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Investigation on woody plant diversity and phytogeography in sitangaza forest reserve, Sokoto state, Nigeria

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https://www.eduzhai.net International Journal of Plant Research 2015, 5(4): 73-79 DOI: 10.5923/j.plant.20150504.01 Diversity and Phytogeographic Investigation into Woody Plants of West Tangaza Forest Reserve, Sokoto State, Nigeria Daniel A. Zhigila1,*, Fatima B. J. Sawa2, Suleiman D. Abdul2, Halima M. Abba3, Murna Tela1 1Botany Programme, Department of Biological Sciences, Gombe State University, Gombe, Nigeria 2Biological Sciences Programmes, Abubakar Tafawa Balewa University, Bauchi, Nigeria 3Biology Unit, S.B.R.S., Gombe State University, Gombe, Nigeria Abstract The diversity and phytogeography of woody plant species in the West Tangaza Forest Reserve, Sokoto, Nigeria was studied. Taxonomic/floristic and geographical diversity were integrated to put the forest in focus for the local and global conservation efforts that it deserves. Stratified random sampling using point centred quarter (PCQ) method was employed. A total of 22 species of trees and shrubs belonging to 19 genera and 12 families were identified. The family Combretaceae had the highest number of species (6); followed by the family Fabaceae (5), families Anacadaceae, Asteraceae, Asclepediaceae, Euphorbiaceae, Rhamnaceae, Tiliaceae and Lamiaceae were represented by one species each. The Importance Value Indices revealed that the forest was dominated by Guiera senegalensis (127.70) – Phyllanthus amarus (43.08) – ASpilia africa (22.24) complex. The lowest importance value indices were observed for Combretum glutinosum, Detarium micranthum and Lannea microcarpa with 2.68 each. These species showed the urgent need for conservation efforts. The Simpson’s index of diversity was 0.5268 and the species richness was 0.8029. The values were high indicating a more complex and healthier community because a greater variety of species allows for more species interactions, hence greater system stability, and indicates good environmental conditions. Keywords West Tangaza, Forest, Taxonomy, Diversity, Conservation, Shrubs, Trees 1. Introduction Living things are interdependent, intricately linked in birth, death and renewal. Human beings are just one small part of the vibrant component of the biological systems on the earth but human beings are the vital and key biological system and put tremendous amount of pressure on species and the environment and ecosystem. As a result, many plants and animals are at risks as well as natural processes such as pollination by insects and the regeneration of soils by microorganisms and also the survival of microorganisms. Woody plants are such vital components of the ecosystem that have productive, protective and recreational functions (Atiku et al., 2013). They control soil erosion, stabilize regional and global climates; provide carbon sinks, and acts in pollution control (Adamu, 2006). The extent to which forest trees are being exploited calls for urgent attention (Zaki, 2004). The world forests are diminishing rapidly and each year about 294,020 square kilo meters of forest * Corresponding author: dandrawuszhigila@gmail.com (Daniel A. Zhigila) Published online at https://www.eduzhai.net Copyright © 2015 Scientific & Academic Publishing. All Rights Reserved disappear (Fries and Herman, 1990). Taxonomic diversity mostly interpreted as the variation among and within species which includes the variation of taxonomic unities such as Phyla, Orders, Families, Genera and Species (Moksia et al., 2012). Ecosystem diversity or even better biogeographic diversity concerns with the variation in biogeographic regions, landscapes and habitats. The problems facing at present is the over exploitation of bio-resources/natural resources which would not only have negative impact on the environment but also sometimes totally destroy and erode the important bio-resources which are available at local level, regional level and national levels. Therefore, ecosystem management in a particular location is important and integral part for the conservation and protection of biological diversity of Nigeria (Bello, 2005). By understanding the status of the natural forest in terms of tree species composition, richness and diversity, recommendations can be made for the restoration and future management of the reserve. The study was a step in that direction. Specifically, the objectives of the study were: (1) to capture the composition, diversity and richness or otherwise rarity of tree species in West Tangaza Forest Reserve (2) to compare the tree species composition, diversity and richness between climax vegetation within the 74 Daniel A. Zhigila et al.: Diversity and phytogeographic investigation into woody plants of West Tangaza Forest Reserve, Sokoto State, Nigeria same environment and (3) Taxonomic/floristic and biogeographical studies are integrated to investigate the biodiversity in West Tangaza Forest Reserve and to put the region in focus for the local and global conservation efforts that it deserves. 2. Materials and Methods 2.1. The Study Area Tangaza Local Gov’t Area, Sokoto state (Nigeria) is locate at latitude N13.56 to 13.57 and E4.42 to 4.46° (Figure 1) while West Tangaza Forest Reserve is located at Latitude 13° 25' 00" N and Longitude 4° 30' 00" E (NGIA, 2012). Some of the villages surrounding the reserve include Yartagimba, Mulawa: Tungarnoma, Tungarfilani, Daiji, Marakenbori, Wassanniya and Jimajimi 1 and Jimajimi 2 (Atiku et al., 2013). Most of the inhabitants are Peasant farmers, Cattle rearers and Local wood carvers all of whom are dependent on forest resources for raw materials. Gazetted by colonial order number 38 in December 1937, the reserve covers an area of 174 square miles (Abegunde et al., 2001). 2.2. Vegetation Cover Sampling Procedures The materials used for the field work include secateur polythene bags, large jute bags, pen, labelling tapes, specimen bottles, hand lens, improvised hook and measuring/calibrated tapes. Sampling for diversity and abundance was carried out randomly in every community. The point centered quarter method procedure of vegetation estimation was used in data collection as described by Mueller and Ellenberg (1974). The plant species includes all the saplings, shrubs and trees present in the study areas. 2.3. Plant Collection and Identification Species were identified on site with the help of taxonomic keys, field guides and floras and texts containing coloured photographs (Von Maydell, 1990; Akobundu and Agyakwa, 1998; Blench and Dendo, 2007 and Odugbemi, 2008). The unidentified plant samples collected from the study areas were flattened-out on flimsies and pressed between the absorbents under heavy pressure immediately after collection on the field; these were packaged with ventilators in the plant press for drying in the oven. The dried plants were separated and properly identified with appropriate labels for easy reference with herbarium specimens of the Gombe State University and Biological Sciences Programme Tafawa Balewa University, Bauchi., Nigeria. Unidentified specimens were deposited at the herbarium of Gombe State University. Nomenclature of the species follows Hutchinson and Dalzeil (1972). The list of identified plants was presented in Table 1. 2.4. Species-Effort Curve The thoroughness of the survey, in terms of the proportion of plant species surveyed, was estimated using a species-effort curve (Figure 2). The species effort curve shows the cumulative number of plant species per section of the four different sites. The curve shows that new species were added more quickly at the beginning of sections as it lengthened. The curve reached a clear plateau at some point and continued on an upward trend where it levels up. It became less likely that more species would be found; indicating that enough total area had been sampled to give a reliable picture of variation in plant species richness and diversity in West Tangaza Forest Reserve. Tangaza West Figure 1. Map of Nigeria Showing the location of West Tangaza Forest Reserve (Map Data, 2015) International Journal of Plant Research 2015, 5(4): 73-79 75 Figure 2. Overall species accumulation during survey effort at West Tangaza Forest Reserve 3. Data Analyses Data obtained were quantitatively analyzed for Relative density, Relative frequency, relative abundance and Importance value index and calculated as follows (Curtis and McIntosh, 1951). Density is calculated by the equation: Density = ???????????????????????????????????????? ???????????????????????????????????????? ???????? ???????????????? ???????????????????????????????????????????????????????????????????????????????????????? ???????????????? ???????? ???????????????????????????????????????????????????????? ???????????????? ???????????????????????? ???????????????????????????????????????????????????????????????? ???????????????????????????????????????? ???????????????????????????????????????????????? ???????????????? ???????????????????????????????????????????????????????????????? ???????????????????????????????????????????????????????? Relative Density = ???????????????????????????????????????????????? ???????????????? ???????????????????????????????????????????????????????????????????????????????????????? ???????????????? ???????????????????????? ???????????????????????????????????????????????????????? ???????????????????????????????????????? ???????????????????????????????????????????????? ???????????????? ???????????????????????? ???????????????????????????????????????????????????????????????????????????????????????? ???????????????????????????????????????????????????????? ???????? 100 Frequency = ???????????????????????????????????????????????? ???????????????? ???????????????????????????????????????????????????????????????? ???????????????? ????????ℎ????????????????ℎ ????????ℎ???????? ???????????????????????????????????????????????????????? ???????????????????????????????????????????????????????? ???????????????????????????????????????? ???????????????????????????????????????????????? ???????????????? ???????????????????????????????????????????????????????????????? ???????????????????????????????????????????????????????? Relative Frequency = ???????????????????????????????????????????????????????????????????????? ???????????????? ???????????????????????? ???????????????????????????????????????????????????????? ???????????????????????????????????????? ???????????????????????????????????????????????????????????????????????? ???????????????? ???????????????????????? ???????????????????????????????????????????????????????? ???????? 100 Abundance = ???????????????????????????????????????? ???????????????????????????????????????????????? ???????????????? ???????????????????????????????????????????????????????????????????????????????????????? ???????????????? ???????? ???????????????????????????????????????????????????????? ???????????????? ???????????????????????? ???????????????????????????????????????????????????????????????? ???????????????????????????????????????? ???????????????????????????????????????????????? ???????????????? ???????????????????????????????????????????????????????????????? ???????????????? ????????ℎ????????????????ℎ ????????ℎ???????? ???????????????????????????????????????????????????????? ???????????????????????????????????????????????????????? Relative Abundance = ????????ℎ???????? ???????????????????????????????????????????????????????????????????????? ???????????????? ???????????????????????? ???????????????????????????????????????????????????????? ???????????????????????????????????????? ???????????????????????? ???????????????????????????????????????????????????????? ???????????????????????????????????????????????????????? ???????? 100 Importance Value Index = Relative Frequency + Relative Density + Relative Abundance Species diversity index was calculated using Simpson’s index as follows: D = ∑(???????? )2 ???????? Where: D = diversity index N = Total number of organisms of all species found n = number of individuals of a particular species The value of D ranges between 0 and 1. With this index, 0 represents infinite diversity and 1 no diversity. Species Richness = D = ???????? √???????? Where D = the Menhinick's index; S = the number of different species represented in the sample and N = the total number of species in the sample. The important quantitative analysis such as density, frequency, and abundance of tree species, shrubs and herbs species were determined as per Curtis and McIntosh (1951). 4. Results and Discussion A total of 22 species of trees and shrubs belonging to 19 genera and 12 families were identified in West Tangaza Forest Reserve (Table 1). Plant species such as Gueira senegalensis (shrub), Combretum spp (shrubs), Piliostigma thonningii (shrub), Acacia senegalensis (shrub), Zizziphus mauritiana (shrub), Aspilia Africana (shrub) and Calatropis procera (shrub) were identified to be most common. The family Combretaceae had the highest number of species (6). This was followed by the family Fabaceae with five species. The families Anacadaceae, Asteraceae, Asclepediaceae, Euphorbiaceae, Rhamnaceae, Tiliaceae and Lamiaceae were represented by one species each. These finding are in confirming that Fabaceae and Combretaceae are families known to be native species in most savannah-woodland 76 Daniel A. Zhigila et al.: Diversity and phytogeographic investigation into woody plants of West Tangaza Forest Reserve, Sokoto State, Nigeria mosaics in Africa and are important families in tropical deciduous forests (Ceccon et al., 2002). Moksia et al. (2012) and Sawadogo et al. (2007) reported that families Combretaceae and Fabaceae were the important families in Kalfou Forest Reserve, Cameroon and Tiogo forest in Burkina- Faso respectively which are also in the Savannah region. Table 3 shows that Guearea senegalensis recorded the highest (127.70) Important Value Index, it was followed by Phylanthus amarus and aspilia africana with 43.03 and 22.24 respectively. The lowest IVI was recorded by Combretum glutinosum, Detarium microcarpum and Lannea microcarpa with 2.68 each. According to (Curtis and McIntosh, 1951; Cumming, 1990; Cox et al., 1994; Abdullahi, 2010, Abba et al., 2013), high importance value index (IVI) of a species indicated its dominance and ecological success, its good power of regeneration and greater ecological amplitude and also those plants need-monitoring management, while, species which were grouped as low therefore need high conservation efforts. Species diversity The alpha (within-site) diversity for the four sites is shown in Table 3. The Simpson’s index of diversity (1-D) was 0.5267668415 and the species richness was 0.802919708 (Table 3). The values were average indicating a more or less complex community because a community dominated by one or two species is considered to be less diverse than one in which several different species have a similar abundance and greater variety of species allows for more species interactions, hence greater system stability, and indicates good environmental conditions (Abba et al., 2013). The high diversity could also be due to the high fertility related parameters and low moisture contents at some sites. A similar study was carried out by Abdullahi (2010) where it was reported that Simpson’s index of diversity for trees in Yankari National Park which is also found in savannah region was (0.984). Richard et al. (2011) similarly reported Simpson’s index of diversity as (0.957) for the Miombo woodland of Bereku Forest Reserve, in Tanzania. These values were higher than those of the present study because of the statute of Yankari as a National Park and Bereku Forest Reserve as a Forest Reserve and also the sizes of their reserves were larger. It is on these bases that the statute of West Tangaza Forest Reserve should be changed to have more species diversity. Results from the general linear model (Table 4) showed that study sites showed significant differences in plant species diversity. Relative to other study sites, site 4 had the highest species diversity while Site 2 had the least. Table 1. Nomenclature of Trees and shrubs in West Tangaza Forest Reserve, Sokoto State S/N Family Scientific Name and Authority Hausa Name Common Name 1 Anacadiaceae Lannea microcarpa Faru 2 Asclepiadeae Calatropis procera R. Br. Tumfafiya 3 Asteraceae Aspilia africana (Pers.) C.D. Adams Kalankuwa 4 Caesalpiniaceae Detarium microcarpum Taura 5 Piliostigma thonningii (Schum.) Kalgo 6 Combretaceae Anogeisus leiocarpus Marke 7 Combretum ghaselense Engl. & Diels Bakin taramniya 8 Combretum glutinosum Perr. ex DC. Jar taramniya 9 Combretum micranthum Geiza 10 Combretum nigricans Guill. & Perr. Tsiriri 11 Gueira senegalensis Sabara 12 Euphorbiaceae Phyllanthus amarus Schum. & Thon Riyariaya 13 Fabaceae Bauhinia rufescens Jirga 14 Parkia aculeate Bagaruwar kara 15 Prosopis africana Kirya 16 Dichrostachys cinera Ɗunɗu 17 Lamiaceae Hyptis suaveolense Poit 18 Mimosaceae Acacia sieberana Farar kaya 19 Mimosa pigra Linn. Gumbi 20 Papilionaceae Pterocarpus erinaceus Madobiya 21 Rhamnaceae Ziziphus abyssinica Magarya 22 Tiliaceae Grewia mollis Kamomowa Lannea Giant swallow wort Haemorrhage plant Tallow tree camel`s foot Axlewood Combretum Combretum Combretum Combretum Gueira Amarus plant, Phyllanthus Parkia Iron tree West African sickle bush Bush tea Acacia Sensitive plant African rose wood Jujub tree Moshi medicine International Journal of Plant Research 2015, 5(4): 73-79 77 Table 2. The occurrence of trees and shrubs species at the four sites in West Tangaza Forest Reserve Scientific Name Acacia sieberana Ageratum conyzoides Anogeisus leiocarpus Aspilia africana Bauhinia rufescens Calatropis procera Combretum ghaselense Combretum glutinosum Combretum micranthum Combretum nigricans Detarium microcarpum dichrostachys cinera dundu Grewia mollis Gueira senegalensis Lannea microcarpa Mimosa pigra Pakia aculeate Bagaruwar kara Phyllanthus amarus Piliostigma thonningi Prosopis africana Pterocarpus erinaceus Ziziphus abyssinica Total Mean Site I 1 12 1 1 1 1 1 6 1 1 179 1 2 208 29.71 Site II 34 2 1 4 1 7 71 2 1 1 124 22.55 Site III 1 12 1 8 3 162 1 55 1 244 48.80 Site IV 1 6 1 4 1 1 2 88 1 58 11 1 175 26.92 Total 2 58 2 4 2 7 5 1 19 2 1 11 2 500 1 1 3 113 13 1 1 2 751 65.30 Mean 0.50 14.50 0.50 1.00 0.50 1.75 1.25 0.25 4.75 0.50 0.25 2.75 0.50 125.00 0.25 0.25 0.75 28.25 3.25 0.25 0.25 0.50 187.75 16.33 Table 3. Importance Value Index (IVI) and Diversity index of Woody plants in West Tangaza Forest Reserve Scientific Name Acacia sieberana Ageratum conyzoides Anogeisus leiocarpus Aspilia africana Bauhinia rufescens Calatropis procera Combretum ghaselense Combretum glutinosum Combretum micranthum Combretum nigricans Detarium microcarpum dichrostachys cinera Grewia mollis Gueira senegalensis Lannea microcarpa Mimosa pigra Pakia aculeat Phyllanthus amarus Piliostigma thonningii Prosopis africana Pterocarpus erinaceus Ziziphus abyssinica Total Simpson’s index of Index Species Richness Relative Frequency 4.26 6.38 4.26 6.38 4.26 4.26 4.26 2.13 8.51 4.26 2.13 6.38 2.13 8.51 2.13 4.26 4.26 4.26 4.26 4.26 4.26 4.26 100.00 = 1 - D = = Relative Density 0.27 7.72 0.27 0.53 0.27 0.93 0.67 0.13 2.53 0.27 0.13 1.46 0.27 66.58 0.13 0.13 0.40 15.05 1.73 0.13 0.13 0.27 100.00 0.526766841 0.802919708 Relative Abundance 0.42 8.14 0.42 0.56 0.42 1.47 1.05 0.42 2.00 0.42 0.42 1.54 0.84 52.61 0.42 0.42 0.63 23.78 2.74 0.42 0.42 0.42 100.00 IVI 4.94 22.24 4.94 7.48 4.94 6.66 5.97 2.68 13.04 4.94 2.68 9.39 3.24 127.70 2.68 4.81 5.29 43.08 8.72 4.81 4.81 4.94 300.00 Diversity Index 0.0000070921 0.0059645280 0.0000070921 0.0000123687 0.0000070921 0.0000868793 0.0000443262 0.0000017730 0.0006400698 0.0000070921 0.0000017730 0.0002145386 0.0000070921 0.4432616250 0.0000017730 0.0000017730 0.0000159574 0.0226400300 0.0002996449 0.0000017730 0.0000017730 0.0000070921 0.4732331585 78 Daniel A. Zhigila et al.: Diversity and phytogeographic investigation into woody plants of West Tangaza Forest Reserve, Sokoto State, Nigeria Table 4. Comparing plant species diversity across the four different study sites – Model (diversity ~ site 1 + site 2 + site 3 +site 4). N = 4, Adjusted R = 0.99 ANOVA values DOF F value P value Parameter estimate values Estimate SE t- value Intercept Sites 4 4.5 0.001 Site 1 Site 2 Site 3 Site 4 -2.35 2.52 -5.68 -4.26 4.65 9.86 -2.34 1.34 18.86 1.56 -3.64 3.19 -0.13 3.03 1.53 P values in bold are significant. Diversity is set at zero based on alphabetical order and it is the intercept P-value 0.029 <0.001 0.002 0.89 0.14 5. Conclusions and Recommendations The Tangaza West Forest Reserve could be best described by the following plant types Guearea senegalensis – Phylanthus amarus – Ageratum conyzoide complex. The lowest IVI was recorded by Combretum glutinosum, Detarium microcarpum and Lannea microcarpa indicates the need for urgent conservation efforts for those species and the following recommendations are made.  Alternative source of energy should be provided to the masses so that less tension may deter people from cutting trees as source of energy  Government should initiate programs that promote the farming of forest trees and their products (fruits, wood, gums) around the reserve to avoid cutting down of trees in the forest  Strategic coaching assistance to Forest Guards at the Reserve should be provided.  From a socio-economic sustainable development point of view, the Forest Reserve if enhanced properly will increase employment opportunities and improve the standard of living of the surrounding communities in the long run  Local farmers should be involved in all activities of forest development within their domain  The potentials of the forest to be diverse is evident from the results of this study but requires a change in its statute from government and the local community REFERENCES [1] Abba, H. 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[17] Mueller D.D. and Ellenberg H. 1974. Aims and Methods of Vegetation Ecology. John Wiley and Sons ltd England, Pp. 206. [18] National Atlas for Nigeria 1974. Department of Federal Survey Pp. 23-24. [19] NGIA (2012). National Geospatial-Intelligence Agency. Bethesda, MD, USA. Pp. 76 http://www.geographic.org/geo graphic_names/name.php?uni=-2821375&fid=4316&c=nige ria. [20] Richard A.G., Emmanuel K.B., Canisius J.K., Emmanuel B.M., Almas M.K. and Philipina F.S. 2011. Species Composition, Richness and Diversity in Miombo Woodland of Bereku Forest Reserve, Tanzania. Pp. 54. [21] Sawadogo P., Tigabu M., Sawadogo L. and Oden P.C. 2007. Woody species composition, structure and diversity of vegetation patches of a Sudanian Savanna in Burkina Faso, Bois et Forets des Tropiques 294(4):5-20. [22] Von Maydell, H. 1990. Trees and Shrubs of the Sahel. Their Characteristics and Uses. GTZ. Verlag Josef Margraf Sceintific Books. Weikershem, Germany. Pp. 67. [23] Zaki M.A. 2004. 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