Factors influencing use of multipurpose trees and shrubs in arid and semiarid lands of Kenya

Abstract

Multipurpose trees and shrubs are vital components of arid and semiarid ecosystems. They offer both regulatory and production services, yet there is inadequate information on their actual use and factors affecting utilization of these plant resources. A study was carried out in three agroecological zones (counties) of southeastern Kenya: Machakos (subhumid zone), Kajiado (semiarid zone), and Kitui (arid zone). The research objective was to assess the local uses of multipurpose trees and shrubs and determine how socioeconomic factors (gender, type of occupation, and education level) influenced their use. A field survey was conducted along a 324-km transect across the three agroecological zones. Data were collected from 196 respondents using focus group discussions, key informants, and individual household questionnaires. A total of 86 plant species belonging to 47 plant families were recorded. The Mann-Whitney U-test revealed that women significantly used a higher number of different plant species than men (P < 0.05). The level of education and type of occupation also significantly affected plant use (P < 0.05), with subsistence farmers having primary or no formal education, reporting the highest number of species. Fifteen plant-use categories comprising production and service provision were identified. Plant species use-value index (UVI) revealed 10 indigenous and wild woody species of high value in the study area. Acacia tortilis (Forssk.) Hayne had the highest UVI of 0.33, followed by Commiphora africana (A. Rich.) Engl. (0.17), Terminalia brownii Fres. (0.13), and Zanthoxylum chalybeum Engl. (0.12). There was a significant positive correlation between the reporting frequency for woody species and the overall UVI (P < 0.05). Economic development, climate change, and land use changes jeopardize distribution, utilization, and knowledge preservation of multipurpose woody species. There is a need for monitoring and adoption of gender-sensitive strategies for their sustainable utilization in order to safeguard these unique plant resources from degradation and overexploitation.

Introduction

Multipurpose trees and shrubs are valuable components of arid and semiarid ecosystems and contribute to maintaining suitable conditions for crop cultivation, livestock grazing, and human livelihoods (Malagnoux et al. 2007). They are defined as “all woody perennials that are purposefully grown to provide more than one significant contribution to the production and/or service functions of a land-use system. They are so classified according to the attributes of the plant species, as well as to the plant's functional role in the agroforestry technology under consideration” (Wood and Burley 1991; Foroughbakhch et al. 2009). The term “high value” as applied to the 10 priority plant species determined in this study refers to “valuable” species with monetary value; worth a good price; having desirable or esteemed characteristics or qualities; and of great use or service (FAO 2001). High-value multipurpose trees and shrubs (HVMTs) can therefore be defined as woody perennials that provide more than one significant product and/or service of high use and/or economic value, whereas “use value” relates to product or service characteristics that are of technical, environmental, social, cultural, or aesthetic value rather than monetary.

Multipurpose trees and shrubs on arid and semiarid lands (ASAL) in Kenya and elsewhere in Africa and Southeast Asia support a variety of local livelihoods, providing a wide range of goods and services. On farms, they help build farmers’ resilience to environmental, climate, and weather-related stress by supplying additional food, fodder, and alternative sources of income (Lasco et al. 2016). Moreover, they regulate the microclimate by providing shade and wind breaks for crops and livestock (Nguyen et al. 2013), contribute to improved soil structure and fertility (Nacoulma et. al. 2017), control the incidence of pests and diseases (Nguyen et al. 2013), increase water use efficiency (Matocha et al. 2012), and often are of ritual or spiritual value (Teklehaimanot 2004). Other benefits include the provision of medicine, fuel, building materials, domestic woody items, timber, fragrance, honey, dye, fiber, beverage, condiments, fruits, living fences, gums, tannins, resins, and wood crafts (Quave and Pieroni 2015).

Over past decades, however, multipurpose trees and shrubs have been harvested and destroyed at such a high rate that they are rendered “nonrenewable” in certain areas (Magdoff 2013). In the latter case, adverse agroecological conditions may speed up the degradation process, ultimately leading to the depletion of the plants' seed banks. This form of overexploitation threatens not only the continued existence of the habitats of these trees and shrubs but also the lifestyle and livelihood of local communities (Bodeker et al. 2014). The local overexploitation of multipurpose tree and shrub species is mostly related to anthropogenic activities, which include clearance of natural forests for agriculture and settlement, charcoal burning, overgrazing, harvesting for medicinal purposes, construction, and firewood (Kiruki et al. 2016 and 2017). In many cases, it is the (agro-)pastoralists and the smallholder and subsistence farmers who rely on the natural environment for their main source of livelihood who are the most affected by overexploitation of multipurpose trees and shrubs. This is more so as, contrary to other, better-off, occupational groups in society, they have less—or no—alternative means of livelihood at their disposal.

This study was conducted among rural residents of Kitui, Machakos, and Kajiado counties in southeastern Kenya. Most of these residents are smallholder and subsistence farmers who depend heavily on the exploitation of natural resources including multipurpose trees and shrubs. The counties are home to more than 700 woody plant species that have socioeconomic value and can supply local livelihoods (Malonza et al. 2006; Kawada et al. 2012). Despite the usefulness of multipurpose trees and shrubs species, there is a general lack of knowledge of how these species are being used. Moreover, it is unclear which factors influence the current knowledge, management, and sustainable utilization of multipurpose trees and shrubs species in the region. Inadequate knowledge limits strategic decision making on measures for protection and sustainable utilization of these species (Segnon and Achigan-Dako 2014).

The main objective of this study was to assess local knowledge and use of multipurpose trees and shrubs in three agroecological zones in southeastern Kenya. The specific objectives were to document socioeconomic uses of multipurpose trees and shrubs species identified in the study area, determine the influence of socioeconomic factors in the utilization of these species, and determine the HVMTs species based on use-value index (UVI) and multiple use values (MUVs).