Landscape and Urban Planning 100 (2011) 251–267 Contents lists available at ScienceDirect Landscape and Urban Planning journal homepage: www.elsevier.com/locate/landurbplan Alien plant species dominate the vegetation in a city of Sub-Saharan Africa Joseph Bigirimana a,b,∗ , Jan Bogaert a , Charles De Canniere a , Jean Lejoly a , Ingrid Parmentier c a Université Libre de Bruxelles, Research group of Landscape Ecology and Plant production Systems CP 169, 50 Av. F. Roosevelt, 1050 Brussels, Belgium Ecole Normale Supérieure du Burundi, Département des Sciences Naturelles, BP 6983 Bujumbura, Burundi c Université Libre de Bruxelles, Evolutionary Biology & Ecology, CP 160/12, 50 Av. F. Roosevelt, 1050 Brussels, Belgium b a r t i c l e i n f o Article history: Received 27 April 2010 Received in revised form 17 December 2010 Accepted 23 December 2010 Keywords: Biological homogenisation Bujumbura Burundi Invasive plants Urban ecology Urbanization a b s t r a c t Although many African cities are confronted to an important population growth, there are almost no studies describing their vegetation and how it is affected by the urbanization process. We present here the description of the spontaneous vegetation of the capital city of Burundi, Bujumbura, through the analysis of 437 vegetation plots. Ruderal plant assemblages dominate in the most urbanized areas while in the outskirts of the city, the vegetation shows similarities to natural plant assemblages in the region. The variability of the plant assemblages is further influenced by the degree of shade, the presence of a permanent source of humidity and trampling by humans and cattle. Over the 404 species recorded in the plots, 57% are native and 43% are introduced. Sixty percent of the 173 introduced species originate from tropical America. It is very likely that in the future, if no biodiversity conservation measures are taken, the urbanization process will lead to the homogenisation of the vegetation in favour of ruderal plant assemblages and introduced species. Similarly to what is done in temperate countries, urban planners in African cities should take measures to preserve the last patches of semi-natural vegetation, not only for their conservation value, but also for the diversity of services they offer to the population. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Urbanization is a major driver of landscape transformation, leading to the conversion of land from wild and agricultural uses to urban and suburban occupancy (Pickett et al., 2001). The urbanization process has many consequences on ecosystems such as habitat fragmentation, air, water and soil pollution, disruption of hydrological systems, alteration of energy flow and of nutrient cycling (Williams et al., 2009). This impacts the biodiversity and raises several questions such as how the city influences adjacent ecosystems, how to maximize biodiversity within the urban ecosystem and how to manage undesirable species (Savard et al., 2000). Unexpectedly, most cities are richer in species than surrounding areas (Araújo, 2003). As an example, Brussels, the capital city of Belgium, counts 671 angiosperm species, which is half the number of species present in the country (Godefroid, 2001; Ricotta et al., 2010). This is due to both deliberate and accidental introductions of non-native species, but also to natural factors because most cities were build ∗ Corresponding author at: Université Libre de Bruxelles, Research group of Landscape Ecology and Plant production Systems, CP 169, 50 Av. F. Roosevelt, 1050 Brussels, Belgium. Tel.: +32 2 650 21 32; fax: +32 2 650 21 25. E-mail addresses: jbigirim@ulb.ac.be, bigjos5@yahoo.fr (J. Bigirimana), Jan.Bogaert@ulb.ac.be (J. Bogaert), cdecanni@ulb.ac.be (C. De Canniere), jlejoly@ulb.ac.be (J. Lejoly), inparmen@ulb.ac.be (I. Parmentier). 0169-2046/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.landurbplan.2010.12.012 up in areas of natural heterogeneity which supports natural biodiversity (Fjeldsa and Burgess, 2008; Kuhn et al., 2004). However, it is crucial to determine whether plant species are indigenous or not. Indeed, urbanization reduces the diversity and abundance of indigenous species, because of the homogenisation of the habitat (McKinney, 2006). Along a gradient from the city outskirts to the centre, native species are replaced by widespread “weedy” non-native species (some of which are invasive) well adapted to anthropized habitats (Kowarik, 1995; Kuhn and Klotz, 2006). This biodiversity loss is often accompanied by a negative economical impact (Williamson, 1996). However, the species richness and abundances of plants along an urban to rural gradient cannot be explained by a simple distance-related succession of native and non-native species (Brunzel et al., 2009; Kinzig et al., 2005). Indeed, this distance is a surrogate for other causal mechanisms, such as disturbances and dispersal, which are varying according to the socioeconomic and cultural characteristics of the residential areas (e.g. human mobility patterns, traditional gardening practices . . .). Studies about invasive and introduced species have been numerous in the fields of biogeography and conservation ecology these two last decennia, but with an under-representation of studies from Asia and Africa (Pyšek et al., 2008). Cilliers and Bredenkamp (2000) studied the roadside vegetation along an urbanization gradient in South Africa. Plant assemblages varied according to the degree of humidity, soil types, the use of adjacent areas, the level of perturbations, the use of herbicide, trampling and the time since 252 J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 Fig. 1. Distribution of the four main plant assemblages in the vegetation of Bujumbura (TF1, TF2, TF3, TF4, see Table 1) (a) in relation with soil types according to Kabeya (1992) and (b) urbanization degree according to Sindayihebura (2003). Soil types: sand (1), swamps with swelling clay (2), clay (3), clay + sand (4), clay + sand + silt (5), clay + silt (6), alterites and limonite material (7), no data (8). the road was constructed. They counted 26% of introduced species, mainly from South America but also from Europe and Asia. In Kenya, Stadler et al. (2000) analyzed the distribution of native and introduced species in 20 ecogeographical zones. The regions richest in species were also those with most introduced species. The area around the capital city Nairobi had the highest overall species richness and also the highest number of introduced species, originating mainly from Europe and America. In central Africa, to our knowledge, the only existing study is the 1982 PhD thesis by Mutabana Nyakabwa on the plant assemblages of the urban ecosystem of Kisangani (D. R. Congo). The author describes 60 plant assemblages and lists 1338 species. This large number of species can be explained by the diversity of biotopes in the city. Most of these species were largely distributed within the tropical regions of the world. We present here the first detailed analysis of the urban vegetation in Burundi. This country has a high population density (354 hab./km2 ) and a growing population (growth rate 3.6% in 2010). Although the population density in Burundi is less than that of its neighbour Rwanda (420 hab./km2 ), it is much higher than that in most other countries in Sub-Saharan Africa (Tanzania: 44 hab./km2 , D. R. Congo: 30 hab./km2 , CIA, 2010). Already 10% of the population in Burundi is urban and the rate of urbanization (2005–2010) is 6.8% (CIA, 2010). So far, no description of Bujumbura’s flora and vegetation exists, although it is essential to foreseen the effects of the urbanization process on the urban ecosystem and its surroundings and to take appropriate management measures. Specifically, we will answer the following questions: (a) Which are the different plant assemblages in the vegetation of Bujumbura? Is their variability determined by natural ecological factors and/or by human induced factors? (b) What are the ecology and the geographical distribution of the species composing these plant assemblages? What is the proportion of introduced species in the vegetation and what is the geographical origin of these species? (c) What is the conservation value of the vegetation of Bujumbura? 2. Materials and methods 2.1. Study area Bujumbura is the capital city of Burundi (Fig. 1). It is located in the western part of the country (29◦ 36′ E 3◦ 40′ S) on the shore of Lake Tanganyika. The city’s extent was around 146 km2 in 2003 (Sindayihebura, 2003). The latest population census, realized in 2008, indicates that 478 155 people live permanently in the city (Présidence de la Répubique du Burundi, 2009). Altitude varies from 777 m at the lake shore to 1100 m in the eastern part of the city, at the foot of the Miwa Mounts. Climate is tropical with one dry season (May–September) and one rainy season (October–April). Mean annual temperature varies between 23 and 25 ◦ C and mean annual precipitation between 800 and 1300 mm. During 4 months (June–September), mean monthly precipitation is below 50 mm. Natural vegetation in the region (excluding wetlands) has almost disappeared and is only maintained in the Rusizi National Park. It includes savannah, miombo and sclerophyllous forests (Reekmans, 1980). Elsewhere, natural vegetation has mostly been replaced by fields and fallows. This is a rather recent evolution: in 1950 the Rusizi Plain still had a very natural character (Reekmans, 1980). Vegetation covers half of the territory of Bujumbura, mostly in the suburb. But even inside the more densely urbanized part of the city, there are unconstructed areas covered by spontaneous vegetation. J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 Soils in Bujumbura originate from sediments deposited by the rivers or by the Tanganyika Lake and piedmont colluvial deposits from the Mirwa Mountain. This results in a mosaic of different soil types (Fig. 1a). The northern section of river Ntahangwa and its surroundings is characterized by a dominance of clay, its southern section by a mix of sand and clay. The shore of Lake Tanganyika is composed of sandy soils and sand dunes. At the foot of the Miwa Mounts, soils are mainly composed of alterites and colluvial deposits. According to the phytogeographical classification of White (1983), Bujumbura belongs to the Lake Victoria Regional Mosaic. It is located at the intersection of several phytochoria and consequently, most species are also distributed in the adjacent regions. 2.2. Data collection Field data was collected from 2005 to 2007, between February and June in unconstructed land inside the city limits, in the terra firme vegetation. Plots were established within homogeneous patches of vegetation. In each plot, all angiosperm and pteridophyte species were listed. The investigated area was increased until almost no new species could be added, or until the entire continuous patch was investigated. Plot area is therefore variable (average surface 42 ± 32 m2 , min = 4 m2 , max = 150 m2 ). Species abundances were scored in the plot using the Braun-Blanquet scale (BraunBlanquet et al., 1932). At least one specimen of each species that could not be identified with certainty on the field was deposited in the herbarium of the Université Libre de Bruxelles (BRLU) and in that of the Université du Burundi (UB). There are 1255 herbarium samples in this reference collection. The Angiosperms nomenclature follows African Plants Database (2009) and the Tropicos.org. (2009). Family names are those of the Angiosperm Phylogeny Group II classification (Stevens, 2003). For each plot, the habitat type (agricultural fallow, savannah, ruderal habitat), the degree of trampling by man and/or cattle (low, medium of high), the presence of shade (yes/no), and the existence of a permanent source of humidity (yes/no) were noted. The geographical coordinates of the plot have been projected on a soil map (Kabeya, 1992) and on an urbanization map (Sindayihebura, 2003). 2.3. Data analyses The main floristic gradients were identified with a Detrended Correspondence Analysis of the vegetation plots (DCA, Jongman et al., 1995). The environmental variables measured on the field were added as passive variables to this analysis. DCA was preferred to CA because of a strong arch effect. To test the relative influence of human induced factors and natural ecological factors on the plant assemblages, we realized a variance partitioning (Borcard et al., 1992), using partial canonical correspondence analysis (CCA, Ter Braak, 1986). The ordinations (DCA, CCA and partial CCA) were realized with Canoco for Windows 4.5 (Ter Braak and Smilauer, 2002). The natural ecological factors included soil type, the humidity level and the shade level and the human induced factors included the degree of urbanization and the degree of trampling by humans or cattle. Partial Monte Carlo permutation tests were used to assess the statistical significance of each natural ecological factor and human induced factors before introducing them in the ordination model (forward selection, Ter Braak and Smilauer, 2002). To partition the variance, we realized four separate CCA using: (1) species and natural ecological factors; (2) species and human induced factors; (3) species and human induced factors with natural ecological data as covariables; and (4) species and natural ecological factors with human induced factors as covariables. In this variance partitioning analysis, we used the same number of statistically significant natural ecological factors and human induced factors 253 to ensure the same degree of freedom for both classes of variables. The plant assemblages were defined from the cluster analysis of the matrix of the 437 terra firme plots and of the 246 species that were at least present in four of these plots (UPGMA, BrayCurtis index, Legendre and Legendre, 2003). The indicator species of each level or the hierarchical classification retained from the cluster analysis were defined with the indicator method of Dufrene and Legendre (1997). This method calculates an indicator value (IV) for each predefined group of plots: it is an integrated measure for the relative mean abundance and the relative frequency of the species in each group. Only species that have both a high mean abundance and are present in the majority of the plots in a group will score a high IV for that particular group. To test whether the observed IV of a species in a group was higher than expected based on a random distribution of individuals over the locations, the observed IV was compared with 999 randomly generated IVs (see Dufrene and Legendre, 1997). A synoptic table was produced indicating the IV value of the species, their frequency (10 frequency classes I–X, each 10% wide) and their mean cover in the plots of the plant assemblage. The linear correlation between plot size and plot species richness was investigated with Spearman correlations. This was done for all plots as well as within each of the plant assemblages with more than five plots. ANOVA tested for significant differences of plot size between the four main plant assemblages. Life form, phytogeographical and ecological spectra were calculated for each plant assemblage. These were realized in presence–absence and with abundance data (weighted by the sum of the mean cover of the species in the plant assemblage). Pearson’s chi-square (2 ) tests were used to assess the significance of differences in the spectra between the different plant assemblages. Life forms follow the definitions of Raunkiær (1934): therophytes (Th), chamaephytes (Ch), geophytes (G), hemicryptophytes (H) and phanerophytes (Ph). Ecological groups follow Schmitz (1988): ruderal species (R), savanna species (S), psammophile species (P), sclerophyllous forest species (SF), wetland species (W), hygrophilous forest species (HF) and cultivated species (Cu). The ecology and the geographical distribution of each species were defined with the help of floras and online databases: “Flore du Rwanda” (Troupin, 1988) “Flore graminéenne du Burundi” (Ndabaneze, 1989), the African Plants Database (2009), Tropicos.org. (2009), and the Royal Botanical Gardens Database (2009). Additional information was found in the literature (Galinato et al., 1999; Wester, 1992; Wet, 1977). We characterized the distribution of the species following the phytogeographical classification of Lebrun (1956) and White (1983). We distinguished the origin of species from its geographical distribution, the latter being dynamic and, for many species, influenced by human activities. The following phytogeographical elements were considered: - widespread species (WS): cosmopolitan (Cos), paleotropical (Pal), pantropical (Pan) and Afro-Asian (Af-As), - African species: Afro-Madagascarian (Af-Ma), African pluriregional (AP), Tropical African (T Af), East African (EA), East and South African (EA-SA), Guineo-Congolian and Lake Victoria Regional Mosaic (GC-V) and Afro-montane (Mo) species, - Lake Victoria Regional Mosaic species (V), - species endemic to the Western Graben District (E): this phytogeographic district was defined by Lebrun (1956) and designates the Imbo plain (which includes the Ruzisi Plain and Bujumbura). Introduced species (alien, exotic, non-native, non-indigenous) are defined according to Weber (1997) and Pyšek et al. (2004) as species that are not indigenous in a given geographical unit (here Burundi). Their presence in the country is due to intentional or unintentional human involvement, or they have arrived there without the help of people from an area in which they were J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 introduced. They include invasive plants: plants that produce reproductive offsprings, often in very large numbers, at considerable distances from the parent plants, and thus have the potential to spread over a large area. Introduced species are opposed to native species: taxa that have originated in a given area without human involvement or that have arrived there without intentional or unintentional intervention of humans from an area in which they are native. In this study, we consider as native the species from the Lake Victoria Regional Mosaic, the species endemic to the Western Graben District and the African species. The status of widespread species is more complicated to establish. When the species is distributed on several continents, its distribution could be natural (long distance dispersal) or human induced. We decided here to follow Thorne (1972) by considering Afro-Asian distributions as potentially natural. For the other inter-continental distributions, if the origin of the species is known, it can be classified as native or not. If its origin is unknown, we classify it according to Bean (2007); these species can also be considered as native under the following conditions: - if they are aquatic, semi-aquatic or littoral plants (long distance dispersal by water), - if they are terrestrial species with adhesive fruits (long distance dispersal by birds), - when they are only found in undisturbed habitats. In conclusion, in this study, the number of native species N = N1 + N2 (N1 : species with a continuous distribution including Burundi and N2 : widespread species that might be considered as indigenous according to Bean, 2007). The number of introduced species I = I1 + I2 (I1 : introduced species with known origin and I2 : widespread species that do not conform to the criteria for the native according to Bean, 2007). 3. Results 3.1. Plant assemblages and their relationship to human induced and natural ecological factors A total of 404 species has been recorded in the 437 plots. These species belong to 236 genera and 71 families. The five main families are the Poaceae (18%), Fabaceae (14%), Cyperaceae (7%), Asteraceae (6%) and Euphorbiaceae (5%). The most frequent species are annual plants. The main floristic gradient (DCA axis 1) was best correlated to the urbanization degree, while the degree of trampling by humans and cattle and the presence of a permanent source of humidity are correlated to the two first DCA axes (Fig. 2). Soil types are weakly correlated with these floristic gradients. The highly urbanized areas are mainly covered by ruderal vegetation (TF1), while the fallow vegetation and relict savannas (TF2) are mainly located in the less urbanized areas (see Fig. 1). Only 4.7% of the total floristic variance was correlated to the two natural environmental factors (humidity and shade) and the two human induced factors (degree of trampling and degree of urbanization) selected for the variance partitioning analysis. These 4.7% were equally distributed between the two categories of factor (50% each), there was no common effect (0%). Most of the floristic variance is thus unexplained (95%). Four main plant assemblages were defined from a dissimilarity level of 0.93 in the dendrogram resulting from the cluster analysis. Sub-assemblages were further defined within two of these plant assemblages (Table 1). The mean plot size, mean species richness, total number of species and the number of plots are given for each plant assemblage. Note that the correlation of plot size and species Trampling Axis 2 254 Urbanisation Shade Humidity Axis 1 Fig. 2. Detrended Correspondence Analysis (DCA) of 437 vegetation plots realized in the terra firme vegetation of Bujumbura. Four main plant assemblages can be distinguished (see Table 1 for more details): TF1 (crosses), TF2 (circles), TF3 (boxes), TF4 (triangles) and black stars (soil types). Environmental variables were passive in the analysis. Axes 1 and 2 represent respectively 2.8% and 2.2% of total floristic variability. richness is positive and significant (P < 0.001) for all plots and for the plots of plant assemblage TF1 and TF2, but weak (R2 < 0.12). This was not tested on TF3 (there are only four plots in this group) and the correlation was not significant for TF4. As plot size varies significantly between the plant assemblages (ANOVA, P < 0.001), the mean species richness of the plots from the different plant assemblages given in Table 1 have only indicative values. The plant assemblages are briefly described below (see Table 1 for more details). 3.1.1. Ruderal grasslands (TF1) This plant assemblage is developing on different soil types in habitats highly influenced by man such as roadsides, playing grounds and abandoned ditches. It is composed of ruderal species, including several nitrophytes like Ageratum conyzoides and Sida acuta. Two sub-assemblages can be distinguished according to the high (TF11) or medium (TF12) degree of trampling of the vegetation by man and/or cattle. TF11 is distinguished from TF12 by the abundance of Sporobolus pyramidalis, a pantropical weed resistant to trampling and to annual fires, disliked by livestock. 3.1.2. Fallow vegetation and relict savanna (TF2) This plant assemblage is mainly present at the outskirts of the city, in unconstructed land and agricultural fallows and in small patches in the city centre. Most characteristic species are grasses like Panicum maximum and Setaria pumila. Four sub-assemblages can be distinguished: TF21 are grasslands in young agricultural fallows and abandoned land on strong slopes. It is characterized by the abundance of Tithonia diversifolia. This Asteraceae of Mexican origin is now invasive in Burundi. TF22 are grasslands in agricultural fallows on very poor soils. These soils have been exhausted by over-cultivation and/or are eroded because of strong slopes. This plant assemblage is characterized by Imperata cylindrica. In Bujumbura, it is mainly present on the slopes above the Ntahangwa and Nyabagere rivers. TF23 is the plant assemblage of old agricultural fallows and of relict savannas. It is characterized by three grasses amonst which Hyparrhenia madaropoda, a species endemic to the Lake Victoria Table 1 Plant assemblages of the vegetation of Bujumbura city (excluding wetlands). IV: Indicator value of character species (only significant values are indicated). F: Frequency class (I–X each 10% wide) and C: mean cover of the species within the plots of the plant assemblage. Invasive species are mentioned by ‘*’. Only the most representative species within each plant assemblage are listed. TF11 TF12 TF21 TF22 TF23 TF24 TF3 TF4 Number of plots Average surface of plots and standard deviation Total mean cover and standard deviation Number of species Mean number of species per plot Characteristic species of IV 46 72 ± 31 81 ± 19 176 16 F C 262 34 ± 28 61 ± 26 337 18 F C 5 52 ± 32 67 ± 3 36 11 F C 7 34 ± 24 63 ± 32 90 18 F C 22 53 ± 36 54 ± 21 131 17 F C 70 55 ± 34 48 ± 16 169 18 F C 4 41 ± 20 78 ± 39 43 14 F 21 83 ± 39 34 ± 22 113 14 F TF1: ruderal grasslands Ageratum conyzoides L. * Digitaria longiflora (Retz.) Pers. * Sida acuta Burm. f. * Synedrella nodiflora Gaertn. * Acanthospermum hispidum DC. * Cynodon nlemfuensis Vanderyst var. nlemfuensis Eleusine indica (L.) Gaertn. subsp. indica * 39 35 33 31 30 30 25 III III V III II VII III 0.2 0.2 0.4 0.1 0.1 1.4 0.3 VI V V IV IV IV III 2.0 3.5 3.3 3.2 1.7 7.7 0.2 TF11: grasslands trampled by people or/and cattle Sporobolus pyramidalis P. Beauv. Paspalum notatum Flüggé * Chloris pycnothrix Trin. Desmodium triflorum Kyllinga bulbosa P.Beauv. Gomphrena celosioides Mart. * 35 32 25 32 39 21 VII IV IV VII V III 3.5 16.7 8.6 2.0 0.3 0.2 II 0.2 V II II V II 0.3 0.1 0.1 0.3 0.1 III II II 0.2 0.1 0.2 II 0.2 IV II II II II 8.8 11.3 8.3 7.3 3.2 TF12: grasslands not or weakly trampled Same asTF1 TF2: fallow vegetation and relict savannah Panicum maximum Jacq. Setaria pumila (Poir.) Roem. & Schult. * Aristida adscensionis L. Hyperthelia dissoluta (Steud.) Clayton Pennisetum polystachion (L.) Schult. subsp. polystachion 31 11 16 14 16 C C J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 Communities 255 256 Table 1 (Continued) Communities TF11 TF12 TF21 TF21: grasslands of young agricultural fallows and abandoned land on high slopes Tithonia diversifolia (Hemsl.) A.Gray * 98 83 TF23: grasslands of old fallow and relict savannah Hyparrhenia filipendula (Hochst.) Stapf H. madaropoda Clayton Heteropogon contortus (L.) R & Sch. 65 46 46 X TF23 TF24 99 TF4: psammophile steppe Ipomoea pes-caprae (L.) R.Br. subsp. brasiliensis (L.) Ooststr. Crotalaria pallida var. obovata (G. Don) Polhill * Eragrostis tremula Steud. * Triumfetta rhomboidea Jacq. * 75 57 47 49 Ubiquitous species Euphorbia hirta L. * Tridax procumbens L. * Bidens pilosa L. * Desmodium tortuosum (Sw.) DC. * Hyptis suaveolens Poir.* Phyllanthus amarus Schumach. & Thonn.* Asystasia schimperi T. Anderson Cassia obtusifolia L. * Cassia occidentalis L. * Euphorbia heterophylla L. * Dactyloctenium aegyptium (L.) Willd.* Cyperus esculentus L. * Corchorus olitorius L. * Manihot esculenta Crantz * Leonotis nepetifolia (L.) R.Br. IX 67.4 VIII V V 39.1 16.1 30.9 VII VI V V 12.6 13.1 12.2 0.5 X IV II II II II II I I I I I III I I 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.0 0.0 0.2 0.0 0.0 IV IV V III III IV IV III III III III II III II II 0.5 1.0 2.1 0.6 2.2 0.3 0.3 3.9 0.2 1.5 0.3 0.3 0.3 0.3 1.6 TF4 90.8 TF24: grasslands of agricultural fallows on slightly degraded soils Melinis repens (Willd.) Zizka subsp. repens 39 B. decumbens var. ruziziensis (R. Germ. & Evrard) Ndab. 29 Aspilia kotschyi (Sch.Bip.) Oliv. 31 Crotalaria ochroleuca G.Don 30 TF3: ruderal grasslands on moist clay soils Paspalum conjugatum P.J.Bergius * TF3 II 0.2 IV 0.3 V V II II 0.3 0.3 0.1 0.1 II II III II II III V 0.1 0.1 0.2 0.1 0.1 0.2 0.3 IV IV III V III II II I I I I I I 0.3 0.3 0.2 0.4 0.2 0.1 0.1 0.1 0.0 0.1 0.1 0.1 0.0 I 0.0 V IV III V V III II II II I II II III II I 0.4 0.4 0.2 0.4 0.4 0.2 0.2 0.2 0.1 0.1 0.2 0.2 0.2 1.0 0.1 V III III 91.4 0.3 0.2 0.2 VIII VIII V I 24.6 22.2 9.8 8.2 II V 0.3 3.4 I III I I II IV I II I I II I 0.1 0.4 0.1 0.1 0.6 0.5 0.1 0.2 0.1 0.1 0.2 0.1 J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 TF22: grasslands of agricultural fallows on very poor soils Imperata cylindrica (L.) Raeuschel * TF22 J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 257 Table 2 Life form and phytogeographical spectra (% of species mean cover) of the species composing plant assemblages of Bujumbura. Life forms: therophytes (Th), chamaephytes (Ch), geophytes (G), hemicrytophytes (H), phanerophytes (Ph). Distribution: widespread species (WS), African species (Af), Endemic to the Lake Victoria Regional Mosaic (V) and Endemic to the Western Graben District (E). Origin status: Native species (N), Introduced species (I). Life form and origin status spectra differ between plant assemblages (X 2 = 62.18 > 2df28, ˛5% = 41.34 and X 2 = 16.19 > 2df7, ˛5% = 14.07), but distribution spectra are not different (X 2 = 16.70 < 2df21, ˛5% = 32.67). For details about the plant assemblages, see Table 1. Plant assemblages TF11 TF12 TF21 TF22 TF23 TF24 TF3 TF4 All plots % of species mean cover Life form Th Ch G H Ph 21 63 4 12 0 49 41 3 5 2 2 95 2 0 1 16 7 72 2 3 8 3 1 87 1 33 17 2 47 1 3 95 1 0 1 22 65 12 0 1 45 44 3 7 1 Distribution WS Af V E 84 15 1 0 90 7 1 2 98 2 0 0 90 9 1 0 78 2 20 0 71 15 1 13 99 1 0 0 96 2 2 0 89 8 2 1 Origin status I N 57 43 65 35 97 3 82 18 5 95 19 81 97 3 55 45 65 35 176 337 36 90 131 169 43 113 404 Number of species Regional Mosaic. This plant assemblage is very rare in Bujumbura, subsisting mainly at the outskirts of the city. TF24 are the young fallow grasslands characterized by Melinis repens and by Brachiaria decumbens var. ruziziensis, a species endemic from the Western Graben District. 3.1.3. Ruderal grasslands on moist clay soils (TF3). These grasslands are dominated by Paspalum conjugatum, a Poaceae originating from tropical America. This plant assemblage is located on the moist clay soils of the shore of Lake Tanganyika. 3.1.4. Psammophile steppe (TF4) This plant assemblage is located on the sandy soils of the shore of Lake Tanganyika. The most characteristic species is Ipomoea pescaprae subsp. Brasiliensis, a Convolvulaceae typical of dunes and beaches in the tropics worldwide. 3.2. Ecology, life form, origin and distribution of the species The list of the 404 species identified in the 437 vegetation plots is provided in the supplementary material (Appendix A), with information about their ecology, life form and phytogeography. Ruderal species are abundant in all plant assemblages (>90% of the total vegetation cover, see Appendix B) except in TF23 and TF24 that are dominated by savannah species. Most species are therophytes (41%), chamaephytes (25%) and geophytes (17%, see Appendix C). Phanerophytes are rare. Life form spectra differ significantly between the eight plant assemblages (Chi-square tests, Table 2). Chamaephytes dominate the ruderal grasslands (TF11 and TF3), hemicryptophytes are most abundant in old agricultural fallows and in relict savannas (TF23). The dominance of geophytes in young fallows on very poor soils (TF22) is due to I. cylindrica. The phytogeographical spectra of the eight plant assemblages are given in Table 2 and in Appendix C. Appendix D gives the origin of the species as well as their actual geographical distribution and origin status (native or introduced). Native species and introduced species constitute respectively 57% and 43% of the flora. Sixty percent of the introduced species have their origin in tropical America, 24% in Asia and 6% in Africa (Table 4). The less anthropized habitats (TF23 and TF24) show the largest dominance of native species (95% and 81% respectively). The other plant assemblages have more than 55% to 97% of their total vegetation cover composed of introduced species (Table 2). The 231 native species belong to 42 families and the 173 introduced species to 48 families. In both cases, the most important families are the Fabaceae and Poaceae (Table 3). Thirty nine percent of the introduced species were introduced deliberately and 61% accidentally. Seventy-four percent of these introduced species are invasive, mainly weeds. Four species occupy large areas in the town: T. diversifolia, Mimosa invisa, Lantana camara, and I. cylindrica. Very dense stands of these species can occupy areas about 1 ha or more. Plant assemblages dominated by these species indicate the presence of degraded soils. L. camara is the most invasive species in Bujumbura and likely also in the whole Rusizi plain. Most species are widely distributed in the tropics (67%, Table 2) and widespread species dominate all plant assemblages (71–98% of total vegetation cover). Nine percent of the species are endemic to the Lake Victoria Regional Mosaic and two species are endemic to the Western Graben District: B. decumbens var ruziziensis and Portulaca centrali-africana. 4. Discussion 4.1. Influence of natural ecological factors and human induced factors on the urban vegetation Like in most urban ecosystems, plant diversity in Bujumbura is linked both to natural ecological factors and to human induced factors. In the most urbanized areas of the city, the human factor is predominant and the vegetation is ruderal, whatever the soil types (Figs. 1 and 2). Variance partitioning between human induced factors (degree of urbanization and trampling by humans and cattle) and natural ecological factors (humidity and shade) influencing the floristic variability yielded similar percentages (50%) of variance explained and no common effect. Note however that these two groups of factors are not easily separated in the city of Bujumbura, as permanent soil humidity and shade sometimes result from sewage water and planted trees, and could then be regarded as human induced factors. Only 4.7% of the total floristic variance was correlated to the four factors introduced in the variance partitioning analysis. Most of the floristic variance is thus unexplained (95%). This is due to the high stochastic variation associated to the very large number of plots and species (typical for studies in tropical J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 258 Table 3 Most important families and % of introduced and native species, comparaison between the flora of Bujumbura and that of the city of Chonju in South Korea (Zerbe et al., 2004), the flora of Mexico (Villaseñor and Espinosa-Garcia, 2004) and the world’s flora (Pyšek, 1998). Family Fabaceae Poaceae Asteraceae Amaranthaceae Euphorbiacaea Cyperaceae Solancaeae Malvaceae Convolvulaceae Nyctaginaceae Bujumbura Bujumbura Chonju Mexico World Native 20 22 6 3 3 8 1 6 3 0 Introduced 18 13 8 5 5 5 5 3 3 2 Introduced 11 5 22 3 2 – – – 6 – Introduced 9 28 9 1 2 1 2 3 – – Introduced 9 15 14 2 2 1 3 2 1 0.3 regions!) and to the fact that there certainly are more factors that influence the vegetation than those measured in this study. 4.2. Ecology, life form, origin and distribution of the species Therophytes, chamaephytes and geophytes dominate all plant assemblages and phanerophytes are less abundant than in the natural vegetation of the Rusizi plain (savannah, miombo and sclerophyllous forest). It is well known that phanerophytes respond negatively to perturbations (Grime, 2001) and that annual species and short life pluri-annuals are more abundant in urbanized habitats (Fanelli et al., 2006). Ruderal therophytes have a weak competition capacity, but they produce a large quantity of seeds that allows them to maintain populations in a frequently disturbed environment (Simonová and Lososová, 2008). Chamaephytes are stress-tolerant (Grime, 2001). Their proportion is particularly important in the psammophile steppe plant assemblage TF4 (drought due to sandy soils), the grassland plant assemblage of young agricultural fallows and abandoned land (TF21) and in the ruderal grasslands plant assemblage trampled by human and cattle (TF11). Our results are different from those obtained by Mutabana Nyakabwa in Kisanagani (R. D. Congo), where the flora is dominated by 50% phanérophytes, 17% therophytes and 15% chamaephytes. Differences in the natural vegetation type (rain forest in Kinsangani versus miombo and savanna in Bujumbura) may partly explain the greater number of phanerophytes in Kinsangani. Our results indicate a striking regression of the species of the Lake Victoria Regional Mosaic (9%) and a large dominance of species present in the tropics worldwide (67%). Indeed, Germain (1952) studied the flora of the Congolese section of the Rusizi Plain and concluded that 43% of the species belonged to what was later named the Lake Victoria Regional Mosaic element. Later, in his study of the flora of Burundi between 800 and 1000 m altitude (including Bujumbura), Lewalle (1972) quoted 36% of species belonging to this element. The urbanization process in Bujumbura resulted in the progressive elimination of natural vegetation (mosaic of savannah, miombo and sclerophyllous forests) and its replacement by grasslands dominated by ruderal species. This is the well-known process of biological homogenisation: unique native species become extinct and are replaced by species that are widespread (Kuhn and Klotz, 2006; Lockwood and McKinney, 2001). This process could be explained by the fact that in the urban environment, sites available to the colonization of plants are fragmented and their vegetation is quite diverse. Introduced species are better adapted to colonize such diverse and fragmented environments than native species, notably because many of these species are more efficient at using limited resource during short times (Celesti-Grapow et al., 2006; Funk and Vitousek, 2007). Two main factors are considered for the establishment of introduced species in a country: climatic similarities with the country of origin and historical factors (Arévalo et al., 2005). Almost all plants currently cultivated in Burundi have been introduced in the 17th and 18th century and later (Manirakiza, 2008). These voluntary introductions have been accompanied by the uncontrolled arrival of weeds from several countries. Today, introduced species in the flora of Bujumbura are mainly agricultural weeds. The origin of introduced species in the flora of Bujumbura is compared to that of the flora from other cities and countries in the world in Table 4. Burundi was colonized by European countries (in 1890), but very few introduced species come from that continent: most originate Table 4 Geographical origin (in %) of the introduced species in the flora of Bujumbura compared to that of introduced species in other countries. Data from Chonju city in South Korea (Zerbe et al., 2004), Brussels city in Belgium (Ricotta et al., 2010), 20 ecogeographical region in Kenya (Stadler et al., 2000), South Africa (Milton, 2004), 32 States of Mexico (Villaseñor and Espinosa-Garcia, 2004) and the Kashmir Himalayan region (Khuroo et al., 2007). n = number of introduced species considered. New world Tropical America North America South America Caribbean region North and south America Old world Asia Africa Australia Europe Eurasia Mediterranean region Eurasia and Africa Old world and new world Bujumbura city (n = 173) Chonju city (n = 88) Brussels city (n = 186) Kenya (n = 181) South Africa (n = 113) Mexico country (n = 604) Kashmir Himalaya region (n = 571) 62 60 2 – – – 32 24 6 1 0 0 1 0 6 41 6 32 3 0 0 59 30 – – 19 – – 10 0 16 0 16 0 0 0 84 34 16 0 34 – – 0 0 44 – – – – – 51 5 8 2 23 13 – – 5 20 20 – – – – 60 0 0 0 0 0 60 – 20 14 – 2 10 1 1 85 – – – – – – – 1 18 0 10 8 0 0 82 27 15 2 38 0 0 0 0 J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 from tropical America. Dominant families in the introduced flora are similar in Bujumbura as in other cities and countries in the world (Table 3): Fabaceae, Poaceae and Asteraceae. These three families also dominate the native flora. 4.3. Conservation value of the vegetation of Bujumbura A total of 404 species were identified, which is roughly one third of the number of species listed for the whole Ruzisi Plain by Reekmans (1980). The total flora of the city is very likely to be more important as wetland vegetation and gardens were not included here. Within the 404 species listed in this study, 57% are indigenous and 9% have their distribution limited to the Lake Victoria Regional Mosaic. Consequently, there is still a potential for biodiversity conservation within the territory of Bujumbura. The vegetation of the city also presents several socio-economical interests. Grasses like B. decumbens var. ruziziensis, P. maximum and Hyparrhenia spp. are grazed by livestock and are essential for the agro-pastoral activities. In his inventory of medicinal plants, Niyongabo (1985) compiled a list of 101 species present in Bujumbura. Even very invasive species can prove to be useful. Like in many other parts of Africa, I. cylindrica causes many problems for the local agriculture (Chikoye and Ekeleme, 2003). However, this species is used to cover the roof of houses in peri-urban areas. T. diversifolia is used in other countries to restore soil fertility (Jama et al., 2000), as forage plant (Roothaert and Paterson, 1997), to produce fire wood or as fence to control erosion (Ng’inja et al., 1998). But these potential uses of T. diversifolia are currently unknown from the population of Bujumbura. 5. Conclusion, perspectives and recommendations Like in other cities in the world, the urbanization process in Bujumbura reduces the diversity and abundance of indigenous species. In the most urbanized areas, ruderal plant assemblages with a high abundance of introduced species dominate the vegetation. In the city outskirts, plant assemblages vary according to soil type, humidity and shade, and native species are more abundant. This study will be completed with analyses of the city’s spontaneous wetland vegetation and of the flora in private gardens. We will then get a better knowledge of the vegetation inside the city and of its spatial organization. This could be a first step in monitoring the evolution of the vegetation with the expansion of the city. 259 Similarly to what is done in temperate countries, urban planners in African cities should take measure to preserve the last patches of semi-natural vegetation, not only for their conservation value, but also for the diversity of services they offer to the population. Measures should be taken to avoid the propagation of alien invasive plant as it is well established that it costs much less to act preventively than trying to control these plants when they are already well established. Acknowledgements We thank the editor, Paul Gobster, and two anonymous reviewers who took the time to give useful comments and suggestions on an earlier draft of this manuscript. Joseph Bigirimana has a research grant from the Government of Burundi, the Université Libre de Bruxelles and “Fonds David et Alice Van Buuren”. Ingrid Parmentier is a post-doctoral researcher of the FRS-FNRS. We thank the botanists of the National Botanical Garden of Belgium who contributed to the determination of the herbarium plant specimens. Appendix A. Informations about the life form, ecology and phytogeography of 404 species in the spontaneous flora of Bujumbura. Life forms (LF): therophytes (Th), chamaephytes (Ch), geophytes (G), hemicrytophytes (H), phanerophytes (Ph). Geographical distribution (GD) and origin (GO) of species: Cosmopolitan (Cos), Paleotropical (Pal), Pantropical (Pan), Afro-Asian (Af-As), Afro-Madagascarian (Af-Ma), African pluriregional (AP), Tropical African (T Af), East and South African (EA-SA), East African (EA), Guineo-Congolian and Lake Victoria Regional Mosaic (GC-V), Afro-montane (Mo), Lake Victoria Regional Mosaic (V), Endemic to the Western Graben District (E), As (Asia), Aus (Australia), Equatorial Africa (Eq Af), Madagascar (Mad), Mediterranean region (Med), North Africa (N Af), North America (N Am), Tropical America (T Am) and West Africa (W Af). Origin status (OS): native species with a continuous distribution including Burundi (N1 ), widespread species that might be considered as native according to Bean (2007) (N2 ), introduced species, introduced species with known origin (I1 ) and widespread species not considered native (I2 ). Ecological groups (EG): ruderal species (R), ruderal species in wetland (RW ), savanna species (S), psammophile species (P), sclerophyllous forest species (SF) wetland species (W), hygrophilous forest species (HF) and cultivated species (Cu). LF GD GO OS EG Family Species Th Ch Th Th Ph Ph Ch Th Th Ch Th Ch Ch Th Ch G G Th Ph Th Th T Af Pan Af-Ma AP T Af V V Pal V T Af Pan Pan Af-Ma T Af Af-Ma Pan Pan Pan Pan T Af T Af T Af AP Af-Ma AP T Af V V AP V T Af T Am AP Af-Ma T Af Af-Ma T Am T Am T Am As T Af T Af N1 N1 N1 N1 N1 N1 N1 N1 N1 N1 I1 N1 N1 N1 N1 I1 I1 I1 I1 N1 N1 R SF R R S S R R R R R R HF W W Cu Cu R Cu S R Cyperaceae Fabaceae Malvaceae Malvaceae Fabaceae Fabaceae Euphorbiaceae Euphorbiaceae Euphorbiaceae Euphorbiaceae Asteraceae Amaranthaceae Asteraceae Poaceae Fabaceae Agavaceae Agavaceae Asteraceae Fabaceae Orobanchaceae Orobanchaceae Abildgaardia hispidula (Vahl) Lye subsp. hispidula Abrus precatorius subsp. africanus Verdc. Abutilon angulatum (Guill. & Perr.) Mast. Abutilon mauritianum (Jacq.) Medic. Acacia hockii De Wild. Acacia polyacantha subsp. campylacantha (Hochst. ex A. Rich.) Brenan Acalypha bipartita Müll.Arg. Acalypha brachystachya Hornem. Acalypha ciliata Forssk. Acalypha ornata Hochst. ex A.Rich. Acanthospermum hispidum DC. Achyranthes aspera L. var. aspera L. Acmella caulirhiza Del. Acroceras amplectens Stapf. Aeschynomene schimperi A.Rich. Agave americana L. Agave sisalana (Engelm.) Perrine Ageratum conyzoides L. Albizia chinensis (Osbeck) Merr. Alectra sessiliflora var. senegalensis (Benth.) Hepper Alectra vogelii Benth. J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 260 LF GD GO OS EG Family Species Ch Th Th Th Th Th Th Th Th Th H Ch Ph Th G Ch Th Th H Th Th Th Th Ch Ch Ph Th G Th Ph Ph Th Th Th Th Th Ph Ch Ch Th Th Ph Ph Ch Ch G Ch Ph Ph Th Ch Th Ph Th Ph Ch Ch Ph Th Ch Ch Ch Th Th Th Th Th Th Ch Ch Ch Th Ph Th Th Ph Pan Pan Af-As Pan Pan Cos Cos Cos Cos AP Af-Ma V Pan T Af Pan Pan Cos Pan Pan V V T Af V Pan V Af-As T Af Pan Af-Ma Pan Pan Pan Cos Pan Pan Pan Pan E Af-As V T Af V Pan Pan Pan Cos Pan Pan Pan Pan Pan Pan Pan Pan Pan Pan Cos Pan Af-Ma Af-As Pan Pan Af-Ma Cos EA Cos Pan Pan T Af AP V Pan Cos Cos Pan GC-V T Am As Af-As T Am T Am T Am T Am T Am T Am AP Af-Ma V T Am Eq Af T Am T Am T Am T Am AP V V T Af V Af-As V Af-As T Af As Af-Ma Mad As T Am T Af T Am T Am Af-As T Am E T Af V T Af V T Am As T Am T Am T Am T Am T Am T Am As T Am As T Am T Am AP Mad T Am Af-Ma AP As Pal Mad T Am EA T Af AP T Am T Af AP V AP As T Am T Af GC-V I1 I1 N1 I1 I1 I1 I1 I1 I1 N1 N1 N1 I1 I1 I1 I1 I1 I1 N1 N1 N1 N1 N1 N1 N1 N1 N1 I1 N1 I1 I1 I1 N1 I1 I1 N1 I1 N1 N1 N1 N1 N1 I1 I1 I1 I1 I1 I1 I1 I1 I1 I1 I1 I1 I1 N1 I1 I1 N1 N1 I1 N2 I1 I1 N1 N1 N1 I1 N1 N1 N1 N1 I1 I1 N1 N1 R Rw R R R R R R R W R R Cu R Cu R Cu R S S R S HF R R S Rw Cu Rw Cu Cu R R R R R Cu S R R R S Cu Cu R Cu R Cu Cu R R R Cu R Cu S R Cu R P R R R R R R R R R SF SF R Cu R R SF Amaranthaceae Amaranthaceae Fabaceae Amaranthaceae Amaranthaceae Amaranthaceae Amaranthaceae Amaranthaceae Amaranthaceae Lythraceae Poaceae Commelinaceae Annonaceae Poaceae Araceae Polygonaceae Fabaceae Papaveraceae Poaceae Aristolochaceae Asteraceae Asteraceae Asteraceae Acanthaceae Acanthaceae Salvadoraceae Fabaceae Poaceae Lamiaceae Fabaceae Fabaceae Asteraceae Oxalidaceae Nyctaginaceae Nyctaginaceae Poaceae Nyctaginaceae Poaceae Poaceae Poaceae Poaceae Capparaceae Fabaceae Fabaceae Fabaceae Cannaceae Solanaceae Caricaceae Apocynaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Lauraceae Apocynaceae Meliaceae Amaranthaceae Poaceae Apiaceae Fabaceae Fabaceae Chenopodiaceae Chenopodiaceae Poaceae Poaceae Asteraceae Poaceae Menispermaceae Vitaceae Cucurbitaceae Rutaceae Capparaceae Capparaceae Verbenaceae Alternanthera pungens Kunth Alternanthera sessilis (L.) DC. Alysicarpus glumaceus (Vahl) DC. Amaranthus caudatus L. Amaranthus dubius Mart. ex Thell. Amaranthus graecizans L. Amaranthus hybridus L. Amaranthus spinosus L. Amaranthus viridis L. Ammannia prieuriana Guill. & Perr. Andropogon eucomus Nees Aneilema spekei C.B.Clarke Annona muricata L. Anthephora cristata (Döll) Hack. ex De Wild. & T.Durand Anthurium andraeanum André Antigonon leptopus Hook. & Arn. Arachis hypogaea L. Argemone mexicana L. Aristida adscensionis L. Aristolochia petersiana Klotzsch Aspilia helianthoides (Schumach. & Thonn.) Oliv. & Hiern Aspilia kotschyi (Sch.Bip.) Oliv. Aspilia pluriseta Schweinf. Asystasia gangetica (L.) T. Anders. Asystasia schimperi T. Anderson Azima tetracantha Lam. Bakerophyton lateritium (Harms) Hutch. ex Maheshw. Bambusa vulgaris Schrader Basilicum polystachyon (L.) Moench Bauhinia monandra Kurz Bauhinia purpurea L. Bidens pilosa L. Biophytum petersianum Klotzsch Boerhavia diffusa L. Boerhavia erecta L. Bothriochloa insculpta (Hochst. ex A.Rich.) A.Camus Bougainvillea spectabilis Willd. Brachiaria decumbens var. ruziziensis (R. Germ. & Evrard) Ndab. Brachiaria deflexa (Schumach.) C.E.Hubb. ex Robyns Brachiaria leersioides (Hochst.) Stapf Brachiaria scalaris Pilg. Cadaba farinosa subsp. adenotricha (Gilg & Gilg-Ben.) R.A. Graham Caesalpinia pulcherrima (L.) Sw. Cajanus cajan (L.) Millsp. Calopogonium mucunoides Desv. Canna indica L. Capsicum frutescens L. Carica papaya L. Cascabela thevetia (L.) Lippold Cassia hirsuta L. Cassia obtusifolia L. Cassia occidentalis L. Cassia siamea Lam. Cassia sophera L. Cassia spectabilis DC. Cassytha filiformis L. Catharanthus roseus (L.) G.Don Cedrela odorata L. Celosia trigyna L. Cenchrus biflorus Roxb. Centella asiatica (L.) Urb. Chamaecrista absus (L.) H.S.Irwin & Barneby Chamaecrista pratensis (R.Vig.) Du Puy Chenopodium ambrosioides L. Chenopodium ugandae (Aellen) Aellen Chloris pilosa Schum. Chloris pycnothrix Trin. Chrysanthellum indicum subsp. afroamericanum B.L. Turner Chrysochloa hindsii C.E. Hubbard Cissampelos mucronata A.Rich. Cissus quadrangularis L. Citrullus lanatus (Thunb.) Matsumara & Staples Citrus limon (L.) Burm.f. Cleome gynandra L. Cleome rutidosperma DC Clerodendrum schweinfurthii Gürke J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 261 LF GD GO OS EG Family Species Ch Th G Ch Ch Ch Ch Ch Ph Th Th Th Th Ch Th Ch Th Th Th Ch Th Th Ch Th Th Ph Ch Ch Ch Th G G Th G G Th G G G G G Th Th Ch Th Th Th Ch Ph G Th Th Th Th Th Th Ch Ch Th Th Th Ph Th Th Th Th Th Th Th Ch Th H Th G Ph Ph Th Th Cos V Pan Af-As EA-SA Cos Af-Ma V V Pan Cos Mo Pal T Af Pan Pal T Af Pan Af-Ma Pan Pan AP T Af T Af Cos V V EA-SA Af-As Pan GC-V Pan Cos Pan Af-Ma Pan Pan Af-Ma Af-Ma Af-Ma Cos Pan Cos V Pan Cos Pan Pan Pan Pan Pan Pan Pan V Af-Ma Af-As Pan V Pan Pan Pan Pan Cos V Pan Af-Ma EA Pan V EA-SA AP Pan Pan Af-As Af-Ma Pal Pan Pan EA V As T Af EA-SA As Af-Ma V V T Am As Mo Pal T Af T Af Pal T Af T Af T Af T Am T Am AP T Af T Af T Am V V EA-SA T Af Pan GC-V Pan Med Pan Af-Ma Eur T Am Af-Ma Af-Ma Af-Ma As T Am Cos V As As T Am Pan Pal T Am T Af As T Af V Af-Ma AP Pan V EA T Am T Am Eq Af As V Af-As Af-Ma EA Pan V EA-SA AP Af-As Af-As Af-As Af-Ma Aus T Am T Am N1 N1 I1 N1 N1 I1 N1 N1 N1 I1 I1 N1 N2 N1 N1 I2 N1 N1 N1 I1 I1 N1 N1 N1 I1 N1 N1 N1 N1 I2 N1 N2 I1 N2 N1 I1 I1 N1 N1 N1 I1 I1 I2 N1 I1 I1 I1 N2 N2 I1 N1 I1 N1 N1 N1 N1 N2 N1 N1 I1 I1 I1 I1 N1 N1 N1 N1 I2 N1 N1 N1 N1 N1 N1 N1 I1 I1 I1 R R Cu R R Rw R R S R R R R S R R S R R R R R R R Cu S R S R R R W Rw R W R W W R W R R Rw SF R R R R S Cu R R R R R R Rw R Rw W Rw Cu R R R R R R R R R R R W S Cu R R Fabaceae Fabaceae Araceae Commelinaceae Commelinaceae Commelinaceae Commelinaceae Commelinaceae Burseraceae Asteraceae Malvaceae Asteraceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Cucurbitaceae Cucurbitaceae Araliaceae Commelinaceae Asclepiadaceae Poaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Vitaceae Poaceae Solanaceae Fabaceae Fabaceae Fabaceae Agavaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Caryophulaceae Acanthaceae Poaceae Poaceae Asteraceae Arecaceae Poaceae Asteraceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Fabaceae Myrtaceae Euphorbiaceae Euphorbiaceae Clitoria ternatea L. Clitoria ternatea L. var. angustifolia Hochst. ex Baker f. Colocasia esculenta (L.) Schott Commelina africana L. Commelina benghalensis L. var. benghalensis Commelina diffusa Burm.f. Commelina latifolia Hochst. ex A.Rich. Commelina nigritana Benth. Commiphora habessinica (O.Berg) Engl. Conyza bonariensis (L.) Cronquist Corchorus olitorius L. Crassocephalum montuosum (S. Moore) Milne-Rendle Crotalaria calycina Schrank Crotalaria chrysochlora Baker f. ex Harms Crotalaria goreensis Guill. & Perr. Crotalaria laburnifolia L. subsp. laburnifolia Crotalaria lachnophora A.Rich. Crotalaria ochroleuca G.Don Crotalaria ononoides Benth. Crotalaria pallida var. obovata (G. Don) Polhill Crotalaria retusa var. retusa Crotalaria spartea Baker Crotalaria spinosa Hochst. ex Benth. Cucumis maderaspatanus L. Cucurbita pepo L. Cussonia arborea Hochst. ex A.Rich. Cyanotis lanata Benth. Cynanchum schistoglossum Schltr. Cynodon nlemfuensis Vanderyst var. nlemfuensis Cyperus amabilis Vahl Cyperus angolensis Boeckeler Cyperus articulatus L. Cyperus difformis L. Cyperus distans L.f. Cyperus dives Del. Cyperus esculentus L. Cyperus haspan L. Cyperus latifolius Poir. Cyperus macrocarpus (Kunth) Boeckeler Cyperus maculatus Boeckeler Cyperus rotundus L. Cyperus sphacelatus Rottb. Cyperus squarrosus L. Cyphostemma adenocaule (Steud. ex A.Rich.) Desc. ex Wild & R.B.Drumm. Dactyloctenium aegyptium (L.) Willd. Datura stramonium L. Desmodium tortuosum (Sw.) DC. Desmodium triflorum (L.) DC. Desmodium velutinum (Willd.) DC. Dieffenbachia seguine (Jacq.) Schott Digitaria abyssinica (Hochst. ex A.Rich.) Stapf Digitaria longiflora (Retz.) Pers. Digitaria nuda Schumach. Digitaria pearsonii Stapf Digitaria perrottetii (Kunth) Stapf Digitaria ternata (A.Rich.) Stapf Drymaria cordata (L.) Willd. Ex Roem. & Schult. Dyschoriste radicans Nees Echinochloa colona (L.) Link Echinochloa crus-pavonis (Kunth) Schult. Eclipta prostrata (L.) L. Elaeis guineensis Jacq. Eleusine indica (L.) Gaertn. subsp. indica Emilia caespitosa Oliv. Eragrostis amabilis (L.) Wight & Arn. Eragrostis aspera (Jacq.) Nees Eragrostis caespitosa Chiov. Eragrostis ciliaris (L.) R. Br. Eragrostis exasperata Peter Eragrostis heteromera Stapf Eragrostis patens Oliv. Eragrostis tenuifolia (A.Rich.) Steud. Eragrostis tremula Steud. Eriochloa fatmensis (Hochst. & Steud.) Clayton Eriosema psoraloides (Lam.) G. Don Eucalyptus globulus Labill. Euphorbia heterophylla L. Euphorbia hirta L. J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 262 LF GD GO OS EG Family Species Th Th Ch Ph Ch Ph Th Ph H Th G Ch Ch Ch Ph Ph Th Th Ch H Ch Th Ch Th Th Ph Th G H H H H Th G Th Ch Ch Ch Th Th Th Th Ch G G G Th Ch Ch Ch G Ph G Th Ch Ch G G G Th Th Ch Ch Ch Th G Th H Ph Th Ch Ch Ch Th Ch Ph G G Af-As Pan Pan Pan Pan Pan Pan Pan Pan Cos Pan Pan Pan Pan Pan V Pan Af-As T Af Cos Pan Pan Af-Ma T Af Pal AP V T Af Pal V Pan Pan Pan Pan V Af-As V V T Af Pan T Af T Af Pan Pan T Af Pan Pan Pan Pan Pan Pan Pan Pan V Pan T Af Af-As Af-Ma T Af Pan Af-Ma GC-V Af-Ma Pan Pan Pan Pan Af-As Pan Af-Ma Af-Ma Af-Ma T Af Pan Pan Pan Pan Pan Af-As T Am As EA T Am Af-As As AP Pan T Am Af-As T Af T Am T Am Aus V Pan Af-Ma T Af Cos Af-As Pan Af-Ma T Af Af-As AP V T Af Af-As V AP T Af T Am T Am V Af-As V V T Af Pal T Af T Af Af-As T Am T Af As Af-As T Am Pan As Pan T Am T Am V Mad T Af Af-As Af-Ma T Af Pal Af-Ma GC-V Af-Ma T Am T Af Pan T Af Af-As T Am Af-Ma Af-Am Af-Ma T Af As T Am As T Am T Am N1 I1 I1 N1 I1 N1 I1 N1 N2 I1 N1 N1 I1 I1 I1 N1 I2 N1 N1 N2 N1 N2 N1 N1 N1 N1 N1 N1 N1 N1 N1 N1 I1 I1 N1 N1 N1 N1 N1 N2 N1 N1 N1 I1 N1 I1 N1 I1 N2 I1 N2 I1 I1 N1 I1 N1 N1 N1 N1 N2 N1 N1 N1 I1 N1 N2 N1 N1 I1 N1 N1 N1 N1 I1 I1 I1 I1 I1 R R R S W SF W S W R SF R R Cu Cu S R R W S R S SF R R SF R W S S S S R R R R R S R R S R R Cu R R R R P Cu HF Cu Cu R R R R Rw W R R SF SF R R W R S Cu R W W W R R Cu Cu Cu Euphorbiaceae Euphorbiaceae Euphorbiaceae Euphorbiaceae Convolvulaceae Moraceae Cyperaceae Euphorbiaceae Cyperaceae Asteraceae Colchicaceae Fabaceae Amaranthaceae Malvaceae Proteaceae Malvaceae Poaceae Boraginaceae Poaceae Poaceae Convolvulaceae Malvaceae Malvaceae Malvaceae Malvaceae Lamiaceae Violaceae Acanthaceae Poaceae Poaceae Poaceae Poaceae Lamiaceae Poaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Convolvulaceae Convolvulaceae Convolvulaceae Convolvulaceae Convolvulaceae Convolvulaceae Convolvulaceae Convolvulaceae Bignoniaceae Euphorbiaceae Acanthaceae Crassulaceae Malvaceae Cyperaceae Cyperaceae Cyperaceae Cyperaceae Asteraceae Cucurbitaceae Cucurbitaceae Verbenaceae Urticaceae Poaceae Lamiaceae Poaceae Fabaceae Lamiaceae Onagraceae Onagraceae Onagraceae Cucurbitaceae Fabaceae Anacardiaceae Euphorbiaceae Euphorbiaceae Euphorbia inaequilatera Sond. Euphorbia prostrata Aiton Euphorbia thymifolia L. Euphorbia tirucalli L. Evolvulus nummularius (L.) L. Ficus exasperata Vahl Fimbristylis dichotoma (L.) Vahl. Flueggea virosa (Roxb. ex Willd.) Voigt Fuirena umbellata Rottb. Galinsoga parviflora Cav. Gloriosa superba L. Glycine javanica L. Gomphrena celosioides Mart. Gossypium hirsutum L. Grevillea robusta A.Cunn. ex R.Br. Grewia similis K.Schum. Hackelochloa granularis (L.) Kuntze Heliotropium ovalifolium Forssk. Hemarthria natans Stapf Heteropogon contortus (L.) R & Sch. Hewittia malabarica (L.) Suresh Hibiscus cannabinus L. Hibiscus diversifolius Jacq. subsp. diversifolius Hibiscus mechowii Garcke Hibiscus surattensis L. Hoslundia opposita Vahl Hybanthus enneaspermus (L.) F.Muell. var. enneaspermus Hygrophila auriculata (Schumash.) Heine Hyparrhenia filipendula (Hochst.) Stapf Hyparrhenia madaropoda Clayton Hyparrhenia rufa (Nees) Stapf Hyperthelia dissoluta (Steud.) Clayton Hyptis suaveolens Poir. Imperata cylindrica (L.) Raeuschel Indigofera ambelacensis Schweinf. Indigofera arrecta Hochts. Ex A. Rich. Indigofera colutea (Burm.f.) Merr. var. colutea Indigofera drepanocarpa Taub. Indigofera fulvopilosa Brenan Indigofera hirsuta L. Indigofera secundiflora Poir. Indigofera simplicifolia Lam. Indigofera spicata Forssk. Ipomoea batatas Poir Ipomoea blepharophylla Hallier f. Ipomoea cairica (L.) Sweet Ipomoea eriocarpa R. Br. Ipomoea hederifolia L. Ipomoea pes-caprae (L.) R.Br. subsp. brasiliensis (L.) Ooststr. Ipomoea quamoclit L. Ipomoea rubens Choisy Jacaranda mimosifolia D.Don Jatropha curcas L. Justicia matammensis Oliv. Kalanchoe pinnata (Lam.) Pers. Kosteletzkya grantii (Mast.) Garcke Kyllinga bulbosa P.Beauv. Kyllinga erecta Schumach Kyllinga sphaerocephala Boeckeler Kyllinga squamulata Thonn. ex Vahl Lactuca inermis Forssk. Lagenaria rufa (Gilg) C.Jeffrey Lagenaria sphaerica (Sond.) Naudin Lantana camara L. Laportea aestuans (L.) Chew. Leersia hexandra Sw. Leonotis nepetifolia (L.) R.Br. Leptochloa obtusiflora Hochst. Leucaena leucocephala (Lam.) De Wit. Leucas martinicensis (Jacq.) R.Br. Ludwigia abyssinica A. Rich. Ludwigia leptocarpa (Nutt.) Hara Ludwigia stenorraphe (Branan) Hara Luffa cylidrica (L.) Roem. Macroptilium atropurpureum (DC.) Urb. Mangifera indica L. Manihot esculenta Crantz Manihot glaziovii Müll.Arg. J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 263 LF GD GO OS EG Family Species G G H G Ch H Th Ch Ch Ch Ph Ch Ch Th Th Ph Ch Th G G Th Th Ch Th Ch Th Th Ch Th Ch G Th Th H G H G Ch Ch G Ch Ch H H H Ch Th Th Ph Th Th G Ch Th Th Ch Ch Ph Ph Ph Ch Ph Th Th G G Ch Ch Th Th Ch Ph Th Ch Ph G G Th T Af Af-As GC-V Af-As V Pan Pan V Pan Pan Pan Pan Cos Pan Pan Pal T Af Pan Pan Pan Pan Pan Pan Cos Pal Pan Af-As Pan Pan Cos Pan AP Af-As Pan Pan T Af Pan Pan Pan Pan Pan Pan Pan Pan Mo EA-SA Pan Af-Ma Pan Pan T Af Af-Ma Pan Pan Af-As Cos Pan Pan Af-As Af-As Af-As Pan V T Af Af-As T Af E Cos Cos Cos Af-Ma Af-Ma Pan V Pan Pan Cos V T Af Af-As GC-V Af-As V Af Pan V As T Am T Am T Am T Am T Am Pan As T Af As As As T Am T Am As As Af-As Af-As Af-As Pan As As T Am AP Af-As Af-Ma T Am T Af T Am T Am T Am T Am T Am As Af-Ma T Af Mo EA-SA Af-As Af-Ma T Am T Am T Af Af-Ma T Am T Am Af-Ma T Am T Am T Am AP V Af-As T Am V T Af Af-As T Af E T Am T Am T Am Af-Ma Af-Ma Pan V T Am Pan Cos V N1 N1 N1 N1 N1 N1 I2 N1 I1 I1 I1 I1 I1 I1 I2 I1 N1 I1 I1 I1 I1 I1 I1 I1 N1 N1 N1 I2 I1 I1 I1 N1 N1 N1 I1 N1 I1 I1 I1 I1 I1 I1 N1 N1 N1 N1 N1 N1 I1 I1 N1 N1 I1 I1 N1 I1 I1 I1 N1 N1 N1 I1 N1 N1 N1 N1 N1 I1 I1 I1 N1 N1 I2 N1 I1 N2 N2 N1 R R R R R S R R R R HF R R R R Cu SF R Cu Cu R Cu R R R R R R Cu R R R R S Rw Rw W R R W R Cu S Rw S S Rw R Cu Cu SF W P R R R Cu Cu W W W Cu R R R W R R R R R W R S Cu SF W S Cyperaceae Cyperaceae Cyperaceae Cyperaceae Malvaceae Poaceae Malvaceae Convolvulaceae Fabaceae Fabaceae Fabaceae Fabaceae Nyctaginaceae Rubiaceae Molluginaceae Moringaceae Fabaceae Fabaceae Musaceae Musaceae Solanaceae Solanaceae Lamiaceae Lamiaceae Rubiaceae Rubiaceae Rubiaceae Poaceae Poaceae Oxalidaceae Oxalidaceae Polygonaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Passifloraceae Euphorbiaceae Poaceae Poaceae Poaceae Asclepiadaceae Rubiaceae Poaceae Lauraceae Fabaceae Acanthaceae Poaceae Verbenaceae Phyllanthaceae Phyllanthaceae Solanaceae Solanaceae Fabaceae Asteraceae Asteraceae Asteraceae Apocynaceae Polygalaceae Polygalaceae Polygalaceae Polygonaceae Portulacaceae Portulacaceae Portulacaceae Portulacaceae Urticaceae Fabaceae Asteraceae Fabaceae Myrtaceae Pteridaceae Poaceae Fabaceae Mariscus cylindrystachyus Steud. Mariscus dubius (Rottb.) Kük. ex C.E.C.Fisch. subsp. coloratus (Vahl) Lye Mariscus dubius (Rottb.) Kük. var. macrocephalus (C.B.Clarke) Chiov. Mariscus maderaspatanus (Willd.) Napper Melhania velutina Forssk. Melinis repens (Willd.) Zizka subsp. repens Melochia corchorifolia L. Merremia tridentata (L.) Hallier f. var. angustifolia (Jacq.) Ooststr. Mimosa diplotricha var. inermis (Adelb.) Verdc. Mimosa invisa Mart. ex Colla Mimosa pigra L. Mimosa pudica L. Mirabilis jalapa L. Mitracarpus hirtus (L.) DC. Mollugo nudicaulis Lam. Moringa oleifera Lam. Mucuna poggei Taub. Mucuna pruriens (L.) DC. var.pruriens Musa acuminata Colla Musa paradisiaca L. Nicandra physalodes (L.) Gaertn. Nicotiana tabacum L. Ocimum americanum L. Ocimum basilicum L. Oldenlandia affinis (Roem. & Schult.) DC. Oldenlandia corymbosa var. corymbosa. Oldenlandia herbacea (L.) Roxb. Oplismenus burmannii (Retz.) P.Beauv. Oryza sativa L. Oxalis corniculata L. Oxalis latifolia Kunth Oxygonum sinuatum (Hochst. & Steud. ex Meisn.) Dammer Panicum atrosanguineum Hochst. ex A.Rich. Panicum maximum Jacq. Panicum repens L. Panicum trichocladum K.Schum. Paspalidium geminatum (Forssk.) Stapf Paspalum conjugatum P.J.Bergius Paspalum notatum Flüggé Paspalum scrobiculatum L. Passiflora foetida L. Pedilanthus tithymaloides (L.) A.Poit. Pennisetum polystachion (L.) Schult. subsp. polystachion Pennisetum purpureum Schumach. Pennisetum trachyphyllum Pilg. Pentarrhinum insipidum E.Mey. Pentodon pentandrus (Schum. & Thonn.) Vatke Perotis patens Gand. Persea americana Mill Phaseolus vulgaris L. Phaulopsis imbricata (Forssk.) Sweet Phragmites mauritianus Kunth Phyla nodiflora (L.) Greene Phyllanthus amarus Schumach. & Thonn. Phyllanthus nummulariifolius Poir. Physalis lagascae Roem. & Schult. Physalis peruviana L. Pithecellobium dulce (Roxb.) Benth. Pluchea dioscoridis (L.) DC. Pluchea ovalis (Pers.) DC. Pluchea sordida Oliv. & Harms Plumeria rubra L. Polygala albida Schinz Polygala arenaria Willd. Polygala erioptera DC. Polygonum pulchrum Blume Portulaca centrali-africana R.E.Fr. Portulaca grandiflora Hook. Portulaca oleracea L. Portulaca quadrifida L. Pouzolzia guineensis Benth. Pseudarthria hookeri Wight & Arn. Pseudoconyza viscosa (Mill.) D’Arcy Pseudoeriosema borianii subsp. borianii Psidium guajava L. Pteris vittata L. Hyparrhenia filipendula (Hochst.) Stapf Rhynchosia micrantha Harms J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 264 LF GD GO OS EG Family Species Th Ch Th Ph Th G Ph Th Th Ph Ch Th Th Th Ch Ch Ch Ch Ch Ch Th Ch Ch Th Th Ch H H H Ph Th Th Th H H Ch Th Ch Th Ch Ch Th Th Th Ch Ph Ph Ph Ch Ch Th Th Th Th Ch Ch G Ch Ph Th Th Ch Ch Ch Ch Th Ch Th Ch Th G Th Ch Pan AP Pan Cos Pan Pan Pan V Af-As Pan AP AP Cos Cos Pan Pan Pan Pan Pan Pan Af-As Af-Ma Af-As Cos Cos Mo Pan Pan AP GC-V Af-As EA-SA Pan AP Pan Pan Pan Af-As Pan Pan Cos Af-Ma Pal AP Pan Pan Pan Pan Pan V Cos Cos Pal Pan Pan V Pan Pan AP Pan V Pan Af-Ma Af-Ma Pan T Af Pan T Af AP Cos Pan Cos Af-As T Am AP T Am N Af As As T Am V T Af Pal AP AP As Med T Am T Am Pan T Am Af-As Pan AP Af-Ma AP T Am As Mo AP AP AP GC-V Af-As EA-SA As AP Af-As T Am Af-As As T Am Af-As T Am Af-Ma T Af AP As As Mad W Af T Am V N Am AP Pal T Am T Am V Pan T Af AP As V Pan T Af Af-Ma AP Eq Af Pan T Af AP N Am T Am T Am Af-As I1 N1 I1 I1 I1 I1 I1 N1 N1 N2 N1 N1 I1 I1 I1 I1 N2 I1 N1 N2 N1 N1 N1 I1 I1 N1 N1 N1 N1 N1 N1 N1 I1 N1 N1 I1 N1 I1 I1 N1 I1 N1 N1 N1 I1 I1 I1 I1 I1 N1 I1 N1 I2 I1 I1 N1 N2 N1 N1 I1 N1 N2 N1 N1 N1 I1 N2 N1 N1 I1 I1 I1 N1 R R R R R Cu Cu R R HF R R S R Cu R R R R R R R R Cu R R S Cu R Cu R R Rw R R R R R R R R R R R R Cu Cu Cu R SF R R R R R SF W R SF R R W R R R Cu SF R R R Cu Cu R Fabaceae Fabaceae Rubiaceae Euphorbiaceae Poaceae Poaceae Sapindaceae Pedaliaceae Fabaceae Fabaceae Poaceae Poaceae Poaceae Poaceae Commelinaceae Malvaceae Malvaceae Malvaceae Malvaceae Malvaceae Solanaceae Solanaceae Solanaceae Solanaceae Solanaceae Asteraceae Poaceae Poaceae Poaceae Bignoniaceae Rubiaceae Rubiaceae Sphenocleaceae Poaceae Poaceae Verbenaceae Orobanchaceae Fabaceae Asteraceae Portulacaceae Portulacaceae Fabaceae Fabaceae Fabaceae Fabaceae Combretaceae Combretaceae Combretaceae Asteraceae Euphorbiaceae Aizoaceae Zygophyllaceae Boraginaceae Asteraceae Malvaceae Fabaceae Typhaceae Malvaceae Asteraceae Asteraceae Asteraceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Malvaceae Asteraceae Araceae Poaceae Cucurbitaceae Rhynchosia minima (L.) DC. Rhynchosia sublobata (Schumach. & Thonn.) Meikle Richardia scabra L. Ricinus communis L. Rottboellia cochinchinensis (Lour.) Clayton Saccharum officinarum L. Sapindus saponaria L. Sesamum angustifolium (Oliv.) Engl. Sesbania macrantha Welw. ex E.Phillips & Hutch. Sesbania sesban (L.) Merr. Setaria homonyma (Steud.) Chiov. Setaria incrassata (Hochst.) Hack. Setaria pumila (Poir.) Roem. & Schult. Setaria verticillata (L.) P. Beauv. Setcreasea purpurea Boom Sida acuta Burm. f. Sida alba L. Sida cordifolia L. Sida rhombifolia L. Sida urens L. Solanum campylacanthum Dunal Solanum dasyphyllum Schumach. & Thonn. Solanum incanum L. Solanum lycopersicum L. Solanum nigrum L. Sonchus luxurians (R.E.Fr.) C.Jeffrey Sorghum arundinaceum (Desv.) Stapf Sorghum bicolor (L.) Moench Sorghum versicolor Andersson Spathodea campanulata subsp. nilotica (Seem.) Bidgood Spermacoce pusilla Wall. Spermacoce senensis (Klotzsch) Hiern Sphenoclea zeylanica Gaertn Sporobolus molleri Hack. Sporobolus pyramidalis P. Beauv. Stachytarpheta indica (L.) Vahl Striga gesnerioides (Willd.) Vatke Stylosanthes fruticosa (Retz.) Alston Synedrella nodiflora Gaertn. Talinum portulacifolium (Forsk.) Ascher. ex Schw. Talinum triangulare (Jacq.) Willd. Tephrosia linearis (Willd.) Pers. Tephrosia nana Kotschy ex Schweinf. Tephrosia pumila (Lam.) Pers. Tephrosia purpurea (L.) Pers. Terminalia catappa L. Terminalia mantaly H.Perrier Terminalia superba Engl. & Diels Tithonia diversifolia (Hemsl.) A.Gray Tragia brevipes Pax Trianthema portulacastrum L. Tribulus terrestris L. Trichodesma zeylanicum (Burm.f.) R.Br Tridax procumbens L. Triumfetta rhomboidea Jacq. Tylosema fassoglensis (Schweinf.) Torre & Hillc. Typha domingensis (Pers.) Steud. Urena lobata L. Vernonia amygdalina Delile Vernonia cinerea (L.) Less. Vernonia melanocoma C.Jeffrey Vigna luteola (Jacq.) Benth. Vigna oblongifolia A.Rich. var. parviflora (Baker) Verdc. Vigna parkeri Baker Vigna unguiculata (L.) Walp. var. unguiculata Vigna unguiculata subsp. sesquipedalis (L.) Verdc. Vigna vexillata (L.) A. Rich. Vigna vexillata (L.) A.Rich. var. angustifolia (Schumach. & Thonn.) Baker Wissadula rostrata (Schumach.) Hook.f. Xanthium strumarium L. Xanthosoma sagittifolium (L.) Schott Zea mays L. Zehneria scabra (L.f.) Sond. J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 Plant assemblages TF11 Ecological group % of species R S P SF HF W Cu Ecological group R S P SF HF W Cu Number of species 75 5 1 1 2 8 8 TF12 64 8 1 4 1 7 15 TF21 83 5 0 6 0 3 3 FT22 66 11 0 4 1 9 9 72 19 0 2 2 2 3 TF24 74 12 0 4 1 1 8 TF3 79 0 0 5 0 7 9 TF4 71 7 3 3 4 9 3 All species 62 9 1 5 1 8 14 % of species mean cover 96 3 0 0 0 1 0 94 3 0 0 0 2 1 98 1 0 0 0 1 0 91 2 0 1 0 5 1 11 88 0 1 0 0 0 20 79 0 0 0 0 1 98 0 0 0 0 1 1 71 1 25 0 1 2 0 92 5 1 0 0 1 1 176 337 36 90 131 169 43 113 404 the Appendix B. 8.62 < 2df42, ˛5% = 58.1). For details about the plant assemblages (TF11, TF12, TF21, TF22, TF23, TF24, TF3, TF4), see Table 1. (X 2 = 3.56 < 2df28, ˛5% = 41.34, X 2 = Geographical distribution (GD), geographical origin and origin status of 404 species of the vegetation of Bujumbura (number of species). Cosmopolitan (Cos), Paleotropical (Pal), Pantropical (Pan), Afro-Asian (Af-As), Afro-Madagascarian (Af-Ma), African pluriregional (AP), Tropical African (T Af), East and South African (EA-SA), East African (EA), Guineo-Congolian and Lake Victoria Regional Mosaic (GC-V), Afromontane (Mo), Lake Victoria Regional Mosaic (V) and Endemic to Western graben district (E). Native species (N): with a continuous distribution including Burundi (N1 ), widespread species that might be considered as native (N2 ). Introduced species (I): with known origin (I1 ) and widespread species with unknown origin not considered native (I2 ). Life form and phytogeographical spectra of the species composing the plant assemblages in Bujumbura. Life forms: therophytes (Th), chamaephytes (Ch), geophytes (G), hemicrytophytes (H), phanerophytes (Ph). Distribution: widespread species (WS), African species (Af), Endemic to the Lake Victoria Regional Mosaic (V) and Endemic to Western Graben District (E). Origin status: Native species (N), Introduced species (I). Life form, distribution and origin status spectra are not different between TF12 assemblages Appendix D. Appendix C. TF11 plant 2.23 < 2df21, ˛5% = 32.67 and X 2 = 1.07 < 2df7, ˛5% = 14.07 respectively). For details about the plant assemblages, see Table 1. Ecological spectra of the species composing plant assemblages of Bujumbura (% of species and % of species mean cover): ruderal species (R), savanna species (S), psammophile species (P), sclerophyllous forest species (SF), wetland species (W), hygrophilous forest species (HF) and cultivated species (Cu). Percentages of species mean cover differ between plant assemblages(X 2 = 91.17 > 2df42, ˛5% = 58.1), but % of species are not diffent (X 2 = Plant assemblages FT23 265 TF21 TF22 TF23 TF24 TF3 TF4 All plots % of species Life form Th Ch G H Ph 44 29 13 5 9 42 30 11 6 11 33 45 6 6 6 36 28 11 13 12 47 28 6 8 11 50 26 6 8 10 32 42 12 0 14 44 35 8 5 8 41 29 12 6 12 Distribution WS Af V E 71 21 7 1 69 22 8 1 83 14 0 3 72 20 8 0 66 18 15 1 72 18 9 1 86 12 2 0 71 17 12 0 67 24 9 0 Origin status I N 48 52 47 53 61 39 41 59 37 63 44 56 58 42 44 56 43 57 Number of species 48 337 36 90 131 169 43 113 404 J. Bigirimana et al. / Landscape and Urban Planning 100 (2011) 251–267 266 Geographical origin Origin status GD I1 Cos Pan Pal Af-As Af-Ma AP T Af Mo EA-SA GC-V EA V E Total Cos Pan Pal Af-As Af-Ma AP T Af Mo EA-SA EA GC-V V E 34 123 2 1 1 – 2 – – – – – – 3 – – – – – – – – – – – – – 23 – – – – – – – – – – – – 5 3 – – – – – – – – – – – 15 3 15 – – – – – – – – – – 2 – 2 28 – – – – – – – – 1 12 1 4 – 16 – – – – – – – 2 11 1 4 2 – 31 – – – – – – – – – – – – – 3 – – – – – – – – – – – – – 5 – – – – – – – – – – – – – – 5 – – Total % 163 40 3 1 23 6 8 2 33 8 32 8 34 8 51 13 3 1 5 1 5 1 % I 1 1 – – – – – – – 2 – – – – – – – – – – – – – – 38 – – – – – – – – – – – – – 2 40 192 10 26 33 34 53 3 5 4 5 38 2 10 48 2 7 8 8 13 1 1 1 1 9 0 34 123 2 1 1 – 2 – – – – – – 1 7 2 – – – – – – – – – – – – – 33 32 34 51 3 5 4 5 38 2 2 16 6 – – – – – – – – – – 4 1 38 9 2 0 404 100 163 40 10 3 207 51 24 6 I1 References African Plants Database, 2009. 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