ASSESSMENT OF TREE SPECIES DENSITY AND DIVERSITY ON SMALLHOLDER FARMS IN PARTS OF KANO STATE

ASSESSMENT OF TREE SPECIES DENSITY AND DIVERSITY ON SMALLHOLDER FARMS IN PARTS OF KANO STATE

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ABSTRACT

This study attempts an assessment of tree species density and diversity on smallholder farms in Wudil, Bichi, Ungogo and Gaya areas of Kano State. A systematic random sampling was adopted in collecting data. Ten smallholder farms were surveyed in each of the four local government areas. In total, forty farms make up the sample area. A 100m tape was placed in straight line on each farm. 10m x 10m measurement of quadrats were established along the line transect in each of the farms which resulted in a total number of forty quadrats. Tree details such as the density, diversity, height and girth were obtained within each quadrat. The significant difference in tree species within the four locations was computed using chi-square test. Result revealed that 12 different types of trees were found in the average of 1.83tree/m2 of the smallholder farms. There was an average of 4.7 tree species in every meter square in the smallholder farm. It was evident that the most dominant tree species found in the four areas was Azadirachta indica (Darbeija) 37.5%. This dominant species is exotic, planted as a village tree for its shade and fuel wood supply. Mangifera indica (Mangwaro) is the second most dominant tree species which is fruit bearing and produces shade with 16.7%. Adansonia digitata is the third in importance 8.4%. However, among the rare species were Ceiba pentandra (Rimi) with 2.1%, Ziziphus spina-christi (Kurna) (2.1%) and Psidium guajava (Goba) with (2.1). These species are found to be very important for medicinal and fuel wood. It was concluded that the density and diversity of tree species in the study areas had significant variation. Parts of the trees were found to be essential, therefore it is recommended that effort should be made to support, replant and protect these species which are both indigenous and exotic.

CHAPTER ONE

1.1 INTRODUCTION

A tree is a plant cover of the earth surface which prevents the surface from degradation. The stems are known as trunks, which do not branch until a considerable height above the ground. To be considered a tree a stem must have a minimum circumference of 30cm (Spencer et al, 1969)  A tree should have a single trunk or main stem, and a clear crown, formed by side stems or branches. In case the plant has several woody stems or a minor height, the plant is said to be a bush. Having a woody stem and producing side shoots or branches are essential for a plant to be considered a tree. In a broad sense, taking into account the shape and size, plants as the palm trees can be included within the same definition, although they are devoid of branches and they are actually formed only by stems and leaves.

Trees are of great importance to man and his environment. Trees are significant in purification of the atmosphere through providing a microclimate which makes the environment conducive for healthy living. Trees play a major role in providing the oxygen we breathe and removing carbon dioxide, causing global warming. Trees are important features that tell the quality of land. It provides food, shelter, wild life habitat, fuel and daily supplies such as medical ingredients and paper. Trees contribute in balancing the earth’s CO2 supply and exchange, acting as a key link between the atmosphere, biosphere and hydrosphere (Archer et al, 2000). Man has conserved and cultivated trees to provide food, shelter, building materials and serves as source of energy. Trees protect the soil from direct impact of rainfall which could lead to erosion.

When trees are destroyed the natural ecosystem is undermined leading to environmental imbalance. The International Union for the Conservation of Nature (I U C N, 1993) reported  that over one-tenth of known tree species of the earth are considered to be under threat. Furthermore, UNEP (2008) noted that deforestation may primarily lead to the extinction of between 5 to 15 percent of the world species between 1990 and 2020. Therefore, tree composition and management becomes very important in achieving sustainable development. The type of trees species growing in a specific location is related to factors such as climate, topography, geology, soil conditions, natural disturbance and anthropogenic disturbance. Due to the importance of trees and its lineages with the environment and human activities, geographers have long been interested in the classification of trees and the proves that structure vegetation over global, regional, and local spatial scales (Mac Donald 2003). The scientific classification of the earth into biomes, regions with similar vegetation and climate regions, was of great interest to early biogeographers such as Alexander Von Humboldt (1969-1859) Today, there are a number of vegetation classification systems in use around the world, as well as many theories and models of how vegetation responds to disturbance and environmental change over different spatial scales. Any vegetation classification system or consideration of how environment change or disturbance impacts vegetation, must be based upon, supported with, or tested by, data on present or past distribution that are collected in the field in a systematic and scientific manner. One way to quantity vegetation is to examine the present or past species composition of a vegetation type. Species composition is defined as a list of plants found in a particular region of the world or study site. Species composition and abundance can also be examined from a specific time period for historic studies of vegetation. Bio-geographers have quantified the species composition of regions around the world by collecting and identifying plants in different vegetation types. At a global spatial scale, this has resulted in the identification of a number of bio-geographic floristic provinces, which contain many endemic species that are unique to each region. Geographers also quantity species composition by adding up the number of different species encountered in a study area, often referred to as species riches and bio-geographers have long been interested in patterns of species riches across a number of environmental gradients. A second way to quantity vegetation is to examine the structure or physiognomy of the dominant vegetation canopy. This is a two-dimensional view or profile of plants in an area. A distinction is often made between natural and semi-natural vegetation and between them and cultivated crops. Natural vegetation is a plant community which has been totally unaffected by human activities whether directly or indirectly. This type of vegetation is rare to come by in the world today because of the rising world population and intensity of land use. Since farmlands and tree plantations occupy a very large proportion on the earth’s surface, the cultivated crops and trees form a significant component of the vegetation cover of the earth. A variety of field method can be used to study vegetation types (Bonham, 1989). These include the line transect, belt transect, point-centered quarter method, and quadrat or plot.

The study of vegetation by bio geographers applies the perspectives of both space and time to understand the form and functioning of the earth’s planets. Almost all life on the planet depends upon the thin cover of vegetation. Not only do plants capture solar energy through photosynthesis to power the food-chain, but they also provide habitat for animals and many resources for people. The state of the world’s vegetation is a major concern today. Vegetation loss and fragmentation due to human land-use and climate changes due to global warming place stresses upon vegetation and require careful and informed management strategies to mitigate such loses. Biogeographers, through the use of pale ecological techniques such as pollen analysis and tree-ring analysis, can help in understanding the natural dynamics of vegetation, responses to past climate and environmental changes, and the prehistoric impact of people. Through modern survey techniques, biogeographers document the present distribution of plants and vegetation formations, detect recent changes and provide critical information on the current distribution of the planet’s biodiversity. Carefully conducted pale vegetation studies and modern vegetation surveys provide data that is not only useful today, but can be drawn upon by future biogeographers, ecologists, and resource professionals to help in their efforts to understand and conserve plant species and vegetation communities.                

1.2 STATEMENT OF RESEARCH PROBLEM

The contemporary effect of deforestation, climate change and population pressure are militating against the diversity of trees (Yakubu 2010) and the major impact of this could be loss of these diverse species which could become endangered. Hence the need for information on both the density and diversity of tree species to be documented on cultivated farmlands. The study area is a fragile ecological zone which is highly susceptible to land degradation. This research intends to provide first hand information on the density and diversity of tree species on smallholder farms situated in four local government areas of Kano.  It compares the types and number of trees per meter square, with a view to providing land managers with the necessary information for effective land resource management.

1.3  RESEARCH QUESTIONS

1.      What are the actual types of trees found on smallholder farms in the study area?

2.      How are tree species distributed on smallholder farms in the study area?

3.      What are the height, girth (trunk diameter) and density of trees in the study area?

4.      What are the dominant species as well as the rare (endangered) Species found on smallholder farms in the study area?

1.4 AIM AND OBJECTIVES OF THE STUDY

The aim of this research is to assess tree species density and diversity on smallholder farms in parts of Kano Close-Settled-Zone

The aim will be achieved through the following specific objectives.

(i)                 To assess the current density of tree species on smallholder farmlands in the study area.

(ii)               To determine the diversity of tree species in the study area. 

(iii)             To spell out the distribution of tree species according to their height and girth.

(iv)             To identify the dominant species as well as the rare (endangered) species on smallholder farms.

1.5       SCOPE OF THE STUDY

The study is limited to Wudil, Bichi, Ungogo and Gaya Local Government areas of Kano State, Northern Nigeria. These areas are characterized by small Smallholder cultivation. The study assesses the changing density and diversity of trees on smallholder farms in this fragile ecological zone where over 70 percent of the population are reported to be peasant farmers.

1.6 JUSTIFICATION OF THE STUDY

Trees play an important role in protecting the environment. They are responsible for providing the oxygen we breathe and removing carbon dioxide, causing global warming. The trees protect the soil from erosion. Most people in the study area do not know the importance of trees, and some even believe that trees may always be there. Some people cut down trees because they lack the necessary knowledge, they do not know the importance of trees. Other reasons could be attributed to difficult economic situation which makes alternative sources of fuel expensive, therefore, people resort to fuel wood because it is a cheaper source when compared with kerosene or cooking gas. Increasing demand for wood for various purposes has however greatly reduced the density and diversity of indigenous trees species such as Parkia biglobosa (Dorawa, Acacia) etc in the study area (Olofin et al, 2002). This study investigates the current level of tree species density and diversity on smallholder farms in four Local Government areas of Kano Close-Settle-Zone with a view to assisting land developers in planning and development.        

1.7 LITERATURE REVIEW AND CONCEPTUAL FRAMEWORK

According to Spencer et al (1969) a tree may be described as a plant cover of the earth surface which prevents the surface from degradation. It most often has many secondary branches, supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3m to 6m. Some authors set a minimum of 10 cm trunk diameter (30cm girth). Trees are long-lived, some reaching several thousand years old and growing up to 115m (379ft). Trees are an important component of the natural landscape because of their prevention of erosion and the provision of weather – sheltered ecosystem in and under their foliage. They also play an important role in producing oxygen and reducing carbon dioxide in the atmosphere, as well as moderating ground temperatures. Trees have a great job of pumping up water from underground to the atmospheric vapour which comes down as a rainfall. Through Agro forestry, trees and shrubs help to maintain soil fertility by fixing nitrogen and returning nutrient to the soils in form of organic matter. Farmers have always grown trees on their land, some no doubt with the shrewd idea that this has useful effects on the soil and crop yield (Young, 1998).

Field studies of vegetation began in the early nineteenth century with the work of Alexander Von Humbolt (1805) in plant geography. This was a study of the spatial distribution of taxa and their evolutionary relationships, and has become the classic of the natural sciences concerning dispersal. Overtime, various areas of specialization within vegetation study have developed and the approaches that have developed towards vegetation study are very widespread. The vegetation cover of the earth is extremely complex and, thus, all vegetation data gathering must be selective since it would be impractical to undertake total recording or description of vegetation.

Before any method of vegetation sampling is used in the field a large number of considerations must be examined. Firstly, the primary aim in making the data collection must be appreciated since too little or too much data and a lack or excess of data must be avoided. Secondly, consideration both of time and expense are needed since both are usually limited, and the normal requirement is the most useful information with the least amount of time and money spent. Thirdly, the nature of the vegetation cover must be assessed.

Daura (2011) carried out an assessment of tree diversity on farmed parkland agro forestry systems on smallholder farms in Daura, Katsina State. Seven transects were taken at an interval of 1km across the main access route (Daura-Katsina) because they cut across the major land units in the study area, with five farmlands selected on either side of the road along each transect, thus giving a total of 70 farmlands. On each farmland, four parameters were studied, namely; tree diversity, nitrogen fixing trees, total number of tree species and size of farmland. The results obtained show that average size of farmlands in the area is 0.34ha across the 7 transects. The mean diversity of trees in the area is 0.59. Majority of the farms (98%) in the area are under mixed cropping system.

According to Altieri et al (2008), Africa has approximately 33 million small farms representing 80% of all farms on the continent. Majority of African farmers are smallholder farmers with two third having farm sizes below two hectares (2ha) (Altieri, 2008). Smallholder farming in Northern Nigeria is characterized by small and fragmented plots using simple implements with little investment and depending largely on self and family labour (Yusuf, 1994).

Yusuf (2013) examined and assessed the farmed parkland vegetation diversity, composition and change. Satellite imagery and topographical map were used for quadrat demarcation and sampling six quadrats of 1km2 each were used to inventory the total vegetation species. Fifty different vegetation species were found and categorized into trees (64%) and shrub (36%). The trees and shrubs average densities were found to be 569 per km2, and 1066 per km2 respectively. It was also found that the three most dominant species accounted for 51% of the total trees inventoried (Parkia biglobosa, Anogeissus Leiocarpus and Adosonia digitata). However, there was evidence of some indigenous species, being threatened to extinction. There species include Ficus ingens, Acacia polycantha, Terminalia arecenniodes, Lannea acida and Annona senegalensis.

Egodawatta et al (2014) Compares the types and density of tree species in home gardens of inherited and settled lands in close proximity of Anuradhapura city, Sri Lanka. Mean harvestable tree density was 54.5 trees/ac in inherited lands compared to 40.3 trees/ac in settled lands. Certain tree species are more abundant in one than the other. Exotic timber tree flora represented approximately 30% of total tree population in settled compared to 16% in inherited. Exotic timber tree flora mainly dominated by Tectona grandis, and Berrya cordifolia in settled lands concerning more economic returns. In inherited lands, multipurpose trees i.e. Artocarpus heterophyllus, Azadirachta indica and Mangifera indica were highly abundant concerning diversity and food security. Cocos nucifera was the most abundant tree species in both categories accounting more than 40% abundance. Tree species such as Tamarindus indica was restricted to inherited lands and Felicium decipiens and Swietenia macrophylla to the settled lands.

Studies were conducted in the early 1970s and 80s in the Kano West and Kiru using field inspect and air photo interpretations. The two sites represent in and out of Kano close settled zone. Maps were provided to depict points of data generation.

In the earlier study 250m x 250m (6.25ha) parkland and 10m x 10m for forest quadrats were selected at fifteen points on the ground at the Kano West area and 15 at Kiru area with the help of the existing maps of the selected points and Kabo NE and SE topographical maps, these points were identified both in the laboratory and in the field through reconnaissance study. Communities where the earlier study was conducted helped in locating the sites of the earlier research. The points were mapped out on base maps to guide where to collect the samples. In the laboratory, the areas were also identified and marked on the google – earth image map to identify the exact spot, for the data collection. With the help of GPS, these spots were tracked down physically for the field work. A total of 30 points were identified for data generation.

Kent and Coker (1992) identified four consideration in vegetation studies. They are:

1.                  The purpose of the survey

2.                  The scale of the study

3.                  The overall habitat type – where different techniques are necessary to be employed for different habitat types and growth; and

4.                  Resource availability; which include finance, equipment, manpower, and time.

It is evident that wood cutting is on the increase with technology of using saw machines (Areola, 1991). This of course takes place even in parked plots and remaining unprotected, forest, like Gyarana.

Additionally, due to the increasing demand for fuel farmers lop branches from trees of the parkland either for sale or for their on use (Cline – Cole, 1990:50)

Government, non-governmental organization and other stakeholders should take initiative to educate the populace on the importance of trees. Government should also concentrate on improving the livelihood of the poor so as to reduce deforestation. People should realize that destroying trees reduces the amount of rainfall an area receives. Trees are very important to our environment, it purifies air and provides fruits, wood for human beings. Some trees such as Neem tree (Azadiractha indica) have medicinal values.

A smallholder farm is defined as a farm plot smaller than 2ha and in Kano, in semi-arid northern Nigeria, the average size of farms is 0.3ha (Essiet 1990). The smallholder agricultural production system is the oldest farming system in semi-arid northern Nigeria. It has undergone several modifications over the years in direct response to changes in the environment occasioned by climate changes. This has resulted in a wide array of farm practices within the system, some of which have been described by Essiet (1995). The whole system is anchored on three interactive components of cropping, livestock production and farm forestry (Mortimore et al, 1990) with livestock production farming the strongest link in the system. Most operations are manually executed, and the system exhibits considerable variability in the intensity of cultivation, labour and capital input per unit area of land. Most smallholder farmers in Kano, like their counterparts elsewhere, have always had to cope with a degree of uncertainty in relation to local weather. LEISA (2008) noted, however, that there is little or no doubt that, today, farmers are facing a changing context, with rainfall and temperature patterns moving outside the regular variability ranges.

Yakubu (2010) investigated the density of Faidherbia albida on smallholder farms in the degraded lands of Kano, Nigeria and noted that the density of F. albida on smallholder farms in the degraded land of Kano had declined by 55% (3.56SEM). the implication of this reduced density is not only a decline in animal feed, but more importantly, reduced soil fertility improvement service, in an area where majority of the farmers may not afford chemical fertilizers. According to Yakubu (2010) the diversity of trees on smallholder farms in the degraded lands of Kano, northern Nigeria has also declined by 38% (2.47SEM). This decline which may be attributed to several factors that may have been amplified by climate change, could mean reduction in the vital ecological service provided by such trees on farms. Yakubu (2010) identified that Parkia biglobosa, a nitrogen-fixing tree of the Savanna is presently the most abundant tree on smallholder farms in Kano, with 34% (1.23SEM). This tree species occupies this prominent position mainly because, in addition to its possible fertility improvement, potentials, it is also an economic tree whose leguminous fruits are widely traded and used across the region. Yakubu (2006) reported that exotic tree species, such as Azadirachta indica and Eucalyptus camaldulensis, are becoming quite prominent on smallholder farms in Kano. The implication of this, he noted, is that while some of these species may confer advantage of fast growth and possibly ameliorate the wood fuel crises, others like A. indica may have allelopathic and or other effects that may  inhibit the development of agricultural crops.

Barau (2010) Investigated the flora composition in the Kano Emir’s palace gardens. Field measurements and observations were undertaken at the two gardens for identification of the floral species. That was achieved through mounting of quadrats. Series of interviews with a purposively sampled section of the palace residents aged between 60 and above were carried out. Further measurements and analysis of the gardens were carried using the Google Earth satellite images as well as Kenting Africa Airphoto mosaic of 1980. Findings; The scrublands in this palace have been in existence for centuries and it was converted into gardens during colonial regime and many exotic species were introduced. They served as places for leisure seeking, cattle rearing, royal folkloric services and security. The palace residents hold the gardens with awe many believe there are spirits that reside in the gardens. The two gardens (east/west) are sanctuaries of some endangered plant species. Results of field survey indicated that the gardens have tree neighbourhood of 1.5 metres; with leaf layer of more than 10cm; the average height of trees is 12 metres; the frequency of exotic species is higher than that of local species; and the average girth of trees is 1.3 metres

Faunal  Composition of Emir's Palace Gardens

Floral Composition

Balanites aegyptiaca (desert

date) Azadirachta indica (neem) Ficus thonningii,

Mangifera indica (mango)

Adansonia digitata (baobab)

Psidium guajava (guava),

 Tamarindus indica

(tamarind)

Carica papaya (pawpaw)

Khaya senegalensis

(mahogany)

Vitis xx (grape) Snails Bee

Luffa aegyptiaca

(loofah gourd)

Flamboyant Scorpion

mushroom spp. Firefly

Mubi (2008) investigated species distribution within riparian landscape and came up the following findings; Three distinct zones of vegetation types were identified along the reach. Zone A, the riparian forest was mapped from and within 5 meters away from the channel banks edge and is composed of trees, shrub, tangle and climbing plants. Some of the tree species in this zone include the most conspicuous because of its height and red bright flowers Brachystigia eurycoma, others are Vitex doniana, Andria enermis, and Diospyros spp. Shrubs, tangle and climbing vegetation add up to the thickness of vegetation in this zone. The riparian zone gives way to the out ward adjoining relatively large zone B which is 9 meter wide on average. The zone is dominated by grass and few isolated tree stands. The most occurring tree species in this zone are Anogeissus leocarpus, Perinari excelsa, Crossopteryx februfuga and Nauclea latifolia. The 11 meter wide outermost zone C is covered by woodland and grass; trees constituted the larger proportion of the cover type. Uapaka togoensis, Terminalia glaucoscens, Grewia mollis are some of the common species in zone C. Examination of species distribution in the 117 investigated quadrats of the three zones shows variation in both density and diversity numbers. Minimum species density of 5, and diversity of 5 per 625m2 at sampled unit on the outer straight bank, and maximum species density of 83 and diversity of 8 per 625m2 for the diversity are recorded at sampled unit on the outer convex bank of the channel while, mean values are density 42 and diversity 12. Accordingly, the means densities and diversities for zones A, B and C are 10 and 4 per 125m2 10 and 3 per 225 m2 and 23 and 5 per 275 m2. Zone A which has an average width of 5 meters represent the valley floor area adjacent to the river channel. The section constitutes the genetic flood plain which is largely horizontally bedded and composed of alluvium deposits adjacent to the channel. The section is present throughout the surveyed reach. The location of zone A therefore makes it to have high moisture availability throughout the year, hence the riparian forest in the zone. The high species density 10 and diversity of 4 per 125m2 in the zone could also not be un-connected with the nearness of this zone to the river channel. Soils on the banks within 5 meters from the channel comprised largely of silt loam and sandy loam soils, conditions for the cover type. The high content of litter fall adds up to the quality of soil in the zone. Zone B consist of silt loam to clay loam soil and support relatively low density of 10 and diversity of 3 per 225m2. This could be attributed to the fact that zone B is lying some distance that is within 5 to 14 meters away from the main channel/its genetic flood plain. This makes it moisture deficit for riparian plants which inhabit zone A and is relatively wetter to favor plant species of zone C. Zone B is characterized by silt loam and clay loam soils and its location can best be described as the hydraulic flood plain (to be distinguished from the genetic flood plain) which is inundated at least once during a given return period of a river flood activity. Thus, the low species density and diversity in zone B in partly caused by the periodic hydro-dynamics of the soil, which makes moisture not sufficiently available all year round for the riparian vegetation, particularly for species like Brachystigia eurycoma, Diospyros spp, and Andria enemies the distinctive and specialist tree species in zone A to thrive in the zone. While plant species such as Uapaka togoensis, Psedocidria kochyell, Vitelaria paradoxum of the well drained elevated zone C also found zone B not favorable for their habitation. Nonetheless, annual grasses and few widely dispersed trees for example, Terminalia glacoscens, Crossptaryx februfuga, and Parinari excelsa are the obligaes plants in this moisture transient zone B.    

Furthermore, low species density and diversity in zone B can also be linked to the conservation method practiced by the Park Management. The prescribed annual burning technique to quicken the sprout of new grasses/succulent and nutritious plants for animals to feed on has additionally affected plant species in zone B. When set on fire the grasses and some of the few trees in the zone get burnt completely, rendering the soil bare of surface cover and/or concentration of tree stands. Therefore, species types, low density and diversity in zone B are the result of the interactive effects of the hydro- dynamics and annual burning. As such, only plants that can withstand the dynamic conditions of the zone thrive there. Low density of species in zone B could further be attributed to the contributing effect of the apparent trail of animals along the path, because of the adjacent location of zone B to zone A (close to water channel) and the absence of tangle vegetation that assures ease of movement. On the gravel-sand and sandy loam soils of the 11m wide outermost zone C, large proportion of trees and scattered grasses constituted the cover types. Uapaka togoensis, Terminalia glaucoscens, Grewia mollis are some of the common species in this zone. Species like Brachystisia encrycoma are specialist to their environment, found only on the bank forms of the river in zone A. While, species such as Upaka togoensis, and Anonna senegalensis are generalist of zone B and C. In the study area species types and their distribution vary with distance from the river channel in the same way soil types, elevation and slope gradient vary with relative location to the river channel. With distance from the channel soil type and moisture, slope gradient all varied so also change in species type, density and diversity. This pattern is in agreement with findings, Wittmann et al. (2004) species distribution and diversity var





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