ABSTRACT

This research on tree species diversity and soil status of Kogo Forest Reserve was carried out to determine tree species composition, richness and evenness, relative density and dominance. Soil physical and chemical properties as well as microbial count were also determined. Eight sample plots each of dimension (100m x 100m), were laid at random within the Forest Reserve, and tree species found were enumerated by point centered quarter (PCQ) method. Composite soil samples were collected at three different depths from each sample plot. A total of 249 tree stands were encountered in the Reserve, belonging to twenty nine different tree species, distributed within 25 genera and into sixteen 16 families. Family Caesalpiniaceae had the highest number of six species in five genera, followed by Mimosaceae with four species belonging to four different genera. Families Anacardiaceae and Combretaceae had three species each while family Moraceae had two species within a genus and all the other eleven 11 families had one species each. Species Anogeisus leiocarpus had the highest relative density and dominance of 24.49% and 23.23% respectively, followed by Isoberlinia doka with 18.07% and 13.14%, and the least was Annona senegalensis having 0.40% and 0.05% respectively. Shannon’s diversity index was 2.626, Species evenness (EH) 0.78, Species richness (d) 1.84 and Shannon’s maximum diversity (Hmax) was 3.37. Bulk density of the soils varied from1.3-1.5gcm3, porosity 36-57% and particle density ranged from 2.24–2.41gcm-3 and not significantly different (p>0.05). Sand, silt and clay contents ranged from 71.9-88.2%, 8.7-16.5% and 3.1-11.6% respectively and significantly different (p<0.05). Textural classes of the soils were predominantly loamy sand. Soil pH was weakly acidic (6.13-6.63) and significant (p<0.05). Organic carbon content of the soil was moderate (3.72-7.11g/kg) which decreased significantly with increased depth. Total Nitrogen ranged from 0.29-0.41g/kg with no difference (p>0.05) by location but differed significantly with increase in depth. Available phosphorous varied significantly with location (1.87-2.21mg/kg) and decreased with increase in depth but statistically there was no significant difference (p>0.05). Exchangeable Ca, Mg K and Na were all significantly different (p<0.05) by location and decreased with increase in depth but only Ca and Na differed (p<0.05) significantly. CEC also varied significantly by location (p<0.05) and decreased with increase in depth with no significant difference. Kogo had a moderate diversity on a fairly fertile soil, hence closure of the forest for exploitation with maximum protection to allow the forest to fully regenerate will enhance the fertility of the soil and is therefore recommended.

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CHAPTER ONE

1.0         INTRODUCTION

1.1         Background of the Study

Forest trees help in improving forest soil fertility through biological nitrogen fixation, phosphorus solubilization and decomposition of organic matter in their rhizosphere and non-rhizosphere zone, which play an important role in plant community nutrition, and maintaining the forest soil fertility, thus enhancing species and structural diversity. These forests are disappearing at alarming rates owing to deforestation for extraction of timber and other forest produce (Murphy and Lugo 1986; Raghubanshi and Tripathi 2009) or total conversion to other uses. Nigeria is among the ten countries with the highest annual net negative change rates from 2000–2005 degrading at the rate of 3.3% (FAO, 2006). Forest degradation is usually accompanied by species extinction, reduction in biodiversity and decrease in primary productivity. This highlighted the need to quantify or determine habitat characteristics like soil status, floristic composition and species richness in our forest reserves for proper conservation and sustainable management of the forests resources.

Tree species are perennial woody plants. Huxley (1992) defined tree as a woody plant that has many secondary branches supported by single main stem or trunk with clear apical dominance. It has a minimum height specification at maturity varying from 3m to 6m, and a minimum of 10 cm trunk diameter (30 cm girth) (Ghate, 2007). Compared with most other plants, trees are long-lived, some reaching several thousand years old and growing to up to 115 m (377 ft) high (Friis and Balslev, 2005). Tree species is a plant form that occurs in

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many different sets of species, orders and families. They show a variety of growth forms, shapes, vegetative and reproductive characteristics, leading to their great range of diversity.

Species diversity refers to the variety of species within a community or a region. It is a count of the different species present in an area. Species richness is essentially a measure of the number of species in a defined sampling unit. And it is the basic component of diversity of any community, while species evenness refers to relative abundance or proportion of individuals among the species. The distribution and abundance of different tree species over a landscape is what constitutes diversity in respect of tree species.

This study investigated the tree species diversity and soil properties of Kogo forest reserve in southern Katsina State, North western Nigeria.

1.2         Problem Statement

An indepth and up to date knowledge about the number of tree species and status of soil condition in most of the existing forest reserves is lacking or inadequate. Surrounding these natural areas are villages, agricultural lands and cities in some cases. As the most populous country in Africa, Nigerian populace exerts extreme pressures on biodiversity of the remaining forests. Wildlife, trees, and many other plants are over exploited and poached, and the natural environment faces increased degradation from expanding unsustainable agriculture, water pollution, air pollution, and a variety of other anthropogenic factors (USAID/NIGERIA, 2008). On the global scale, the total net change in forest area in the period 1990–2000 is estimated at 8.9 million hectares per year equivalent to a loss of 0.22% of the remaining forest area each year during the period, and by 2000–2005 it is estimated

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at 7.3 million hectares per year, equivalent to a loss of 200 km2 of forest per day, about 0.18% of the remaining forest area each year during the period compared to the 1990s (FAO, 2006).

Lack of strong conservation ethics, law enforcement, corruption and extreme poverty, leads to severe encroachment and illegal exploitation of forest tree resources had also resulted to depletion in biodiversity of the existing forests, reduced productivity and tree species extinction. This has excessively exposed most of the forest soil surface to solar radiation, which provoke to desertification. And as trees depend on soil to supply four basic needs; stability, nutrients, water, and oxygen (TFF, 2007), soils also depend on trees to provide raw materials that sustain its productivity under forest condition.

Lack of information about the present status of most reserved areas, in terms of species composition and soil status makes management difficult. Knowing the available forest tree species composition and soil status will aid in suggesting appropriate silvicultural treatments that will enhance productivity and maximum protection of our environment.

1.3         Justification of the Study

The dynamic interaction between vegetation and soil is so strong that it's unclear which is dominant. Because soil helps secure and renew the forest and on the other hand, forest helps secure and renew the soil. The forest cover protects the soil from extreme heat and cold while slowing the natural forces of erosion like water, wind, and gravity. Soil sustains the forest and provides raw materials for its life; fallen leaves, woody debris, and dead animals recycle through the soil (TFF, 2007).

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The importance of soil chemical and physical properties to tree growth has gained considerable attention in recent years, largely because of greater demands placed on forest soils in terms of productivity, but also because of indications that the recent decline in forest cover may be related to soil changes induced by atmospheric pollution and indiscriminate removal of vegetation as a result of land use changes (Vanmechelen et al., 1997). This requires management intervention to maintain the overall biodiversity, and to improve productivity and sustainability of the existing forests.

This pointed out the need to determine and document the soil properties for proper management planning, these properties or parameters which may include; soil pH, soil bulk density, particle size distribution, soil organic matter/carbon content, soil microbial content, micro and macro nutrient contents among others. This may be used to assess the soil’s capacity to perform its ecological functions within the forest ecosystem (Vanmechelen et al., 1997).

Therefore, determination of the current characteristic features such as the tree species diversity and soil status will no doubt reveal an insight on ways to prescribe and execute appropriate managerial measures based on identified specific objectives.