Stephen P. Broker
Location: Donana is a 7500 square mile lowland habitat found on the southwestern coast of Spain (Atlantic Ocean portion) on the Gulf of Cadiz. It extends east from the border between Spain and Portugual to the western part of the province of Cadiz, and it incorporates parts of three provinces, Huelva, Sevilla, and Cadiz. The two large rivers which flow through Donana are the Rio Guadalquivir (which forms its eastern boundary) and the Rio Guadiamar, a tributary of the Guadalquivir.
Climate and Geology: The climate of this southern region of Spain is temperate. Donana has been shaped in different ways in the last 18,000 years, depending on the persistence of wet or dry periods. Extended wet periods led to the establishment of estuarine marshes, lagoons, and braided river systems, while arid periods encouraged the deposition and reshaping of wind-blown (aeolian) dunes, with their greater elevational relief. Changing sea levels resulted variously in expansion of marshland (regressions) or silting up of estuaries (transgressions). Donana has taken on its present look in the last 2000 years. The current system of dunes, described below, are an estimated 500 to 700 years old.
Ecology: Donana is a complex combination of estuarine environment, marshes, lakes, salt ponds (lucios), sand dunes, scrubland and wooded habitat, shaped by Atlantic waves, blowing winds, and transporting river waters. Its principal ecosystems are tidal flats and beaches, marshland (originating from the Rio Guadalquivir estuary, but today of continental character rather than tidal), stationary dunes (on sands of marine origin), multiple chains of mobile dunes (aeolian, or windblown sands), pine forests (such as El Faro pine forest in the south, separated from the coast by a zone of dunes), and Mediterranean scrub woodland. Intensive human activity over a period of centuries has had an impact on virtually every ecological system found in Donana, creating what can be referred to as a "humanized landscape." Today Donana is bordered on the south by the Atlantic Ocean, tidal flats, beach, and a prominent band of dunes known as El Asperillo. Inside the zone of dunes are the Donana marshes, also called the Guadalquivir marshes. Covering 27,000 hectares, they are considered the most distinctive feature of Donana. They are comparable in significance to the Florida Everglades, but they go through considerable seasonal change. Half the input of water comes from the Guadiamar, the Guadalquivir, and associated rivers, but half comes from rainwater, accounting for the seasonality of Donana's marshes. The present marshland, formerly a heavily channeled tidal marsh but now cut off from the coastal estuary, is blanketed by 1-2 meters of water in the wet season and is reduced to cracked mudflat in the dry season. Stream flow is minor, and water is nearly brackish. Ponds, basins, pools, and grooves are scattered through portions of the marshland. Subtle changes in topographic relief and in substrate give rise to different patches of marshland, different levels of pH and mineral content, and different water depths. The changing levels of water produce the saltpools, or lucios. While the Florida Everglades consist of 50 mile wide, one foot deep sheet flow of water, Donana marshes circulate north to south, drain into the Guadalquivir River, and dry up nearly completely by the end of spring. Summer drought and cracked mudflat surfaces present a totally different picture from that of spring.
The coastline at Donana has more than 30 kilometers of sandy beach and setback dunes. Sea sands that wash up on the beach are the source of the sand fields and dune trains here. The two basic types of sand sheets are fixed or arrested dunes and mobile dunes. Each dune system is fairly parallel to the coast, extending several kilometers inland. Fixed dunes are located on the upper beach, held down by a cover of vegetation, and mobile dunes are continually moved and reshaped by prevailing coastal winds. The moving dunes take on parabolic shapes (best seen in the El Asperillo dunes), with the coast-facing surfaces having a gentle slope and the parabolas facing inland with a slope of more than 30 degrees. The parabolic dunes assume different heights and migrate inland at different rates, but they move on average 5-6 meters per year and achieve a maximum rate of migration of 30 meters per year. Sand is removed from the trailing edge of the dune and is redeposited on the parabolic face during migration. The present dynamic system of dune migration has persisted nearly for 400 years. These dunes bear a resemblance to the dune systems of the Provincelands of Outer Cape Cod in their mobility and their ability to bury and kill large trees. The hollows that form between bands of dunes are called corrales. They are the sites of springs, pools, and lagoons, with their higher water table. Some lagoons connect to the marsh via small creeks.
A more detailed ecological examination of Donana's arid scrubland recognizes three types of scrub: (1) monte negro, consisting of low-lying, moist lands with heathland plants; (2) monte blanco, which occurs at intermediate elevations and is dominated by helianthemum; (3) xerophilous Mediterranean scrub, occurring on the highest and driest lands, vegetated with rosemary, rockrose, lavendar, and marjoram. The monte negro lands bear similarity to Cape Cod's coastal heathland critical habitat.
Stone pine forested regions of Donana are low and dense, and they support little wildlife. Cork oak forests are more open, and they have abundant wildlife.
Representative Trees and Wildlife: Donana's marshland plants include grasses, rushes, and salt-loving plants such as saltwort. The dry, open country of Donana is characterized as dune scrub, heathland, and fire-loving helianthemum scrub. Understory plants include savin, lentisk, rosemary, and rockrose - all xerophytic, or dry soil plants. The most widely represented genera of trees in Donana's forested regions are Quercus (oak), Pinus (pine), Juniperus (Juniper), Fraxinus (ash), and Populus (poplar). Cork oak and Umbrella oak are the two most common trees in this genus, and the most common species of Pinus is stone pine, originally a native species, extirpated by 500 years ago and subsequently reintroduced. Ash and poplar are found along marsh edges and flowing waters. Juniper has grown historically along coastal regions, as it does in Connecticut. Donana is rich in invertebrate and vertebrate life, and it is particularly known for its resident and migratory birds and its mammals. Approximately 250 bird species are considered residents or common migrants, and an additional 100 species are rare species, transients, or vagrants. These numbers are fairly comparable to the numbers of bird species in Connecticut (approximately 400), but the abundance and diversity of Donana birds and the size of the migration make this region special. An estimated one million birds spend the winter at Donana. The major aviaries and heronries of Donana are found around marsh lagoons. Ecotones, the contact zones between the marshes and the sandbanks, are very species rich. Bird life has been reduced in richness in historic times by the conversion of tidal wetland to continental marsh. Fallow deer have been introduced, and they number about 2000 within the park, as do the red deer. Wild boar are abundant, and they have long been a preferred species for hunting. There are 30-40 Iberian lynx in the park. Their principal food items are rabbits, the primary consumers near the base of the food web. Coastal and inland waters have diverse species of native and introduced fishes.
Land management: Information on the ecological conditions of Donana extends back to the 13th century, as this area was long used as a hunting preserve for Christian monarchs and aristocrats. The Spanish word Coto refers to the preserve, but also to the sand sheets of Donana. Much of the eastern boundary of Donana has been given over to agricultural fields through drainage and filling of marshland. Grazing animals (introduced livestock - cattle, horses, pigs, sheep) have reduced the extent of forested land and favored development of scrubland. Overgrazing continues to be a problem. The religious pilgrimage that annually traverses the park occurs along a 20 meter wide livestock trail, the Sanlucar de Barrameda - Almonte path. Charcoal-making has been common for a long time, also contributing to the loss of forested land and the development of fire-dependent scrub. National Park ecotours take visitors to several villagers' huts where charcoal-making is practiced. There is a long history of logging of pine trees for charcoal-making, timber, firewood, and ships' masts. Reforestation efforts in some regions of the park have been attempted for at least 300 years. The National Park is carrying out a reforestation program using cork oak trees, with the aim of doubling the number of these trees in Donana. Commercial fishing for shellfish and fish occurs in the marsh system. The Guadalquivir River experiences substantial water pollution, which poses a continuing threat to aquatic and terrestrial life. Industry continues to crowd the Donana reserve, with open pit mining for heavy metals, especially in the Rio Tinto area, being a major threat to the larger region. Introduction of exotic tree species, such as eucalyptus, has caused disruption of some expanses of mobile dunes, especially in the northern part of the park. The National Park is attempting to remove some of the invasive eucalyptus plantations here. Tourism has existed for a hundred years, and there is a concerted effort within and outside the national park to extend tourism opportunities, including the construction of major coastal resorts and real estate developments. Disparate groups of people, including members of industry, agriculture, conservationists, and local villagers, have recognized the importance of protecting the remaining wetlands and dune systems of Donana. Today, the National Park is administered by the Spanish Ministry of Agriculture, Fishing and Food, and the Higher Council for Scientific Research.