Vegetation
Senior 1 · Geography
Vegetation
Lesson 2 of 3
24 min
Walk up Karisimbi from the farms at its foot to the summit (usually a two-day trek) and you pass through bands of vegetation as different as those you would meet travelling thousands of kilometres from the Equator towards the poles: farmland, bamboo, mossy woodland, strange giant plants, and finally cold grassland and bare rock. Why does each plant grow only where it does?
Figure 1. Vegetation zones on Karisimbi. Heights are approximate and the zones overlap; the figures follow the Wikipedia article "Volcanoes National Park".
Definition
Vegetation zone (altitudinal zonation): a band of similar vegetation at a particular height on a mountain. Because temperature falls and conditions become harsher with height, the vegetation changes in belts up the slope. Example: the bamboo zone on the Virunga volcanoes between about 2,500 and 3,200 m.
Worked example 1: how much of Volcanoes National Park is each zone?
Volcanoes National Park covers about 160 km². Bamboo forest covers about 30% of it, Hagenia–Hypericum woodland about 30% and the giant-lobelia zone about 25%.
So the three zones cover 85% of the park; the remaining 15% is lower forest, grassland, marsh and bare rock.
| Factor | How it affects vegetation | Rwandan example |
|---|---|---|
| Climate: rainfall | Plenty of rain all year supports dense forest; a long dry season favours grass with scattered trees | Wet Nyungwe is forest; drier Akagera is savanna |
| Climate: temperature | Plants need warmth to grow; cold limits which species survive | Only hardy grasses and giant plants survive near the summit of Karisimbi |
| Relief and altitude | Height lowers the temperature; steep slopes have thin soils; slopes facing the rain-bearing winds are wetter | Vegetation belts on the Virungas |
| Soils and drainage | Deep, fertile soils support tall forest (and attract farmers); waterlogged soils support papyrus and reeds; thin soils support grass | Papyrus in Rugezi; farms on volcanic soils |
| Human activities | Clearing for farms, grazing, burning, logging and building remove natural vegetation; planting and protection restore it | Gishwati cleared, then restored; eucalyptus planted on hills |
| Animals and fire | Grazing and browsing animals and dry-season fires stop trees from spreading into grassland | Savanna fires and grazers in Akagera |
Important
Case study: Gishwati, a forest lost and returning
In the 1970s Gishwati, in the north-west, was a large mountain rainforest linked to Nyungwe. From the 1980s to the early 2000s most of it was cleared for cattle ranches, tea estates and small farms as the population around it grew. By 2001 only a small patch of natural forest remained. Without tree roots to hold the soil, the steep slopes suffered from erosion and landslides, and rivers below became muddy and flooded more often.
Since 2007 the forest has been protected and replanted with local trees, and farmers around it have been helped to keep livestock on improved pastures instead of in the forest. In 2015 Gishwati and the nearby Mukura forest were joined in Gishwati–Mukura National Park, which now protects the small group of chimpanzees that survived there, along with monkeys and many birds. Gishwati shows that human activity can be the strongest factor of all, in both directions.
Worked example 2: how fast is tree cover being lost?
Satellite data (Global Forest Watch) show that Rwanda lost about 49,775 hectares of tree cover between 2001 and 2024, from about 497,955 hectares in 2000. Find the average loss per year and the percentage lost.
1 km² = 100 ha, so about 21 km² of tree cover is lost each year on average, while new planting adds some back.
Gishwati-Mukura National Park: a story of community-led conservation, by Visit Rwanda (5.5 min). Watch for the changes that brought the forest back and who took part.
Which factor do you think is the most important in deciding Rwanda's vegetation today: climate, relief, soils or human activity? Use Figure 1 and the Gishwati case study to support your view.
Tip
Five factors: "Can Really Strong Humans Act?" Climate, Relief (altitude), Soils (and drainage), Human activities, Animals and fire. Always pair each factor with a Rwandan place.
Practice
Remember
Sources and credits
The lesson text, zonation diagram, table, worked examples and practice are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
