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1.0         INTRODUCTION




importance of

trees to  smallholder farmers  is well-known, and includes the

provision of


products (fodder, fuel, construction materials,

food, income)

(Ardayfio 1986;

Becker, 1986; FAO, 1986;  Gutteridge  and


1993; Larsson,

1990), as well

as  a

host of environmental services (Arnold, 1992).

Agroforestry  is  a natural  resources  management  system


through   the

integration of


on  farms and  in the agricultural  landscape, diversifies and


sustains production for increased social, economic and environmental benefits for land users at all levels (ICRAF,2004).

Agroforestry has therefore been widely promoted within smallholder farming systems as a means to enhance rural livelihoods while reversing the degradation of soil, water, biodiversity and related environmental services. However, tree planting is often uncritically equated with environmental conservation, leading also to negative repercussions. Trees cultivated on farm can have both positive and negative affects on other system components (crops, water, livestock) and users. Yet despite the potential for managing these trade-offs so as to foster more socially and environmentally optimal outcomes, many research and development organizations continue to behave as if agroforestry were a purely technical activity devoid of any social or systems


repercussions beyond the household level (Lwakuba, et al., 2003; Ssekabembe, 2004). Lessons on how to more optimally integrate trees into densely-settled agricultural landscapes are therefore sorely needed.

Improving soil fertility is a key entry point for achieving food security, reducing poverty and preserving the environment for small holder farms in sub-saharan Africa (FAO, 2007). As noted by (Stoorvogel et al 1993), land degradation and declining soil fertility are being viewed as the critical problems affecting agricultural productivity. Sustaining soil fertility has therefore become a major issue in agricultural research and crop production. Since sub-saharan Africa is the home of the world poorest people of whom 90% live in villages and rely on substance agriculture (Bationo and Buenkert, 2001), sustaining soil fertility must be based around affordable practices which attempts to achieve the result of having higher crop production at low cost. One good example of such a system is agroforestry as noted by (Gnankambary, 2007).

Nair (1989) has explained that the agroforestry approach to land management offers a viable option to make use of the indigenous knowledge about such underexploited species and integrate them with other preferred species for the production of multiple outputs and services from the same unit of land in a sustainable and socially acceptable manner. Several such plants that are already known to exist in many indigenous agroforestry systems in different parts of the tropics and subtropics include palms, bamboos, fruit trees, medicinal and aromatic plants, etc., to name a few. Most


of these provide multiple products (and services), often in repeated harvests at annual or shorter intervals; many are nitrogen-fixing and/or have other soil-improving attributes, and all of them thrive in association with other herbaceous and woody species.

Agroforestry has focused its strategies on ways of improving crop yield to meet the demand of human subsistence (Akinnifesi, 2008). Trees are a very vital component of the ecosystem and feature prominently through their use by man through the centuries. Trees according to Muhammed (2009) serve man‟s needs in several ways, including carbon sequestration, used for food (fruit trees) and fodder for animals, improvement of biodiversity, increase crop yield, source of fuelwood. Trees and shrubs are of value in agriculture as they directly or indirectly contribute to crop and livestock production. They provide fodder to animals and replenish soil fertility. Similarly, they are useful to people when they provide wood for various purposes, when used in human and veterinary medicine and also for environmental conservation.

Natural resource degradation in many areas is of increasing concern to the global community. This is not due solely to a concern about poverty and the loss of environmental services to local residents; it is also about ensuring the provision of these services to off-site (downstream, urban) users. Watershed management, integrated natural resource management and other multi-stakeholder approaches have


gained increasing momentum as promising approaches for reversing these trends. Agroforestry has an important role to play in integrating livelihood and conservation objectives in upper catchments (Denning, 2001; FAO, 1976; Nair, 1993). However, the „„deliberate growing of woody perennials on the same unit of land as agricultural crops and/or animals‟‟ and „„significant interaction (positive and/or negative) between the woody and non-woody components of the system‟‟ which define agroforestry (Lundgren, 1982) often result in negative interactions or involve trade-offs between system components and user groups. This is in large part due to the failure to match particular system niches with the species best suited to them, and the interests of the landowners with the interests of other affected parties.

Man through his interference with natural vegetation communities in form of bush burning, perennial cultivation, and settlement has greatly altered the natural vegetation (Ibrahim, 2005). Trees as an integral part of the ecosystem help in maintaining the integrity of the ecosystem. Trees when present help in absorbing carbon dioxide in the atmosphere. Through sequestration, levels of carbon dioxide in atmosphere is lowered thus helping to reduce global warming and protecting the biosphere. The Intergovernmental Panel on Climate Change (IPCC, 2007) notes that world carbon dioxide concentration in the atmosphere is about 387 parts per million volume (ppm). It is believed that if values of carbon dioxide keep rising, there will be dire consequences for man such as catastrophic heat waves, melting of ice caps and


drought in subtropical areas which impact negatively on crop production (UNEP, 2008).

Ibrahim (2005) emphasized that Nigeria has been estimated to have 9.6 million hectares of forest and woodlands and that if just two-third are actively maintained rather than cleared, or just left to decay, it could absorb 50% of carbon dioxide emissions from burning fossil fuels and dung in homes of more than 70 million rural dwellers.

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 small holder farers with two third having farm sizes below two hectares (2 ha) (Altieri, 2008). Small-holder 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).

Trees play an important role in maintaining soil fertility (Zakariya, 1997). Trees like Faidherbia albida on small holder farms have the propensity of maintaining soil fertility because of its nitrogen fixing ability through its rooting system and litter of high quality (high nitrogen content) that it drops (Yakubu, 2009). Young (2002) and Zakariya (1997) attest to the propensity of Faidherbia albida to boost crop yield under its canopy. Other tree species such as Eucalyptus camldulensis are not favoured in boosting crop yield (Young, 1989), because of its large uptake of water, thereby impacting negatively on adjacent crop yield conversely, Eucalyptus camaldulensis


has been employed to lower water table and so reduce salination (Young, 1989). The binding effects of tree roots help curb menace of escalated erosion which could be in form sheet erosion as a result of non-concentrated runoff which removes topsoil substantially (Jeje, 1987). This ultimately leads to loss of productivity of farmland.

The contemporary effect of deforestation, climate change and population pressure are militating against the diversity of trees and also their relative density (Yakubu, 2009) and the major impact of this could be loss of these diverse species which could become endangered.


The density of trees and their diversity is a very critical element of improving land productivity in farming ecosystem. Monitoring of biodiversity, which entails periodic assessment of occurrence (or abundance) of a subset of plant, animal and microbial taxa in sample localities has for long been recognised as a significant scientific challenge.There is hence the need for information on both the density and diversity of tree species to be documented on cultivated lands. This is especially so in areas of marginal productivity which are highly susceptible to land degradation.

In semi-arid areas of northern Nigeria, trees are allowed to grow on farmlands for multiple reasons, including source of food, medicines and fodder, improving land productivity, as well as provision of wood for both fuel and non-fuel wood uses. Given the multiplicity of the uses as well as the well-known benefits of trees on especially farmlands of degraded areas, there is the need to have adequate


documentation on both the diversity and density of tree species growing on such farmlands.

Previous researches on trees growing on smallholder farmlands in northern Nigeria have concentrated largely on assessing the influence of tree density on soil properties (Musa, 1994; Akinifesi, 2008;Omotayo 2008) or the changes over time in tree density over farmlands (Muhammed, 2009). Not much research information is particularly available on the influence of density and diversity of tree species smallholder farmlands on crop yield from such farms. This study hence seeks to advance an understanding in this regard using Daura area of Katsina state as a case study.


The aim of this study is to examine the spatial pattern of changes in density and diversity of trees on smallholder farms and assess the influence of the changes on crop yield in Daura area of Katsina state.

1.3.1     OBJECTIVES

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