Introduction
Sacred forests are forest areas which have been conserved from open access situation in different ways depending on the type.  The term is also used in a generic sense as a place that is venerated and held in awe. While they may be a site of religious importance, they also encompasses places that are of symbolic significance where space, place, memory and spiritual meaning come together and is valued for contemplation or meditation (UNESCO, 1998).

All the plants and animals that inhabit these forests according to Udo (1983), Liu et al., (2002), Telly (2005), and Shengji (2005) are considered to be companions of the god or ‘sacred living things’ in the god’s garden. Thus, a violence to or disturbance of plants and animals in the forest will be punished by the gods, hence hunting, gathering and collection of both fauna and flora species are strictly prohibited in there. The traditional management concept of sacred forest is not only consistent with the modern environmental conservation practice, but has been its basis since the belief in the sacredness of the forest and practices of protection initiated from time immemorial, is still playing an important role in the conservation of the forest biodiversity the world over.

According to WRM (2002), it has been shown that traditional systems of African culture, far from constituting an obstacle to environmental protection, are the best guarantee in the protection of ecosystems and conservation of biodiversity. Experience shows that sacred places can become real biodiversity reserves in the African continent. 
According to Holdgate (1991), Lyster (1991), Nokoe (1993) and Awake (1997), a sacred forest in the tropical rain forest region can conserve over 80% of the area’s biodiversity. Undoubtedly, in China, according to Wang and Chen (2004) and Shengji (2005), the sacred forest from which the Xishuangbana biosphere reserve was built upon, plays a key role in conserving this rich biodiverse area. The reserve is said to have 3,890 identified species of vascular plants, including 53 species under the priority protection of the state, and 620 species of terrestrial vertebrates of which 109 species are under the priority protection of the states.  Also, there are 102 species of mammals (20 percent of China’s total); 38 species of amphibians and 60 species of reptiles (43 percent of China’s total) in the Xishuagbana reserve, including 1,437 identified insect species (Wang and Chen, 2004).

The establishment of these sacred forests/groves in certain sensitive ecosystem including river banks, streams, ponds, mountain and forests has helped to preserve the biodiversity of these areas and serve gene pools for plant seeds and seedlings available for regeneration in the degraded areas outside and around the forests/groves (Telly, 2005). The practice of leaving a number of trees standing for sacred or economic reasons and probably in some cases (where culture allows) incorporation of various farming systems alongside these trees, serve as a basis for agroforestry interventions such as mixed cropping. The prohibition of hunting in the forests/groves, which serve as wildlife sanctuaries for the rapidly diminishing populations of birds, mammals and reptiles, is an important conservation practice. The non-burning of these groves has assisted in maintaining the biological diversity in the groves to the extent that the laws of nature are fully operational in these groves, hence the soils are much richer in nutrients (Telly, 2005).

This study therefore examine the vegetation of a few sacred forests in the rain forest zone to ascertain its structure, species composition, families and diameter at breast height class of available trees in the areas.

Materials and Methods
1 Study Area
The study was conducted in both Akwa Ibom and Cross River States in the Southeastern part of Nigeria.  Akwa Ibom State lies between latitudes 4° 33¹N and 5° 33¹N and longitudes 7° 30¹E  and 8° 20¹ E, while Cross River State lies on latitude 5° 23¹N and 4° 27¹N and longitude 7° 50¹E and 9° 28¹ E (Daniel, 2010). Akwa Ibom state has a total land mass of 8,412 km² with 15.2% of its land area under forest cover and Cross River State has 46.2% of its 23,074.425km² land mass under forest cover (FORMECU, 1999). Akwa Ibom State has a mean rainfall and temperature of 2500mm and 27℃/annum respectively (Etukudo, 2001). Cross River State, though sharing a common border with Akwa Ibom State has a mean annual rainfall and temperature of 3000mm and 25℃ respectively (Ibor and Abi, 2005). The relative humidity in both states is high with abundant sunlight to support long growth period for luxuriant vegetation all year round. However, though the two states are predisposed to the luxuriant tropical rainforest such as fresh water swamp forest, mangrove forest and lowland rainforest because of their location on the shores of Atlantic Ocean and the presence of good climatic factors, there are marked differences in their vegetation with the existence of Oil Palm belt, in Akwa Ibom State (Etukudo, 2001) and Guinea Savanna in Cross River State (Ibor and Abi, 2005). These differences are due largely to the distance from the ocean, change in elevation, soil variations, and marked climatic fluctuation among the two states.

The two states having co-existed as one state (Cross River State) before state creation in 1987 when Akwa Ibom was created out of it. They have a common traditional administrative setting with the village head as the traditional head of the village/community, supported by the family heads who together with other selected indigenes, constitute the village council. Group heads, Clan heads and Paramount rulers are the other traditional hierarchy in both states, responsible for protecting the culture of the people. (Figure 1).

Figure 1 Map of Nigeria showing the study areas

2 Selection of sample area
The two states were independently studied, after which a multi-stage sampling procedure was used to select the study samples. Akwa Ibom State was divided into three clusters based on senatorial district (Uyo, Ikot Ekpene and Eket). Random sampling procedure was thereafter utilized to select two Local Government Areas (LGA) from each cluster. Purposive sampling procedure based on availability, accessibility (cultural restrictions) and size of the forests, was finally utilized to select one sacred forest from each LGA.

In Cross River State, the same cluster sampling was used namely Northern, Central and Southern, as the first stage sampling. Purposive sampling was hereafter adopted in selecting two (2) LGAs from North and Central senatorial districts and one sacred forest was studied in each of the selected LGA. As in Akwa Ibom, the factors considered were; availability, accessibility (cultural restrictions) and size of the forests. In both cases, only the forest whose sizes were approximately one hectare (1ha) and above, were considered in order to accommodate the sampling units. The following sacred forests (Table 1) were finally selected as sample areas for studies.

Table 1 Sacred forest selected as sample areas in the study areas

3 Sampling units
The study was carried out between May 2008 and February 2009. The forests were studied using 20 m x 20 m Temporary Sample Plots (TSP) as recommended by Alder and Synnoth (1992). Maps produced by a transverse survey of each sacred forest, were grided into 20 m x 20 m TSP and Fixed effect Model (Equal Sample Allocation) as discussed by Wahau (1994) was used to select five 400m2 sample plots totaling 2 000 m² (0.2Ha) within the core of each sacred forest.  All the 20 m x 20 m plots bordering the free area were not given consideration to avoid edge effect.  Prismatic compass was used to locate the selected plots.  Adjacent plots were considered where the intended plot had obstacle like steep valley, massive cluster of plants with thorns e.g. rattan, or a restricted/prohibited cultural site like shrines.

4 Data collection procedure
The procedure for data collection involved tree identification, enumeration and measurement of merchantable height of tree species with diameter at breast height (dbh) ≥ 10cm, using sunto clinometer and diameter tape.

5 Data processing and analysis
Every tree measured and noted in the field was identified taxonomically using Keay (1989), Etukudo (2000) and (2003) as guide. The life-form spectra of various plant communities encountered in the study areas were presented in line with Raunkareir Life-form Classification Scheme (Raunkareir, 1934) as follow:
(a) Megaphanerophytes (MgP) -Trees over 30 m high
(b) Mesophanerophytes (MeS) -Trees from 8-30 m high
(c) Microphanerophytes (MiP)-Trees and shrubs between 2-8 m height.

Distribution status of each family was based on its availability among the study areas. Any family that appeared in at least 7 of the 8 study areas was considered Very Common (VC), a family that appeared in at least 4 of the study areas was considred a being common (C), while a family which appeared in less than four study area was considered as Not Common (NC).

Data gathered from each 20x20 m TSP were summed up to represent the 2000 m² (0.2Ha) sample area of each sacred forest and later extrapolated to per hectare bases. The site Diversity/Richness Index (D) was determined using equation (1) adopted by Whittaker et al. (2001).
D = S / Log A  (1)
Where; D = Richness (Diversity Index), A= Sample Area in square meters = 2000 m², S = No. of species in a sample of standard size A.

Results
i. Structure of the sacred forests
The result obtained indicates that all the sacred forests in Akwa Ibom State (Akoho Itit, Abaam Itak, Akai Mbiam, Akai Uya, Akai Anwa Ibok and Utai Ikot) had a forest structure of two stratum made up of the mesophanerophyte and microphanerophytes life forms while those in Cross River State (Evat Quna and Odim Akerot) expressed a three-stratum structure of Megaphanerophytes, mesophanerophyte and microph- anerophytes life forms (Table 2).
 
Celtis integrifolia, Amphimas pterocapioides and Ricinodendron heudolotii constituted the Megaphan- erophytes spectrum or the emergent crowns for Evat Quna and Odim Akerot sacred forest, while Pentaclethra mycrophylla, Ptrocapus species, Irvingia gabonensis, Coelocaryon species, Alstonia boonei, Cyclicodiscus gabonensis, Ceiba pentandra, Pachypo- ndanthum staudii, Baphia nitida, Sterculia tragacantha and Pycanthus angolensis were the mesophanerophyte, thus forming a continuous upper canopy, where their crowns clustered to form a very large/wide cover for the sacred forests. The microphanerophytes constituted the under storey which were not pronounced in most of the sacred forests due to the covering effect of the interlocking canopy structure of the sacred forest.

Table 2 Distributions of the various Species encountered in all the sacred forests

ii. Species composition and Diversity index
Abaam Itak sacred forest had the highest species composition of 38 species with a diversity index of 12.12 which differ between species (5 and 11) and diversity index (3.94 and 2.12) from other sacred forests (Table 2). Also, Abaam Itak had the highest number of trees family (22) followed by Utai Ikot and Akai Anwa Ibok with 21 and 20 families respectively. Akoko Itit, Akai Uya, and Evat Quna all had a tree composition of 19 families each while Odim Akerot and Akai Mbiam had the least tree family composition of 18 and 17 families each (Table 3).

Table 3 Distributions of the various families encountered in all the sacred forests

The result obtained in Table 3 shows that a total of 34 tree families where encountered during the study. 12 families (35%) and 6 families (17.5%) were classified as very common and common respectively, while 16 families (47.5%) were also classified as Not Common. However, Euphorbiaceae and Fabaceae (Caesalpinlaceae, Mimosaceae and Papilionaceae) were the dominant families in the all studied sacred forests.

Discussion
All the studied sacred forests were structurally complex as expected of a tropical rainforest (Dike et al., 1996), and there was little evidence of logging in few of them. Evat Quna and Odim Akerot sacred forests both in Cross River State, expressed a three-stratum system of emergent crown, upper canopy and lower canopy as described by Dawkins (1958), while Akoho Itit, Abaam Itak, Akai Mbiam, Akai Uya, Akai Anwa Ibok and Utai Ikot, expressed a two stratum of upper and lower canopy. The above finding collaborate a report on the Nigerian lowland forests as described by Were (2001). The report states that within the southern rainforests, a number of forest types can be recognized, one of such is rich in species of Meliaceae family, with a middle story of dense-crowned, wide-spreading trees and a ground flora that is mainly herbaceous and characterized by an abundance of creepers, mostly Acacia ataxacantha and rattan (Calamus deerratus).  

The near mono-specific nature of the families as revealed in Table 3 was also reflected in the similar trend in the species diversity index. This number of species recorded for each 0.2 hactre was high as evidenced in the figures for the Diversity/Richness Index (Table 2). This agrees with studies by Onyekwelu et al., (2005), Ukpong et al., (2012), Udoakpan et al., (2013) and Jacob et al., (2015) that Nigeria tropical lowland rainforests is dominated by members of Sterculiaceae, Moraceae, Meliaceae, Euphorbaceae, Mimosaceae (Fabaceae), Apocynaceae etc.

Diversity index is a measure of variety of species (Sax, 2002) or the number of species and individuals (Spellerberg and Fedor, 2003) in an area. According to Ekeke et al., (2005), any species having a diversity index greater than one (> 1) is regarded as rich in relation to the area while the species with a less than 1 (< 1) diversity index referred to as being less dense.  The result obtain in Table 2 therefore reaffirms that the vegetation type of the studied sacred forests is a lowland rainforest, which is noted for its high number of species per square area (Gomez-pompa and Burley, 1991; Nokoe, 1993).

This study also showed a usual preponderance of stem at lower size classes (Ojo, 1998), thus revealing a typical inverse J-shape structure (Figure 2) of the dbh class distribution. This is consistent with the natural tropical forest structure (Onyekwelu et al., 2005) and gives an indication of good regeneration of the constituent species (Onyekwelu et al., 2005, Nath et al., 2005). This observation reinforced the hope that the various sacred forests if not destroyed can sustainably produce the various indigenous species that are threatened in other forest settings.

Figure 2 Stem diameter class distribution of tree species

Though one may be prompted to question the size of these forests and its capacity to conserve these biodiversity, especially those ranging from a quarter of an hectare to few hectares, the study result collaborate the opinion of Okoji (2001) that even when the relic of the tropical rain forests are quite small in size, biodiversity are sufficiently stocked within it. This is supported by Whitehouse (1991) and Pauda (1994) that size alone, in terms of biodiversity conservation is not a sufficient measure of the significance of an area of tropical forest, because many small areas have a high percentage of endemic species.

Conclusion and Recommendation
The sacred forest is a traditional forest reserve (TFR) meant to fulfill not only the cultural needs but also specific functional needs of the community and the management of their environment which, is similar functions as government-declared protected area. The spiritual values attached to these sites result in restrictions of access and collection of flora and fauna products in these sites therefore resulting in a natural or near natural ecosystems and biotopes devoid of alteration. In all the studied sacred forests, it was observed that they were still stocked with important tree species and the evident or presence of secondary species/colonizers, which is encourage by human activities were minimal within the sacred forests. Thus, there is hope arising from the tree composition and dbh distribution of the tree species in the sacred forests as they are likely to prove most valuable (when compared with other forest settings) in ensuring indigenous species production, a potential gene pool for biodiversity, restoration of other degraded environment and reduction or sequestration of carbon dioxide to reduce global warming. This study therefore suggest or recommend that as effort is being made to increase the total areas of the country’s forest reserves, the sacred forest should be studied to unveil the socio-cultural matrix of traditional belief systems that has helped conserve such sites or how to integrate them into existing protected area networks to help safeguard them without affecting rights, wishes and traditional practices of traditional owners.

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