Travelling about the Galápagos, we find that the similarities and differences in the floral inhabitants of different areas seem to conform to a pattern. The plants (and animals) found at an altitude of 300 meters on Santa Cruz are different from those found near sea level. Observations such as these have led scientists to propose the concept of "communities". A "community" is an assemblage of populations of living organisms in a prescribed area or habitat.

The vegetation zones of the Galápagos are an example of the concept of communities, and these zones display many features of community organization. Amounts of rainfall varying with the formation of vegetation zones ranging from desert to lush cloud-forest and moorland. The assemblage of species that we find in any one area are all, more or less, adapted to the range of environmental conditions found in that particular area. This change in vegetation from seashore to summit has led botanists to propose various zones.

The Littoral (Coastal) Zone

The coastal strip of the Galápagos is mainly evergreen. This zone is not strictly a climatic vegetation type but is an ecological one based on salt tolerance abilities of certain species at the land/sea interface. The type of vegetation found varies greatly and depends on the type of coast. Many plants in this zone are adapted to dispersal by the sea, especially the mangroves. Few plants found in this zone are endemic as a result of the unstable nature of the environment.

Just inland from the coast is the archipelago's major vegetation zone-- a semi-desert forest dominated by deciduous trees and shrubs such as Bursera, and evergreen drought-tolerant species such as Croton scouleri and the Opuntia and Jasminocereus cacti. The Arid Zone is the most extensive vegetation zone and has by far the greatest number of endemic species. Lichens are abundant in this zone because they are tolerant of dry conditions and are capable of absorbing moisture from the occasional garúa mist.

The Transition Zone

The Transition Zone is intermediate in character between the Scalesia and Arid zones, but it is dominated by different species than either of the adjacent zones. The characteristic Bursera, Opuntia and Croton of the lower elevations become less abundant or disappear. The forest is still mainly deciduous and is dominated by the endemic Pega-pega (Pisonia floribunda) and the Guayabillo (Pisidium galapagensis), trees, and the Matazarno (Piscidia carthagenensis). The Transition Zone is much more dense and diverse than the forest of the Arid Zone, and it is often difficult to say whether any species is dominant. There are many tangled shrubs and perennial herbs. There are also more epiphytes, especially lichens.

The Scalesia Zone

At its upper limit, the Transition Zone merges into the evergreen Scalesia forest, a lush cloud-forest dominated by Scalesia pedunculata on Santa Cruz. The trunks and branches of trees in this zone are covered with epiphytes, mostly mosses and liverworts, but also ferns, orchids, some Peperomia species and the bromeliad Tillandsia. There are fewer shrubs in this zone, while herbaceous plants, including ferns and lycopods, abound.

The Scalesia forest is diverse and also has many endemic species. During the lowland dry season, it is almost continually drenched by garúa mist.

This type of forest occurs only on the higher islands and, being the richest zone in terms of soil fertility and productivity, has been extensively cut down for agricultural and cattle-ranching purposes. On Santa Cruz, San Cristóbal, and southern Isabela, only fragments of this once extensive zone remain. On Santiago Island, goats have destroyed much of the moist Scalesia Zone vegetation.

The Zanthoxylum or Brown Zone

Little of this zone remains on Santa Cruz, but the few remnants indicate that it is an intermediate between the dense Scalesia forest and the Miconia shrub vegetation. It is an open forest dominated by cat's claw (Zanthoxylum fagara), Tournefortia pubescens, and Acnistus ellipticus. Trees are heavily draped with epiphytes, especially mosses, liverworts and ferns, which give this zone a brown appearance during the dry season. This zone has to a large extent disappeared because of human colonization.

The Miconia Zone

The southern slopes of San Cristóbal and Santa Cruz are the only places where there is a dense shrubby belt of Miconia robinsoniana. Native trees are absent from this zone and ferns are abundant in the herb layer. There are also many more liverworts than elsewhere.

The Pampa Zone

Above the Miconia Zone there are virtually no trees or shrubs, and the vegetation consists largely of ferns, grasses and sedges. The tallest plant is the tree-fern Cyathea weatherbyana which has fronds two to three meters long and grows to three meters (10 feet) tall. This is the wettest zone, especially during the garúa season, receiving as much as 2.5 meters of rain in some years.

There are also species that are adapted to other factors and whose distributions do not reflect the general zonation. A good example of such species is Hippomane mancinella, the poison apple, which occurs from sea level to the Scalesia Zone, primarily near ponds and clearings. Zanthoxylum occurs in a wide range of communities, but only reaches tree size in the upper Scalesia Zone.

-- Michael H. Jackson