With its unique flora and high levels of endemism, Zanzibar is an important location for conservation. 2290 species of flowering plants have been recorded from the Zanzibar archipelago, with an estimated 30% endemism. A preliminary Red Data assessment has indicated that 225 species are under threat of extinction. This essay will focus on these plants, the threats they face, the conservation measures that have been taken to ensure their survival, and the role that they play in the lives of rural Zanzibar. Endemism is the occurrence of species in a specific area, and nowhere else in the world. The flora of Zanzibar has many ranges and close neighbors, and between them they are the result of a complex evolutionary history. The Zanzibar archipelago and Pemba are situated just south of the equator, and have been isolated and possibly submerged several times during the past 36 million years. It is likely that many of the plants have evolved from ancestors that arrived from the African mainland, possibly by long distance dispersal across the sea. During the period of isolation, these plants would adapt to the new environments that were being formed, and would have speciated due to geographic separation. The formation and breaking of land bridges between Zanzibar and Madagascar would have provided opportunities for further long distance dispersals and exchanges between the floras of the two regions. This essay will give only a brief overview of how these historical processes have resulted in the uniquely diverse flora of Zanzibar, before focusing on the specifics of individual species and the threats they face today.
Zanzibar, with its unique climate and geography, is home to several endemic and rare plant species. These plants are found exclusively on the island or are extremely rare, making them of particular interest to botanists, conservationists, and nature enthusiasts. Some of the endemic and rare plant species of Zanzibar include:
- Zanzibar Red Banana (Ensete ventricosum): This banana species is native to Zanzibar and is characterized by its vibrant red coloration. It is primarily grown for ornamental purposes and is considered rare outside of its native habitat.
- Zanzibar Coconut Palm (Cocos nucifera): This variety of coconut palm is indigenous to Zanzibar and is prized for its sweet, aromatic coconuts. It is well-adapted to the island’s coastal conditions and is an important source of food and livelihood for local communities.
- Zanzibar Clove (Syzygium aromaticum): Cloves are one of Zanzibar’s most famous exports, and the island is renowned for producing some of the highest quality cloves in the world. While not strictly endemic to Zanzibar, the island’s cloves are highly valued for their unique flavor and aroma.
- Zanzibar Pepper (Piper nigrum): Although black pepper is cultivated in various parts of the world, Zanzibar is known for producing a particularly high-quality variety. Zanzibar pepper is prized for its bold flavor and is used in a wide range of culinary dishes.
- Zanzibar Aloe (Aloe vera): Aloe vera is a succulent plant species that is native to Zanzibar and other parts of East Africa. It is valued for its medicinal properties and is used in traditional medicine to treat various ailments.
- Zanzibar Henna (Lawsonia inermis): Henna is a flowering plant that is native to Zanzibar and is cultivated for its leaves, which are dried and ground into a powder used for body art and hair dyeing.
- Zanzibar Ebony (Diospyros mespiliformis): This tree species is found in the coastal forests of Zanzibar and is known for its dense, dark wood, which is prized for furniture making and carving.
These are just a few examples of the endemic and rare plant species that contribute to Zanzibar’s rich biodiversity and cultural heritage. Efforts to conserve and protect these plants are essential to preserving the island’s natural ecosystems and ensuring their survival for future generations.
Zanzibar’s plant biodiversity
Zanzibar is a group of islands located in the Indian Ocean, 30 km from the east coast of Tanzania. The islands are located between 5° 40′ and 6° south of the Equator. Because of its unique location, the islands of Zanzibar are home to a rich and varied plant biodiversity. As a group of islands formed from the emergence of coral rock, each island is small, making the whole area of the archipelago have a small amount of total land area. The islands also have a varied topography ranging from sea level to approximately 120 meters above. Zanzibar experiences a tropical climate with an average annual temperature of 26°C, and also has two rainy seasons: the long rains which occur from March until May, and the short rains which occur from October until December. All of these factors have contributed to the diversification of plant life in Zanzibar. The plant life of Zanzibar is extremely varied, but unlike the animal life, the overall number of species is relatively small. This is primarily due to the fact that most of Zanzibar’s flora has come from the African mainland or from overseas. It is estimated that approximately 30% of plant species are indigenous, and there are a further 200 species that have been introduced by man. This being said, the remaining 70% are made up of species that have been imported whether purposely or accidentally, and some of these plants have become so widespread that they are considered indigenous. Each of Zanzibar’s many different types of vegetation can be attributed to the different types of soil and the amount of rainfall, but the primary factors that have influenced the distribution of plant life are man’s influence by agriculture and clearing the land, and wildlife pressures, both past and present.
Endemic Plant Species
Endemic plant species are those found in a specific area and nowhere else in the world. The reasons why a plant spreads widely to become cosmopolitan, or whether it stays within a restricted area, are complex. Zanzibar’s complex geological history has led to great diversity and a high proportion of plants found nowhere else. The area of the Zanzibar archipelago is 2500 km2 and it is estimated that there are 2222 native seed plants. Of these, about 1030 are coastal or marine species and 10% are endemic. Lowland forests and coastal thickets have the highest concentration of endemics, but there are also many plants restricted to other areas such as coral rag, montane, and dune forests or to specific offshore islands. The smallest area of endemism is the unique Chwaka Bay area where there are 29 endemic species. The most famous and diverse genera of Zanzibar’s endemics are the palms with 6 species, the violets, and the Impatiens.
Definition and characteristics of endemic plants
Another characteristic of endemic plants of Zanzibar is that many of them bear Malay/Indo Polynesian names. This is indicative of the fact that a large proportion of Zanzibar’s non-African plant diversity hails from a period of long interaction between Zanzibar and countries of the former Malaya and Indo Polynesian.
A characteristic of endemic plants of Zanzibar is that these species may be found in a single forest area, on one of the islands, on one or two neighboring islands, or in some combination of these. A few, however, are found in a wide range of habitats over both Pemba and Unguja. A number of species show strong habitat preference, while others can be found in many different types of habitats. All of these species have small populations, and some are now extremely rare. A high level of endemism is a general indication of a region with high conservation importance, and Zanzibar is no exception to this rule.
Endemic plants can be defined as those native to a particular area or habitat and nowhere else. To a greater or lesser extent, all isolated land masses have endemic species because they have evolved independently of the rest of the world. The degree of endemism of an area can be considered as an index of its isolation and the length of time it has been isolated. Given this consideration, it is stated that Zanzibar has a lot of endemic plant species that only grow and are found in Zanzibar. This is because of Zanzibar’s distinct geography, climate, and biogeography history, which have caused ideal conditions for plant speciation to occur, leading to the formation of more than 40 endemic plant species to date. However, some of these species may sadly now be extinct.
Factors contributing to endemism in Zanzibar
Analysis of Zanzibar’s current flora suggests that approximately 30% is exotic. Of the native species, it is thought that around 20% are endemic. Given that this is a much higher proportion than the surrounding areas, there must be something about Zanzibar which favors the evolution of endemic species. One theory put forward by Birkinshaw is that Zanzibar’s long history of human disturbance has actually favored the evolution of endemic species. Most of Zanzibar’s indigenous forest has been heavily logged and few areas remain which have not been altered by human activity. It’s known that due to the fragmentation of the forest, plant populations become isolated and in small populations, plants are more likely to be inbred. It has been suggested that inbred plant populations are more likely to undergo genetic mutation and hence some form of speciation. Plants that have evolved this way are likely to be very specialized and adapted to their environment and hence are less likely to be able to survive in the changed environments outside their small forest fragment. This would lead to a higher proportion of endemic species in Zanzibar. A classic contributor to island endemism is geographic isolation. Zanzibar has many small offshore islets, some of which have quite unique flora. Perhaps the most interesting of these is Chumbe Island, which lies 10km west of Zanzibar town. It is surrounded by large areas of relatively undamaged coral reef ecosystem and the only development on the island is a small-scale eco-tourist operation. There is a very unique forest type on the island said to be the last example of littoral forest in the region. This type of forest has almost disappeared from the East African coast and the species within it are likely to be quite specialized and in some cases may be different from similar species found on the mainland or other islands. This gives the Chumbe Island forest a high potential for endemism.
Notable endemic plant species in Zanzibar
McClanahan and Muthiga (1988) have published a comprehensive list of Zanzibar’s endemic fauna and flora. Their research has been drawn from numerous sources with much information obtained from local inhabitants, particularly elders, who are most familiar with the natural environment. Much of Zanzibar’s original forest has been destroyed and habitat fragmentation is common, meaning that certain species exist only in very specific locations. Endemic species are therefore more vulnerable to extinction and considerable efforts are being made to conserve what is left of Zanzibar’s indigenous flora and fauna, particularly through the work of the Department of Commercial Crops, Fruits and Forestry (DCCFF).
The existence of Zanzibar’s rich and unique flora is largely due to its long isolation from the African mainland. Since the receding of the last ice age around 10,000 years ago, Zanzibar has been a land of its own. It is widely accepted that the majority of plant species thought to be endemic in Zanzibar today are relics from when the island was more forested. There are 27 plant species that are strictly endemic to Zanzibar, one to Unguja, and one to Pemba. This represents a staggering 3.7% of the total plant species in Zanzibar. There are also a number of species that are near-endemic, meaning that they are also found in Pemba and/or Mafia islands. These species will not be discussed in this paper but include a number of very interesting plants such as the Pemba flying fox and the Pemba scops owl, which are not found anywhere else in the world.
Rare Plant Species
Extinction of a plant species is a natural event. However, people and the changes brought to their environment are the greatest contributors to the high rate of plant species loss today. Perhaps as many as one half of all tropical rainforest plant species may become extinct. In some relatively well-studied Zanzibar forest reserves, at least 20 plant species are either believed extinct or are highly endangered. The lowland coral rag forests harbor a number of endemic plants, some of which are regarded as endangered species. Keartland’s cycad (Cycas ianata) is a good example of a rare plant that is also endangered, although not yet listed. This species is known from two populations in forest reserves at Brungi and Masingini. A protected cultivation project for this plant was started in 1998 after it was admitted to the Botanic Gardens at Kew, England. This species will be involved in a community replanting program at Longo village where the forest has been degraded. The tree is important locally and internationally due to its primitive status as a gymnosperm and living fossil, and only between 50-250 mature plants remain in the wild. It is also the host plant of the extinct giant endemic butterfly Papilio nandensis. These are just two examples that show the vital need for research and conservation of Zanzibar’s endemic and rare plant species.
Definition and characteristics of rare plants
Rare plants are those species with such small populations that they are at risk of becoming extinct. Within the context of this essay, rare plants are those which are endemic with 5 or fewer populations, or known only from herbarium collections. Such plants are, by their nature, difficult to study as are their habitats. This difficulty stems from the fact that rare plants are often hard to find. Even when populations are known, site protection is not always possible. Traditional conservation methods, which focus on protecting the area of land on which a species occurs, are not always appropriate for rare plant populations. Many occur in very small areas of, for example, scrub or grassland which are not officially protected. In the case of agriculture, it is conceivable that a rare plant population occurring in an unprotected area could be ploughed up despite already having legal protection because the farmer was unaware of its presence. There is a fine balance between protecting rare plant populations and giving away the location in order to raise awareness and funds for their protection. If a population is too widely known, it could attract plant collectors and poachers.
Threats to rare plant species in Zanzibar
Charcoal is a major source of fuel for Zanzibarians and is produced by slow-burning wood in earth mounds. It is estimated that half of the trees cut down for charcoal never reach the market, with the process often taking place in large areas of forest where wood is then used for pitprops in the clove plantations. More methodical yet equally destructive is the conversion of forest to clove plantations, which is now taking place in a forest reserve near Wete Pemba.
The immature logging at Namemba and the degradation of the Pterocarpus population is of particular concern. It is normally the first localized step in the chains of degradation which leads to replacement of these valuable hardwood species with short rotation, exotic species, or conversion to agriculture. Logging is also part of the process of forest clearing for cardamom and other cash cropping, with trees normally felled and left to dry for use as fuelwood. High rural populations and only 15% of Zanzibar being arable land means immense pressure on forest land, with agricultural encroachment being a cause for deforestation and degradation in many areas.
Infinite resources effectively mean a complete lack of forest management. Zanzibar’s trees and forests are constantly managed now for timber, fuelwood, and construction poles. This causes many problems. Trees are felled at a tree which is too young, poorly selected trees are felled, and trees are damaged during extraction. All of these have serious implications for the likelihood of regeneration and impact on forest composition. Logging is particularly taking place within the profitable stands of Zanzibar’s indigenous species “Namemba” and Pterocarpus angolensis.
Conservation efforts for rare plants in Zanzibar
The establishment of ex situ plant conservation sites in Zanzibar will also greatly enhance our ability to conserve rare plant species. At the moment, there are no functioning botanical gardens or arboreta in Zanzibar. However, at The National Herbarium of Tanzania in Zanzibar, much living plant germplasm could be maintained. There are a number of species at Masingini Forest and elsewhere that could easily be grown in a botanical garden situation. A plant conservation and propagation programme could easily be established at MBOSC or in other suitable areas. Finally, the concept of a gene bank for maintaining seeds of endangered species should be considered for the future.
In the longer term, propagation of rare species for outplanting will be the best way to safeguard the future of the species concerned. Before attempting this, more information on the ecology and germination biology of the species involved will be necessary. It will then be possible to establish propagation protocols and grow plants for outplanting in areas where they have become locally extinct.
Several strategies may be employed to guard the more threatened plants from extinction. Each plant species will require its own plan of action. In some cases, the only possible action may be a programme of in situ protection where the plant is fenced off from grazing animals. This technique is limited in scope and its success is largely dependent upon the attitude of local communities.
Ecological Importance of Endemic and Rare Plants
The presence of a variety of vegetation types and plant characteristics has made this archipelago the focus of many naturalists. The Zanzibar archipelago belongs to the Eastern Afromontane biodiversity ‘hotspot’ due to its high proportion of endemic species and a high degree of habitat loss. Afromontane regions are noted for their high levels of biodiversity and endemism, yet they are one of the most threatened and least studied ecosystems on the continent. The remaining fragments of the natural vegetation of Zanzibar are now restricted to the highest parts of the larger islands, with the notable exception of Ngezi forest on Pemba. In these areas, it is still possible to find much of the original flora and is considered crucial to preserve these areas in order to conserve the maximum levels of biodiversity. In this context, the conservation of the remaining Afromontane areas is likely to be of great importance both locally and at a global scale. This is especially true for the conservation of Zanzibar’s endemic and/or rare plants. Endemic plants are plants which are found only in one particular region. They are generally at a higher risk from extinction compared to more widespread species since their habitat is often restricted and they tend to have small population sizes. A plant may have a restricted range either because it is a habitat specialist (it has very specific habitat requirements), or because it has become so well adapted to a particular area that it has out-competed other species and spread into all the available habitat. The loss of endemic species can have a disproportionately large effect on the overall level of biodiversity in an area, and thus conservation of these species is often a high priority.
Role of endemic and rare plants in the ecosystem
Endemic plants have a special and important role in the ecosystem. They grow in specific habitats and are found in definite locations. They occupy microhabitats not occupied by widespread species. The rare and endemic species are important for the study of plant science. These plants have survived for thousands of years and have many morphological and physiological adaptations. They provide lots of information about plant species, genetic variation, and protect endangered species. Due to deforestation and shifting cultivation, many habitats of rare and endemic species are being destroyed. Plant species are fundamental to the functioning of all ecosystems and provide a wide range of ecosystem services, such as primary production and decomposition, nutrient and water cycling, and provision of habitats for other organisms. For instance, mycorrhizal associations are unique to plants and are known to influence the composition of plant communities. As yet, we know little about the influence of rare and endemic plant species on ecosystem processes and it cannot be assumed that they fulfill the same functions as widespread species. The islands and places with high endemism are more likely to have a high proportion of rare species. Therefore, knowing the ecological role of rare species might help to understand the likely consequences of global species loss. One approach is to compare the functional traits of rare and endemic species with those of allied widespread taxa. For instance, on the Canary Islands, Gallot et al compared the functional traits of 16 endemic and rare species with those of common species from the same or related genera. They found that the endemics were less competitive. Any thorough understanding of rarity, conservation, and ecosystem function will require manipulative studies, but these authors recommend measures to reduce extinction risk, such as propagation and species translocation.
Unique adaptations of endemic and rare plants
Researching into the floral biology and reproductive systems of rare and endemic plant species will give insights into their regenerative abilities that underpin their persistence and population viability. Devis and Silva found that for the Brazilian Cerrado, the primary conservation concern for endemic plant species was their low seed production and poor seedling establishment. Other research has indicated that many rare and endemic plant species have lost the ability to replace or regenerate themselves after a disturbance. This would suggest that such plant species are particularly vulnerable to local extinction and may require human intervention if they are to persist in the landscape.
Endemic and rare plants of an area are the unique species which are found only in a particular area or region and not grown anywhere else. Endemic and rare plants make a considerable part of many natural areas, professionals in land management and conservationists have to deal with the specific needs of these plants when considering the use of fire. Endemic plants exhibit a limitation in their distribution to a specific area or zone by showing spatial exclusiveness. This concept involves the plant species being found only in a single place, island, lake or mountain top. High rates of endemism are one of the principal qualities of the world’s “biodiversity hotspots”. Plant traits related to regeneration are considered as any biological trait that enables or enhances chances of a plant species regenerating. These traits include seed production, dispersal, and germination. A good understanding of these traits in relation to fire is crucial for effective conservation management aiming to avoid extinction of any rare or endemic plant species.
Conservation value of endemic and rare plants
The islands’ communities are only likely to do this if they can see a direct benefit, and here is where a knowledge of the potential uses of the endemic plants can be turned to their advantage. Although it is often assumed that traditional medicine is a ‘safety net’ for conserving useful plants and local knowledge about them, recent studies in several villages have indicated that the use of endemic species is limited and that knowledge about them is being rapidly lost. This is due to the root causes of habitat destruction and the fact that many traditional medical practitioners are now turning to plant species that are cheaper and easier to obtain from other areas. In some cases, a species may be highly valued but knowledge of its collection and use may be known only by a few elderly people. An example of this is the critically endangered, endemic tree Adenia isaloensis, for which only one elderly man now knows the location of the last remaining, inaccessible population in the Ngezi forest. His recent illness and the fact that the area is now slotted for clearance by a commercial tree plantation company highlights the urgency of identifying and protecting the areas where endemic plant populations still persist.
Since many of the endemic plants are poorly known and do not have a direct economic value to the local communities, their conservation requires an approach that emphasizes their value for maintaining ecological processes and preserving the full range of biodiversity on which the islands’ people depend. Treating these plants simply as symbols of a rapidly disappearing natural heritage, and saving a few of them in ex-situ collections will not be sufficient. It will be necessary to identify and protect the areas where the process of speciation and the development of complex ecosystems involving endemic species are still occurring. In most cases, this will involve working with local communities to promote land-use practices that are compatible with the continued existence of ecosystems on which the communities themselves depend.
More than half of the world’s endangered plant and animal species are endemic to 25 biodiversity ‘hotspots’, yet none of these areas have as many highly threatened species as insular Eastern Africa. Various factors have caused the decline of the natural habitats on the Zanzibar islands; only one fifth of the original forest cover now remains, cropped and browsed by an ever-increasing population of humans and domestic animals. The situation is further compounded by the fact that nearly all of the islands’ endemic plant species are threatened, mostly by habitat destruction. Thus, the importance of these plants lies in the fact that their conservation is critical to preserving the remaining natural ecosystems of the islands.
Habitat loss and fragmentation
Simulation results showed that for a given pattern of gene flow, a reduction in habitat size led to an accelerated loss of variability. The demographic and genetic factors specific to fragmented habitats are compared with those of small isolated populations, leading to a synthetic view of population viability in habitat fragments which may carry over to other rare plant species.
The immediate and long-term effects of habitat fragmentation on genetic variability and population viability of a rare Impatiens taxon in the Jura Mountains were analyzed by means of allozyme diversity in extant populations and a simulation model. Stepwise multiple regression revealed that (1) current population size and (2) the size of available habitat are strong predictors of genetic variability. Small habitats may maintain variability levels similar to large ones only in the presence of gene flow from other populations.
Fragmentation results in habitat patches of diminishing size, and species have less area for movement, finding mates, maintaining viable population sizes, continued natural selection, and keeping ecological processes functioning. Over time, such small patches will lose plant species. The patches will become more similar due to colonization extinction dynamics and environmental changes, edge effects, and the species within them will be more prone to genetic and demographic stochasticity.
Invasive species and their impact on endemic and rare plants
Endemic and rare plant species are at heightened risk from the impacts of invasive species due to the specific evolution of the endemic species and their often precarious hold on survival in relict habitats. Zanzibar, Pemba and India have had a long history of plant introductions, beginning with early cultivation by Arab and Persian settlers, a myriad of introductions by European colonial efforts and industrial scale plantings in an attempt to establish cash-crops by the British and Sultanate governments. Most recently Zanzibar has had to deal with the introduction of the highly invasive Lantana camara across all forest habitats. Lantana is particularly damaging to forest ecosystems through allelopathic toxins in its leaves and roots which inhibit seed germination and seedling growth of native and endemic species and has rapidly formed near monospecific stands in many cleared forest areas. Lantana’s impacts have been observed in Jozani forest where the plantings abandoned in the establishment of the tourist campsite rapidly spread into adjacent forest and are now being spread eastwards by a small population of wild pigs. Introduced animals have also had a significant impact as agents of seed dispersal for invasive species and local rumour suggests that Lantana was first introduced to Zanzibar by European colonists who dropped the seeds while riding horses across Pugu forest in a failed attempt to establish a settlement. Inadequate management has mainly been due to a lack of resources and biological expertise and associated research into the impacts and control of invasive species. Information on the distribution and abundance of invasive species is often poor as demonstrated Lantana’s sudden emergence across Zanzibar and Pemba over a period of just a few decades. This presents a difficult scenario for conservation planners as to whether to focus on eradication of new invasive species with small affected area and abundance or invest into control efforts for well established species with larger affected area and abundance despite the potential for local and regional extinction of endemic species in the meantime.