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Tropics

Fern
Photo: sh / traditura

Outstanding features of the tropics are the almost constant day length throughout the year, with the sun always high at midday and the annually recurring rainy season. In addition, biodiversity is more pronounced in the tropical regions than in all other climate zones.1)

The tropics lie between the Tropic of Cancer and Tropic of Capricorn and border the subtropical zones polewards. They are frost-free all year round with an annual average temperature of over 18° C.1)

As the tropical zone contains both humid and dry regions, we categorise them into four categories that are characteristic of their vegetation:

  • Hot and humid rainforest
  • Humid savannahs
  • Dry savannahs and forests
  • Thorn savannas

The first two are also known as the ever-humid tropics, as these regions have high temperatures and rainfall all year round. Dry savannahs and forests, on the other hand, are referred to as alternating humid tropics, as they have distinct dry and rainy seasons, while thorn savannahs belong to the tropical drylands region. 

The hot and humid rainforest is always humid due to the very high annual precipitation, with average annual temperatures fluctuating by only around 6° C between 24° C and 28° C. More pronounced are the differences between daytime maximum and night-time minimum temperatures, which can be up to 10° C (= daytime climate). Distinct seasons with vegetation breaks are therefore largely absent.2)

In addition to this constantly hot and humid climate, the rainforest is characterised by an outstanding variety of animal and plant species, many of which only occur in this area.2) The annual growth period is 365 days, so that the natural vegetation consists of biomass-rich, tall-growing, evergreen tropical rainforest with a canopy-like structure between the ground and the tree canopy.1) Often, up to six different, merging levels are described. These are home to an estimated 30 million different animal and plant species in all the world's rainforests. The levels of the rainforest are known as the ground layer, herb layer, shrub layer, low tree layer, canopy layer and giant tree layer.2)  

Mammals such as elephants, primates (e.g. chimpanzees and orangutans), tigers and panthers are only represented by a small group of species in the rainforest. The vast majority are arthropods, i.e. insects, arachnids, millipedes and crustaceans. Reptiles such as crocodiles or snakes, fish in the rivers as well as numerous striking and very colourful feathered birds such as parrots and birds of paradise are also well represented. 

Tropical rainforests still make up around 8% of the earth's land surface, of which over 30% is still uncolonised and in a largely unaffected natural state. Less than 20% can still be regarded as near-natural and relatively unaffected.2) 

The rainforests are still home to a large number of indigenous peoples who lead a rather isolated existence and are able to live largely independently from the forest and its products. As hunters and gatherers, they also cultivate fruit and vegetables in storey cultivation adapted to the ecological and climatic conditions. In addition to larger groups such as the pygmy peoples in Central Africa's rainforests or the indigenous Yanomami ethnic group in the Brazilian Amazon region, there are also some uncontacted and nomadic small groups with only a few hundred individuals.2)

 

Humid savannahs are characterised by high annual rainfall and year-round average temperatures between 22° C and 28° C. There is a longer rainy than dry season with short transitions, which is why the natural vegetation consists mainly of low, rain-green (= deciduous in the dry season) forests and tall grasses such as elephant grass, which can grow up to 6 metres high. Compared to the hot and humid rainforests, the dry seasons in wet savannahs are on average around 2.5 months longer and the vegetation period is around 65 days shorter at over 300 days.1)

In total, the wet savannah covers approx. 9.4% of the earth's solid surface and is one of the largest and quantitatively most animal-rich areas on earth after the tropical rainforest.3)

Typical mammal species such as lions, hyenas, kangaroos, giraffes, zebras, meerkats, gazelles and antelopes, as well as elephants, buffaloes and hippos, live in the continents' wet savannahs. Numerous arachnids and insect species, such as ants and grasshoppers, can also be found in this vegetation zone. Notable bird species include vultures and ostriches.

 

In the humid tropical regions, traditional forms of shifting cultivation, land exchange and horticulture still play a role today. But the rainforests in particular are refuges for the last isolated and near-natural peoples on earth. The diversity of indigenous peoples, ethnic groups and languages is nowhere greater than in the tropics.1)

 

Dry savannahs and forests are warm all year round with very high average annual temperatures of 22° C to 28° C. They have shorter rainy than dry seasons with short transitions, and with less than 7 wet months only a short annual growing season of around 180 days. The potential natural vegetation consists of deciduous, rain-green dry forests. In many regions, however, regular forest fires or browsing have degraded large areas of these to dry savannahs with low, rain-green, wide-stemmed trees (such as the baobab) or groups of trees with a closed plant cover of dry grasses no more than 80 cm high.1) As in the tropical rainforest and the humid savannahs, the daytime climate also prevails here.2)

The dry savannahs or dry forests lie between the wet savannahs and thorn savannahs and belong to the humid tropics with only 4.5 - 7 rainy months. They make up only about 3% of the earth's land area. Together with the humid savannahs, they are the most densely populated regions of the tropics.4)

The inhabitants of this climate zone cultivate a fairly large variety of different crops on small fields in traditional shifting cultivation, which is mostly practised as hoeing without mechanical or animal assistance.4) In Africa, mainly sedentary or semi-sedentary (= semi-nomadic) agropastoralism prevails, in which livestock such as cattle, goats or water buffalo are kept on natural pastures in addition to the cultivation of barley, wheat and millet as winter cereals. In total, between 160 and 460 million people still live from traditional forms of sedentary or semi-nomadic animal and plant production in dry savannahs and forests.5)

 

Thorn savannahs are also warm all year round with average temperatures usually between 21° C and 28° C. They are characterised by a very short rainy season with moderate to very high rainfall and short transitions to a long dry season of 8 to 10 months. The annual growing season is around 180 days, meaning that the potentially natural vegetation already has the gaps typical of dry regions and consists mainly of thorn bushes and water-storing succulents. Thorn savannahs are low grass-covered open land or wide-stemmed thorn forest, whereby the "forest plants" here are only trees in exceptional cases.1) 

Spiny savannahs lie between the desert and semi-desert vegetation zones on the one hand and dry savannah and humid savannah on the other and are widespread on all continents except Europe and Antarctica. Together with cactus deserts, which we have categorised as hot desert vegetation in the subtropics, the areas of thorn savannahs make up about 5% of the Earth's land surface.6)

Only water-storing plants survive in the thorn savannah, such as the thorn bushes that give it its name. The soil is sandy or stony and there is no closed grass cover as in the humid savannah. Many animals are nocturnal or crepuscular in order to minimise fluid loss during the day.6)

 

Even today, indigenous peoples still live in the thorn savannahs, who practise traditional agriculture and live mainly from hunting, gathering and fishing.7)

Unfortunately, the number of people who still actively practise traditional methods of food production and can live completely from and in harmony with nature is also declining here. The original knowledge passed down from generation to generation is therefore gradually being lost.

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In our next article, we provide an overview of the different food groups:

 

 

 


References:

1) Cf. Wikipedia, 2024: Tropen, taken from the internet on 30.03.2024, https://de.wikipedia.org/wiki/Tropen

2) Cf. Wikipedia, 2024: Tropischer Regenwald, taken from the internet on 30.03.2024, https://de.wikipedia.org/wiki/Tropischer_Regenwald

3) Cf. Wikipedia, 2024: Feuchtsavanne, taken from the internet on 30.03.2024, https://de.wikipedia.org/wiki/Feuchtsavanne

4) Cf. Wikipedia, 2024: Trockensavanne, taken from the internet on 30.03.2024, https://de.wikipedia.org/wiki/Trockensavanne

5) Cf. Wikipedia, 2024: Agropastoralismus, taken from the internet on 30.03.2024, https://de.wikipedia.org/wiki/Agropastoralismus

6) Cf. Wikipedia, 2024: Dornstrauchsavanne, taken from the internet on 30.03.2024, https://de.wikipedia.org/wiki/Dornstrauchsavanne

7) Cf. Wikipedia, 2024: Gran Chaco, taken from the internet on 30.03.2024, https://de.wikipedia.org/wiki/Gran_Chaco