Desert environments in Namibia The flora and fauna

Desert environments in Namibia The flora and fauna of Namibia

Key Question 1. 1 What are the characteristics of a desert environment that make it extreme? * The climatic, biotic and soil characteristics of a desert environment. * The links between climate, biotic and soil characteristics. Key Question 1. 2 How is human activity causing pressures on the desert environment? * The threats that are posed by (i) population growth; (ii) mineral exploitation; (iii) farming; (iv) tourism. * The positive and negative outcomes of human activity. Key Question 1. 3 What are the strategies that can be used to manage human activity in deserts? * Strategies that attempt to (i) conserve the desert environment; (ii) alleviate the impacts of human activity; (iii) control the use of the desert environment (iv) monitor the impacts of human activity. * The role of local, national and international groups in the management of the desert environment.

The biotic environment

Vegetation zones The major vegetation zones in Namibia are arid or semi-arid. Along the coast vegetation is very sparse. Deeper into the interior hardy succulents appear followed by stunted acacias. Desert scrub is a feature of the south with the quivertree growing around Keetmanshoop. Over the Kalahari the scrub make way for a combination of scattered trees with bunch grasses (savanna). In the north deciduous trees are more important.

Therophytes are annual plants which regenerate from seed. These are very common Cryptophytes are adapted to extremes of heat or cold and persist because they regenerate from buds, bulbs or rhizomes that are completely buried in the soil. Hemicryptophytes are typical of moist temperate regions. They die back at the end of the growing season and buds are protected by the withered leaves and soil. Chamaephytes include small shrubs and herbs that grow close to the ground. Snow offers some protection during cold winter months. Phanerophytes are trees and small shrubs. They carry buds on the tips of branches. They are characteristic of hot or mild moist environments where plants are not subject to drought or frost. Types of plants found in the desert

Factors influencing desert ecosystems Small leaved

Types of plants Xerophytes plants which can cope with conditions of drought Phreatophytes plants which have long tap roots to exploit water resources deep underground Halophytes plants which can cope with saline soils Therophytes plants which are annual and grow from seed in the ground, therefore able to exploit rain straightaway

Characteristic plant life forms in deserts Succulent perennials – very specialised plants but which typify many desert landscapes Non-succulent perennials – these represent most of the plants in the Namib Desert Annuals – plants which exploit the little rain the desert gets by growing from seed very quickly and having a quick life cycle

Succulent perennials Clockwise from top Welwitschia mirabilis Aloe dichomata (Kokerboom tree) Euphorbia virosa Euphorbia damarana Pachypodium namaquanum (Halfmens) Pachypodium lealii (Cobas tree)

Aloe namibensis Aloe pillansii Bastard Quiver Tree Moringa ovalifolia Tylecodon paniculatus Botterboom

Specialised succulents Lithops ruschiorum looks like a rock camouflage Conophytum stephanii has hairy leaves to collect droplets of fog. Conophytum wettsteinii Conophytum pupicalyx also collects droplets of fog

Non-succulent perennials Grasses, e. g. Stipagrostis Bushes, e. g. Nara melon (Acanthosicyos horridus) Trees, e. g. Camelthorn (Acacia erioloba)

Suaedia articulata occurs as a low lying shrub on the salt pan at Etosha Sporobolus spicatus Commiphora saxicola Commiphora dinteri

Annuals Gazania Nineawn pappusgrass Enneapogon desvauxii Lovegrass - Eragrostis annulata Sarcocaulon patersonii Cleome hirta

Adaptations of plants to arid environments Drought escaping – therophytes (annual plants) which grow from seed whenever rain falls. Although seed do not rot easily in the desert environment many may be lost to predators. Some plants display amphicarpy by bearing seeds both above and below ground.

Adaptations of plants to arid environments Stipagrostis obtusa Stipagrostis sabulicola – Dune grass Drought evading – perennial plants which live above surface continually but wither during times of drought and grow again when rain falls. Roots are shallow but are able to remain dormant when water is not available. In Namibia many of these are dune grasses of the Stipagrostis family.

Adaptations of plants to arid environments Drought enduring – plants which can endure drought by deep roots(up to 50 m deep), which grow even during periods of extreme drought, which have small shiny leaves, where the leaves can change direction in order to face or avoid the sun (heliotropy), and where stomata within the leaves are rolled up to reduce transpiration Acacia erioloba – the camelthorn has roots up to 50 m deep

Adaptations of plants to arid environments Drought resisting – plants which have learnt to use very little water, i. e. succulent plants where leaves are reduced to spines, surfaces are heavily waxed to reduce water loss, and where water is stored within a thick trunk to be used slowly

Many plants show allelopathy, i. e. they are poisonous either to herbivores or to the soil. Allelopathy There is an intense struggle for resources in the desert – not so much for light as in the tropical rain forest, but for nutrients, space and water. The sap of Euphorbia virosa is used by bushmen to tip poison arrows. Euphorbia damarana leaves toxins in the soil around it which create circular patches where no other plants can grow and compete for water. Geigeria africana (above) and Cotyledon orbiculata (left) cause the disease vermeersickte in cattle and sheep if they eat the plant. The animals become paralysed.

Many flowers open at night to attract moths. Others open at midday for bees to pollinate the plant. Pollination Hoodia has vibratile hairs which move even when there is no wind, attracting flies. Its scent and colour is that of rotting meat so that flies do the pollination. Several plants, such as Hoodia (right) and Euphorbia Fenestraria is a plant which hides in the sand leaving only ephedroides (below) are brown the top of its leaves showing, which are transparent. in colour as a protection against the high radiation Colour

Animal strategies to obtain water The meerkat and African ground squirrel stay beneath the sand in burrows during the day. Tenebrionid beetles such as the species Onymacris unguicularis collect water from the fog by standing on their hind legs and facing the moist wind. The shovel-snouted lizard Meroles The sun spider is anchietae buries a solifuge. It itself in the sand avoids the hot where the ground by temperature is a jumping off the few degrees cooler ground every few seconds.

The gemsbok or oryx saves water by having solid urine. It pants to lose heat and has a short shiny coat. These are all characteristics of a hyperthermic animal, i. e. one which can cope with high temperatures. Some animals display aestivation (the opposite of hibernation) and sleep for the hot summer months. Fauna - herbivores Most animals are nocturnal to avoid the heat of the day. Animals are prepared to migrate many miles in search of water, e. g. the desert adapted elephant.

Fauna - carnivores Desert adapted lion can travel many miles in search of prey. The bat eared fox and caracal have large ears which lose heat rapidly. The sand viper Bitis peringueyi gets the water it needs from its prey.