Population Density and Diversity of Plants Species in Ikot Efre Itak Community Forest, Akwa Ibom State, Nigeria

I.U. Nelson<sup>1</sup>; U. I. Udoakpan<sup>2</sup>; D.E. Jacob<sup>2</sup>

Population Density and Diversity of Plants Species in Ikot Efre Itak Community Forest, Akwa Ibom State, Nigeria

I.U. Nelson¹

, U. I. Udoakpan²

, D.E. Jacob²

1. Biodiversity Preservation Center, Uyo, Nigeria
2. Forestry and Wildlife Department, University of Uyo, Nigeria

Author

Correspondence author
International Journal of Molecular Ecology and Conservation, 2015, Vol. 5, No. 5 doi: 10.5376/ijmec.2015.05.0005
Received: 02 Mar., 2015 Accepted: 13 Apr., 2015 Published: 06 May, 2015

This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Preferred citation for this article:

Nelson et al., 2015, Population Density and Diversity of Plants Species in Ikot Efre Itak Community Forest, Akwa Ibom State, Nigeria, International Journal of Mol. Ecol. and Conserv, Vol.5, No.5 1-6 (doi: 10.5376/ijmec.2015.05.0005)

Abstract

This study was aimed at assessing the diversity and population of plants species in Ikot Efre Itak Community forest in Nigeria. A total of 59 plant species were identified in the study area comprising 33 tree species, 12 shrub, 7 herbs, 34 climbers and 3 palms species. Mimusops heckelii and Canarium schweinfurthii, had the highest tree population density of 16 and 12 individual/0.6 ha respectively, all other tree species has a density of less than 10 individual/ha. In the shrub category, Bambusia vulgaris had the highest shrub population density with 31 individual/0.6 ha. Also, Costus afar and Hippocratea africana had the highest density of 53/0.6 ha and 11/0.6 ha respectively in the herb category. The result further shows that Ancistrophyllum secondiflorum had the highest population density of 23 in the palm category. Given the high rate of forest destruction in the country, there is need for to ensure sustainable conservation of the forest area to avoid further destruction by provision of alternative means of livelihood for the local population to reduce their dependence on these forest.

Keywords

Population density; Diversity; Rainforest; Akwa Ibom; Nigeria

A forest is a natural resource of multiple values, oftentimes, estimated from the stand point of population density or standing volume of timber tree species present, while ignoring the more valuable non-timber species (Udo et al., 2009). The Nigerian forest is predominantly a rainforest occupying only 9.7% (95 372 km²) of the country’s land area of 983 213 km² (Onyekwelu et al., 2005). The tropical rainforest is the most biologically diverse terrestrial ecosystem on earth (Jacob, 2012). It is also a complex community whose framework is provided by trees of many sizes, form and species. Trees are often the most conspicuous plant life form in a tropical rain forest. Upon the framework of these trees and within the microclimate of the canopy of the trees, grow a wide range of other kinds of plants such as epiphytes, strangling plants, climbers, parasitic and saprophytes. Unfortunately, only a fragment of the country’s tropical rainforest (21% of the rainforest ecosystem and 2% of the country’s land mass) has been constituted into forest reserves (Udo et al., 2009).

Nigeria has one of the highest rates of deforestation (3.3 percent/year) in the world (Sodhi et al., 2004). Between 1990 and 2000, the country has lost some 6.1 million hectares or 35.7 percent of its original forest covers. Currently, since 2000 Nigeria has been losing an average of 11 percent of its primary forests per year—doubles the rate of the 1990s (Mongabey.org). These figures give Nigeria the dubious distinction of having the highest deforestation rate of natural forest on the planet, consequently our pristine ecosystems have been significantly altered (Turner, 2001) with severe consequences on biodiversity, soil and climate (Udofia et al., 2011).

The need to conserve the remaining areas of tropical rainforest cannot be over emphasized given the high rate of forest destruction, degradation and fragmentation threatening the survival of both fauna and flora species in the country. As efforts are geared towards preventing the utter destruction of our ecosystem and ensuring the conservation of its rich biodiversity, adequate quantitative and qualitative ecological data of the flora and fauna species is imperative. Such data is needed for effective and realistic conservation strategies. The required ecological data include species composition, abundance of each species, stem diameter distribution and abundance of regeneration of each species. This study was therefore carried out to assess the diversity and population densities of plants species in the study area. The data obtained may serve as a basis for formulating strategies for sustainable management of the forest and other similar forest tracts in the country.

1 Methodology

1.1 Study Area

The study area is located in the southern part of Nigeria in the western axis of Akwa Ibom State between latitudes 5° 00` - 5° 25` N and longitudes 70° 35` - 8° 00" E. Ikono Local Government Area is bounded in the North by Ini, in the South by Uyo Local Government Area, East by Ibiono and in the West Ikot Ekpene, Essien Udim and Abak Local Government Areas (Figure 1). The forest fragment is an evergreen forest fragment with an area of 3.2ha managed by the Ikot Efre Itak community as a sacred grove. The forest is only access by the consent of the Village council who gives such permission.

1.2 Sampling Method and Design

Three 300 m linear transect were laid into the core of the forest 20 m away from the access routes. Each transect was separated by a distance of 100 m. All plant species producing valuable forest products within 20 m on both sides of the transect lines were identified and enumerated. Thus, the total sample area assessed was 0.6ha. The data collection was undertaken between November, 2011 and January, 2012.

1.3 Data Processing and Analysis

The identified and enumerated plant species were classified into four life-forms, namely; trees, Shrubs, herbs and climbers. The frequency of each plant species was determined in order to estimate its population per hectare by dividing its total population by the sampled area. The Diversity Index of the plant species was determined using Shannon Weiner index (H1) as described in Magurran (1988)

Diversity Index (H1) = ∑Pi In Pi (1)

Where: Pi = Ni/N, Ni – Total number of individuals of species i, N – Total number of individuals of all species

Species Richness was also calculated using Margalef Index (d) as described by Aremu (2010)

Species Richness (d) = S-1/ln N (2)

Where: S – Total number of Species, N – Total number of individuals of all species

The Species evenness was calculated using Pielon Index (E) as described by Aremu (2010)

Pielon Index (E) = H1/ln S (3)

Where: H1–Diversity Index, S-Total number of Species

F_k = ∑Y_i/n × 100 (4)

Where: F_k– frequency, Y_i – incidence of species k in site i, n – number of species sampled

*ln = Natural log (Figure 1).

Figure 1 Map of Akwa Ibom showing Local Government Areas and study area

2 Results

2.1 Plant species population density, diversity index, richness and evenness

A total of 59 plant species were identified in the study area. The distribution indicated 33 species of trees (Table 1), 12 shrub (Table 2), 7 herbs (Table 3), 34 climbers (Table 4) and 3 palms species (Table 5). In table 1, the result showed that Mimusops heckelii had the highest population density of 16 individuals/0.6ha, followed by Canarium schweinfurthii, Dracaena sp., Combretodendron macrocarpum and Antrocaryon klaineanum with density of 12, 7, 6 and 6 individual/0.6 ha respectively. Other tree species varied between 2 and 1 individual/0.6ha respectively. The tree Species diversity index, Richness and Evenness of tree species in the study area was -1.320 7, 16.295 0, -0.869 7 respectively.

Table 1 Tree species producing valuable forest products in Ikot Efre Itak community forest, Uyo Local Government Area, Nigeria

Table 2 Shrub species producing valuable forest products in Ikot Efre Itak community forest, Uyo Local Government Area, Nigeria

Table 3 Herb species producing valuable forest products in Ikot Efre Itak community forest, Uyo Local Government Area, Nigeria

Table 4 Climber species producing valuable forest products in Ikot Efre Itak community forest, Uyo Local Government Area, Nigeria

Table 5 Palm species producing valuable forest products in Ikot Efre Itak community forest, Uyo Local Government Area, Nigeria

2.2 Shrub species population density, diversity index, richness and evenness

Table 2 indicates that Bambusia vulgaris had the highest shrub population density of 31 individuals/ha followed by Glyphaea brevis, Harungana madasgarensis, Coelocaryon preussii, Maesobotrya dusenii with 4/ ha and Garcinia mannii, Homalium letestui with 3 individuals/0.6 ha respectively while the least shrub species had a population density of 1 individual/0.6 ha. The Species diversity index, Richness and Evenness of shrub species in the study area was -0.7840, 6.4745, -0.7265 respectively.

2.3 Herb species population density, diversity index, richness and evenness

In the herb category, Table 3 shows that Costus afar and Hippocratea africana had the highest density of 53 individuals/ha and 11 individuals/0.6 ha respectively while the other five other herb species enumerated had a population density of less than 10 individual/0.6 ha. The Species diversity index, Richness and Evenness of herb species is -0.462 5, 3.251 9, -0.547 3 respectively.

2.4 Climber species population density, diversity index, richness and evenness

Table 4 indicates that Cissus quadrangularis had the highest population density of 7 individual/0.6 ha, Gnetum africanum 3 individual/0.6 ha and Piper guineensis 2 individual/0.6 ha while Dioscorea bulbifera had the least population density of 1 individual/0.6 ha. The Species diversity index, Richness and Evenness of climber is-0.495 7, 2.693 1, -0.823 3 respectively.

2.5 Palm species population density, diversity index, richness and evenness

Table 5 indicates that Ancistrophyllum secondiflorum had the highest palm population density of 23 individual/0.6 ha and Elaeis guineensis 2 individual/0.6 ha while Raphia hookeri had the lowest population density of 2/0.6 ha. The Species diversity index, Richness and Evenness of palm was -0.339 3, 1.305 9, -0.711 1 respectively.

3 Discussion

The existence and population density of a plant species in a tract of a rainforest is a function of the availability of its seeds or propagules and favorable micro-climate for germination and growth (Udo et al., 2009). Furthermore, the abundance and rarity of a plant species, especially those of great economic value, is a function of the intensity and pattern of exploitation which the forest is generally subjected to (Adekunle et al., 2010). Consequently, the high population of tree species, diversity index, Richness and Species evenness encountered in the study area can be attributed to the favorable micro-climate which included adequate sunlight, created by the canopy gap and the ban on the exploitation of trees in the area for timber as a result of the consecration of the area as a sacred forest, the sanctity of which has been held for generations. This finding agrees with similar works carried out in the tropical rainforest ecosystem that higher population of trees are usually observed in an undisturbed tropical rainforest when compared with those of the disturbed tropical rainforest (Nath et al., 2005; Udo et al., 2009; Adekunle et al., 2010).

The low density of shrubs, herbs, climbers and palms species observed in the forest tract could be attributed to the unfavorable micro-climate and paucity of viable seeds to sustain regeneration. It could also be attributed to over-exploitation for poles and Non Timber Forest Products (NTFP’s collection in the study area. It was observed that both the indigenes and non-indigenes of the community were allowed access to the forest patch for the collection of bamboo for pole and other Non Timber Forest Products (NTFPs) on payment of a stipulated amount of money, thus depleting the population of the plant forms in the study area. Furthermore, the shading of the sunlight and the allelopathic nature of some plant species, such as Ancistrophyllum secondiflorum had made it difficult for the herbs and climbers to thrive in the area. The high presence of Cissus quadrangularis in the study area could also be attributed to it being of lesser economic value to the people than other climber species in the study area.

Most of the plants species in the study area were observed to be less than 10 individuals per hectare except for Canarium schweinfurthii, Mimusops heckelii, Bambusia vulgaris, Costus afar, Hippocratea africana and Ancistrophyllum secondiflorum with a population density of 12, 16, 31, 53, 11 and 23 individual per hectare respectively indicating that these plant species are rare and endangered species (Udo et al., 2009; Olajide et al., 2008). Furthermore, all the plant species identified and enumerated in the study area were observed to be of great economic importance to the people of the community as they produce edible fruits and seeds on which the people depend on for food, oil, poles, leafy vegetable and medicine. The products are usually sold in the rural and urban areas by the people who trade in them as a means of livelihood (Magurran, 1988; Nath et al., Udo et al., 2009).

4 Conclusion and Recommendation

Human activities have been blamed for the extinction of many plants and wildlife species through unsustainable natural resources exploitation and habitat destruction. The result obtained indicates that tree species had the highest population density in the study area followed by the herb species while the climber species had the lowest population density. The population of individual species of climbers, herbs and shrubs in the study area were very few. It is recommended that measures to foster partnership between the community and other forest stakeholders in the area be implemented to ensure sustainable forest resources management in the area. Furthermore, afforestation and re-afforestation programs should be timely carried out in the area to restore the degraded ecosystem.

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