Habitat descriptions

The vegetation descriptions below are the results of vegetation survey work in the North Luangwa National Park in the early to mid 1990s, and are published in the journal Bothalia 28 (2) 197-211 (1998). The habitats described below are largely based upon quantitative tree/shrub data from sample sites, and are equally applicable to the South Luangwa National Park. They are cross-referenced with Bill Astle's classification and vegetation map in Table 1. The herbaceous component is described from qualitative data and collection material. Further division of vegetation types into subtypes is based on substrate. A detailed description of all vegetation types and subtypes is given below.

A. RIPARIAN FORESTS, WOODLANDS AND THICKET

This vegetation class comprises moist forests to woodlands and thicket fringing perennial and seasonal watercourses. At lower altitudes (600-700 m) valley riverine fringe vegetation takes the form of woodland (usually with a well-developed shrub layer), and thicket. It should be noted that even on the valley's perennial rivers (Luangwa, Lufila and Mwaleshi) fringe woodland and thicket is discontinuous being interspersed with other vegetation types such as riverine grassland (F2) and/or non-riverine vegetation types. This is even more noticeable on seasonal watercourses where fringe riverine trees are usually mingled with trees and shrubs characteristic of adjacent vegetation types. At higher altitudes (800 m-1300 m), on the Muchinga Escarpment, riverine fringe vegetation takes the form of dense evergreen forest which, on the larger watercourses, may extend to adjacent swampy areas. This vegetation type tends to be well-developed and distinctive (although narrow) even on the smaller, seasonal watercourses. Valley riverine woodland (A1), as described in the present study, is readily recognizable in the Luangwa valley surveys of Astle et al. (1969), Naylor et al. (1973) and Phiri (1989) (Table 1). Escarpment riverine forest (A2) however, is not described in detail in any of the above studies but is covered thoroughly by Fanshawe (1971). Vegetation type A2 contains elements of Fanshawe's “Riparian forest” (p.34) and “Swamp forest” (p.32).

B. BUSHLANDS AND THICKET

Both vegetation types described below are characterised by thicket species which form closed stands. However, in some places more open stands occur and therefore vegetation types B1 and B2 are best regarded as mosaics of bushland and thicket. Both Mixed alluvial thicket (B1) and Combretum thicket (B2) are confined to the alluvial areas adjacent to the valley's larger rivers (Luangwa, Mwaleshi). Together, vegetation types B1 and B2 occupy a niche on soils of an intermediate nature between the low, poorly drained clays of vegetation type F1 and the higher, sandy soils of vegetation type D1. Mixed alluvial thicket is the characteristic thicket vegetation type north of the Mwaleshi river, while Combretum thicket largely occurs to the south of the Mwaleshi. Both types are dominated by different species of thicket-forming shrubs, but share many species in common. The absence of C. elaeagnoides and C. celastroides in large areas of Mixed alluvial thicket, north of the Mwaleshi river, which led to the distinction being made in the present survey, is apparently a local phenomenon because these two species do occur further north, on the Lufila river. The reason for their absence in the middle of the park is unknown, and requires further study. Astle et al. (1969) make no distinction between Mixed alluvial thicket (B1) and Combretum thicket (B2), referring to this vegetation type as “Thicket on freely draining alluvium”. Their species list for this vegetation type contains the dominant elements of both B1 and B2.

C. MIOMBO WOODLANDS

Miombo woodlands are the dominant vegetation type of the Muchinga escarpment and its attendant foothills, Chinshenda, Soma and the Mvumvwe range. The vegetation described under the umbrella of miombo woodlands is physiognomically diverse, ranging from closed woodland to open woodland to scrub woodland. For the purposes of this classification, miombo woodland has been divided into two types, C1 Upper escarpment and C2 Lower escarpment/hill miombo woodland, a division largely based on floristic composition. Further division into subtypes is dependent on substrate. Miombo woodland is clearly recognized in all three of the previous valley surveys (Table 1), but again information on species composition lacks detail. Fuller descriptions are available from Trapnell (1953) and from Fanshawe (1971).

D. COMBRETACEAE WOODLAND AND WOODED GRASSLAND

Open woodlands to wooded grasslands dominated by (distinct) species of the genera Combretum and Terminalia. Both vegetation types described below have well-developed grass layers. Vegetation type D1, Combretum-Terminalia woodland, closely resembles the “Terminalia sericea tree savanna” of Wild and Barbosa (1967). White (1983) refers to it as “North Zambezian undifferentiated woodland”, comprising miombo associates but not Brachystegia/Julbernardia species. Fanshawe (1971) groups this vegetation type together with the miombo woodlands of the valley floor, but refers to it as “Erythrophleum woodland”. The classification of the present survey is largely based on floristic composition and our ground survey data strongly indicates that vegetation type D1 does not fall into the miombo class. Julbernardia/Brachystegia species do occur in the ecotones where vegetation type C2 intergrades with Combretum-Terminalia woodland, but elsewhere they are never dominant and over large areas of this woodland, particularly in the east, they do not occur at all. Astle et al. (1969) and Phiri (1989) refer to this vegetation type as “Erythrophleum africanum woodland savanna” and “Erythrophleum woodland” respectively (Table 3). This nomenclature can be related to our results in that Erythrophleum africanum is an important component of this vegetation type. However, in the NLNP at least, Combretum/Terminalia species are more frequent, more abundant and account for more woody biomass than Erythrophleum africanum, hence our terminology. Like us, Naylor et al. (1973) refer to this vegetation type as “Combretum-Terminalia woodland”. Astle et al. (1969) classify vegetation type D2, Combretum-Terminalia-Diospyros wooded grassland, under “Miombo scrub on shallow soils”, although they do make a topographic distinction between this habitat (3;1 and 5;1) and vegetation type C2 subtype 1 (4;2 and 8;1). In Astle's updated landsystem/vegetation map (Astle, 1989) a further land facet is added (landsystem 7; facet 6) in which this vegetation type is described as:

“semi-deciduous scrubland with local variation in species composition. A mopane and Terminalia stenostachya association on the flatter sites, B. stipulata, Combretum apiculatum, Julbernardia globiflora association in areas of greater relief.”

This is a landsystem description incorporating the floristic mosaic described below, of which vegetation type D2 is the non-miombo component.

E. COLOPHOSPERMUM MOPANE WOODLAND AND SCRUB WOODLAND

Colophospermum mopane is the single dominant tree species in this vegetation class. Mopane may grow as a tall tree of up to 15m, or it may take the form of a multistemmed, stunted shrub <3m tall. The tall form is typical of Colophospermum mopane woodland (E1) and the shrub form is characteristic of Colophospermum mopane scrub woodland (E2). These two vegetation types may occur in discrete areas or they may grow together in mosaic. The difference between the two types is largely the physiognomy of C. mopane, which can be related to browsing damage and substrate as described below. Mopane woodland and scrub woodland are recognized by all of the authors referred to above (Trapnell, 1953; Wild and Barbosa, 1967; Astle et al., 1969; Fanshawe, 1971; Naylor et al., 1973; Edmonds, 1976; Phiri, 1989).

F. GRASSLANDS

The grasslands of the NLNP and SLNP, defined as areas of herbaceous vegetation with less than 10% woody vegetation cover, are all associated with water. Vegetation Type F1 is seasonally waterlogged, while types F2 and F3 are associated with the rivers and dambos of the valley and escarpment respectively. Vegetation type F1 is referred to by Phiri (1989) as “Floodplain grassland” with Echinochloa colona cited as the dominant species. Astle et al. (1969) describe this vegetation type (landsystem 1; facet 7; photo 4) as “Short Echinochloa grassland with Combretum obovatum shrubs on dark cracking clays”. Vegetation type F2 is readily recognizable in the previous valley surveys. The sandbar grassland (landsystem 1; facet 1b) and pointbar deposit grassland (1; 5a) of Astle et al. (1969) are synonymous with vegetation types F2 subtype 1 and subtype 3, respectively, of the present survey. Similarly, the dambos, mudflats and pointbar grass habitats (2b, 2c and 2g, respectively) of Naylor et al. (1973) are directly referable to vegetation type F2. Vegetation type F3 is not dealt with by any of the valley surveys, as it is an upper escarpment and plateau habitat. However, Vesey-Fitzgerald (1963) gives a detailed account of this vegetation type which he calls “Headwater valley grasslands ('dambos')”. Loudetia simplex and Hyparrhenia spp. are named as characteristic species. White (1983) and Fanshawe (1971) also describe this vegetation type, referring to it as “Dambo grassland” and “Bush-group grassland” respectively.

VEGETATION MOSAICS

The representation of vegetation as a series of discrete types, based on communities or associations is, to some extent, artificial in that observed vegetation associations are almost invariably part of a continuum or occur in mosaic with other communities (Craig, 1983). This is a problem of scale. The larger the scale of the map to be produced, the smaller the area of association that can be represented. For practical purposes however, some vegetation communities will always be too small to map separately. This applies in areas of mosaic or in cases where vegetation communities occupy a microhabitat. The vegetation associated with termite mounds, for example, is distinctive (Fanshawe 1968) and may be important to the ecology of an area, yet as a type, it is often too dispersed to be mapped separately.

Table 1: Comparison of vegetation classifications of the Luangwa valley in past and present surveys