SECTION 3. BACKGROUND INFORMATION ON THE ULUGURU FORESTS.
By Jon C. Lovett, Jon Fjeldså and Jens Otto Svendsen.
3.1. The Ulugurus as part of the Eastern Arc Mountains.
The chain of ancient gneissic mountains running from the Taita Hills in South-east Kenya to the Udzungwa Mountains in South-central Tanzania has been termed the Eastern Arc Mountains (Lovett 1990 and 1993; see Figure 1.1). They are defined as the crystalline mountains under the direct influence of the Indian Ocean climatic system (Lovett 1990) and are part of the Tanganyika-Nyasa Mountain Forest Group (Moreau 1966; see Figure 1.1). Uplifted as isolated fault blocks, these mountains appear today as a chain of isolated forest-capped mountains across central Tanzania to the Taita Hills in southeastern Kenya. Most mountains are habitat islands that rise steeply 1-2 km above the "ocean" of dry savanna plains, and harbour a unique flora and fauna, of which many species are endemic to the mountain chain or to single mountains (Lovett 1988, Lovett and Wasser 1993). One of the most outstanding of the Eastern Arc mountain blocks is the Uluguru Mountains. They are situated to the south of the main chain, 180 km from the coast, and isolated from the Udzungwa and Rubeho Mountains by 70 km of low lying plains, which include the Mikumi National Park (see Figure 1.1).
The Uluguru Mountains are a faulted block. The process which has formed this distinctive unit may have started as far back as the Karroo period approximately 300 million years before present (Griffith 1993), with a final uplifting 7 million years ago. The tectonic activity included the uplift and metamorphosis of Palaeozoic (usagaran) limestones in the eastern foothills. These appear today as a "haystack karst" landscape which includes the lowland Kimboza and Ruvu Forests and several small forest patches. Other low foothills are composed of Mesozoic limestones and shales, and cemented Cainozoic sandstones.
The Uluguru Mountains form a 45.5 km long chain, rising steeply from the Mgeta and Mvuha floodplains (150 m elevation) to a peak elevation of 2638 m (Figures 1.2 and 1.3). Although the mountains form a continuous ridge, they are physically divided into the northern Uluguru (20.5 km long and 8 km wide) and the southern Uluguru (25 km long and up to 15.5 km wide), separated by the Mgeta or Bunduki Gap (Figures 1.2 and 1.3).
The mountains have a very rugged topography. Except for the boggy Lukwangule Plateau (2638 m), the ridge is characterised by steep peaks: Kimhandu Hill (2634 m) in the south, and Mnyanza (2140 m), Magari (2340 m), Nziwane (2270 m) and Lupanga (2138 m) in the northern part (Figures 1.2 and 1.3). Even 50-70° steep slopes are usually forested, but in some places landslides have exposed large granite surfaces, which become partly covered by thick masses of herbaceous vegetation, ferns and sometimes surrounded by bamboo. Habitat dynamics associated with landslides may be important for the maintenance of a very large diversity of herbaceous species.
The lower slopes are generally less steep, and to the south and southwest there is a 20 km wide foothill zone of low undulating hills (c. 500 m), which border the swampy lowland plains (Figure 1.2). The area around the Ruvu headwaters is topographically complex, with a mosaic of low areas, which support fruit trees and shambas, and small and larger, steep limestone hills, often capped with forest (Figure 1.2).
3.3. Climatic conditions and altitudinal zonation of the forest.
Moisture-laden winds blow from the Indian Ocean on the eastern side of the Ulugurus. Estimated yearly rainfall for the Uluguru North F.R. is 2900-4000 mm on the eastern slopes and 1200-3100 mm on the drier western slopes (Lovett and Pócs 1993). Estimated yearly rainfall for the Uluguru South F.R. is 2500-4000 mm on the eastern slopes, up to 2000 mm on the drier western slopes (Lovett and Pócs 1993). This can be seen in contrast to a rainfall of 890 mm near Morogoro Municipality (Lyamuya et al. 1994). Precipitation is highest at high altitudes. There is a pronounced dry season on the western slopes (e.g. Lovett and Pócs 1993), whereas the eastern slopes of the Ulugurus have been regarded perhumid, with more than 100 mm of rain in every month reported at Tegetero, areas with perhumid climates are extremely rare in continental Africa (Pócs 1976b, Lovett 1993). However, there was very little rain towards the end of 1993 in the Ulugurus, and according to local people the rainfall pattern has been more seasonal during the last ten years (Lyamuya et al. 1994; pers. comm. with local people during the 1993 survey). More information on rainfall in various altitudes and vegetation types (with further references) can be found in e.g. Jackson (1970), Pócs (1974, 1976a and 1976b) and in Rapp et al. (1973). Estimates of yearly rainfall for all forest reserves in the Ulugurus and nearest vicinity are listed in Appendices 3.1-3. under the particular locality.
Studies of marine sediments from the Indian Ocean reveal that the surface temperature here was only 1‑2° C lower during the ice‑age and did not decline at all off the Tanzanian coast (Prell et al. 1980). This coastal zone may therefore have been permanently warm and humid, and the Eastern Arc Mountains may therefore have had patches of humid forest permanently through long periods. This may apply to the East Usambara Mountains and the high and steep Uluguru and Udzungwa Mountains in particular. These three mountains are notable in East Africa for their high rainfall and moderate seasonality (Lovett 1993). These conditions may be a fundamental cause of the high endemism, as populations of plants and animals may have survived here, in isolation, for long geological periods.
Pócs (1976a) recognised the following, climatically induced, altitudinal zonation of forest in the Ulugurus, which will be referred to later in this report (text below is a quotation):
Low altitude dry forest and savanna woodland zone. Only at the western and northern foot of the Ulugurus, below 600 m altitude. Annual rainfall between 700 and 900 mm, the dry period lasts for 4-6 months. Mean annual temperature 24-26° C. The whole area is densely cultivated, therefore only small remnants of the original vegetation can be detected.
Lowland semi-evergreen rain forest zone. Between 250 and 500 m altitudes at the eastern foothills of the central part of the mountains. Annual rainfall 1700 to 2400 mm, no dry season or maximum 1-2 months, main annual temperature 24-25° C. On the limestone ground of a karst plateau, including the Kimboza F.R., the lowland rainforest exists even through a 2.5 months long dry season (remarks from JF, this survey: because of the ground water supply in that area).
Submontane dry forest and miombo woodland zone. Today this is actually mostly replaced by an open woodland of Pterocarya angolensis, Combretum and Terminalia species, or by dry secondary grassland. On the eastern foothills, only on drier slopes, up to 800 m altitude. Widespread on the western, northern and southern slopes, as high up as 1500 m in the northern, and up to 1600 to 1700 m in the southern Ulugurus. With 950-1300 mm annual precipitation, 2-6 months dry season and 19-23° C main annual temperature. These communities suffer the most from the bush and grass fires.
Submontane evergreen and semi-evergreen forest zone. Contiguous belt on the eastern slopes, between 500 and 1500 m, except in places used for agriculture. These forests occur in small patches also on the western side, in protected valleys at the lower edge of the evergreen forest belt. The submontane rain forests show the best forest growth in East Africa. The average rain fall is well over 1800 mm a year, usually exceeding 2500 mm and in some cases higher than 3000 mm, without being interrupted by a dry season. The main annual temperature lies between 23 and 17° C, at the lower and upper limits of this zone.
Montane evergreen forest zone. This habitat forms a broad belt around both sides of the mountains. The montane forest has remained in relatively good condition, with most of it being inside the protected forest area. Altitude limits are 1500-2100 m in the Uluguru North and 1600-2400 m in the Uluguru South. The annual precipitation varies locally between 1300 and (more than) 3000 mm. Especially the upper edge of this zone receives a high amount of rainfall without a seasonal interruption, or even if short dry periods occur, they are compensated by the contiguous cloud and mist formation at this altitude. Mean annual temperature: 12-17° C. The diurnal change of temperature is very small (when measured [by Pócs, editors remark], it was only 4° C), and occasional frosts occurs.
Upper montane or lower subalpine zone with elfin woodlands, bamboo thickets, peat bogs and with secondary grasslands, above 2100 m in the Uluguru North and 2400 m in the Uluguru South. Although the annual variation of temperature is low, the diurnal change becomes much higher than in the high forest zones, reaching more than 15° C, and it often sinks below or near zero. The dwarf and very closed canopy of the elfin forest is a good adaptation against the strong reradiation during cold nights when the cloud belt usually sinks down and the high summits of the Ulugurus remain exposed.
3.4. Altitudinal position of lower forest edge, Uluguru North and South F.R.s.
Most forest borders are very sharp, with fields extending right up to the forest edge. In some areas small clearings or areas with second-growth exist just inside the forest edge. In areas of easy access the lower part of the forest is disturbed, with strongly biased composition of tree species and often a lack of large timber trees. The following general characterisations can be made about the forest cover of the lower forest edges of the Uluguru North and South F.R.s:
· Large areas of forest and dense woodland, especially in the submontane zone, have been removed by people who now use the area for subsistence agriculture (Temple 1973, Lyamuya et al. 1994). The former extent of the forest in the Ulugurus is discussed in Section 9.3.
· In most parts of the Uluguru South F.R. the lower forest, edge is above 1500 m though narrow strips extends down to 1000-1200 m in certain areas (typically in stream valleys) (Figure 1.2).
· Above the principal agricultural areas on the west slope of the Uluguru South F.R. the lower forest edge is at 1900-2000 m.
· In the Uluguru North F.R. good areas of submontane forest (defined as forest between 500 and 1500 m) still remain in certain parts, mainly on the eastern/north-eastern slopes of the Uluguru North F.R., where the forest ranges down to 1000-1200 m in many places (Figure 1.2).
· A close proximity of evergreen forest and low-altitude woodland mosaics can only be found at the extreme northern end of the mountain range where a few narrow strips extend down to 650 m (e.g. at Kigurunyembe above the teachers college).
3.5. Forest reserves in the Ulugurus.
Efforts to conserve the forest on the Uluguru Mountains date back to 1909, when the government interrupted the system of shifting cultivation by establishing a 277 km² forest reserve with demarcated boundaries (Temple 1973, Lyamuya et al. 1994). Some of the reserves have been established much later, however (see Appendix 3). Information on the forest reserves and the historical development of conservation efforts in the Ulugurus is compiled in e.g. Temple (1973), Lovett and Pócs (1993) and Lyamuya et al. (1994).
The Catchment Forest Reserves on the Uluguru mountains are administered by Morogoro District Catchment Office. Lovett and Pócs (1993) described 15 Catchment Forest Reserves (plus Vigoza Catchment Forest Description) in the Ulugurus and nearest surroundings (Figure 1.3), giving information for each on year of establishment, gazetted area, gazetted boundary length, location, soils, climate, vegetation, catchment values, timber values, biodiversity, human impacts, management proposals and available literature. In Appendices 3.1 and 3.2 we summarize information from their report for the reserves visited on this survey. The same kind of information is given in Appendix 3.3 for forest reserves not visited on this survey. In a few cases where information from the present survey has been added to these appendices, this is stated.
Seven of the Uluguru Catchment Forest Reserves/Descriptions are on the mountains (plus Kasanga Forest Reserve which is mentioned in our Section 5 but not included in Lovett and Pócs 1993), a * indicate that we visited the reserve:
· Uluguru North (*) See Appendix 3.1.
· Uluguru South (*) ---”---
· Bunduki I (*) ---”---
· Bunduki III (*) ---”---
· Nyandiduma See Appendix 3.3.a.
· Shikurufumi ---”---
· Vigoza Catchm. For. Descr. ---”---
· Kasanga F.R. ---”---
Three catchment forest reserves are in the eastern foothills:
· Kimboza (*) See Appendix 3.2.
· Ruvu See Appendix 3.3.b.
· Chamanyani/Mvuha ---”---
One is further east on the plains east of Ruvu Rive
· Mkulazi See Appendix 3.3.c.
Five catchment forest reserves cover outlying hills:
· Mkungwe See Appendix 3.3.d.
· Nguru ya Ndege ---”---
· Mindu ---”---
· Dindili ---”---
· Kitulanghalo ---”---
Of the outlying reserves, those containing substantial forest areas are: Mkungwe, Kimboza and Ruvu. Chamanyani/Mvuha is mostly woodland with some riverine forest, and Mkulazi is all woodland. Nguru ya Ndege and Mindu contain forest patches. Dindili and Kitulanghalo are covered by woodland and drier forest of the coastal type.
Griffith, C.J. 1993. The geological evolution of East Africa. Pp. 9-21 in Lovett, J.C. and S.K. Wasser (eds.). Biogeography & ecology of the rain forests of eastern Africa. Cambridge, UK: Cambridge University Press.
Jackson, I.J. 1970. Rainfall over the Ruvu Basin and surrounding area. Bureau of Resource Assessment and Land Use Planning. University College, Dar es Salaam.
Kayambazinthu, D. 1989. Effects of selected forest types on the water input, Mindu Forest Reserve, Morogoro. M.Sc. thesis, 189 pp., mimeograph. Sokoine University of Agriculture, Morogoro.
Kielland-Lund, J. 1982. Structure and morphology of four forest and woodland communities of the Morogoro area, Tanzania. Pp. 69-93 in: Dierschke, H. (ed.). Struktur und Dynamic von Waldern. Vaduz.
Kielland-Lund, J. 1990. Phytosociology and productivity in four forest and woodland communities near Morogoro. Pp. 2-15 in Mgeni, A.S.M., W.S. Abeli, S.A.O. Chamshama and G.S. Kowero. Proceedings of the Seminar on Management of Natural Forests of Tanzania, Arusha, December 1988. Faculty of Forestry, Sokoine University of Agriculture, Tanzania.
Lovett, J.C. 1988. Endemism and affinities of the Tanzanian montane forest flora. Pp. 591-598 in Goldblatt, P. and P.P. Lowry (eds.). Proceedings of the eleventh plenary meeting in the Association for the Taxonomic Study of Tropical Africa. Monographs in Systematic Botany from Missouri Botanical Gardens 25.
Lovett, J.C. 1990. Classification and status of the moist forests of Tanzania. Mitteilungen aus dem Institut für Allgemeine Botanik Hamburg 23: 287-300.
Lovett, J.C. 1993. Eastern Arc moist forest flora. Pp. 33-56 in Lovett, J.C. and S.K. Wasser (eds.). Biogeography & ecology of the rain forests of eastern Africa. Cambridge, UK: Cambridge University Press.
Lovett, J.C. and T. Pócs 1993. Assessment of the condition of the Catchment Forest Reserves, a botanical appraisal. Report prepared for the Catchment Forestry Project (under the Forestry and Beekeeping Division of the Ministry of Tourism, Natural Resources and Environment, Tanzania).
Lovett, J.C. and S.K. Wasser 1993. Biogeography & ecology of the rainforests of Eastern Africa. Cambridge, UK: Cambridge University Press.
Lyamuya, V.E., L.G. Noah, M. Kilasara, E.J. Kirenga and N.D. Burgess 1994. Socio-economic and land use factors affecting the degradation of the Uluguru Mountains catchment in Morogoro Region, Tanzania. Unpublished report, Regional Natural Resources Office of Morogoro Region, Tanzania, and The Royal Society for the Protection of Birds, Sandy, UK.
Moreau, R.E. 1966. The bird faunas of Africa and related islands. London: Academic Press.
Pócs, T. 1974. Bioclimatic studies in the Uluguru Mountains (Tanzania, East Africa) I. Acta Botanica Academiae Scientarium Hungaricae 20: 115-135.
Pócs, T. 1976a. Bioclimatic studies in the Uluguru Mountains (Tanzania, East Africa) II. Correlations between orography, climate and vegetation. Acta Botanica Academiae Scientarium Hungaricae 22: 163-183.
Pócs, T. 1976b. Vegetation mapping in the Uluguru Mountains (Tanzania, East Africa). Boissiera 24: 499-503.
Prell, W.L., W.H. Hutson, D.F. Williams, A.W.H. Bé, K. Geitzenauer and B. Molfino 1980. Surface circulation of the Indian Ocean during the last glacial maximum, approximately 18000 yr B.P. Quaternary Research 14: 309-336.
Rapp, A., L. Berry and P. Temple 1973 (eds.). Studies of soil erosion and sedimentation in Tanzania. BRALUP Research Monograph Number 1, 1973. Dar es Salaam: Bureau of Resource Assessment and Land Use Planning, University of Dar es Salaam. Published in association with the Swedish Society of Anthropology and Geography an is distributed internationally as Geografiska Annaler, 54A, 3-4, 1972.
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