Growing trees on farms diversifies crop production options for smallholder farmers and can provide a wider range of nutritious foods for healthier diets, economic revenue and ecological services (Vinceti et al., 2013; Jamnadass et al., 2015; Prabhu et al., 2015; Hughes et al., 2020). Food trees provide fruits, leaves, seeds, nuts and edible oils, which contribute to food and nutrition security (Jamnadass et al., 2015). Tree foods are often a rich source of vitamins, minerals, proteins, fats and other nutrients that can be used to diversify staple diets, thus preventing nutrient deficiencies that most often affect women and children (Kehlenbeck et al., 2013; Kehlenbeck and Jamnadass, 2014). Food trees can provide food during the “hunger gap” period or the time before the harvest of annual staples (Kehlenbeck et al., 2013; McMullin et al., 2019). Other evidence shows that tree cover has been found to be positively associated with dietary diversity and increased fruit and vegetable consumption (Ickowitz et al., 2014). Food trees can also contribute to the livelihoods of smallholder farmers through the income pathway with the sale of fruits and non-fruit products, which can also improve household food security (Jamnadass et al., 2015; Keding et al., 2017).

Due to the multiple uses and benefits of trees, farming households have used a diversity of food tree species for generations and accumulated a wealth of knowledge on their contributions to livelihoods, which may differ according to gender, age and ethnicity (Elias, 2015; Faridah et al., 2017; Hegde et al., 2017; Karambiri et al., 2017). Men and women farmers often prioritize cultivation and use according to gender and age-related needs. Yet, differences in these priorities are often not investigated and documented, which can result in inadequate agricultural development interventions.

Women have developed specific knowledge of food crops through their role as primary food producers, their social position, responsibilities, and status within their communities (Howard, 2003). However, they are often not recognized as important users and custodians of knowledge on genetic resources (Curtin, 1997; Howard, 2003). Men, who are considered the heads of households in many cultures, are often perceived as the more legitimate knowledge holders and managers of trees and other food crops and are therefore more often selected to participate in research and agricultural interventions (Howard, 2003; Kiptot and Franzel, 2012; Müller et al., 2015).

Age also shapes local ecological preferences and priorities for use. Yet, little is known about younger women's and men's preferences for food trees species, and how these relate to the specific interests and constraints younger women and men may face as they decide to engage (or not) in agricultural activities. The diversity of “youth” in terms of socio-economic, ethnic, educational, and other backgrounds (Pyburn et al., 2015) further influences their experiences, knowledge, interests, aspirations, and challenges. Understanding the preferences that youth hold in agriculture, and specifically in cultivating food trees on farms, which are a long-term investment, is particularly important for supporting younger farmers to stay engaged and motivated to pursue agriculture (Giuliani et al., 2017).

This study builds on previous gender and age-responsive research on food tree species by examining local communities' preferences for food tree species, and why they vary based on gender and age factors in selected sites in Uganda and Kenya. Three research questions are addressed: (i) how knowledge and preferences for food trees vary according to gender and age; (ii) which factors underpin the perceived value of food trees and how do these differ according to gender and age; and (iii) what motivations and constraints influence food tree preferences by women and men of different ages. The data collected in this study demonstrates how engaging a diverse range of farmer populations can generate a more relevant representation of the local knowledge and preferences of communities, and therefore inform our understanding for designing suitable programs which may involve the promotion of a diversity of food tree species for different uses. Such analyses can inform contextually appropriate interventions and more equitable agricultural production strategies to help meet the needs of smallholder farming communities in East Africa.

Building on previous research on local ecological knowledge, our findings provide three key insights for understanding food tree growing and management in agroforestry systems. First, our study confirms previous research illuminating differences in farmer knowledge of, and preferences for food tree species based on gender and other factors of social differentiation. Although variations across gender and age groups are consistently reported (Elias et al., 2018), these differences may be more significant across gender lines, as in Uganda, or across generational lines, as in Kenya, and the direction of the relationship may vary. For instance, in our study, older women in Kenya identified more food tree species than other groups; a finding also seen in Malaysia, where women were more conversant with fruit trees (Faridah et al., 2017), and in the coastal provinces of Kenya, where older men and women had more knowledge of indigenous fruit trees (Fukushima et al., 2010). Such local ecological knowledge is closely tied to gender-specific roles, including responsibilities related to use and management of trees and the processing and selling of tree products (Elias and Carney, 2007). Women are primarily responsible for providing food for their families (Ureta et al., 2016), and their knowledge of food trees is especially critical during lean months, when food supplies are limited.

Second, our findings show that differences in knowledge and preferences are particularly significant with regard to indigenous species. In Kenya, younger men and women had the least knowledge of indigenous food tree species. Similar results have been noted in Ethiopia (Seyoum et al., 2015). Young people's lack of knowledge on indigenous food tree species may be associated with their limited presence in present-day farming systems and in the wild, as compared to the past. The erosion of traditional knowledge brought about by the loss of vegetation (Lengkeek and Carsan, 2004; Teketay et al., 2010) and of wild fruit tree species (Asfaw and Tadesse, 2001) have been well-documented.

The low economic value of many indigenous food tree species is also partly responsible for younger people's dwindling knowledge of these species. In other studies of Coastal Kenya and Ethiopia, income generated from the sale of food tree products harvested from the wild was reportedly marginal because of several social, economic, and cultural factors (Fukushima et al., 2010; Seyoum et al., 2015). In this study, younger men and women as well as older men associated their low preference for indigenous food trees to low or null economic value. In all study sites, a strong preference for exotic species such as mango, avocado, pawpaw and citrus were associated with their economic value and their role as food. Men and women participants noted, as also reported elsewhere, that sales of food tree products increase their household's purchasing power to buy staples and legumes for the family (Keding et al., 2017) and to cover other household costs such as school fees (Schreckenberg et al., 2006). Moreover, the slow growth of local varieties and indigenous food trees compared to the faster growth rates of popular exotic trees, which have been domesticated and improved over time (Lengkeek and Carsan, 2004), discouraged some younger farmer participants who are most interested in short-term cash income. This is conveyed in the words of a younger man from Kitui west, who stated that: “Growing indigenous food trees is not profitable, it takes a long time to mature, and has no good income returns.”

Nonetheless, at both study sites, women–especially older groups–were more favorable to indigenous food trees than men due to their contribution to meeting household and children's nutritional needs and their other uses as firewood and medicine. This interest in indigenous species, despite their lack of economic value, can be attributed to rural women's food provisioning responsibilities, but also to women's often disadvantaged position in the household that limits their income generating activities to those disregarded by men due to their low earning potential. As an older woman in Kitui put it “Indigenous fruits are ready during drought seasons when other fruits are not in season and some fruits like java plum and tamarind we normally sell in small quantity and we do not need to seek permission to utilize or sell.” As other studies have shown, many indigenous fruit trees are particularly beneficial for women in harsh environments with frequent crop failures, pest attacks, and droughts (Schreckenberg et al., 2006; Seyoum et al., 2015).

The third important point is that despite their interest in growing food trees, farmers in the study sites face common, as well as gender and age-specific constraints in this regard. Study participants identified several barriers to the cultivation of food trees that echo previous studies. For example, nearly all farmers indicated that they have limited access to quality planting material and rely on a narrow offer of species diversity—a concern shared across many parts of Africa (Jamnadass et al., 2011; Nyoka et al., 2011). Participants also reported a lack of knowledge of tree cultivation and management practices; a known constraint affecting expansion of fruit tree production on smallholder farms (Snelder et al., 2007). The absence of a well-organized, stable and reliable market for food tree products, despite their local and international market potential, which was flagged as a constraining factor in our study, has also been noted as an important determinant of species choice in other research (Degrande et al., 2006). Land size and ownership was also identified as a key constraint, other studies have described how this influences decisions about whether to plant and/or retain trees on farms (Degrande et al., 2006; Ureta et al., 2016; Gachuiri et al., 2017), how many trees to plant, and which species to plant (Lengkeek et al., 2005).

The gender- and age-specificity of these constraints, which has received less attention in the literature, were obvious in our study. For example, land tenure considerations were mentioned mainly by women and young men. Young women are particularly affected since, unlike young men who may outgrow this constraint, traditional land and tree tenure systems in Kenya and Uganda do not allow women to own land, but rather to access it through marriage (Degrande et al., 2006; Musangi, 2017). This was conveyed in the words of a young woman participant: “only men inherit land once they reached that age of 18 or when they marry.” Another example relates to lack of knowledge and skills in food tree propagation and management that were also more often cited by women and youth in both study sites, possibly due to oversight from governmental and non-governmental rural extension agents. The perception shared by participants that most agriculture training opportunities target a few better resourced farmers possibly reflects the commonly used figure of “lead farmers” in extension activities. Lead famers have been found to concentrate among elder, better educated men who are well-regarded in the community (Chinsinga and Chasukwa, 2012; Ragasa, 2020).

Crucially, women and young men also experienced a lack of time and motivation to plant food trees. Women's domestic responsibilities (e.g., cooking, cleaning, and caring for children) associated with traditional gender roles, in addition to their farming activities, limit their time for tree management. As a case in point, Villamor et al. (2015) substantiate that female farmers generally manage smaller parcels of land near their homestead due to labor and time constraints. In terms of motivations, we found that these were also closely related to gender and generational roles and interests. In Kitui, where men usually control the sales of the most marketable fruits during the peak season while women are often responsible for selling surplus fruit off-season, women were more interested in food tree species that were available throughout the year and could be sold in small quantities. A woman in Kitui stated, “we prefer farming agriculture crops that take less time or fruit such as pawpaw, lemon, guava, that are normally sold in small quantity and we do not need to seek permission to sell” (sic). In the case of younger men and women, the lower interest in growing food trees was consistent with the literature on youth and rural transformation, which identifies a general apathy among younger generations toward rural farming and rural futures (White, 2012; Clendenning et al., 2019), as illustrated by a young woman in Nakaseke, Uganda, who aspired to leave her rural community and find work in an urban town: “I don't want to plant trees. It is tedious work. I better do business.”

Financial constraints that often hinder farmers from practicing agroforestry (Ureta et al., 2016) were more often reported by women and younger men in our study. Kenyan women participants, for example, were interested in options to add value to fruit produce, including processing the fruits into juices, but they were limited by lack of skills and training, and critically by their low access to capital. Rural women have not only fewer income-generating opportunities than their male counterparts (Jabeen et al., 2020), but also less access to credit (FAO, 2019). Rural youth, in turn, are often under-employed in low paying activities and predominantly provide labor for their own households and farms (Bennell, 2007).

The complex interactions between the diversity of preferences, constraints and challenges described above shapes knowledge of food trees and their uses. But predominant gender norms still curtail the level of participation and voice of different household members in the selection of tree species to be planted, or cared for, and mediate how farming land is used to satisfy household and family needs. In Uganda, among the Baganda community, and as a result of their position as landowners, men dominate tree planting and are also responsible for deciding where and which trees women plant (Kiptot, 2015). Similarly, among the Kamba people of Eastern Kenya, tree planting and felling have traditionally been seen as a male's domain and while women enjoy use and access rights to fodder, fuelwood, fruits and mulch, more valuable tree products like charcoal and timber are still under men's control (Kiptot and Franzel, 2012). Recent research in Kenya points to a tendecy toward more joint decision-making regarding farming and land use decisions, in large part as a result of women's increased participation in agricultural trainings and development initiatives, as well as larger regulatory (e.g., constitutional recognition of the right to inherit land; laws against domestic violence) and societal (increased out-migration of men in search of off-farm work) changes. Yet, women's priotities and preferences are still seen as secondary to their husband's and men are still seen as the household heads and final decision makers (Bullock and Tegbaru, 2019; Crossland et al., 2021). Increasing women's and youth's participation and voice in the selection of food trees on farm would thus require going beyond identifying their preferences and attempting to transform the gender norms that designate men as final decision-makers and undervalue women's priorities and needs (Bullock and Tegbaru, 2019; Crossland et al., 2021).

The study demonstrates the need to unpack knowledge, preferences, and constraints in relation to food trees according to gender and age. These different priorities and preferences along with other important variables such as presence of markets or seed availability, that were not examined here, affect the interest and ability of farmers to grow food trees, as well as their choice of species.

Diverse gender- and age-related sets of knowledge, preferences and challenges in relation to food trees underpin complex decisions about which food tree species to grow or use. Differences in knowledge and preferences are distinct not only across gender lines but also generational lines. They are shaped by gender and generational roles, such as those related to child rearing and household food provisioning, and responsibilities related to the use and management of trees, and the processing and selling of tree products. The diversity of preferred species mentioned by all groups was high, however dominated by exotic species. Indigenous food trees are perceived to be of a low or null economic value and were only highly appreciated by older women due to their children's nutritional needs and use as firewood and medicinal properties. Men and younger women gave priority to species with high economic value due to the sale of their fruit and the potential for income. The study also identified several barriers to the cultivation of food trees, some of which were gendered, with more, younger women mentioning lack of knowledge about planting and management, as well as cultural restrictions, such as only having access to land when married, and a lack of time due domestic responsibilities associated with traditional gender roles. Younger men faced different challenges related to limited markets, and land scarcity and ownership.

Indigenous food trees, which often are slower growing and don't have well-developed market opportunities, were not identified as preferred species across different gender and generational groups, expect by older women who value them for their food contribution, particularly for children, and during lean seasons. These species do have the potential to contribute in local food systems because of their nutritional value, seasonal availability and because they are adapted to their landscapes. More research and investment are needed to assess the potential of these species, and a good starting point is to identify which one's local communities do use, and for what reasons. Also, sensitization to increase knowledge on their usefulness and nutritional value. Knowledge gaps which need to be addressed are how to improve the delivery mechanism for inputs such as high quality and diversity of seedlings for exotic and indigenous species and capacity development of farmers on food tree growing and management and agriculture extension services to support better distribution and delivery systems of quality seedling.

Sensitization efforts should target the youth and older men to allow them to better understand the benefits of these food trees. In addition, there is a need to support collective action, access to market information, linkages to markets and value chain development for both exotic and indigenous tree species to expand marketing opportunities for farmers.

Overall, our findings suggest that consulting farming communities about their preferences for food tree species and the constraints they experience in growing them, by gender and age group, is important to inform the design of project strategies for promoting a diversity of food tree species to meet the multiple interests and needs of smallholder farmers.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.

AG prepared manuscript and carried out data collection and fieldwork. All authors contributed ideas and text, provided input for the literature review, development of the methodology, manuscript preparation, proofreading, and critical analysis of the submitted review.

The research presented in this study was funded by the European Union, as part of the European Commission's support to AR4D to World Agroforestry Centre (ICRAF) through the International Fund for Agricultural Development, and it was conducted as part of the Gender Research Fellowship Programme of the CGIAR Research Program on Forests, Trees and Agroforestry.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.