zfsheet08

Factsheet No#8: Biological Diversity

Biological diversity, or biodiversity, is the total variety of organisms and the diversity of genes species and ecosystems found on Earth. It covers plants, animals, fungi, microbes, and any other form of life, large or small.

In the Convention on Biological Diversity, the term biodiversity is described as the variability among living organisms, including, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species (genetic diversity), between species (species diversity) and of ecosystems (ecological diversity).

Biodiversity measurement and importance

Biodiversity can be surveyed and quantitatively described at one of the three levels: genes, species and ecosystems. Measurement is in units of diversity, such as numbers of species or processes.

It is estimated that of the 10 million to 50 million species in the world, over 80,000 of plant species are edible. Of these, only 30 supply over 90 percent of food requirements.

As little as 1.5 million plants and animals have been recorded and classified. The contribution of plants and animals to medical needs cannot be overemphasised. Nearly half of the drugs given to patients worldwide are derived from natural biological resources.

Other gains from biodiversity include protection of water resources mainly by the roots of plants, soil formation and protection, nutrient and other chemical cycles, contribution to climate stability, general maintenance of ecosystems and recovery from unpredictable catastrophes such as fires and droughts.

Other benefits are social, and include research and education, recreation and cultural values.

Biodiversity of the Basin

The Zambezi Basin can be classified into four main biological zones: the Guineo-Congolian, the Zambezian, the Montane and the East African Coastal region.

Eight major vegetation groupings are found in the basin. Few studies have focused on the biodiversity of the basin as a whole.

This is mainly because most studies observe political and administrative boundaries, and some studies are specifically targeted on one or just a group of species.

Ecologically, the Zambezi Basin can be subdivided into three main sections. The Upper Zambezi exhibits traits of the original Zambezi River, which flowed to the Okavango Delta, then to Lake Makgadikgadi, where an inland sea is believed to have existed.

The Middle Zambezi is between Victoria Falls and the Lupata Gorge below Tete in Mozambique, and is much younger, and mixed environment. It includes the Luangwa Valley and most of northern Zimbabwe. The Lower Zambezi stretches from the Lupata Gorge to the Indian Ocean, and it includes the Shire River.

Lake Malawi, one of the many natural lakes formed by faulting and rifting which resulted in the Great African Rift Valley, is sometimes treated as a separate entity, therefore, the fourth section, because of the large number of endemic species in the lake.

Recording all forms of life in an ecosystem as large as the Zambezi Basin would be very difficult, but it is estimated that over 95 percent of flowering plants and less than half of other more difficult species such as beetles have at some point been observed and recorded.

Also, taxonomy is comparatively better for the larger plants and animals than for the smaller ones.

While it is possible to make reasonable statements on the biodiversity of such groups as flowering plants, mammals, birds and fish, perhaps even on groups such as butterflies and dragonflies, it is very unclear on total diversity and patterns of diversity in groups such as bacteria, beetles and other invertebrates.

Vegetation

The vegetation of the Zambezi Basin has three broad areas of associated plant species within which many are endemic: the Zambezian, the Congolian, the Afromontane and the Coastal.

In terms of broad vegetation types, almost half of the basin is classified as wetter or drier miombo woodland.

Other widespread vegetation types are mopane woodland, open woodland dominated by various species of acacia, Combretum or Terminalia, mosaics of various types of woodland, forest and grassland (including that dominated by Zambezi Teak, Baikiaea plurijuga) dry forest and wetland grassland. The vegetation of the basin can be described under eight broad types as shown in Table 1.

Table 1. Broad vegetation groups of the Basin

Table 1. Broad vegetation groups of the Zambezi Basin (adapted from White 1983)

Vegetation group	% of the basin	Vegetation group	% of the basin
Miombo woodland	49	Montane forest/grassland	2
Mopane woodland	12	Coastal forest/grassland mosaic	1
Woodland/forest/grassland mosaic	19	Swamp & pan	4
Only evergreen forest	6	Lake	3
Acacia/mixed woodland	7	Lake	3

_{Adapted from White 1983}

Animal and plant groups

The Zambezi Basin has about 700 bird species, 200 species of reptile and 90 species of amphibian. There are 165 recorded species of fish from the basin, excluding Lake Malawi, which has about 500 species, nearly all of them endemic.

Fifty-nine of these are found exclusively in the Upper Zambezi and 43 exclusively in the Middle and Lower Zambezi. Around 195 mammal species have been recorded in the basin. A total of 6,000-7,000 species are believed to be in the Zambezi Basin.

Conservation areas

Much of the effort to conserve the larger forms of animal and plant life can be seen from the large tracts of land designated as protected areas, national parks, safari areas and game reserves.

More than 10 percent of the basin is generally protected.

Table 2. Area in Basin conserved as National Parks

Country	Proportion of basin (%)	Area under NP (km²)
Angola	18.3	14,450
Botswana	2.8	10,570
Malawi	7.7	1,425
Mozambique	11.4	0 (?)
Namibia	1.2	1,334
Tanzania	2.0	0
Zambia	40.7	88,092
Zimbabwe	15.9	20,727
TOTAL	100	136,598
= 10.3%of Basin

The basin has large wetland areas along the Zambezi River itself, and along the main tributaries such as the Kafue River. The major ones are the Barotse Floodplains in western Zambia, and the flood plains and swamps associated with the Kwando/Linyanti/ Chobe/Zambezi confluence in the eastern Caprivi of Namibia.

The others include the Lukanga and Busango swamps on the Upper Kafue in central Zambia, the Kafue Flats in southern Zambia, the marshes of the Lower Shire in southern Malawi, and the extensive swamps and floodplains associated with the Zambezi Delta in central Mozambique. Lakes Kariba, Cahora Bassa and Malawi are large water bodies, each with their own biodiversity.

Apart from supporting specialised aquatic and birdlife, wetlands in most cases act as sponges; collecting large volumes of water and releasing it slowly over time. The Zambezi River has a constant good flow throughout the dry season because floodplains collect water during floods and release it slowly. The inhabitants of the floodplains cultivate the higher grounds during the summer floods and practise winter agriculture when the waters subside.

The basin is important for conserving biodiversity, especially those species endemic to the basin. Changes in biodiversity can be usefully monitored by focusing on "flagship species." The Wattled Crane is one such species, where of the 13,000-15,000 birds worldwide, over 90 percent live in selected wetlands in the Zambezi Basin.

Changes in these few wetlands will have direct impact on such species. Other bird species of conservation concern from the Zambezi wetlands are given in Table 3. Another "flagship species" of the wetlands is the lechwe (Kobus leche).

Table 3. Bird species of conservation concern or with substantial populations in Basin wetlands

The biodiversity of the Zambezi Basin is threatened by various factors, both direct and indirect. The factors can be grouped into six categories: pollution, fire, exotic (alien) species, dams and other hydrology structures, land clearance and overexploitation. The severity of each of these factors varies from place to place in the basin, and often more than one of these factors are experienced together.

The effect of pollution is usually felt after a lengthy period of continuous discharge of waste. Pollution emanates from definite sources called point sources such as mining compounds and industries or from general or non-point sources such as pesticides and fertilisers in runoff from agricultural land.

Two examples of pollution observed in the basin include pollution of the Lake Chivero near Harare where fish deaths were observed in 1995 and the effect of mining on tributaries such as the Kafue in Zambia.

Large areas of the Barotse Floodplains and many other parts of the basin are subject to regular fires. The vegetation in these areas has since modified to suit the prevailing conditions.

Introduction of alien species has mixed effects on the biodiversity of the basin. Pine trees have invaded the grasslands of Nyanga in Zimbabwe and Mt. Mlanje in Malawi.

The Nile Tilapia fish was introduced in the waters of the Middle Zambezi, and the Kariba Weed (Salvinia molesta) into the Chobe system. The water hyacinth weed is now in most tributaries of the Zambezi, reducing the biodiversity of indigenous species.

Introduction of the kapenta (Limnothrissa miodon) in Lake Kariba in the 1960s is believed to have had more positive effects than negative as it was introduced in a newly created habitat. The construction of dams has the greatest effect on biodiversity of wetland species as new habitats are formed and old ones destroyed or modified. The hydrology of the Zambezi River system was modified by the construction of the Kariba, Cahora and Itezhi-Tezhi dams.

Human settlements have sprung up in areas previously belonging to the natural environment. As the settlements expand due to population increases and other factors, more land is acquired and cleared for agriculture, urbanisation and expansion of human development initiatives.

Such large settlements include the Copperbelt towns of Zambia, the large urban settlements of Harare, Lusaka, Lilongwe and many other towns in the Basin. Land is also cleared to make way for farms and plantations that replace a rich diversity with a monoculture of plants.

Associated with human development is overexploitation of species of particular interest to human needs.

Examples include the destruction of large mammals such as the elephant, rhino, and antelope over wide areas, harvesting of valuable timber such as mukwa, African Ebony and Zambezi Teak, overgrazing in various parts of the basin and overfishing in Lake Malawi.

Due to the size of the Zambezi Basin, the diversity of its flora and fauna is difficult to comprehensively document. Most of the larger animals and birds have at least been recorded, but knowing their exact numbers and distribution is a huge task.

One major reason is that some areas have received more attention than others, merely because of the economic and social benefits associated with them.

It is important to know that conserving biodiversity involves looking at the environment as a large ecosystem, and that each species, great or small, is an important role player. Another usual oversight is that of allowing socio-economic development to take place at the expense of the environment and the biodiversity it supports. Biodiversity is increasingly becoming an important subject at the local, national, regional and global levels. One way of tackling the issues involved is from an ecosystem approach, for example, the basin as a unit and not the sum of parts influenced by national boundaries.

Development Workshop C. P. 3360 Luanda Angola Tel: 244-2-348371 Fax:244-2-349494 Email: dwang@angonet.org

Ministry for the Coordination of Environmental Affairs C.P. 2020 Maputo Mozambique Tel: 258-1-465708/843 Fax: 258-1-465849 Email: micoa@ambinet.uem.mz

University of Zambia (UNZA) P. O. Box 32379 Lusaka ZAMBIA Tel: 260-1-293029 Fax: 260-1-253952 E-mail: pnkunika@natsci.unza.zm

Ministry of Agriculture P Bag 0032 Gaborone Botswana Tel: 267-350506 Fax: 267-303744

Ministry of Environment and Tourism (MET) Directorate of Environmental Affairs P Bag 13306 Windhoek Namibia Tel: 264-61-249015 Fax: 264-61-240339

Department of Natural Resources Harare Street/Herbert Chitepo Avenue P.O. Box 385 Harare Zimbabwe Tel: 263-4-793124/730931 Fax: 263-4-793123/730218

SADC/IUCN/SARDC, 1994, State of the Environment in Southern Africa, Maseru/ Harare.

SARDC, 1998 (unpublished), The Biodiversity of Indigenous Forests and Woodlands of southern Africa, Harare.

Timberlake, J., 1998, The Biodiversity of the Zambezi Basin, Paper presented at a regional workshop on State of the Environment Reporting for the Zambezi Basin, Mazvikadeyi.

Species	Where found	Conservation category¹	Species	Where found	Conservation category¹
White-winged Flufftail	Zambia, Zimbabwe	Endangered	Lesser Flamingo	All areas in ZB	Near-threatened
Slaty Egret	Botswana, Namibia, Zambia	Vulnerable	Great Snipe	Anywhere	Near-threatened
Wattled Crane	most wetlands; not L. Shire	Vulnerable	Black-winged Pratincole	Western parts of ZB	Near-threatened
Corncrake	Malawi, Zambia, Zimbabwe	Vulnerable	Rock Pratincole	Namibia, Zambia, Zimbabwe	Major population
Madagascar Squacco Heron	Malawi, Moz(?), Zimbabwe	Near-threatened	African Skimmer	Throughout ZB	Major population
Shoebill	Only Bangweulu within ZB	Near-threatened	Carmine Bee-eater	Mid-Zambezi & Shire	Major population