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Zanzibar – “Spice Island” is an archipelago teeming with coastal vegetation and flora, located on the Indian Ocean that is politically united with Tanzania. The name “Zanzibar” is of Persian origin; “Zangi-bar” is usually translated as “coast of the blacks” and is thought to be derived from the Persian words “zangi” (black) and “barr” (coast). Though this translation was once quite controversial, the recent discovery of an inscription dated to 975 A.D. found at Khole, southeast Tanzania, where Zanzibar is mentioned as “Zinj el Barr” seems to have firmly established its origin. The islands of Zanzibar have an extensive cultural and historical heritage that is inextricably linked with its natural environment.
It’s warm and humid climate provides an excellent environment for plant growth. Zanzibar is inhabited by approximately 500 species of plants, of these, 16 are unique to Zanzibar and do not occur on the mainland. This preserved forest that exists within the National Park and other forest remnants is a stronghold for the survival of many species of plants and animals, including some that appeared shortly after the dinosaurs became extinct, over 65 million years ago. Unfortunately, due to pressure from human activities and introduced species, the forests are under grave threat. Unless serious stewardship of this easily degraded environment is imposed, much of what remains today will be destroyed and the unique flora and fauna represented within will become extinct. This will indeed be a great loss, not only for the people of Zanzibar, but for the world at large, considering the global significance of its biodiversity.
Zanzibar is a group of islands located about thirty miles from the Tanzanian mainland in East Africa between longitude 39° and 40° east and latitude 5° and 6° south of the Equator. The largest island of the group is Unguja. Zanzibar’s flora is very diverse due to the wide range of habitats present – these include thicket vegetation of the coastal regions, a number of remnant patches of lowland rainforest, and the more recent clove and coconut plantations. At least 1000 species of seed plants have been recorded. Insects are an integral part of the plant communities, but many of these are still poorly documented. Today, Zanzibar’s natural vegetation is greatly reduced from what it once was, due to clearance for agriculture and construction. This has had serious repercussions on the fauna as well, many species of which are now extinct in Zanzibar. In a relatively small area it is possible to see great biological and phenological diversity among the plants on Zanzibar.
The Zanzibar archipelago has a very old geological history and the islands are believed to be 15-25 million years old, with the oldest rocks being found in Pemba. At the time of their creation, oceanic islands were free of vascular plants and it was not until some millions of years later that plants arrived, probably through long distance dispersal by wind, bird or sea. Some groups of Zanzibar’s plants have very few species and appear to be recently arrived on the islands, for example, the twelve species of Euphorbia and four species of Pemba are less diverse than on the African mainland. Other groups of plants, for example the palms, have clearly been more established on Zanzibar, with five endemic species of the palm genus Nephrosperma. Evidently, they have evolved new species when isolated from their relatives on the mainland. This is an area with much current work being done in molecular studies to determine the relationships between species and genera of Zanzibar’s plants and reasons for their diversity or lack of it.
The environmental importance of flora can be seen through the use of mangrove forests and sand stabilization plantations. Mangroves grow in shallow coastal waters and are commonly found in Zanzibar. They are vital to the environment, offering a natural habitat and playing a key role in coastal defense. Unfortunately, over-harvesting has caused a depletion of the mangrove population. This has led to several projects to try and replant around the coastal regions. Sand stabilization plantations were introduced when it was found that the original vegetation had been cleared, causing sand dunes to engulf farmlands. The Dutch introduced a variety of plants including the Neem Tree, Casuarinas, and Aloe to stabilize the sands and prevent soil infertility.
From an economical standpoint, flora directly contributes to the island through the use of agriculture. Many small-scale farmers depend on the growing of various crops and seeds for their livelihood. Farmers intercrop food crops with cash crops, food crops with cloves or coconut, or alternate cash crops to derive maximum utilization of their land. To assist with soil fertility, a popular practice is to plant a crop of Pigeon Pea which is grown for two years and then uprooted, allowing a food crop to be grown for a year or coconut to be interplanted. Pemba has many farmers growing various spices, coconuts, and a variety of fruit-bearing trees. The most economic benefit associated with agriculture is Zanzibar’s cloves. A high percentage of export earnings have come from the clove industry through production and sales to other countries.
Fringing the coastline where the sea meets the land are three types of coastal vegetation. Mangrove communities are found along sheltered coastlines, in estuaries or on islands where there is a ready supply of soft, waterlogged silt. The five true mangrove species found in Zanzibar form only a small percentage of the total forested area in this zone, occurring near the upper boundary, but they are significant in that they represent a disproportional resource in terms of the goods and ecological services they provide. Beach vegetation, essentially that which grows on the unstable sand dunes, is probably the most threatened of all the communities described in this book, due to high demand for the land it occupies and the fragility of the substratum on which it grows. It is mainly composed of pioneering species which have special adaptations for growing in dry, low-nutrient, well-drained sand, and is thus different from coastal cliff vegetation. Seagrasses are an important community in the shallow subtidal soft sediments of sheltered coasts and bays. The only flowering plants to recolonize the sea, they can form extensive meadows in areas where light penetrates to the sea floor. This community is significant for the role it plays in the life cycles of a large variety of marine organisms, as a source of food, and as a stabilizer of the sea floor.
The largest areas of natural forest occur in the east and south of Unguja. Tropical rainforests exist on coral rag in the east and along the central and eastern ridge of the island, with the largest tracts at Chwaka, southeast of Chwaka Bay and in the Korongwe Forest. The coral rag forests are characterized by many ancient and immensely valuable hardwood trees. The variously colored and patterned woods, strong solid timber, natural oil content, and the ability to take a high polish make these species of wood highly sought after and consequently they have been heavily logged. The remaining areas of rainforest occur on the steeper, more inaccessible hillsides and consist largely of small trees and shrubs. Coastal forests are a type of coral rag forest and occur in small patches around the coastline. They are specially adapted to resist high dry woodlands areas can be found in the center of the island at the higher plateau areas and around the east, south, and west coast. These areas consist of a mosaic of farmland and small remnants of native forest. The largest areas of native forest are found in the far southeast around the villages of Dongwe and Bwejuu. The remaining areas of forest consist mainly of small bushy trees and shrubs, and they have been heavily cleared for agriculture. At Kizimbani to the northwest of Stone Town, there is a small area of artificially planted forest consisting mainly of teak and mango trees, which were planted in the 19th century for forestry research. Native forest areas are incredibly diverse in plants and usually contain some endangered or endemic species. Due to the ongoing habitat destruction, logging, shifting cultivation, and the browsing of domestic animals, many sections of Zanzibar’s forests can be heavily degraded and contain little regenerating natural vegetation.
Zanzibar has only a few hectares of tropical rainforest left. It used to cover the islands, its gradual removal due largely to the development of the spice industry and the cultivation of rice and coconuts. Most of this deforestation took place over the last 150 years. The most extensive of the remaining lowland forests is that of the Jozani – Chwaka Bay National Park, a protected area of about 50 km2. Here, the ground is permanently damp in the deeper valleys where small streams are found, and the dominant vegetation type is a 30m tall evergreen thicket of varying species. The park includes a small tract of mangrove forest. The area has a full complement of monkey species and a rich birdlife.
Other areas of lowland forest survive at isolated patches from Chwaka to the southeast of the main Zanzibar Island. These tend to be on the edge of steeply sloping ground that is unsuitable for cultivation, or on coral rag where again cultivation is not practical. This forest type has more variety in terms of tree height and includes emergent trees of up to 40m in height. There are remnants of good ground flora and the bird and insect life is still relatively diverse. Forest areas of this nature also occur on the smaller islands, and it is here that Zanzibar has managed to dump alien creatures, such as rats and goats, very successfully. The surest hope for the long-term survival of good tropical forest in Zanzibar may lie in the future eradication of the same species.
The coastal belt of Zanzibar is characterised by various types of coastal forests. These range from thick vegetation to areas with small patches of trees. The main type of coastal forest is known as the mixed forest. This is characterised by a wide variety of tree species, including many rare and endangered. These forests vary in density depending on proximity to the sea, with the densest forests further inland. The most significant forest type in terms of rarity and size. Only a few small patches of this forest type exist today, all of which are under threat from human activities. One of the most important and larger tracts of this forest type is located at Masingini. This forest type is also characterised by a wide variety of tree species, and contained a number of very old trees which supported a rich epiphyte and wildlife population. Another important forest type is the Cynometra-Maniltoa forest. This forest is generally located on coral rag and gives way to the mixed forest. It is characterised by its namesake tree species and dense undergrowth. At present only a few small patches of this forest type remain, and none are officially protected. Finally, the smallest and rarest of the coastal forest types is the Pandanus forest. This forest type is only found in a few isolated patches, the largest of which is at Mchingeni near Jozani. This forest too has a specialised and limited flora and fauna, with some species that are likely to be under threat. An outstanding feature of the Mchingeni forest is its relative undisturbed nature and the width of the transition to adjacent habitat types. This forest has an important role in scientific and applied research as a reference for clear, undisturbed forest.
Dry woodlands are found in the interior of the island where the average annual rainfall is lower than 1000 mm. The seasonal distribution of rainfall is more important than the total amount, and dry woodlands are distinctive in having a long dry season when leaf fall is a characteristic feature. Many trees shed their leaves at the beginning of the dry season and re-foliate at the first sign of new growth in the understory. This can be seen to best effect on the high ground around Masingini Forest where Swynnerton’s Ironwood (Stromatium longipes) and a variety of other deciduous trees shed their leaves to give way to an open forest of shrubs and small trees. Re-foliation coincides with the first rains, and the high ground types are the only evergreen dry woodland formations to be found.
At lower altitudes, local human disturbance has led to the degradation of dry woodlands to secondary vegetation types dominated by areas of small-scale cultivation. Original types can still be found in areas protected from clearance and browsing animals, particularly in the less accessible parts of the island. Characteristic trees of these woodlands include Dalbergia holothriax with its distinctive seed pods, Pterocarpus lucens, Acacia spp., Commiphora spp., and the fruiting succulent subspecies of Euphorbia hildebrandtii. Between woodlands, there are often expanses of a different type of secondary vegetation dominated by the soft-barked Croton shrubs, which expand discontinuously into fully fledged (though often sparse) woodland of its own type.
Section 4 talks about the different kinds of crops cultivated in Zanzibar. In earlier times, cloves were considered white gold because of their high value in the market. Zanzibar was the world’s leading producer for cloves because of climate and soil conditions favoring the crop. Apart from the clove tree, other spices like cardamom and cinnamon were also introduced to Zanzibar by the Mainland Asians, although they were less popular than cloves. Clove trees are found ubiquitously around Zanzibar, with individual trees sometimes being as old as 100 years. As spice plants are vital to the economy, they were placed under the jurisdiction of the ZSTC and are now being rehabilitated after neglect during bad times in the economy.
The next crop type is the fruit orchard. The most common fruit trees found in Zanzibar are mango, banana, citrus, avocado, and guava. Most of these trees were introduced during the colonial period; however, the mango tree is native to Zanzibar. Mangoes are loved by the local people and many mango trees can be found on small-scale farms. Banana trees are found everywhere and are an important staple for Tanzanians. Wild bananas also exist and it is suspected that they were introduced very long ago, long before the known history of Arab and European contact. In earlier times, Sultans were known to have fruit gardens with a variety of fruit trees… the most recent evidence of a fruit orchard in Zanzibar is a fruit tree planting project on the research farm. Crops are still in minor quantities on Zanzibar; little is exported as there are high internal demands for fruit. Although fruit is not a major crop, efforts are being made to improve fruit crops and they may be an important crop for the future.
Ongoing research in villages all over Zanzibar is uncovering a wealth of information on what ailments are most prevalent in different areas and which plants are used to treat them. This information is of great importance, as it provides an insight into the categories of disease and the etiology attributed to them, as well as a comparison between traditional and allopathic medicine, highlighting where traditional medicine might complement modern health services.
The use of medicinal plants is of great importance in many rural areas of the world. Zanzibar is no exception, with a variety of home remedies used to treat common ailments. These range from the use of specific plants to spiritual healing using a combination of plants, religious symbols, and specific rituals. Medical practitioners range from those with a good understanding of the allopathic properties of the plants they use to traditional healers and elders with inherited knowledge and no small amount of mysticism. In many cultures, it is claimed that a disease is caused by a disturbance in the equilibrium of the person or their relationship with the natural or supernatural environment. Traditional healing methods aim to correct this imbalance.
The next part of the assignment is a crucial one, dealing with medicinal plants on Zanzibar. The complex subject of traditional medicine and the use of plants as medicine cannot be separated from the culture in which it is based, so a brief outline of Zanzibar culture is necessary.
A wide assortment of herbs, leaves, barks, and even whole plants are prescribed for a variety of ailments and illnesses. Many are prepared in combinations with food and tea, while some are used as poultices or even as talismans to be worn or hung in the home. Healing practices often involve spiritual ceremonies and special blessings to heal the afflicted. For many, traditional practitioners are the first line of defense against illness. A majority of these healers are older people with a deep knowledge of tribal lore, herbal medicine, and spiritual healing. These people have learned their art from their forefathers and are passing it on to future generations. Unfortunately, their knowledge is being lost as young people are less interested in learning the old ways. This exodus of knowledge is a serious concern for the health of future generations and the integrity of the unique tribal culture. The most effective way to keep these practices alive is to show the young people the efficacy of traditional medicine.
The bioassay-directed approach links the informants with the scientific community by involving the informants in the extraction and testing of plant compounds. This approach can lead to the development of phyto-pharmaceuticals, a Zanzibari example being the production of an anti-malarial drug from the plant Artemisia Afra, a plant that was introduced to Zanzibar from the Cape of South Africa to treat an outbreak of Black Water Fever. Although directed questioning is rapid and low in cost, the reliability and validity of the information obtained are arguable. The second approach is extremely costly and may lead to the extinction of the very plants being studied.
Usage of plant medicines to cure ailments and treat various physical and emotional maladies is a common practice in traditional medical systems. This has been studied by anthropologists and is a recent yet promising field of interdisciplinary research. There are two main approaches used to determine the relative importance of medicinal plants in traditional medical systems. The first is ‘directed’ questioning where the researcher asks the informants to list the ailments that can be treated using plant medicines. This is usually followed by the second approach which involves the collection of plant specimens cited as remedies and the subsequent testing of these specimens for bio-active compounds, such as alkaloids which are associated with particular physiological effects.
It is thought that there are approximately 54 endemic plant species in the Zanzibar archipelago, most of which are flowering plants. The Zanzibar Red Colobus monkey is dependent on these forest fragments for its survival, as are a number of other species. According to recent estimates, only about 25% of the island’s original forest coverage remains, and although not all of these areas are home to endemic species, this is still the biggest threat to Zanzibar’s endemic flora. It is noted that some of these species have yet to be formally described and recorded by scientists, and with the declines in forested areas, it is highly likely that some of these plants will become extinct before even being known to man.
Alien species have become increasingly widespread internationally and have had many negative effects on indigenous species and ecosystems. In Zanzibar, invasive species are replacing indigenous ones at a local and regional level, threatening the unique biodiversity for which the area is renowned. Invasive species are regarded to be the second most significant threat to biodiversity after habitat loss. Many of Zanzibar’s indigenous species are found only within the forest habitats, and some of the key economic species are also under threat. The negative impacts of invasive alien species on the forests of Zanzibar are both direct and indirect, and it is likely that the severity of these impacts is underestimated.
Invasive alien species are having direct negative impacts on Zanzibar’s forest resources. They are a major threat to the endemic and indigenous species and high biodiversity of the forests as they out-compete native plants and may lead to the extinction of indigenous species. This situation is particularly critical in areas where the forest is fragmented, as the loss of gene pool from localized extinctions of indigenous species can be severe.
