Woody Species Composition and Diversity of Wawa-Zange Forest, Gombe State, Nigeria ASIAN JOURNAL OF PLANT BIOLOGY

According to recent research, severe human-induced deforestation is causing 65 percent of the thirty Forest Reserves spread over Gombe State to progressively transform into the desert. The research was done in the Wawa-Zange Forest Reserve in Gombe State, Nigeria, to assess the richness of woody species and biodiversity preservation. The vegetation was sampled with the Point Centered Quarter technique. A complete enumeration of Woody (Trees and Shrubs) with (Diameter at Breast Height or DBH) ≥10 and ≥5cm was carried out. Using Simpson's Diversity and the Shannon-Wiener index, alpha diversity was evaluated. A total of 51 woody species from 16 families and 41 genera were discovered. 34 were trees while 17 were shrubs. Most species were found in the Fabaceae family. Ceasalpinoidae (10), Mimosoideae (4), Papilionoideae (3), Combretaceae (7), Rubiaceae (5), Anacardiaceae, Burseraceae, Capparaceae , Moraceae, Tiliaceae had two species each. The other families are namely Apocynaceae, Ebanaceae, Loganiaceae, Meliaceae, Rhamnaceae, Sapotaceae, Zygophyllaceae with one species each. Simpson index of Diversity was (0.55) and the Shannon-Wiener index was (2.07). This study concluded that plants with low Importance Value Index or IVI such as Pterocarpus erinaceous, Capparis mitchelli, and Pericopsis laxiflora need urgent conservation measures. Therefore, it is important to properly adopt conservation and sustainable management measures.


Data Collection
Data were collected across the whole Forest reserve, which was sampled using Point Centered Quarter (PCQ) Sampling method according to [7]. Using the PCQ method, a steel pin was inserted into the ground to serve as a marker after a starting location was randomly chosen [7,8]. This sampling point had a tape affixed to it, and four quarters were marked off, with the nearest plant (trees and bushes) measured in meters (m) in each quarter. Each transect's sampling points were treated in this manner. Each of the four transects per hectare has 10 sampling locations. Additionally, 40 sampling points with 160 species per hectare were taken, resulting in 4 species at each sample point. Furthermore, the separation between the sampling site and the trunk's or base's center was measured. In each quadrant, the distances between the sampling location and the adjacent tree's midpoint were measured and noted. Within the quadrats, singlestem woody perennials up to 5m tall and 10cm in diameter at breast height (DBH) were counted and classified to the species level. However, with a measuring tape, the diameter at breast height of trees and shrubs (DBH ≤ 10 cm, ≥ 4.5 cm) was measured in each quarter and recorded. For trees with flutes or buttresses, the diameter was measured 30 cm above the spot where the flute or buttress vanished into the stem.

Identification of species
All species encountered were recorded at each sampling point. Field guides and Floras, as well as literature featuring coloured images, were used to identify species on-site [9,10,11] and as done by (Abba HM, 2014, unpublished data). Those individuals that could not be identified were brought to the Department of Botany at Gombe State University in Gombe, where they were identified by an expert, and also compared with herbarium specimens. Hutchinson and Dalziel's [12] nomenclature was used. Total density for all species = Unit area =10000 (Mean area per plant) 2 Mean area per plant

Data analyses
The mean area/tree (M.A.) = D2 Where D= the mean distance of 4 points to the nearest tree distances taken in each of four quarters i.e. D1, D2, D3 and D4.
For the woody species the following relation stands. The vegetation was evaluated quantitatively using total, relative, and absolute densities, frequency, relative frequencies, dominance, relative dominance, and important value [7].
Absolute density and Relative density by species

Species diversity index
Measurement of alpha diversity. Two common approaches for measuring alpha diversity are species richness and evenness/ heterogeneity [13].

Simpson's diversity index
The formula used for calculating D is: 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 [14].

Shannon-Wiener index
The Shannon index was used to calculate the community diversity using the formula: Where H= the Shannon -Weiner index and pi = the proportion of individuals of the total sample belonging to the ith species. ∑ = Sum. [15].

RESULTS AND DISCUSSION
In Wawa-Zange Forest Reserve, fifty-one species from 16 families and 41 genera were discovered. Out of this number 34 were trees and 17 were shrub species. The species obtained showed characteristics of Sudan Savanna plants ( Table 1). The fact that the study area is designated as Sudan Savanna and the area's species diversity suggest that this is a significant conservation site. The amount of woody (tree and shrub) plants discovered is comparable to that found in the Kanawa Forest Reserve, which has 25 tree species and 35 shrub species, as reported by [16]; (Abdullah MB, 2010, unpublished data) in Yankari Game Reserve in 2003 with 38 tree species, in 2004 with 42 tree species, and 2005 with 43 tree species; [17] reported 37 tree and shrub species belonging to 17 families in the Falgore wildlife reserve in Kano state, and also [18] collected 16 woody species in Girei forest reserve in Adamawa State. Direct comparisons with other studies of a comparable nature are challenging such as [19], which collected 50 woody species in the Ipinu-Igede sacred forest in Benue State, North-Central Nigeria and [20] obtained 14 species in North-Eastern Nigeria. Due to the fact that the floristic data that are now accessible are either site-specific or span a wide range of vegetation zones. While biological factors and the presence of adequate environmental gradients seem to have a greater influence on diversity at the site level, climate and topography appear to have broad effects on diversity across the landscape.
The study found 10 different species in the Fabaceae (Caesalpinoidae) family, which has the most species overall. This is due to the fact that these families are well-known as native species in the majority of Savanna-Woodland Mosaics in Africa, and they are more characteristic of Sudano Sahelian zones [21,22]. Also, Fabaceae's ecology and reproductive biology may also play a role because of its effective and successful dispersal capacities and better adaption to a variety of ecological settings. In Nigeria apart from Poaceae, Fabaceae is known to dominate the angiosperm biodiversity of both the Southern and Northern Savanna of Nigeria [21]. According to Harris [23], no family has a wider worldwide spread in a wider variety of ecosystems than the Fabaceae, with the possible exception of the Poaceae. Also [24,19] identified Fabaceae as the dominant family in Benue State, Nigeria.  [25]. Species management and conservation priorities are established using it as well [26].

Diversity indices
The richness, variety, and evenness of the species were all measured in the research area at 2.5, 0.55, and 2.07, respectively ( Table 3). This indicates a moderate level of species variety and variable species distribution in the study area, as well as an old assemblage with diversified and abundant vegetation. When compared to (H'= 3.646) from Ipinu-Igede Sacred Forest as reported [19]; (H'= 3.21) as found by [17], and [18] reported (H' = 2.6). A higher level of anthropogenic disturbance in the studied area could explain the difference in diversity indicators. Based on the focal group discussion and field observations, it is also obvious that the locals' destruction of trees for the purpose of expanding the farmland they currently possess to grow cereals, pulses, and perennial crops has a significant impact on the reserve's cultivated areas. The Shannon-Wiener index typically ranges between 1.5 and 3.5 and is rarely above 5.0 [27]. The values discovered in this study are within the anticipated range. The distribution of trees in circumference classes formed a "J" shape, in accordance with the species composition of the Forest Reserve (Table 4). These results were similar to that of [17], who obtained the J-shape diameter distribution Tree stands in the lower DBH class of 6-10cm had higher values (1,300 individuals), followed by shrub stands in the lower DBH class of 1-5cm with (700 individuals) and the higher DBH class of 21.0cm -above with 100 individuals. ( Table 4). This indicates that the lower class diameter could develop into mature trees if conservation measures are implemented. The diameter class findings in this study back up the claim that Girth -Class frequencies decreased monotonically as girth classes increased.

CONCLUSION
This study concluded that the family Fabaceae: The most prevalent family in the research area is Caesalpinoidae. The densely populated species for trees were (Acacia ataxacantha (12.46) while for shrubs was Senna occidentalis, while the frequently populated species for trees were (Combretum hypopilinum ) while for shrubs was (Guiera senegalensis).
The dominant trees were Anogeisus leiocarpus and Diospyros mespiliformis while the dominant shrubs were Senna singuena. The tree with the highest importance value index was (Combretum hypopilinum ) while the tree with the lowest Importance value index was Pterocarpus erinaceous, Pericopsis laxiflora, and Capparis mitchelle. High IVI value species require low priority conservation efforts, and low IVI value species require high conservation efforts.