Why Vegetation Matters

22 min

What a tree does all day

A single tree on a hillside is working all the time: its leaves slow the rain, its roots hold the soil, it breathes out water vapour that becomes clouds, stores carbon in its wood, shelters birds and insects, and may one day become firewood, a roof beam or medicine. Multiply that by millions of trees in Nyungwe, or the papyrus of Rugezi, and you have one of Rwanda's most valuable resources.

Vegetation, soil and water

Figure 1. Why vegetation protects soil and water.

Worked example: run-off from forest and from bare land

A storm drops 40 mm of rain on 1 hectare (10,000 m²) of hillside. Suppose that on a forested slope about 5% of the rain runs off the surface, but on a bare slope about 40% does (illustrative figures; real values depend on the slope and soil). How much water runs off each?

\text{rain} = 10\,000\ \text{m}^2 \times 0.040\ \text{m} = 400\ \text{m}^3

\text{forest run-off} = \frac{5}{100} \times 400 = 20\ \text{m}^3

\text{bare run-off} = \frac{40}{100} \times 400 = 160\ \text{m}^3

The bare slope sends eight times as much water, carrying soil with it, into the stream within hours. The forest stores most of the water in the ground and releases it slowly, keeping streams flowing into the dry season.

The importance of natural vegetation

Importance	How	Rwandan example
Protects soil	Roots bind the soil; leaves and litter break the force of the rain	Forest and grass cover on steep slopes reduce landslides
Stores and regulates water	Forests and swamps soak up rain and release it slowly to springs and rivers	Nyungwe feeds rivers of both the Nile and Congo basins; Rugezi feeds Lakes Burera and Ruhondo
Influences climate	Transpiration adds moisture for rain; trees store carbon and keep local temperatures lower	Moist, misty air over Nyungwe and the Virungas
Habitat for wildlife	Food and shelter for animals and birds	Mountain gorillas in the Virungas; chimpanzees in Nyungwe; giraffes and elephants in Akagera
Tourism and income	Visitors pay to see forests and wildlife	Gorilla trekking, the Nyungwe canopy walk, Akagera safaris
Products	Timber, firewood and charcoal, poles, fruit, honey, medicinal plants, papyrus for mats	Firewood and charcoal are still the main cooking fuels for many households
Research and education	Living laboratories for science and learning	Research on gorillas at the Karisoke Research Center

Definition

Deforestation: the permanent clearing of forest for other land uses such as farms, pasture, settlements or mining. Example: most of Gishwati forest was cleared between the 1980s and the early 2000s.

Definition

Afforestation and reforestation: afforestation is planting trees where there was no forest before; reforestation is replanting trees where forest was cleared. Example: planting native trees in Gishwati is reforestation.

Definition

Agroforestry: growing trees together with crops or livestock on the same farm, so that the trees protect the soil, provide fodder, fruit or wood, and improve fertility. Example: grevillea trees along terrace edges above bean fields.

Important

Case study: balancing needs and protection in Rwanda

Rwanda has one of the highest population densities in Africa, and most families need land to farm and wood to cook. Natural vegetation has therefore been reduced to protected areas, while plantations of eucalyptus, pine and grevillea supply most of the wood. Rwanda aims to keep at least 30% of its land under forest, including plantations, and is trying to meet everyone's needs with:

Protected areas (Nyungwe, Volcanoes, Akagera, Gishwati–Mukura) and protected wetlands such as Rugezi;
Agroforestry and trees planted along terraces, roads and rivers;
Tree-planting seasons and umuganda work;
Improved cooking stoves and gas, which need less firewood and charcoal;
Sharing tourism income with communities around the parks, so that people living next to forests benefit from protecting them.

Landscape Approach to Forest Restoration and Conservation in Rwanda, by the Rwanda Environment Management Authority (21 min). Watch the first 8 minutes and note two ways the project helps both farmers and forests.

Discuss

A family near Nyungwe has no firewood and little land. A conservation officer wants the forest fully protected. Is there a solution that meets both needs? Suggest at least three actions and say who would carry out each.

Tip

For importance questions, think "SWCHTP": Soil, Water, Climate, Habitat, Tourism, Products, and give a Rwandan example for each.

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Practice

Give four ways in which natural vegetation is important, with a Rwandan example of each.
Explain how a forest reduces flooding downstream.
What is the difference between afforestation and reforestation?
Give one advantage and one disadvantage of eucalyptus plantations.
A storm drops 30 mm of rain on 1 ha. If 40% runs off a bare slope, how many cubic metres run off?
What is agroforestry? Give one benefit for a farmer.
Suggest three ways to reduce the demand for firewood from natural forests.

Show answersHide answers

Any four: protects soil (forest on steep slopes); stores water (Nyungwe, Rugezi); affects climate (moist air over Nyungwe); wildlife habitat (gorillas in the Virungas); tourism (gorilla trekking, canopy walk); products (firewood, medicine, papyrus); research (Karisoke).
Leaves intercept rain, and roots and leaf litter let water soak into the soil, so less runs off quickly; the stored water is released slowly to streams instead of all at once.
Afforestation is planting trees where there was no forest; reforestation is replanting where forest was cleared.
Advantage: fast-growing wood for poles, firewood and timber. Disadvantage (any one): uses a lot of water; gives little food or shelter to wildlife; can dry and impoverish the soil.
Rain $= 10\,000 \times 0.03 = 300$ m³; run-off $= \frac{40}{100} \times 300 = 120$ m³.
Growing trees with crops or livestock on the same land. Benefits (any one): trees hold the soil on terraces; provide fodder, fruit, firewood or poles; improve soil fertility with their leaves.
Any three: improved cooking stoves; using gas, biogas or electricity; growing woodlots and agroforestry trees on farms; using crop waste; reducing waste of charcoal.

Remember

Natural vegetation protects soil, stores and regulates water, affects climate, shelters wildlife, supports tourism and supplies products.
Clearing forests causes erosion, floods, dry-season water shortages and loss of wildlife.
Rwanda protects its remaining forests and wetlands and meets wood needs with plantations, agroforestry, better stoves and community benefits.

1What a tree does all day

2Vegetation, soil and water

3The importance of natural vegetation

4Discuss

What a tree does all day

Vegetation, soil and water

The importance of natural vegetation

Discuss