Burundi

Forest Resource  

Overview
Burundi is moderately forested with around 12 percent forest cover and an additional 38 percent of other wooded land. Burundi’s original forest vegetation consisted of closed sub-montane and montane rainforest along the Nile-Congo watershed, running the length of the country, and savannah woodland along the south-east border and areas surrounding Lake Tanganyika. Much of the forest and woodland has been cleared or degraded to promote agriculture and soil erosion is a significant problem for Burundi. The remaining closed forest is mainly in the north, in and around Kibila National Park, or in the south in the Buriri forest. Common species include Entadrophragma excelsum, Polyscias spp. and Macaranga spp. Significant areas of bamboo forest also occur in the north. The forest savannahs are mainly “miombo” woodland, a Brachystegia-Julbernardia association, in the south, with the drier west comprising Acacia grasslands. Burundi has a modest network of around 10 protected areas, including 3 national parks. Around 12 percent of the country’s forests are in protected areas.

Forest Types

Geographic Description
The Republic of Burundi, located in eastern Africa, is bounded on the north by Rwanda, on the east and south by Tanzania, and on the west by Lake Tanganyika and the Democratic Republic of the Congo. It covers an area of 27 834 km2 (including 2 000 km2 of Lake Tanganyika, which lies along its south-western border). It is situated between latitudes 20° 45´and 4° 28´S and longitudes 29°and 30° 53´ E. Landlocked in the centre of Africa, it is 1 200 km from the Indian Ocean and over 2 000 km from the Atlantic.

The country is split between the Nile and Zaïre (or Congo) basins. The dividing watershed, the Zaïre-Nile ridge, runs more or less north-south, rising to 2 670 m at Mount Héha, while the lowest level in the country is that of the surface of Lake Tanganyika at 780 m, with only about 25 km between these two extreme points. Western Burundi lies between the Zaïre-Nile ridge and Lake Tanganyika and the Ruzizi (a water course flowing between Lake Tanganyika and Lake Kivu) and may be subdivided as follows:

• The Ruzizi plain and the Lake Tanganyika riverain plain, with altitudes between 780 and 1 000 m (Imbo);
• The western foothills of the ridge, between 1 000 and 1 600 m (Mumigwa);
• The ridge, or Bufunda-Mugamba, between 1 600 and 2 300 m, with some higher peaks (Mounts Teza, Manga and Héha);
• The Bututsi or highland region in the south of the country.

The climate is of the high tropical type, on the whole temperate and even cold, with a large number of microclimates and considerable variation from one year to the next. The Great Rift Valley region around Bujumbura has an average temperature of 23 °C and an average annual rainfall of 760 mm. The mountainous western region of the country has an average temperature of 17 °C and an average annual rainfall of about 1 500 mm. On the plateaux, temperatures average 20 °C and about 1 200 mm of rain falls a year. The rainy season in Burundi generally lasts from February to May

Ecological Zones

Forest cover Vegetation 

Introduction

Most of Burundi lying east of the Zaïre-Nile ridge (the Bwéru, Buyensi, Kilimiro, Buyogoma and Mosso regions) is covered by very degraded vegetation, with the exception of Bwéru in the north-east, where there is Sudanian tree savannah of Acacia, and Mosso in the south-east along the border with Tanzania, which is covered in parts by Zambezian-type Brachystegia-Isoberlinia open forest (Reekmans, 1967; Pouilloux, 1976).

Demands for farmland, grazing and fuel have led to serious degradation of both soil and woody vegetation as well as major erosion problems that are aggravated by the uneven nature of most of the country’s terrain. The small amount of land still unused and covered by forest is steadily giving way to agriculture, especially in the mountains where it is vital that it be preserved in order to protect the soil and ensure proper water management. Moreover, not only are closed forests being cleared, but open forests are also being degraded, sometimes to the point of total elimination, through overexploitation for charcoal production (Boisset and Pouilloux, 1977). In recent years, some species – such as Euphorbia dawei, Strychnos potatorum and the Hypaene ventricosa palm, which was endemic to the Ruzizi plain – have either disappeared or are about to do so (Poilloux, 1976)). This is all the more disturbing inasmuch as Burundi’s geographical position at the junction of Guinean, Zambezian and Sudanian influences means that it has a rich flora, despite its small size.

The following description is based mainly on Boisset and Pouilloux (1977) and to a lesser extent on Hecq and Froment (1961) and Pouilloux (1976), adopting the broad categories of Boisset and Pouilloux.

Closed Forests
Broadleaved

Ridge forests are as follows:

• The Bururi Forest in the south covers 1 500 ha and lies between the altitudes of 1 700 and 2 100 m with its lower part touching the Sikuvyaye gallery forest. It is relatively rich in umuyove (Entandophragma excelsum) and is still fairly compact, although it is threatened by illegal logging despite the fact that it has been a reserve since 1932.
• The Rutongo Forest (also known as the Kibezi Forest) covers about 1 550 ha and is in fact made up of a series of strips of forest that follow the valleys, while the ridges have quartzite outcrops. The original species have been replaced to a large extent by umwongo (Polyscias spp.), umutwenzi (Macaranga spp.) and igihondogori (Neoboutonia spp.), which mark stages in secondary growth (and which can be categorised as forest fallow and young secondary forest).
• The largest remaining forest stretches from Bugarama toward the north and the border with Rwanda. Although it, too, has been a reserve since 1932, it has shrunk and is still shrinking back from these limits, which are often marked by a line of exotics – Cupressus or Eucalyptus spp. The shrinkage is particularly apparent in the area north of the Ndora-Rwegura road. This forested area encompasses a closed forest still rich in primary species – umuyove, umuremera (Prunus africana) and umukerekwa (Newtonia spp.) – as well as the large areas covering the high valleys of the Mpanda and the Kitenge and occupied by virtually pure forest of umugano (Arundinaria alpina). Then there are the quartzite ridges populated mainly by Ericaceae, the high grasslands of Eragrostis spp. surrounded by forest, where flocks congregate in the dry season, and the marshy or peaty areas of Sphagnum spp.;
• Small stands – at Rwanagashwa, Ruvani and Nyambeke in the north (the Kifunzi, Runembe, Nzindu, Ruguri or Kanoma hills) – cover less than 1 000 ha in all and are vanishing quickly (overflights in 1976 were unable to make out the outlines seen in photographs taken in 1973).

The only conifer found in Burundi, Podocarpus milanjianus, grows within the ridge forests.

Although the Kigwena Forest in the northern part of Imbo is small in area (about 500 ha) and has been considerably invaded by stands of Elaeis guineensis, it deserves separate mention as the only remaining vestige of Guinean-type rainforest (a “periguinean mesophile forest” according to Reekmans (1967)). Its composition is indeed markedly different from that of other forests in Burundi, with a top storey of umukerekwa (Newtonia buchananii), umusebeyi (Albizia spp.) and umusurugwe (Pycanthus angolensis) up to 30 m tall and an understorey composed mostly of Pseudospondias, Maesopsis, Spathodea and Sterculia species about 15 m tall.

Gallery forests vary in composition depending on their altitude and geographical position. Those in northern Imbo contain umusebeyi, umukerekwa and umushwati (Carapa grandiflora). In the Bugogoma region, which accounts for most of the border area with Tanzania, the Nkoma faults contain umuyove, umuremera (Kigelia aethiopica) and various Celtis spp. Those in Mosso, which are permanently flooded because the slope is so slight, have large quantities of umusange (Acacia polyacantha var. campylacantha). Lastly, those along the river and lakes in the north are similar to those just described, with the trees being separated from the water by strips of papyrus (Cyperus papyrus) and raffia palms (Phoenix reclinata).

It appears that the sclerophyllous forest of Strychnos potatorum (with Tamarindus indica and Grewia mollis in the dominant storey) found in the Cibitoke region (northern Imbo) has vanished. The sclerophyllous forest of Euphorbia dawei (with Tamarindus indica and Cynometra alexandri) has also disappeared from the Katunguru ravine (northern Imbo), where its last vestiges were previously found.

Bamboo Palms

In addition to the stands of umugano (Arundinaria alpina) already noted in the description of the ridge forests, mention should be made of the umusuna (Oxytenanthera abyssinica) bamboo stands that are still untouched by cropping and settlements. Given the disappearance or rapid degradation of other forests in Burundi, bamboo now occupies a considerable area in comparison with other wooded cover.

Open forests

Broadleaved

The palm savannah of Hypaene ventricosa, covers the northern part of Bujumbura. Several authors (Reekmans, 1967; Boisset and Pouilloux, 1977) have pointed out that this palm savannah could be at risk because of agricultural land use.

Open Zambezian miombo-type woodlands are found in southern Imbo and Mosso. The presence of a grassy layer places them in this category, despite their multi-storeyed structure and the high degree of tree cover. The top storey is composed primarily of ihoua (Brachystegia spiciformis), other species of Brachystegia, umurembera (Isoberlinia angolensis) and umutonto (Uapaca spp.), the understorey contains Strychnos innocua and umunazi (Parinari curatellaefolia) and the shrub storey is made up of species of the genera Annona, Ozoroa and Combretum.

The tree savannahs of Bugusera and Bwéru in the north-east are very different from these, with the disappearance of Brachystegia north of the Buruwu River marking the northern limit of the Zambezian zone. Acacia and Combretum spp. are both well represented, plus umunazi and Blighia unijugata.

Forest Map

Other wooded land
Shrubs

The vegetation covering the highest mountains above 2 500 m can be listed as natural scrub. It is composed of sclerophyllous scrub vegetation such as arborescent heaths of the genera Philippia, Erica, Vaccinium, Agauria and Struthiola dominating a grassy carpet. Despite its position, livestock grazing is degrading this vegetation.

References

Boisset, J. L. and Pouilloux, C. 1977. Inventaire des boisements du Burundi – Cartographie forestière. Département des Eaux et Forêts/Mission Française de Coopération – Mission forestière crête Zaïre-Nil. Bujumbura.

Hecq, J. and Froment, D. 1961. Contribution a l’étude des problèmes du reboisement et de la conservation du sol – Structures agraires traditionnelles, rationalisation de l’agriculture, conservation du sol et amélioration de la productivité, le Rwanda et le Burundi. Institut National pour l’Etude Agronomique du Congo. Bruxelles.

Pouilloux, C. 1976. Problèmes forestiers au Burundi – In: Bois et Forets des Tropiques, No. 170. Nogent-sur-Marne, France.

Reekmans, M. 1967. Les groupements ligneux naturels au Burundi. Mimeo. Bujumbura.