EFFECT OF SOIL NUTRIENT VARIATION ON TREE SPECIES COMPOSITION AND DISTRIBUTION IN UNIVERSITY OF UYO, ARBORETUM, NIGERIA
Effect Of Soil Nutrient Variation On Tree Species Composition and Distribution in University of Uyo Arboretum was investigated. Using systematic sampling method in sampling soil and vegetation parameters. A total of eight (8) soil samples were obtained at two soil depths (0 – 15cm and 15 – 30 cm) from four plots. The result revealed that six (6) tree species from 5 families (Lamiaceae, Fabaceace, Urticaceae, Moraceae, and Rubiaceae). Were Gmelina arborea had the highest occurrence with frequency of 100% while Musanga cecropioides, Treculia africana, Acacia auriculiformis and Nauclea diderrichii had the least frequencies of 25% correspondingly. Tectona grandis recorded the highest density (275 stems/ha) while Treculia africana and Musanga cecropioides had the least density (20 st/ha each). Nauclea diderrichii (12.66m) was the tallest species while Tectona grandis(6.12m) was the shortest species .Acacia auriculiformis and Nauclea diderrichii also had the largest basal area (2.0±0.00 m2/ha) while the least was recorded for Musanga cecropioides (0.80±0.00m2/ha). Dominance index ranged from 0.654 to 0.347. Also, Shannon and Simpson diversity indices ranged from 1.079 to 0.529 and 0.653 to 0.345 respectively. Correlation analysis indicated soil total N content limited the distribution of Gmelina arborea, sand, calcium, magnesium and effective cation exchange capacity significantly (P>0.05) influence the occurrence of Acacia auriculiformis and Musanga cecropioides, while potassium significantly (P>0.05) influenced occurrence of Treculia africana in the forest. Conversely, the distribution of Tectona grandis and Nauclea diderrichii were sensible to percentage of silt particles and concentration of potassium ions in the soil respectively. These results further confirmed the notions that pedological indices and nutrient status of soil play critical roles in plant species distribution and vegetation morphology in natural ecosystems. The information obtained in this research could be useful in management of indigenous forest ecosystems.
TABLE OF CONTENTS
Title Page i
List of tables ix
List of figures x
CHAPTER ONE: INTRODUCTION 1
1.1 Background information 1
1.2 Statement of problem 3
1.3 Objectives of the study 4
1.4 Justification of the study 4
CHAPTER TWO:REVIEW OF RELATED LITERATURE 5
2.1 Relationship between soil and vegetation 5
2.2 Physico- chemical features of forest soil ecosystems 5
2.3 Floristic composition of forest ecosystem 8
CHAPTER THREE:RESEARCH METHODOLOGY 11
3.1 Study Area 11
3.2 Vegetation and Soil Sampling 11
3.3 Quantitative Determination of Vegetation Parameters 12
3.3.1 Height 12
3.3.2 Basal Area 12
3.3.3 Girth Size 12
3.3.4 Frequency 14
3.3.5 Density 14
3.3.6 Importance Value Index (IVI) 14
3.3.8 Relative Density (Rd) 14
3.3.9 Relative Dominance (RD) 15
3.4 Laboratory Procedures for Soil Analysis 15
3.4.1 Physical Analysis (Particle Size Analysis – Hydrometer method) 15
3.4.3 Chemical Analysis 17
3.5 Statistical Data Analysis 22
CHAPTER FOUR:RESULTS AND DISCUSSION 23
4.1 Results 23
4.1.1 Tree species composition of the University of Uyo, arboretum by families 23
4.1.2Important value (dominance) of tree species in the study area 23
4.2 Discussion 27
CHAPTER FIVE:CONCLUSION AND RECOMMENDATION 29
5.1. Conclusion 29
5.2. Recommendation 29
1.1 Background information
Vegetation is the assemblage of plant species and the ground cover they provide (Burrows, 1990). It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader than the term flora which refers to plant species composition. The vegetation type is defined by characteristic dominant species, or a common aspect of the assemblage, such as an elevation range or environmental commonality. Ecology is the scientific analysis and study of interactions among organisms and their environment. It is an interdisciplinary field that includes biology and Earth science. Ecology includes the study of interaction organisms have with each other, other organisms, and with abiotic components of their environment. Topics of interest to ecologists include the diversity, distribution, amount (biomass), and number (population) of particular organisms; as well as cooperation and competition between organisms, both within and among ecosystems.
The tropical rainforest has been identified as the most biologically diverse terrestrial ecosystem on earth (Turner, 2001; Gillespie, Brock, and Wright, 2004; Onyekwelu, Mosandl, and Stimm, 2008; Schmitt, Burgess, Coad, Belokurov, Besançon, Boisrobert, Campbell, Fish, Gliddon, Humphries, Kapos, Loucks, Lysenko, Miles, Mills, Minnemeyer, Pistorius, Ravilious, Steininger, and Winkel, 2010; Food And Agricultural Organisation, 2010; and International Union for the Conservation of Nature, 2010). In terms of tree composition and species diversity, tropical rain forests are Earth’s most complex ecosystems (Gebreselasse, 2011). Trees are often the most conspicuous plant life form in a typical tropical rainforest. The rainforest acts as main repository of the genetic diversity of both flora and fauna. According to Ford Foundation(1998), a typical tropical rainforest is a complex community whose framework is provided by trees of many sizes. Upon the framework of the trees and within the microclimate of the canopy of the trees, grow a range of other kinds of plants such as climbers, epiphytes, strangling plants, parasites and saprophytes. Generally, a tract of rainforest is often viewed as a crop of merchantable timber trees rather than an interdependent high diversity ecosystem of potential multiple value (PanayotouandAshton, 1992; Ikojo, Olajide and Uwadinma, 2005).
Nigerian land, which covers a total area of 92.4 million hectares, has 9.7 million hectares, about 10% of the country, as forest (ITTO, 2011). Of which, only a small part of this forest is lowland rainforest. Even in the late 1990s it was estimated that only 1.19 million hectares of lowland rainforest remained in the country, and about 288 000 hectares of which was in official forest reserves (ITTO, 2011). Recent global forest resources assessment revealed that Nigeria is one of the five countries in the world with the highest annual rate of deforestation for the period 2000 –2010 (Steininger, and Winkel, 2009;). These changes have caused the loss of some plant species and a decline in the biodiversity conservation status of the forest and environmental quality. The sustainable management and use of these resources is essential for the nation’s economic and environmental security (Akinsanmi, 1999). The need to provide adequate quantitative and qualitative ecological data to guide forest owners and managers in fashioning out realistic and effective management strategies is imperative.
The need to conserve the remaining areas of tropical rainforest cannot be overstressed. The tropical rainforest ecosystem is a vast source of livelihoods of millions of people from time immemorial. This is because many of the timber trees in the tropical rainforests produce a variety of highly valuable non-timber products like edible and medicinal fruits, seeds, nuts and oils. Also, a considerable number of trees produce industrial materials like latex, tannin, gum exudates, dyes and resin. The timber trees producing economically valuable non timber products have been christened ‘timber plus trees’ (Muul, 1993). Evaluating from a long-term standpoint, non timber products from those trees are more valuable than their timber as the former can be harvested for many years without cutting down the trees, in contrast to timber harvesting and their harvesting activity or extraction has imperceptible perturbation on the ecosystem. Ford Foundation (1998) opined that non-timber forest products are a particularly important part of multiple-use strategies because they increase the range of income generating options of forest-dependent communities, while avoiding some of the ecological costs of timber cutting. As efforts are geared towards preventing utter destruction of the tropical rainforest and ensuring the conservation of its rich biodiversity, adequate quantitative and qualitative ecological data on tree species that produce multiple products are imperative. Such data are needed for fashioning out realistic and effective conservation strategies. The required ecological data include species composition, abundance of each species, stem diameter distribution and abundance and regeneration potential of each species.
Forest structure is both a product and driver of ecosystem processes and biological diversity. Information on forest structure is an essential ingredient for sustainable forest management planning. The importance of forest structure is especially apparent in tropical rainforests where trees can reach great heights and diameters (Gray and Spies 1997; Onyekwelu, Biber and Stimm 2003). In these forests, structures play many roles in the ecosystem functioning. For instance, large leaf areas intercept radiation and precipitation; gaps in dense canopies allow trees, shrubs, and herbs to regenerate; and large live and dead trees provide specialized habitats for many animal species (Turner, 2001; Griffiths, Bradshaw, Mraks, and Lienkacmper, 1996). Height and diameter distributions may provide an indication of the relative proportion of old to young trees, which has implication for conservation and management. The bulk of the remaining virgin tropical rainforests in Nigeria is found within Cross River National Park (CRNP), while forest disturbance and fragmentation, caused by illegal logging as well as land conversion for local agriculture, is visibly increasing in the remaining parts of the country (Bisong, Mfon, 2006; Ogunjobi, Meduna, Oni , Inah, and Enya, 2010).
Also, it is necessary to assess the influence of vegetation of on soil, which will provide the baseline data on which subsequent assessments will be based for conservation and management decisions. Several studies have indicated that tree species abundance has been shown to be co-related with the physico-chemical and nutrient status of soil in many areas (Mata et al. 2011; Nizam et al. 2006; Teixeira et al. 2008). Soil contains nutrients that are required by plants to grow (Othman &Shamshuddin 1982). Hirai et al. (1995) reported that soil physico-chemical characteristics and topography influences the growth of Dryobalanops aromatica and Dryobalanops lanceolata in Sarawak. The physico-chemical makeup of the soil also influences the production rate of seeds and fruits of plants species (Whitmore 1984). An investigation on physical factors of an ecosystem is therefore important to elucidate the possible limiting factors in controlling plant species abundance. It is important to know whether the soil properties and nutrient variation is consistent with the floristic variations found in University of Uyo Arboretum. Information obtained on the soil status in this arboretum is expected to serve as a baseline data for other ecological studies and conservation activities within and between native forests.
1.2 Statement of problem
University of Uyo over the past three decades have nurtured a number of tree species in what is known today as ‘UNIUYO’ arboretum managed under the auspices of the Department of Forestry and Natural Environmental Management. At present this facility serves only for students’ practical’s and commercial purposes since older tree species are selectively exploited for timber. Till date, little is known about the soil nutrient status in relation to trees population distribution in the reserve because no research has been published in this regard. Upon this premise, this study aims at assessing the plant species diversity status, population dynamics and soil nutrient flux pattern in this institutional arboretum with a view to identifying significant interactions.
1.3 Objectives of the study
The aim of this study is to assess the effects of nutrients variation on their abundance and distribution of tree species in the University of Uyo arboretum. Therefore the specific objectives of this research were to:
a. Identify and classify tree species found in the arboretum
b. Determine importance value index (IVI) of the tree species in the arboretum
c. Determine the tree species dominance and diversity in the arboretum
d. Determined the relationship between soil properties and tree species distribution
1.4 Justification of the study
This research incorporates an earnest attempt to appraise the vegetation of University of Uyo arboretum in with a view to highlighting plant diversity status, population dynamics and nutrient-relations in the forest. The findings of this research will help the institution, government and other stake holders by providing useful information which may be useful in the management and conservation of this and other indigenous forests..