Grass assemblages and diversity of conservation areas on the coastal plain south of Maputo Bay, Mozambique

A floristic analysis of the grass species assemblages of the Licuati Forest and Maputo Elephant Reserves south of Maputo Bay, Mozambique, is presented. Sampling of grass data was undertaken in six previously described, major vegeta­ tion types. TWINSPAN divisions distinguished grass assemblages that are characteristic for these major vegetation types of the study area. The results were supported by an Indirect Gradient Analysis. Further TWINSPAN divisions of a larger Maputaland data set indicated a floristic relationship between grass assemblages of similar major vegetation types in the study area and South Africa. This relationship was supported by high similarity values (> 65%), obtained with Sorenson's Coefficient. The coefficient also indicated varying degrees of similarity between grass assemblages of different major veg­ etation types within the study area. A rich diversity of 115 grass species and infraspecific taxa was recorded for the study area. The Chloridoideae and Panicoideae dominate the grass diversity and the genera with the most species include Eragrostis, Panicum and Digitaria. Most grass species in the study area are perennials and have a tufted growth form, but this varies considerably between vegetation types.


INTRODUCTION
Despite the importance of the Poaceae to both subsis tence and commercial agriculture (Myre 1971;Tainton et al. 1976) and the continued documentation of the rich diversity of this family in southern Africa (Gibbs Russell et al. 1990;Kobisi & Kose 2003), some areas still remain poorly studied and documented.One particular area is the coastal plain of Mozambique south of Maputo Bay.Although Myre (1964) and De Boer et al. (2000) provid ed a comprehensive account of the vegetation south of Maputo Bay in Mozambique, the descriptions of the grass layer contained limited taxonomic and floristic information.
In this paper the grass diversity of the coastal plain south of Maputo Bay is revisited to investigate the fol lowing hypotheses based on current knowledge: 1 , dif ferent grass assemblages characterize the major vegeta tion types of the study area; 2 , a floristic relationship exists between grass assemblages of different major vegetation types within the study area; 3. there is a floristic relationship between grass assemblages of the study area and similar vegetation types in South Africa; 4, species that form the grass assemblage for a major vegetation type are characterized by certain life/growth forms; 5, dominance of different Poaceae subfamilies in the study area correspond with predictions made previ ously; and 6 .there is a rich diversity of grasses in the study area.
The study area comprises the Maputo Elephant Reserv e and Licuati Forest Reserve on the Maputaland coastal plain, south of Maputo Bay in Mozambique (Figure 1).Ma putaland is an important centre of plant endemism and diversity of Mozambique.South Africa and Swaziland (Van Wyk & Smith 2001), defined as the biogeographical area bounded by the Inkomati-Limpopo River in the north.Indian Ocean in the east, foothills of the Lebombo Mountains in the west and St Lucia estuary in the south.
The topography comprises high, linear, north-south ori ented dune cordons along the inland margin of the coast.The youngest of these dunes are probably 10 000-30 000 years old.making them in geological terms some of the youngest formations in southern Africa (Botha 1997).These high dune cordons mark a succession of marine regressions that deposited these sediments.Marine siltstone underlies these sediment deposits and in turn, the sediment deposits underlie the dune sand deposits current ly defining the surface relief in this area.
Maputaland lies within a transitional zone between the tropics and subtropical coastal conditions to the south (Bruton & Cooper 1980), with warm to hot summers (mean of 27°C in January) and cool to warm winters with no frost (mean of 16°C in July).Mean relative air humid ity is high along the coast, namely 55% in August and 90% in February.Summers are wetter than winters, although rain is received throughout the year.Mean annual rainfall is higher along the coast ( 1 1 0 0 mm/year) and declines progressively inland (600 mm/year).Morning mist is common in the dry season.
The study area comprises the major terrestrial vegeta tion types recognized and defined for this floristic region by Myre (1964). De Boer et al. (2000) and Matthews et al. (1999Matthews et al. ( . 2001))

METHODS
Sampling sites were randomly selected using topograph ic maps and aerial photographs.Plots were placed in vege tation types conforming to the descriptions of Matthews et a l (1999Matthews et a l ( , 2001)), avoiding the edges of these and refraining from sampling in disturbed areas.Presence/absence of diag nostic woody species was used to identify vegetation types in the field.A vegetation type is a composition of species that recurs in a region as a result of specific combinations of environmental factors (Barbour et al. 1999).Reed Beds could not be sampled adequately due to high water tables.However, wetlands that feed into the Reed Beds were sam pled, and these are referred to as Hygrophilous Grassland for the purpose of this study.
Twenty-one sites were sampled at the beginning of sum mer 2001, the peak flowering season for grasses.At each site all the grass species in a 2 0 x 2 0 m grid were collected and identified.Scientific names conform to Fish (2003).Voucher specimens are listed in a checklist (Appendix 1) and housed at the Maputo Herbarium (LMA), with dupli cates in the Luanda Herbarium (LUAI), Natal Herbarium (NH), Pretoria National Herbarium (PRE) and University of Zambia Herbarium (UZL).The LMA collection was consulted to identify sterile specimens and to locate fertile voucher specimens for these species.If none were found, sterile specimens were provisionally identified, but listed without voucher specimens in the checklist.A floristic classification of grass data for the Licuati Forest and Maputo Elephant Reserves was ob tained by the application of Two-Way Indicator Species Analysis (TWINSPAN) (Hill 1979a).The multivariate analysis divided the data set, comprising all collected grass species and their presence/absence data per plot, into nodes.In MEGATAB (Hennekens 1996) the re sultant classification was summarized in a synoptic table to reflect percentage occurrence of each species per node (major vegetation type) and refined with Braun-Blanquet procedures to group species in as sem blages.Detrended C orrespondence Analysis (DECORANA) (Hill 1979b) was applied to the data set to illustrate vegetation gradients and floristic rela tionships.
A second data set containing grass species pres ence/absence data from the study area was merged with data from studies conducted in Sileza Nature Reserve (Matthews et al. 1999) and Tembe Elephant Park (Matthews et al. 2001).Vegetation types from these con servancies in South Africa were chosen for comparison because of their similar grass flora, status as pristine environments, proximity to the study area, and formal classification and description as representative of north ern Maputaland.The TWINSPAN divisions depicting the floristic relationship are illustrated in a dendro gram (Figure 2).The species richness of grasses was calculated as the number of species per major vegetation type (homoge neous unit) in the study area (Whittaker 1978).Rare and threatened species were identified as either endemic (Van Wyk 1996) and/or Red Data List (Izidine & Bandeira 2002).Character species were defined as species that are relatively restricted to specific vegetation types (Westhoff & Van der Maarel 1978).Recognition as an intro duced alien species was based on Fish (2003).Life cycles (annual or perennial) and growth form (tufted, rhizomatous and/or stoloniferous) of each species followed Gibbs Russell et al. (1990). Sorenson's Index (Mueller-Dombois & Ellenberg 1974) was used to determine the beta diversity between the vegetation types of the study area and between different reserves in Maputaland.
Floristic diversity of the Poaceae subfamilies/tribes, and the distribution of these taxonomic units within the different vegetation types were presented in tables to interpret and compare current patterns of grass diversity with what was previously predicted for southern Africa (Gibbs Russell 1986, 1988).

RESULTS AND DISCUSSION
The resultant hierarchical division of the sample plots from the TWINSPAN analysis (Table 1) resulted in the classification of distinct grass assemblages associated with six major terrestrial vegetation types of the Ma putaland coastal plain in Mozambique, namely Coastal Woodland.Dune Forest, Hygrophilous Grassland.Licuati Forest, Primary Dunes and Woody Grassland.The ordi nation clusters (Figure 3) obtained for the first and second axes tended to substantiate the groups identified in the TWINSPAN classification.A TWINSPAN division of the Mozambican grass data merged with sample plots from South Africa resulted in a hierarchy of assemblages that confirms that a floristic link exists between these differ ent parts of Maputaland (Figure 2).

Grass assemblage o f Primary Dunes
Locality: Maputo Elephant Reserve This assemblage is restricted to the upper reaches of beaches, bordering on the seaward side of primary dunes.Grasses are mostly pioneers and are not only associated with the unstable seashore dunes, but also occur further inland along freshwater and saline marshes, and in dis turbed places such as road reserves.Grasses of the assemblage prefer light shade, but tolerate full sun.
Character species for this grass assemblage are given in species group A (Table 1).The assemblage is species poor and although predominantly characterized by perennials, has the highest proportion of annuals (36%) in the study area.It also has the highest proportion of grass species with a stoloniferous growth form (3 5 %).One naturalized alien grass, Cenchrus brownii, was recorded.Taxonomically the vegetation type is unique in that it is not characterized by the Paniceae (Panicoideae) as in the grass assemblages of the other vegetation types (Table 2), but is dominated by the Eragrostideae (Chloridoideae).The community is floristically most related to Hygrophilous Grassland (Sorenson Coefficient = 15%; Table 1) (Figure 3).

Grass assemblage o f Hygrophilous Grassland
Locality: Maputo Elephant Reserve Hygrophilous Grassland represents a vegetation type of open grassland on seasonally wet.sandy or clay soils.These seasonally wet areas may occur as inter-dune depressions, pans, lake seepages, riverbanks and floodplains, and are characterized by high levels of organic matter and a water table of less than one metre below the soil surface.Soils are also less sandy and with a higher clay content.The biomass of the hygrophilous grass component is the highest due to dense growth under con stant wet conditions.
Character species for the grass assemblage are given in species group B (Table 1).This grass assemblage is species rich (56 taxa) and tufted perennials dominate.It also has the highest proportion of rhizomatous taxa (36%).There are 15 character grass species, which is the most for any of the major vegetation types.This is the only grass assemblage in the study area characterized by representa tives from the Arundineae, Aveneae and Oryzeae (Table 2).Floristically this assemblage is most related to Woody Grassland and Dune Forest (Sorenson Coefficient = 56% and 57% respectively; Table 1) (Figure 3).It also shows a high similarity in grass species composition when com pared with plots from Maputaland Hygrophilous Grass land in South Africa (Sorenson Coefficient = 76%: Table 3) (Figure 2).

Grass assemblage o f Woody Grassland
Locality: Maputo Elephant Reserve Extensive grasslands occur along the coast south of Maputo Bay and is characterized by deep, well-drained sandy to loam soils and an undulating topography (dunes and floodplains).This grassland type is endemic to Maputaland and is dominated by geoxylic suffrutices which are dwarf woody plants with annual or short-lived shoots sprouting from woody, perennial underground axes.Woody Grassland is not as rich in grass species as the Hygrophilous Grassland.
Character species of the grass assemblage are given in species group D (Table 1).A low number of four charac ter species were recorded, because grassland represents a transition between other major vegetation types.This assemblage is characterized by tufted, perennial species.The Andropogoneae (Panicoideae) dominate the assem blage (Table 2).One rare grass species, namely the Ma putaland endemic Trichoneura schlechteri.was recorded.Floristically it is most related to Dune Forest, Coastal Woodland and Hygrophilous Grassland (Sorenson Co efficient = 62%, 58% and 56% respectively; Table 1) (Figure 3).Of all the grass assemblages in the study area, it has the lowest similarity in grass species composition when compared with similar vegetation further south in South Africa (Sorenson Coefficient = 63%; Table 3) (Figure 2).

Grass assemblage o f Dune Forest
Locality: Maputo Elephant Reserve Forests mainly occur on well-established secondary dunes and further inland.Soils are moist, deep and sandy.Forest trees have a higher diversity of creepers and under storey vegetation than the vegetation of surrounding areas.Grass species of Dune Forest prefer semi-shade and are especially common along forest margins, riverbanks.and partially disturbed and overgrazed areas.
Seven character species for this grass assemblage are given in species group F (Table 1).This grass assem blage is the most species rich (57 taxa).It is character ized by tufted perennials, has the highest number of recorded rare grass species (5) and taxonomically it is dominated by the Panicoideae, although the Eragrostideae, a tribe of the Chloridoideae, supports the highest diversity (Table 2).Along the coast.Dune Forest tends to    1) (Figure 3).It also shows a high similarity in grass species composition when compared with plots from Maputaland Dune Forest in South Africa (Sorenson Coefficient = 71%; Table 3) (Figure 2).

Grass assemblage o f Coastal Woodland Locality: Maputo Elephant Reserve and Licuati Forest Reserve
Savanna covers extensive areas along the coast south of Maputo Bay and stretches westwards to the foothills of the Lebombo Mountains.The vegetation type occurs on sandy soils in drier habitats with a deeper water table.The grass assemblage forms a dense herbaceous layer and is associated with light shade or full sunlight and Nine character species were recorded for this assem blage and are given in species group J (Table 1).Tufted perennials typically dominate this grass assemblage.Two rare species were recorded and one naturalized alien grass.Coix lacry ma-jobi.has colonized this assemblage.This is the only grass assemblage that contains a member of the Pappophoreae and is dominated by the Panicoideae (Table 2).Dune Forest forms localized patches within Coastal Woodland, and in turn.Coastal Woodland within Woody Grassland.Hence, its grass assemblage shows a strong floristic link with Dune Forest and Woody Grassland, and to a lesser extent with Licuati Forest on which it borders (Sorenson Coefficient = 62%.58% and 41% respectively; Table 1) (Figure 3).The assemblage is similar to that of corresponding Maputaland woodlands in South Africa (Sorenson Coefficient = 67%; Table 3) (Figure 2).This vegetation type is endemic to Maputaland and has many rare plant species.It is restricted to the ancient coastal dunes of Maputaland.and drier (600 mm per annum) conditions than most of the other coastal forest types in southern Africa.This grass assemblage prefers moister habitats in shady places and is common along forest margins.Based on vegetation structure and species composition the forests of ancient dunes in Maputaland can be divided into Licuati Forest and Licuati Thicket (Izidine et a\. 2003).
Character species of the grass assemblage are given in species group M (Table 1).Although it is a forest system and tufted perennials dominate the grass assemblage, this vegetation type has a high proportion (24%) of annual species.The assemblage is species poor, but a high pro portion of three rare species are recorded for the assem blage.This is the only vegetation type in the study area with representatives from the Arundinelleae.Centotheceae and Ehrharteae.and the only one without a representative of the Andropogoneae (Table 2).This grass assemblage is related to Coastal Woodland and Dune Forest as a result of similar microhabitats (Sorenson Coefficient = 41% and 39% respectively; Table 1) (Figure 3).It also shows a high similarity in grass species composition when compared with plots from Maputaland sand forest in South Africa (Sorenson Coefficient = 71%: Table 3) (Figure 2).

Floristic analysis
In a provisional checklist compiled from available lit erature for the two Maputaland reserves in Mozambique, the Poaceae numbered 52 species/infraspecific taxa and 36 genera.Currently, with 95% of the collected speci mens identified, the updated checklist (Appendix 1) con tains 115 species/infraspecific taxa and 56 genera.However.15 species previously recorded were not col lected again.Most of these taxa are either locally rare (e.g.Panicum genuflexum and Triraphis andropogonoides) or wetland species (e.g.Leersia hexandra and

Percentage of subfamily
Oryzeae HG Dinebra retroflexa var.condensata), for which high water tables made their localized habitats inaccessible.
In the study area the most commonly represented sub families are the Panicoideae with 6 6 species/infraspecif ic taxa (accounting for 57% of the total checklist) and Chloridoideae with 39 taxa (34%) (Table 4).Together they account for 91% of the species in the checklist.The tribes with the most species are the Paniceae (41 taxa), Eragrostideae (32 taxa) and Andropogoneae (24 taxa) (Table 4).The genera with the most species are Era grostis (12), Panicum (10).Digitaria (8 ) and Sporobolus (6 ).Andropogon, Brachiaria and Dactyloctenium are repre sented by four species each.
Interesting species were recorded, such as Panicum kalaharense (usually associated with much drier areas on Kalahari sands) and Monocymbium ceresiiforme (usual ly associated with much higher altitudes on mountains).Many grass species of direct significance for conserva tion initiatives, reserve management and sustainable uti lization were also recorded: 1, three Maputaland endemic grasses belonging to the Eragrostidae (Van Wyk 1996).Brachychloa schiemanniana occurs in Dune Forest, Eragrostis moggii var.moggii is associated with Licuati Forest and Dune Forest, and Trichoneura schlechteri is found in Coastal Woodlands, Dune Forest, Licuati Forest and Woody Grassland.Brachychloa fragilis was not recorded, although it is a typ ical endemic associated with deep sands in South Africa; 2, three alien grasses belonging to the Panicoideae.As is the case in many Centres of Endemism in the world (Stohlgren et al. 1999) Taylor 1996).Both species are locally common and known to occur as far north as Kenya and Tanzania; 4, eight grasses that are important for rural livelihoods.Some species are used as important components to build huts: Phragmites australis for the walls and Cymbopo gon excavatus, Imperata cylindrica and Hyperthelia dissoluta to thatch the roof (Mangue 1999).Dactyloctenium giganteum, Eleusine coracana subsp.africana, Echinochloa pyramidalis and Sorghum bicolor subsp.arundinaceum are used as indigenous grass cereals (Scudder 1971).
Correlation analyses of the floristic data did not reveal any meaningful relationships.The only significant posi tive correlation (n = 6 ; r = 0.827; P = 0.04) was obtained between the number of rare/endemic grass species and the number of annual grass species per vegetation type.Forests/woodlands have higher numbers of rare/endemic and annual grass species than grasslands.

Distribution patterns
All known distributions of the six grass subfamilies extend into southern Mozambique.The diversity of the Chloridoideae and the Panicoideae in the study area was expected and subsequently were the best represented in the major vegetation types.The dominance of the Pani coideae (both Ci and C4 grasses) in the terrestrial vegeta tion types coincides with the centre of diversity of the subfamily in mesic summer rainfall regions (Gibbs Rus sell 1986).However, its diversity was much lower than would be expected (19% instead of the predicted 46-60%) (Table 4).The diversity of species of the Chlori doideae (mainly C4 aspartate producers) was within the expected range of 16-30% (17% of the subfamily's species was recorded) (Table 4), as this subfamily's cen tre of diversity is mainly situated further north in arid summer rainfall regions (Gibbs Russell 1986).Chlori doideae dominated the grass assemblage of the Primary Dunes.The species diversity of the other four subfami lies was as predicted by Gibbs Russell (1988).Arundi-noideae is dominant in Hygrophilous Grassland and the remaining three subfamilies are associated mainly with Hygrophilous Grassland and Licuati Forest.
The tribes, Eragrostideae (C4 aspartate).Paniceae (both G and C4) and Andropogoneae (C4 malate) dominate the grass assemblages of the major vegetation types, probably due to specific regional climatic conditions, such as high temperatures at the local scale, which favour these C4 groups to successfully colonize specific habitats.Eragrosti deae dominate the grass assemblages of Dune Forest and Primary Dunes, the Paniceae dominate in Coastal Wood land.Hygrophilous Grassland and Licuati Forest, and the Andropogoneae in Woody Grassland (Table 2).The Aristideae and Cynodonteae are found in nearly all the vegetation types, but are restricted to a maximum of four species per vegetation type.This is low when compared to the maxi mum of 21, 18 and 15 species respectively recorded for the three dominant tribes.The remaining seven tribes are restricted to single vegetation types.Three of these tribes are associated with Licuati Forest, two with Hygrophilous Grassland and one with Coastal Woodland.

CONCLUSIONS
It is evident from the analysis of the grass diversity on the coastal plain of southern Mozambique that a specific grass flora is present and that six species assemblages are associated with and characteristic of certain major vege tation types of the coastal plain.
The grass assemblage of Dune Forest was qualitative ly the most similar and central to the grass assemblages of the other vegetation types south of Maputo Bay.Primary Dunes have the most floristically unrelated grass assemblage to other vegetation types.
Similarity in grass assemblage composition was more than 60% for each vegetation type shared between reserves in Mozambique and South Africa.This relation ship with areas further south links the grass assemblages to the Maputaland floristic region.

FIGURE
FIGURE 1.-Locality of the Maputo Elephant and Licuati Forest Reserves in Mozambique and the Tembe Elephant Park and Sileza Nature Reserve in South Africa.

FIGURE 2 .
FIGURE 2.-Dendrogram of a TWINSPAN division depicting the floristic relationships between the grass assemblages of the major vegetation types of four protected areas of the Maputaland coastal plain in Mozambique and South Africa.LFR.Licuati Forest Reserve: MER.Maputo Elephant Reserve; SNR.Sileza Nature Reserve; TEP.Tembe Elephant Park.
FIGURE 3.-Relative positions of sampling plots along the first and second ordination axes.Numbers refer to plots; polygons group the plots into grass assemblages.
, alien taxa have also invaded Maputaland.Cenchrus brownii has invaded vegetation of Primary Dunes and Coix lacryma-jobi and Digitaria didactyla occurs in Coastal Woodland in the vicinity of villages; 3, two Red Data List grass species: Panicum pleianthum from Dune Forest which is assessed as Low Risk (Izidine & Bandeira 2002), and Alloteropsis papillosa trom Dune Forest, Coastal Woodland and Licuati Forest which is assessed as Insufficiently Known (Hilton-

TABLE 1 .
-Diagnostic grass assemblages of the major vegetation types of the Maputaland coastal plain south of Maputo Bay in Mozambique.

TABLE 1 .
-Diagnostic grass assemblages of the major vegetation types of the Maputaland coastal plain south of Maputo Bay in Mozambique.

TABLE 2 .
-Numbers of species of Poaceae subfamilies/tribes recorded within major vegetation types of Maputaland, south of Maputo Bay

TABLE 3
* CW.Coastal Woodland; DF, Dune Forest; HG.Hygrophilous Grass land; LF.Licuati Forest: WG.Woody Grassland occurs in a wide range of habitats including floodplains, dune crests, drainage lines, transition zones and dis turbed areas.

TABLE 4 .
-Floristic analysis of subfamilies and tribes recorded for Maputo Elephant and Licuati Forest Reserves 2 *CW.Coastal Woodland; DF, Dune Forest; HG, Hygrophilous Grassland; LF, Licuati Forest; WG, Woody Grassland Fish (2003)Powell (1992)a are mostly perennial.Woody Grassland has the highest proportion of perennial species and Primary Dunes the highest proportion of annuals.Tulted grasses are the most common growth form with the highest proportions in Licuati Forest and Coastal Woodland.Chloridoideae and Panicoideae dominate the grass composition in the study area.The tribes Paniceae.Era grostideae and Andropogoneae are represented most and Eragrostis, Panicum and Digitaria are the largest genera of this part of Maputaland.The coastal plain south of Maputo Bay has a grass diversity of 115 species and infraspecific taxa.Dune Forest and Hygrophilous Grassland have the richest grass diversity.Dune Forest has the most rare and en demic grass species and Hygrophilous Grassland the most character species.APPENDIX 1.-Checklist of grasses recorded for the major vegetation types of the Maputo Elephant and Licuati Forest Reserves Arrangement and classification follow Clayton & Renvoize(1986)and author citations followBrummitt & Powell (1992).Species names followFish (2003)and general practice at Maputo Herbarium (LMA).All specimens are housed at LMA, with duplicates specified for the herbaria of Luanda (LUAI), Natal (NH), Pretoria (PRE) and University of Zambia (UZL).Naturalized alien species are marked with an asterisk*, Maputaland endemic species with **, and Red Data List species with ***.Abbreviations for collectors' names: B. Balsinhas: DHN, De Koning, Hiemstra & Nuvunga; G, Greenwood; H, Hornby; Ma, Martins; MB, Myre & Balsinhas; MC, Myre & Carvalho; MD, Myre & Duarte; My, Myre; N, Nyirenda; P. Pedro; PP, Pedro & Pedrogao; S, Siebert; U, Uiras; V, Viana; Z, field observations of sterile specimens.