Saltatoria Coenoses of High-Altitude Grasslands on Mt
Total Page：16
File Type：pdf, Size：1020Kb
ECOTROPICA 9: 71–97, 2003 © Society for Tropical Ecology SALTATORIA COENOSES OF HIGH-ALTITUDE GRASSLANDS ON MT. KILIMANJARO, TANZANIA (ORTHOPTERA: SALTATORIA) Claudia Hemp & Andreas Hemp Bayreuth University, Dep. of Animal Ecology II and Dep. of Plantphysiology, 95440 Bayreuth 1 Abstract. From 1996 to 2001 field studies on Saltatoria were undertaken in half-year periods from October to April and August to September on the southern slopes of Mt. Kilimanjaro, Tanzania. The focus was on the high-altitude grasslands of the lower montane (1600–1900 m) and subalpine zone (2700–3200 m). Based on phytosociological relevés applying the method of Braun-Blanquet (1964), the grasshopper composition of 52 plots was recorded. Three grasshopper coenoses in three plant communities could be distinguished. Using knowledge of the habitat preferences of Saltatoria the distribution pattern of locally restricted species can be understood, which is here shown for flightless species on the southern slopes of Mt. Kilimanjaro. Accepted 17 January 2003. Key words: Saltatoria, grasshopper coenoses, montane and subalpine tropical grasslands, plant sociology, speciation, bioindication, Mt. Kilimanjaro, Tanzania. INTRODUCTION ston 1937; Kevan 1954, 1967). Comparatively few studies deal with the ecology of African grasshoppers Mt. Kilimanjaro has a variety of ecological zones due (e.g., Joyce 1952, Robertson & Chapman 1962, to its enormous altitudinal range of about 5000 m and Vesey-Fitzgerald 1964, Phipps 1966, Hochkirch 1996). a precipitation that differs with altitude and exposi- Especially African Ensifera are very poorly investi- tion of the mountain massif. Ecological zones are re- gated, with few keys published for groups like Sagi- presented by wet and arid savanna habitats (800–1000 nae (Kaltenbach 1972), Phaneropterinae (e.g., Ragge m), dry to moist grasslands as well as shady banana 1980), or just single genera (e.g., Bailey 1975). plantations in the cultivation belt (1000–1600 m), Grasshoppers are an effective group for bioindi- clearings and differently disturbed and undisturbed cation because of their sharp reaction to climatic fac- forests in the montane zone (1600–ca. 3000 m), and tors. With the aid of indicator species it is possible (sub)alpine grass- and heathlands (2700–4500 m). to measure the quality of certain habitats. In Central Accordingly a great variety of grasshopper species is European habitats various studies have already proved found, ranging from typical widely distributed sa- the usefulness of Saltatoria for measuring the qua- vanna species to endemic species only occurring in lity of grasslands (e.g., Marchant 1953; Schmidt & forest communities or originating from them. Schlimm 1984; Federschmidt 1989; Reich 1991; A general inventory of the fauna of Mt. Kili- Detzel 1992, 1998; Hemp & Hemp 1996, 2000; manjaro, including Saltatoria, was undertaken by an Ingrisch & Köhler 1998). expedition led by Sjöstedt in the beginning of the last In the present study, supported by the phyto- century (Sjöstedt 1909). Most papers on African Acri- sociological method of Braun-Blanquet (1964), Sal- doidea are of a taxonomical nature (e.g., Bolivar 1930, tatoria coenoses are described for grasslands between Dirsh 1965, Descamps 1977), some including keys 1600 and 1900 m and 2700 to 3200 m on the to the species (e.g., Dirsh 1955; Jago 1966, 1981, southern slopes of Mt. Kilimanjaro. Analogous to a 1994; Hollis 1968, 1971; Kevan 1970; Ritchie 1982; plant sociological evaluation, the Saltatoria relevés Grunshaw 1986) or lists of single areas (e.g., John- were united in a table making coenoses apparent and dependent on certain plant communities. Detailed habitat requirements for Saltatoria species can be 1 e-mail: [email protected] derived and information for bioindication obtained 71 HEMP & HEMP to measure the degree of disturbance of habitats. wood, such as Albizia shimperiana, Olea capensis or Processes of distributional patterns and modes of Ekebergia capensis (Hemp, A.1999, Hemp et al. 1999). speciation can be explained. In the cultivated submontane zone of the southern slopes of Mt. Kilimanjaro, forest remnants are re- RESEARCH AREA stricted to deep valleys and gorges with small relicts Mt. Kilimanjaro is located 300 km south of the of Leptonychia usambarensis gorge forests and Mitra- equator in Tanzania on the border to Kenya between gyna rubrostipulata riverine forests. This forest type 2°45’ and 3°25’S and 37°00’ and 37°43’E. This study very much resembles the very diverse wet submon- was carried out on the southern slopes of Mt. Kili- tane (intermediate) forests of the Pare and Usambara manjaro in Tanzania (Fig. 1). Mts. and is floristically completely different from the Mt. Kilimanjaro is a more or less eroded relict montane forests at higher altitudes on Mt. Kiliman- of an ancient volcano with three peaks of different jaro (Hemp, A. 2001). Nearly all of these submon- ages rising from the savanna plains at 700 m a.s.l. tane gorge forests with their unique flora are today to a snow-clad summit of 5895 m. The Shira is completely destroyed by human influence. the oldest part and forms today a wide plateau. The The montane forest belt girdles the whole moun- 5125 m high Mawenzi is also a volcano ruin. Only tain. On the southern slopes of Mt. Kilimanjaro the the main peak, Kibo, shows the typical cone shape so-called half-mile forest strip stretches between 1600 of a volcano. and 1900 m, bordering the natural forest. This area The foothills of the southern slopes receive an is meant for timber production, but in most places annual rainfall of 800–900 mm and the lower slopes is heavily over-used and in certain areas covered by at 1500 m receive 1500–2000 mm. The forest belt meadow communities. between 2000 and 2300 m receives in places over The most important tree species in the montane 3000 mm (Hemp, A. 2002), which is more than on forests of the wet southern slopes is the camphor tree other high mountains of East Africa. In the alpine (Ocotea usambarensis). In the lower montane zone zone the precipitation decreases to 200 mm. The nor- (1600–2100 m) Ocotea usambarensis is associated with thern slopes have much lower annual rainfall, being Agauria salicifolia, Macaranga kilimanjarica, and Polys- in the rain shadow caused by the peaks themselves. cias fulva. This forest zone is heavily influenced by The rainfall is seasonal, the two rainy seasons being human impact, as can be seen from the forest com- from March to June and from November to De- position: Agauria, an Ericaceae, is favored by (man- cember. made) fires, and the two latter species are trees which According to the changing climatic conditions dominate the forests after the logging of camphor several vegetation zones are apparent on the southern (cf. Lambrechts et al. 2002). slopes of Mt. Kilimanjaro (Table 1). Between 700 and The middle montane zone (2100–2400 m) is the 1000 m a.s.l. the dry and hot savanna zone stretches main habitat of the camphor tree (Ocotea usamba- around the mountain base, where most areas are rensis), where it builts pure stands. A characteristic farmed with maize, beans and sunflowers, in West constituent of the montane forests on the southern Kilimanjaro with wheat. Around Lake Chala at the slope is the tree fern Cyathea manniana, indicating the eastern foot of the mountain, and around Ngare high humidity of this part of the mountain. This tree Nairobi of West Kilimanjaro, savanna grasslands are fern plays an important role in forest regeneration. In still intact, providing important habitats for Saltato- gorges and along streams Afrocrania volkensii is a ria and other invertebrates. However, larger mammals typical feature of the tree layer. In the upper montane are almost extinct in these areas nowadays. zone (2400–2800 m) the gymnosperm Podocarpus The main cultivation zone is located between latifolius starts to prevail. The lower subalpine zone 1000 and 1800 m. This area is intensively cultivated (2800-3100 m) is dominated by Podocarpus latifolius, by the Bantu tribe of the Wachagga using an agro- Hagenia abyssinica, and Prunus africana. At this alti- forestry system. Most of the former evergreen forest tude Erica excelsa also plays an important role in the has been replaced by banana-coffee plantations. Some forests, replacing Podocarpus after fire (Hemp & Beck, species of the tree layer still exist in the banana-coffee 2001). Erica excelsa stands form the upper forest plantations, serving as shade trees and used for fire- border in the middle subalpine zone (3100–3600 m). 72 SALTATORIA COENOSES SALTATORIA FIG. 1. Map of Mt. Kilimanjaro. Hatched: 73 study area. HEMP & HEMP TABLE 1. Altitudinal zones and main vegetation units on Mt. Kilimanjaro. Altitudinal zone according to Hemp, A. (2002) The Erica excelsa forests are gradually replaced by elevations of Kibo peak are covered with glaciers (see Erica bush between 3100 and 3500 m a.s.l. In the aspects of the (sub) alpine vegetation of Mt. Kiliman- south-eastern parts moorlands dominated by tussock jaro in Hedberg 1951, Klötzli 1958, Beck et al. 1983). grass fringe the forest, due to regular fires in this A constancy table of the different vegetations units zone (Hemp & Beck, 2001). At an altitude of about of forests and open habitats on Mt. Kilimanjaro is 3900 m the Erica heathlands grade into Helichrysum given by Hemp, A. (2001). cushion vegetation that reaches up to 4500 m. Higher Investigated habitats. This paper concentrates on the altitudes are very poor in vegetation while the highest Saltatoria coenoses of the high-altitude grasslands (Fig. 74 SALTATORIA COENOSES 1) on the lower forest border in the montane zone and their faunistic similarity and the resulting Saltatoria above the upper forest border in the subalpine zone. coenoses are presented in Table 5, giving the abun- The grasshopper composition of grasslands at lower dance of grasshopper species as follows: 3 = > 5 spe- altitudes and of forests is in preparation.