus hond~is ("gusano"), Inga spuria longipes ("mimbre"), Celtis pallida ("granjeno"), ("cuaj inicui 1"), Pachi ra aquat ica (" zapote-"-)-,-­ Prosopis j ul i flora ("mezquit e") and Baccharis Pithecellobium arboreum ("coralillo"), Astianthus glutinosa ("jarilla") are most representative. viminalis, and Guadua aculiata. High-Altitude Riparian Ecosystems Some characteristic of temperate and These ecosystems occur along the mountain subt ropical regions frequent ly OCC'lr in tropical ranges or in the high interior lands such as the riparian ecosystems. Examples are Salix "altiplano" in central Mexico. They are usually chinensis ("sauz"), Platanus chiapensrs­ found at elevations higher than 6,500 ft. (2,000 ("tatacui"), and Taxodium mucronatum m). Some of the common species in these ("ahuehuete"), which a("e present along the ecosystems are: Baccharis glutinosa, Salix riparian lands of the Nepac river, Chiapas. taxifolia, and Taxodium chilensis. Along the river courses in the Chihuahuan Sierras, Acer In subtropical and transitional riparian brachypterum and Platanus wrightii are conspicuous ecosystems, the folLowing species are components. characteristic: Populus spp., Alnus arbuta, and Platanus spp. Among pine species, Pi~ Rzedowski (1978) reports the genuses chiapensis is perhaps the most ("epresentative in Platanus, Populus, Salix, Acer, Alnus, Carya, and east and southeast Mexico (Guerrero, Chiapas, and Fraxinus among others in the gallery forests of Veracruz) . this type up to an altitudinal limit of 9,186 ft. (2,800 m). IMPORTANCE 0.\<' RIPARIAN ECOSYSTEMS

Certain species typical of other types of The importance of MeKican ripa("ian ecosystems habitats (usually drier) are frequently found in can be analyzed from three perspectives: abundance in riparian habitats. That is the case provision of goods and services, preservation of with Casuarina equisetifolia, Eucalyptus spp., and endemic vegetation and wildlife, and water different species of pines, in the Central High regulation and flood control. Basin (Altiplano Central). Provision of Goods and Services Many high-altitude riparian ecosystems are located within forests. In the case of Many ripa("ian ecosystems playa relevant role conifer stands characterized by low precipitation, for the subsistence of rural communities. In arid firs tend to predominate over pines along the lands, they provide productive sites in water courses. A typical pine characteristic of non-irrigated lands for agricultural production. those ecosystems is Pinus ayacahuite, a species In the dry lands of the States of Hidalgo, with great demand for pulp production. Tlaxcala, and Puebla,, in central Mexico, numerous small patches of cultivated Agaves and Opuntias In the northern States of Chihuahua and can be observed in lands adjacent to dry river Durango, Picea chihuahuana behaves as a typical courses. Frequently, these lands offer the only riparian species along the mountain ranges. alternative for crop production. Where conditions are more favoran le, apple and other fruit trees Tropical Riparian Ecosystems are established.

Tropical regions are characteristically in Riparian sites are commonly appreciated for east and southeast Mexico. Most of them occur in their scenic and recreational value. "El the States of Campeche and Quintana Roo in the Contadot:''' national park in Texcoco, State of Yucatan Peninsula, and southeastern Chiapas, a Mexico, is a typical riparian ecosystem with Guatemalan border State. Other tropical forests abundant beaut i ful "ahuehuetes" (Taxodium can be found along the coastal plains of both the mucronatum). The "Barranca de Cup at itzio" park in Gulf of Mexico and the Pacific Ocean. The Mexican Uruapan, Michoacan, is another example of the National Forest Inventory has estimated an area of beauty of a riparian ecosystem and its importance 13.2 million hectares covered by tropical forests. to society from a rect:'eational point of view.

10 Riparian ecosystems also help support rural communit ies by providing goods which are basically consumed locally and occas ionally sold in regional marl<.ets. Examples include fuelwood, wilrilife, fruits, edihle , forage, and ornamental plants.

In some regions, riparian habitats are being rapidly transformed to establish new human settlements. The rate of this transformation is greatest in the Central Plateau, where the demographic explosion is the highest in the nation.

Preservation of Endemic Vegetation and wildlife

Because of their unique natural features, riparian ecosystems have favored the existance of endemic plants and animals. Due to the rate of Fig. 2.--Contamination by garbage disposal on the destruction of these habitats, and the na'rrowness Oacapa river, Guerrero State. of their natural distribution, some species are now endangered. This is the case of Acer Another form of riparian contamination occurs brachypterun in the States of Chihuahua and 'Sonora, Plcea chihuahuana in Chihuahua and mainly in the most populated region of the count ry, the Cent ral Plateau, where many river Durang(),~some species of Platanus in trans it ional regions. In someregions, riparian ditches--mainly near urban centers--are used as ecosystems play an important role for germplasm garbage disposal areas. The Panuco and the Lerma are probably the most contaminated rivers by this preservation. and industrial wastes. The eagle is an endangered species in most of Mexico. One reason is the destruction of its Unplanned Wildland Conversion to Agricultural and natural habitat. Another reason is the intense Forage Production hunting of the species by rural inhabitants. Population growth in ~exico is exerting ~reater pressure on natural resource8. Lands for Water Regulation and Flood Control agricultural and forage production are increasingly demanded. As a consequence of this Even though there is little information pressure, the agricultural frontier is growing by available in Mexico, it is clearly recognized that destruction of natural habitats, such as forest riparian ecosystems are important water flow and riparian lands. This uncontrolled land use regulators. Evidently, riparian vegetation plays conversion is affecting the ecological equilibrium an important role in this regulation, depending on of those sites affected. Silting of rivers and frequency, timing and i~tensity of flooding. Much wildlife mortality are some of the negative has to be learned however, about the nat ure of results. these interactions. Destruction of Endemic Biota PROBLEMS AND LIMITATIONS As previously mentioned, riparian ecosystems Contamination in Hexico 'have been important providers of goods and services, of high value to local commuities. Riparian contamination occurs in two ways. The increasing eKploitation of some of these The first is the result of industrial.residual goods, most of them provided by endemic flara and discharge. This is the typical case with the fauna, is causing severe damage to the biota. sugar industry, pulp and paper plants, refineries, Trees that supply fuelwood and wood for other breweries, and textile, fertilizer, and chemical domesti~ uses, and species that provide forage plant8. In the States of Tabasco, Veracruz, and have been most affected. Tamaulipas, contamination by oil extraction and processing is becoming a major concern. In other By the same token, wildlife species regions, contamination by organic effluents customarily consumed by humans reflect a dramatic (stools) has become a problem. Important rivers, depletlon, as do those species that affect such as the Coat zacoalcos, 131 anco, Zahuapan, domestic animals. In the first group, the Atoyac, term~, and Panuco, to cite a few, reflect white-tailed deer and turkey are probably most different degrees of pollution by the causes cited affected. The second group includes coyotes and above (Urroz, 1973). falcons among others.

In 1973, the sugar industry was the most THE FlJTURE important organic contaminator of Mexican rivers. This industry generated 34 percent of organic Present trends pose serious doubts and pollutants found in the rivers that year. The concern about the future of Mexican riparian chemical industry followed in importance. ecosystems: Particularly in areas of denser

11 population, riparian destruction is ~ost evident. what actions and policies are taken by State Despite this fact, little information exists on organizations, little will be gained to stop the proble~, and apparently no strategy at a natural resource destruction if the total Mexican national level has been applied in Mexico to solve society is not involved in its conservation. Much it. effort will have to be devoted by governmental agencies in educating and creating consciousness If Mexican riparian ecosystems are to be in the citizenship about the importance and vital preserved for the enjoyment and ut i lizat ion of role of natural resources in their well being and future generations, then several urgent tasks that of future generations. should be st arted. Some 0 f them are l,.isted be 1 mIT.

1) A national survey should be conducted to LITERATURE CITED evaluate present conditions of the most important riparian ecosystems in the nation. Such an Coyle, .I. and N.C. Roberts. 1975. A field guide evaluation should iclude not only the level of to the common and interesting plants of Baja hab~tat destruction, but information on agents California. Nat. Pub. Company. La Jolla, Cal. causing the damage. U.S.A. 206 pp.

2) With the information gathered through the Rzedowski, J. 1978. Vegetacion de Mexico. Edit. survey, regional policies and actions should be Limusa, S.A. lao Ed. Mexico. establ ished to preserve or restore endangered and affected ecosystems. These include: Shreve, F. and T.L. Wiggins. 1964. Vegetation - Specific legislation and Flora of the Sonoran Desert. Vol.I. Stanford - Reforestation programs University Press. Stanford, Cal. U.S.A. - Protective measures (stabilization work, erosion control, etc.) Subsecretaria Forestal. 1984. Mexico Forestal. Ci fras 1983. Sec ret aria de Agricult ura y Recursos The challenge, however, is to control the Hidraulicos. 59 pp. Mexico. increasing demographic impact, which affects not only riparian ecosystems, but all natural Tamayo, Jorge L. 1962. Geografia Gener.al de resources. For this purpose, during the present Mexico. lnst. Mex. d~ Invest. Economicas. Tomo II. public administration the Secretary of Urban 2a. Ed. Mexico. Development and Ecology was created. This agency has a highly important historical responsibility, Urroz, E. 1973. Programa Nacional Contra la and will have to face some of the most complex Contaminacion del Agua. Proceedings of the First problems that affect the present Mexican society. National Meeting of Environmental Contamination It should be recognized, however, that no matter Prohlems. p. 51-54. Mexico.

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