Development of an integrated assessment framework for agroforestry technologies: assessing sustainability, barriers, and impacts in the semi-arid region of Dodoma, Tanzania

ABSTRACT

Land degradation continues to be a major concern for agriculture in developing countries, including Tanzania. Agroforestry is one solution that benefits food production and reduces land degradation. However, various challenges hinder its widespread adoption. This study uses an integrated assessment framework, combining MESMIS (an indicator-based sustainability assessment framework) and ScalA (a scaling-up assessment tool), to evaluate sustainability and constraints to the widespread implementation of agroforestry in semi-arid Tanzania. The main goals are to: 1) identify existing agroforestry technologies adopted by smallholder farmers; 2) evaluate farmers’ perception of sustainability regarding each technology's environmental, economic, and social impact; and 3) identify constraints related to the widespread adoption. Results show that farmers consider the following four technologies as the most sustainable: (i) tied ridge + tree intercropping; (ii) contour planting + tree intercropping; (iii) Chololo pits + tree intercropping; and (iv) tree intercropping alone. The findings indicate that, although farmers perceive the technologies positively, adoption is also influenced by local climate, socio-economic status, and institutional factors. The study highlights that a positive perception alone cannot ensure widespread adoption, emphasizing the importance of considering contextual factors. Further testing and application of the proposed framework in similar and comparative settings is encouraged as it provides valuable guidance when evaluating different agroecosystems holistically.

KEYWORDS:

• Agroforestry
• impact assessment framework
• farmers’ perception
• soil and water conservation
• sustainability

1. Introduction

Developing countries depend on agricultural production for livelihoods and development. Nevertheless, agricultural systems are strongly affected by land degradation, which threatens food security (Mbow, Smith, et al., 2014). It is often argued that population growth and poverty are key factors threatening the potential for food security in developing countries (Obaisi, 2017). Hence, there is a need to enhance agricultural production to meet the rising food demand and to combine it with environmental enhancement and reduction of land degradation. Drylands (arid and semi-arid), which account for up to 44% of the world's agricultural systems, are key for global food security. However, these regions are facing degradation from a range of natural and anthropogenic stresses, such as unsustainable agriculture (IFAD, 2016). The majority of these drylands are situated in developing countries and provide habitat for over two billion people, many of whom are affected by food insecurity (Hazell & Hess, 2010). These regions are consistently marked by high levels of climate vulnerability, with drought being a prominent challenge. Tanzania's drylands comprise a wide range of arid, semi-arid, and dry sub-humid areas, covering about 61% of the total landmass (Wells & Winowieck, 2017). The semi-arid area of Tanzania is characterized by erratic rainfall, periodic famine, and high pressure of overgrazing. Tanzania, which ranks low on economic and human development indicators, faces a challenge in meeting its food demand, with over 70% of the population depending on rain-fed agriculture for their livelihoods and development (ICRAF, 2009). Deforestation in the country has been one of the leading causes of biodiversity decline and soil fertility reduction. The high deforestation rate in Tanzania – estimated at 400,000 ha per annum – is caused by factors like poverty, low agricultural productivity, and the need for fuel wood (Kideghesho, 2015). For instance, due to their inability to afford agricultural inputs (e.g. fertilizer) or low soil fertility, farmers are forced to abandon existing farms and clear forests for new farms. This issue is particularly prominent in semi-arid areas, where drought is a major challenge and wood supply from native trees is limited. Therefore, adopting sustainable agricultural practices is vital to enable quick return from land, improve access to wood supply, increase income, and reduce poverty for poor farmers.

As a dynamic, ecologically-based natural resources management system, agroforestry can be a key solution for dryland productivity and sustainability. Agroforestry practice is one of the major features of land-use systems in the drylands of eastern and central Africa, including Tanzania (Krishnamurthy et al., 2019). Leakey (1996) defines agroforestry as the combination of land use practices and systems that deliberately integrate woody perennials, such as bamboo, vines, trees, and shrubs, etc., to create an agroecosystem with both crops and/or animals on the same land management unit. Agroforestry is consistently proven to be an effective solution that enhances agricultural productivity, mitigates land degradation caused by poor farming practices, and addresses land fertility issues, thereby contributing to the alleviation of food insecurity (Kamugisha et al., 2022; Mkonda & He, 2017). Additionally, it enables farmers to address climate change impacts by enhancing rainwater water use efficiency and stabilizing yield in rain-fed agriculture (Meijer et al., 2015).

As studies show that agroforestry has the potential to not just meet rising food demand and enhance local fuelwood supply, but also to minimize land degradation (Hafner et al., 2021; Syampungani et al., 2010), it is acquiring key importance on the international agenda. The National Forest Policy of Tanzania encourages the scaling-up of agroforestry practices to enhance sustainable agricultural practices by recognizing the contribution of trees outside forests to agricultural productivity (Msuya & Kideghesho, 2012). Some examples of agroforestry technologies in Tanzania include tree intercropping, shelterbelts, trees on contours, and improved fallows (Kimaro et al., 2019). Even though agroforestry is widespread in Tanzania and increasingly pushed by (inter)national policymakers and the development community, a wide range of constraints exist, inhibiting the broader adoption of agroforestry technologies in Tanzania. In their studies, Jha et al. (2021) show that only 10.9% of farmers report practicing agroforestry, indicating a need to improve the adoption of agroforestry practices and its scaling-up in the region. One main challenge is maintaining, improving, and adopting long-lasting agroforestry practices under changing circumstances. Moreover, the widespread adoption of agroforestry technologies by smallholder farmers is also hindered by local customs, institutions, and policies (ICRAF, 2009). Not all agroforestry technologies are sustainable and feasible everywhere, and the current state of evidence provides little guidance on which technologies work where, for whom, and under what circumstances (Mbow, Van Noordwijk, et al., 2014). A review of scaling-up agroforestry practices highlights that it can contribute to achieving at least nine of the 17 sustainable development goals (SDGs), but only if designed appropriately; for instance, ‘the right tree for the right place’ (Plieninger et al., 2020; Sharma et al., 2022). Although several studies emphasize that agroforestry is particularly suitable for farmers living in poverty, the system is not sustainable per se, as many positive impacts of the practices are related to the system's complexity. Agricultural innovations are more likely to be accepted if favorable to local biophysical, socio-economic, and environmental conditions (Ndah, 2014). For this reason, an approach that enables the assessment of sustainable agricultural practices, such as agroforestry, and that is tailored to context-specific conditions is needed to enhance the widespread adoption of sustainable agriculture (Coe et al., 2014).

The scientific and technical knowledge of agroforestry systems in dryland and its contribution to dryland livelihoods is limited (Leeuw et al., 2014). According to national agriculture policy (2013), Tanzanian agriculture has inadequately reliable methodologies for measuring and assessing the system's sustainability. Agroforestry technologies, considered sustainability paradigms, face these difficulties when measuring and comparing various agroforestry technologies with one another or with other land-use systems. Kimaro et al. (2012) stress the significance of designing tailored strategies and defining suitable indicators when evaluating climate-smart agriculture, like agroforestry. While research on enhancement and assessment methods is vast, few tailored strategies are congruent with local conditions (Ramos, 2019). Assessment frameworks are usually developed to be realized in a specific setting or sector. According to Bonisoli et al. (2018), two main approaches to developing assessment indicators exist. The first is a top-down approach in which indicators are determined before the assessment process, independent of the system under evaluation. The second is a bottom-up approach, in which indicators are determined through a participatory process involving key end users and stakeholders (Reed et al., 2005). Despite numerous efforts, a set of universally accepted standards for measuring sustainability and evaluating constraints to adoption and scaling-up hardly exist. Some examples of existing indicator-based assessment frameworks include; the framework for participatory impact assessment (FoPIA) (König et al., 2010); the scaling-up assessment tool (ScalA) (Crewett et al., 2006; Loehr et al., 2022); the land degradation assessment in drylands (LADA) (Nachtergaele & Licona-Manzur, 2008); the MESMIS programme (an indicator-based sustainability assessment framework) (López-Ridaura et al., 2002); and sustainability assessment of farming, and the environment (SAFE) (Van Cauwenbergh et al., 2007). However, most assessment frameworks are usually developed for evaluating a specific setting and focus on only one aspect. Reed et al. (2005) emphasize the importance of combining top-down and bottom-up approaches for effective sustainability assessment. The integration not only increases awareness about social and environmental issues but also empowers local communities and provides direction for policy development, stressing the need for more comprehensive strategies involving both expert and local knowledge. Bonisoli et al. (2018) agree with this notion that combining top-down and bottom-up approaches enhances decentralization, local development, and the general trend toward successful sustainability development. An integrated framework that addresses sustainability, adoption, and scaling-up that can be used in a participatory people-centred approach is crucial for evaluating and disseminating research results in agricultural settings before extensive scaling (Coe et al., 2014).

Against this background, this research aims to assess the sustainability, adoption, and ability to scale-up agroforestry technologies in the semi-arid zone of Tanzania using an integrated assessment framework. The specific objectives are 1) to identify existing agroforestry technologies adopted by smallholder farmers; 2) to evaluate how farmers perceive sustainable agroforestry technologies in terms of their environmental, economic, and social impact; and 3) to identify those factors related to the continued and widespread implementation of the technologies using integrated assessment framework. The findings from this case study help answer the following research questions: 1) what are the most relevant social, environmental, economic, and institutional indicators for evaluating the feasibility of agroforestry technologies?; 2) How do farmers in semi-arid areas perceive sustainable agroforestry practices?; and 3) What are the important factors affecting the continuing and widespread implementation of agroforestry technologies? Therefore, a new framework is developed using two existing assessment frameworks as a base, applying both primary (focus group discussions) and secondary data. Although semi-arid Tanzania is used as a case study, the integrated framework can also be applied at a broader scale in comparable settings.

2. Materials and methods

2.1. Description of the case study area

This study was conducted in Kongwa and Chamwino districts, which are located in the Dodoma region of central Tanzania (Figure 1). The study region is located in a semi-arid zone at 1000–1500 m altitude. It receives unreliable unimodal rainfall ranging from 400 to 800 mm annually (Mkonda, 2021). Undulating plains with rocky hills and low scarps with well-drained, low fertile soils generally characterize the area’s topography. The primary income source for the majority of the population is crop farming, sometimes in combination with livestock (Hillbur, 2013). The area of study is suitable for our analysis not only due to its geophysical conditions and existing practices but also because they were part of the Africa RISING project in which different agricultural technologies, such as agroforestry and other climate-smart agriculture, were introduced and implemented under the framework of sustainable intensification. Although agroforestry is not yet widespread in semi-arid Tanzania, it represents a significant source of additional income and other benefits for smallholder households (Jha et al., 2021). The research site is on private land owned by farmers who adopted agroforestry practices following the intervention of the Africa RISING project. This study’s scope and objectives were designed to explore the sustainability aspects of agroforestry practices based on farmers’ perceptions. By choosing a location where agroforestry practices were already introduced, the study can explore the experience and challenges faced by farmers who have adopted agroforestry practices and assess their sustainability perceptions. This allows for gaining valuable insights into factors influencing successful adoption and what needs improvement to enhance continued and widespread adoption.

Figure 1. Location Map of the study area.

For this study, five villages – Mlali, Molet, Nghumbi, and Laikala from the Kongwa district and Ilolo from the Chamwino district – were purposely selected to represent diverse socio-economic and land resource endowment characteristics of the farmers and the study areas. Smallholder farmers in the study sites were introduced to different agroforestry practices. It is within the frame of the project activities that this study was conducted, thereby facilitating access to farmers who practice agroforestry.

2.2. Methodological framework

2.2.1. Integrated assessment framework: combining MESMIS and ScalA

Aligning with this study's objective to assess agroecosystems’ sustainability, adoption, and scaling-up potential, the study uses an integrated framework. For the purpose of this study, after considering the shortcomings and strengths of bottom-up (MESIMS) and top-down (ScalA) approaches, a framework that combines MESMIS and ScalA (Figure 2) is developed. Both methods are complementary and can be applied simultaneously to analyze a system more holistically. Combining the two frameworks creates an opportunity to implement sustainability assessment in a participatory way, from indicator identification to assessing scaling-up and adoption constraints. To ensure that the framework is relevant and effective, a field test was conducted, involving farmers, local experts, and researchers in evaluating the sustainability of different agroforestry technologies. Appropriate steps were selected and incorporated from both frameworks to assess sustainability and identify adoption and scaling-up constraints.

Figure 2. Conceptual framework, integrating MESMIS and ScalA. Source: Own illustration.

ScalA tool: is a Microsoft Excel-based decision support tool for assessing and systematically evaluating the scaling-up potential of sustainable agricultural project interventions at the community level (Crewett et al., 2006). It is a holistic assessment tool that evaluates all three aspects (sustainability, adoption, and scaling-up) (Sieber et al., 2018). As an ex-ante assessment, ScalA ensures that project interventions with the maximum sustainable benefit (environmental, economic, and social dimensions) in a given community are selected for scaling-up. ScalA argues that practice is sustainable if it improves at least one of the three sustainability pillars without negatively affecting others (Rodríguez et al., 2022).

MESMIS: is a participatory and interdisciplinary framework for assessing sustainability to improve the design and development of a system (López-Ridaura et al., 2002). MESMIS evaluates a project's feasibility to identify the system's limits and possibilities of sustainability considering economic, social, and environmental dimensions. This approach assesses sustainability by comparing two or more systems simultaneously or longitudinally. The framework includes four basic methodological principles and a cyclical sustainability assessment (Astier et al., 2012).

Marchand et al. (2014) highlight that the rapid sustainability assessment (RSA) tool (e.g. ScalA) can serve as a starting point, encouraging farmers to subsequently use more comprehensive tools like MESMIS for a thorough assessment of farm sustainably. ScalA, being a rapid sustainability assessment tool, can raise awareness and prompt farmers to consider various sustainability-related issues. Once farmers have developed an interest in sustainability, they can then utilize MESMIS to assess their farms comprehensively. A comparison of MESMIS and ScalA is presented in Table 1. Combining the two frameworks allows for a comprehensive participatory sustainability assessment of agroforestry technologies and helps to evaluate the constraints for adoption and scaling-up. Additionally, it enables smallholder farmers to build their own concept of sustainability and helps them define their priorities (Bonisoli et al., 2018).

Table 1. Comparison between ScalA tool and MESMIS.

Analysis criteria	ScalA tool (Crewett et al., 2006)	MESMIS (López-Ridaura et al., 2002)
Type of assessment	Sustainability, adoption, and scale-up (Jha et al., 2021)	Sustainability (López-Ridaura et al., 2002)
Type of sustainability assessment	Rapid sustainability assessment (RSA) (Marchand et al., 2014)	Full sustainability assessment (FSA) (Marchand et al., 2014)
Sustainability dimension	Environmental, economic, and social	Environmental, economic, and social
Indicator development approach	Top-down Pre-determined and numbers restricted (Schindler et al., 2015)	Bottom-up Not pre-determined, and numbers are not restricted (Schindler et al., 2015)
Stakeholders involvement	High stakeholder involvement during tool application (Sieber et al., 2018)	High stakeholder involvement during tool development and application (Schindler et al., 2015)

2.3. Data collection

As a primary source of data, focus group discussions (FGD), using the principles of the integrated frameworks (MESMIS + ScalA), were conducted. FGDs have gained significant importance as a qualitative data collection method due to its ability to offer various advantages in data collection, including flexibility, diversity, and richness (Gundumogula, 2020). FGD enable the participants to investigate the concept of sustainable agricultural practices and provide insights into participants’ various opinions, experiences, and ideas.

2.4. Selection of FGD participants and scheduling of the FGD

A total of five FGDs were conducted in the five study villages (Table 2). Each FGD was attended by 10–12 participants per session, with a total of 54 (41% female) participants. The participants were selected in consultation with the study villages’ lead farmers and agricultural extension workers. During participant selection, consideration was made for gender balance, age, farm experience, socio-economic status, and a clear understanding of agroforestry. This allowed the study to account for the variation and diversity in the targeted community and avoid the dominance of one community group. Farmers with prior experience in practicing agroforestry technologies for at least two years, agricultural extension workers, and key village leaders participated in the FGDs. The FGDs were conducted in May 2022 in suitable venues.

Table 2. Focus group participants’ demographics.

Village names	Main crops (Staple and cash crops)	Perennial trees (vernacular and scientific names	Land holding size (ha)		Age (years)		Number participants
			Range	Average	Range	Average	Female	Male
Ilolo	Maize, sorghum, millet, ground nuts, cowpeas	Baobab (Adansonia digitata), Mpera (Psidium guajava), Mpapai (Carica papaya), Griclicidia sepium	0.8–2	1.7	33–77	50	5	6
Laikala	Sorghum, maize, cassava, pigeon pea, sun flower, Bambara nut	Mpera (P.guajava), Mtalawanda (Markhamia platycalyx, Mkole (Grewia), Mkungugu (Acacia tortilis), G. sepium,	0.8–2	1.4	30–57	54	4	6
Mlali	Maize, sorghum, groundnuts, pigeon peas, sunflowers, cowpeas, legume plants	Miguruka (Securidaca longipedunculata,) Mkungugu (A.tortilis), Mkerewila (Grevillea robusta,), G.sepium	1.2–2	1.5	34–73	48	5	5
Molet	Maize, sorghum, groundnuts, sunflower, cowpeas, legume plants	Mkerewila (G.robusta,), Mkungugu (A.tortilis), Mmelia (Melia azedarach), Baobab,(A.digitata), G.sepium	0.8–2	1.8	19–72	45	4	6
Nghumbi	Sorghum, maize, cassava, sunflower	G.sepium, Baobab (A.digitata), Mkungugu (A.tortilis)	1.6–2	1.4	36–65	46	4	7

2.5. Implementation of the FGD

The FGDs were conducted by the first author and assistant moderator. All FGDs were conducted in Kiswahili, which is the local language, and were facilitated by the assistant moderator, who is fluent in Kiswahili and has good knowledge of the culture. With permission from the participants, the discussions were audio recorded and backed up by field notes. At the start of the FGD, the moderator informed the FGD participants of the discussion's context and objectives. Following the brief introduction, the moderator presented and explained two guiding questions to the participants, which were the basis for the discussion. After each question, the answers were translated into English so the researcher could enquire for further explanation when required. The questions were: i) how do farmers perceive sustainable agroforestry technologies in terms of their environmental, economic, and social impact?; and ii) What are the main factors that influence farmers’ competency to practice agroforestry technologies? Each FGD lasted between 3 and 4 h. Throughout the FGDs, the following six steps were employed to answer the outlined questions.

1. One principle of the MESIMS framework is the involvement of stakeholders throughout the entire cycle of the assessment process. Thus, first, the participants were asked to identify and characterize agroforestry technologies practiced in the study villages.

2. A rapid sustainability assessment was conducted using the ScalA tool. The tool, comprising closed-ended questions about five economic, five environmental, and seven social factors, was explained to the participants.

3. After the rapid sustainability assessment, FGD participants were asked to choose their best-preferred technology for each sustainability dimension based on their perception. The final rankings were based on the participants’ average number of votes (%) using the questions from ScalA.

4. The final ranking of the technologies was presented to the participants, and additional discussions were conducted to triangulate the numeric result with discussions. In this stage, farmers discussed the main factors that influence farmers’ competency to practice sustainable agroforestry technologies by applying MESMIS-driven principles.

5. At this stage, farmers were asked to discuss the factors and attributes they consider important (environmental, economic, social, and institutional aspects) to assess their farm sustainability.

6. Finally, a list of indicators from ScalA was presented to the participants, who then evaluated the appropriateness, relevancy, understanding, and use by the farmers and non-experts for making new management decisions (Astier et al., 2012; Bonisoli et al., 2018; Escribano et al., 2015). Subsequently, farmers listed additional sustainability indicators they consider missing, which will be included in future assessments.

At the end of each FGD, the research team visited at least two farmers’ plots out of the FGD participants, which helped us become more familiar with the topic of our study, allowing us to observe the agroforestry technologies in the study districts directly.

Additionally, to enhance the comprehensiveness of the study and ensure data triangulation, key informant interviews (KIIs) and village surveys were carried out along with FGDs. The KKIs and the village survey were conducted with FGD participant farmers, including lead farmers, to gain deeper insights into individual agroforestry practices and experiences. Village leaders and extension workers from each village were also part of the key informant interviews. This approach enriched the data collected and strengthened the validity and reliability of the study findings.

2.6. Data analysis

Data from FGDs and KIIs were analyzed using qualitative content analysis. This method allows researchers to identify data patterns, themes, and variations, providing a more comprehensive understanding of the participants’ perspectives and experiences (Bengtsson, 2016). The data were transcribed and translated from Kiswahili to English and then analyzed using MAXQDA 2022 software. Multiple steps were used in the analysis, including coding, text searches, and word clouds to identify emerging themes and sub-themes related to farmers’ perceptions of sustainable agroforestry, factors affecting their ability to practice agroforestry, and critical aspects for assessing farm sustainability. Seven sustainability attributes, as listed in (Table 3), were also used to categorize the identified indicators (López-Ridaura et al., 2002).

Table 3. Sustainability attributes driven from MESMIS principles.

Attributes	Description
Productivity	The ability to provide the required level of goods and services.
Stability	The ability to maintain a constant level of productivity under normal circumstances.
Reliability	Maintaining productivity near equilibrium levels under normal conditions of environmental disturbance.
Resilience	Return to equilibrium or levels of productivity similar to the initial level after serious disturbance.
Adaptability	The ability to find new levels of balance or to continue to offer benefits for long-term changes.
Equity	The ability of the system to distribute intra- and intergenerational benefits and costs in a fair manner.
Self-sufficiency	The ability of the system to regulate and control external interactions.

Finally, a complete list of indicators was compiled based on four criteria (Ciaghi, 2017; Escribano et al., 2015): (i) they are used in similar sustainability studies applied in developing country contexts; (ii) The indicators suggested and mentioned by the farmers who participated in the FGDs; (iii) they are coherent with the environmental, social, economic, institutional condition of the study area; and (iv) they address present and future problems of the sustainability of agroforestry technologies.

3. Results

3.1. Identification and characterization of agroforestry technologies in the study area

Several agroforestry technologies are identified and characterized in this study. The predominant agroforestry technologies identified in this study include intercropping with trees, tied ridges + tree intercropping, contour planting + tree intercropping, Chololo pits + tree intercropping, farmer-managed natural regeneration (FMNR), woodlots, and boundary planting. The findings from field observation and FGDs reveal that the most dominant tree species in the study villages primarily consists of native trees. For instance, the common species in the FMNR and woodlots plot include Baobab (A.digitata) and Mkungugu (A.tortilis). Whereas the tree intercropping plot is mainly characterized by the G.sepium, which was recently introduced in the study villages by ICRAF. A brief description of each technology is provided in Table 4.

Table 4. Main agroforestry technologies identified in Ilolo, Laikala, Mlali, Molet, and Nghumbi villages.

Technologies	Description
Tree intercropping	This is a technology that deliberately integrates trees to create an agroecosystem with crops on the same land management unit (e.g. G. sepium + maize/ sorghum/ cassava).
Tied-ridges + tree intercropping	This is a form of conservation tillage where farmers build ridges or raised beds to harvest surface water runoff to conserve soil moisture in farmer's fields for optimizing crop production. When the ridges are blocked with earth ties every 0.5–1.0 m, it is called ‘tied ridges’ (e.g. Tied ridges + Maize + G. sepium).
Contour planting + tree intercropping	This is a landscape-based technology that controls soil erosion. It adopts the principles of contour farming and adds the planting of trees/shrubs on the ridges (e.g. Contour planting + G. sepium) and crops (e.g. maize, sorghum, sunflower, etc.) grown in the area between contours.
Chololo pits + tree intercropping	These are planting basin pits similar to Zai pits in West Africa. The practice is named after the Chololo village, where it was first promoted in Tanzania. The pits hold the runoff and retain soil moisture during cropping. The Chololo pits-G. sepium intercropping (e.g. Chololo-Maize-G. sepium intercropping in Laikala-) is a variant of the planting basin pits that integrated the benefits of in-situ rainwater harvesting and fertilizer tree intercropping to enhance crop production and agroecosystem resilience (Liingilie, 2019).
Farmer-Managed Natural Regeneration (FMNR)	Consists of a set of practices used by farmers to promote the regeneration and growth of indigenous trees on agricultural land. FMNR relies on regrowth from live stumps (e.g. A.tortilis and A.digitata) (Moore et al., 2020; Weston et al., 2015).
Boundary trees	A living fence or barrier planting involves planting trees along all farm boundaries (e.g. G. sepium & G. robusta).
Woodlots	Refers to a cluster of trees grown together to produce timber or fuel wood and support other systems like bee-keeping (e.g. A.tortilis and G. sepium).

3.2. Farmer's sustainability perception of the agroforestry technologies under assessment

Participants perceive that all seven technologies contribute to at least one of the three environmental, economic, and social sustainability factors and that none are perceived as negatively affecting the sustainability of the agroforestry technologies. Accordingly, each technology meets ScalA's minimum sustainability requirements, which state that a system is sustainable if it improves at least one of the three sustainability dimensions without compromising the others. An overview of the 16 sustainability indicators and ranking of each technology, based on farmers’ sustainability perceptions, is presented in Figure 3. Most farmers favour combining soil and water conservation technologies with tree intercropping for better environmental and economic outcomes, while, for social outcomes, they prefer tree intercropping alone (Figure 4). Of the different technologies evaluated, the top four technologies that contribute the most to all the sustainability dimensions, as the farmers perceive it, are (i) tied ridge + tree intercropping; (ii) contour planting + tree intercropping; (iii) Chololo pits + tree intercropping; and (iv) tree intercropping alone. A detailed explanation for each technology is presented as follows.

Figure 3. Comparative sustainability assessment of agroforestry technologies under evaluation. The bars show farmers’ votes (%) for a specific sustainability factor accumulated from the five villages. N = 54; The 17 guiding questions are driven from ScalA tool.

Figure 4. Combined sustainability analysis results for the five villages (Ilolo, Laikala, Nghumbi, Molet, and Mlali). The diagram shows farmers’ perception of sustainability based on the total number of votes (%) (N = 54). The number represents the cumulative percentage resulting from the 17 guiding questions and is summarized into the three sustainability dimensions.

Farmers perceive that contour planting + tree intercropping contribute more to the environmental aspect of sustainability. For example, the results show that combining contour planting with tree intercropping improves soil fertility and reduces soil erosion better than the other technologies. The study shows that 34% of farmers consider contour planting + tree intercropping environmental sustainability contribution. Similarly, farmers perceive that combining tied ridges with tree intercropping contributes more to environmental factors. The results show farmers (28%) perceive that tied ridges + tree intercropping provide a better water supply and have a better beneficial impact on water quality. Furthermore, this combination is perceived to contribute more to economic factors. For instance, it is perceived to improve food security better than the other assessed technologies. Farmers indicate that their income has improved considerably since integrating tied ridges into their farming practices. For instance, one farmer reported that, ‘by practicing tied ridges and tree intercropping, the maize production from my farm doubled; this increase not only led to surplus food for selling but also improved living conditions for my family.’ Similarly, 26% of farmers perceive that Chololo pits + tree intercropping contribute uniquely to the economic factors. For instance, they believe that it leads to more efficient use of external inputs, reduces dependency, and improves resource use efficiency compared to the other options, except for tree intercropping.

According to the farmers, tree intercropping has a unique impact on all three dimensions of sustainability compared to the other technologies, with 47% of farmers considering tree intercropping for social sustainability factors (Figure 4). For example, it is perceived not only as better integrating indigenous knowledge, adapting to social customs, and providing equal access to rights but also supporting the equitable division of labour, income, and access to assets. For instance, having trees on the farm provides security for fuelwood and allows farmers to participate in other social and income-generating activities. In addition to these social benefits, tree intercropping is perceived as uniquely contributing to environmental (20% farmers) and economic factors (26% farmers) by improving biodiversity and increasing competitiveness for small-scale farmers, thus leading to better income improvement.

After tree intercropping, farmers perceive that woodlots contribute to improving biodiversity because of its potential to attract a wide range of insects and animals, creating a more diverse and balanced ecological environment. Additionally, woodlots serve as beekeeping sites, further promoting biodiversity. Similarly, farmers perceived boundary planting positively for its contribution to equitable access to rights next to tree intercropping; for instance, the practice is known for minimizing land use conflict. During the FGD, it was revealed that there is a limited understanding of FMNR in the study villages. The moderator had to introduce the term FMNR as an agroforestry practice, with some participants agreeing that they were already practicing FMNR. However, when they were asked to compare it with other technologies, they overlooked the environmental and economic aspects of FMNR. They only highlighted the social contribution; for example, it improves local people's and consumers’ health status next to tree intercropping and woodlot consecutively.

There was a slight variation in the farmers’ perceptions and preferences for combining tree intercropping with soil and water conservation technologies between villages. For example, while farmers from Laikala village favour the adoption of contour planting + intercropping for an overall better sustainability factor, the majority did not prefer Chololo pits + tree intercropping. In contrast, Molet village farmers perceived that woodlots have a greater social impact (e.g. some tree roots from woodlots are known for their beneficial use) than tree intercropping, which differed from the pattern observed across all other villages. Despite these differences, participants from all villages agreed that tree intercropping alone uniquely contributes to most social sustainability factors and that combining it with water and soil water conservation technologies leads to better environmental and economic factors.

The overall results show that farmers perceived tree intercropping as having the greatest impact on all sustainability dimensions, followed by tied ridges + tree intercropping, Chololo pits + tree intercropping, contour planting + tree intercropping, woodlots, boundary planting, and FMNR.

3.3. Constraints to the continued adoption of sustainable agroforestry practices

Several potential risks that could affect the practice of sustainable agroforestry were identified. Shortage of drought-tolerant seeds, insufficient rainfall, high investment costs, presence of pests, and land use conflicts, such as illegal grazing and harvesting, are the major constraints to the adoption of sustainable agroforestry technologies. The participants emphasized that the shortage of drought-tolerant seeds is one of the main barriers to continuous adoption. It was stated that obtaining quality seeds is often too expensive and that support from institutions typically comes after the seedling period has passed. The participants suggested that government and research institutions aiming to scale up agroforestry practices should prioritize addressing this challenge.

The participants also pointed out that illegal grazing and logging by non-adopters is another obstacle to sustainable agroforestry. Non-adopters illegally cut down trees for firewood or harvest grass for their livestock. Most respondents agree this is a major problem for the region in implementing sustainable agroforestry practices. On the contrary, boundary planting farmers reported that illegal harvesting decreased since practicing boundary planting because of its demarcation use. Some participants perceived this challenge as a learning opportunity that could encourage non-adopters to adopt agroforestry technologies as they realized the benefits of having access to fuel wood and livestock supply from their farms. Although the participants report the existence of by-laws to reduce illegal logging and grazing, their enforcement is another challenge that authorities face.

In addition, high investment costs and labour demand were identified as a hindrance to the adoption of some agroforestry technologies. For instance, a common view among the respondents was that integrating tree intercropping with soil and water conservation technologies requires high investment costs and is labour intensive. Thus, farmers with low incomes are reluctant to continue practicing these technologies because of the high costs associated with land preparation and excavation. Chololo pits + tree intercropping is described as being particularly demanding in terms of labour. Farmers prefer to allocate only a small portion of their land for it or not practice it. This is a particularly pressing issue for female farmers, who often do not have sufficient capital to hire labour or have enough family members to assist with the land preparation work. The participants also noted that farmers who integrate soil and water conservation technologies with tree intercropping are more financially secure than those who only practice tree intercropping.

Access to land is another challenge for the adoption of sustainable agroforestry. With increasing land pressure and population growth, accessing agricultural land is becoming more difficult. Farmers stated that they are not keen to plant trees because trees need at least 2–3 years before they can be harvested and are hesitant to practice agroforestry unless they are secure about the land.

3.4. Modified integrated assessment framework

Throughout this study, the integrated assessment framework that combines MESMIS and ScalA is employed. Using the conceptual framework in section 2 (Figure 2), the study was carried out in a participatory way involving farmers and researchers, thus resulting in a developed, detailed assessment framework (Figure 5) that can be used to assess agroecosystems comprehensively in other similar studies. The integrated assessment framework (see Figure 5) comprises three main components, combining the steps from the MESMIS framework and the ScalA tool with additional new components:

1. Assessment cycle: The overall assessment includes identifying the system to be evaluated, rapid sustainability assessment, scale-up and adoption constraints identification, and indicator derivation.

2. Sustainability impact assessment principles: The integrated assessment follows the Bellagio STAMP sustainability principles (Pintér et al., 2012).

3. Factors to include during the assessment process: i) The ten elements of agroecology (diversity; co-creation and sharing of knowledge; efficiency; synergies; resilience; culture and food traditions; human and social values; responsible governance; recycling; as well as circular and solidarity economy) (Barrios et al., 2020); ii) The seven sustainability attributes (productivity, stability, reliability, resilience, adaptability, equity, and self-reliance), which are critical points that weakening or strengthening the system's sustainability to keep the system's evaluation and the development of indicators theoretically consistent (López-Ridaura et al., 2002); and iii) adoption and scaling-up factors (financial, human, institutional, and infrastructure) (Loehr et al., 2022).

   Figure 5. An integrated framework to assess sustainability, adoption, and scaling-up of agroecosystems. Source: own compilation.

   

While the proposed integrated framework enables the assessment of sustainability, adoption, and scaling-up of agroecosystems, in this research, we apply the section that allows sustainability assessment and identification of adoption constraints based on farmers’ perceptions. The participatory approach used in this study ensures that the framework is relevant and applicable to the local context, making it a valuable tool for sustainable agroecosystem development that can be tailored to other contexts. The components used and tested in this study include the principles, considerations, sustainability assessment cycle (coloured in yellow and grey), and the rapid sustainability assessment stage (coloured in green).

Farmers were asked to identify important benefits and constraints to assess their farm's sustainability. These identified aspects are the important features that weaken or strengthen the system's sustainability and are used by the farmers to assess agroforestry technologies.

The farmers were provided with 17 indicators from ScalA, which they found important but also emphasized the need to include institutional aspects of sustainability in future agroecosystem evaluations, such as the implementation of by-laws to avoid illegal harvesting and ensure the sustainable practice of agroforestry. Collective actions were also seen as an opportunity to control illegal harvesting and improve agroforestry adoption.

The identified strengths and weaknesses were used to drive 20 indicators that can serve as a useful tool to guide future interventions to assess the sustainability of agroforestry technologies. To increase the practical applicability, the indicators were first grouped into environmental, social, economic, and institutional aspects and then into the seven systematic sustainability attributes (Table 5). Stability, reliability, and resilience attributes are grouped together due to their shared focus on the system's ability to cope with changes (Ripoll-Bosch et al., 2012).

Table 5. Indicators developed from FGD and literature (Crewett et al., 2006; Loehr et al., 2022).

Sustainability dimension	Attributes	Strength and weakness	Indicator
Economic	Productivity	Crop productivity	Yield
		Profitability	Cost-benefit ratio
		Efficiency	Labour productivity
		Profitability	Income variation with rainfall
	Stability, Reliability, Resilience	Diversity	Number of income-generating activities
Environmental	Stability, Reliability, Resilience	Shortage of rainfall	Water availability, soil moisture
		Soil erosion	Level of soil erosion, soil fertility
		Diversity	Number of species in the same agricultural land
		Pests and diseases	Presence of pests and diseases
Social	Stability, Reliability Resilience	Work-life balance	Quality of life
	Adaptability	Innovation capability	Capacity to adapt to changes (e.g. to introduced technologies)
		Lack of traditional knowledge	integration to indigenous knowledge
	Equity	Distribution	Equitable access to agricultural supply
		Gender equity	Women's participation (e.g. labour distribution by gender)
		Income distribution	Equal division of income
	Self-reliance	Self-sufficiency	Number of farmers receiving external inputs (e.g. pesticides, fertilizer, and seeds)
Institutional	Adaptability	Accountability (Illegal grazing and theft)	Existed by-laws and implementation
		Extension services	Access to institutions and their services
		Boundary conflicts	Collective actions
		Credit access	Availability of credit associations

4. Discussion

The present study provides valuable insights into farmers’ sustainability perception and factors that influence farmers’ competency in the continued and widespread adoption of sustainable agroforestry technologies. The study also highlights aspects that weaken and strengthen the system and those indicators used to evaluate the system's sustainability.

4.1. Farmer's sustainability perception of the agroforestry technologies

Combining agroforestry technologies with soil and water conservation techniques can be a leading solution that improves crop productivity while conserving natural resources. Tied ridges and Chololo pits combined with tree intercropping are perceived to contribute more to environmental and economic factors (Figure 3), possibly due to their impacts on mitigating drought through soil and water conservation (Gamba et al., 2020). Several studies show the potential of tied ridge practices to enhance crop yields by retaining soil moisture, making it an effective technique for farmers in arid areas to improve crop productivity and food security (Silungwe et al., 2019). These studies also highlight that tied ridges are particularly suitable for growing cereal and cash crops, such as maize, sorghum, millet, sunflower, and legumes; all these are similar to the cash crops in our study area. A similar parallel is evident in the work of Partey et al. (2018), where they investigate the West African semi-arid zone. Their study also reveals comparable outcomes, where farmers used tied ridges to reduce soil erosion and enhance water use efficiency during dry seasons. A similar study by Liingilie (2019) highlights that combining Chololo pits and tree intercropping resulted in higher crop yields than tree intercropping alone and monoculture, congruent with the farmer's perception of sustainability in our study area (Figure 3). Overall, the finding confirms using tree intercropping along with soil and water conservation can lead to sustainable intensification, allowing farmers to enhance crop productivity while increasing resource use efficiency (Kizito et al., 2022).

Conversely, Nyamadzawo et al. (2013) argue that not all soil and water conservation practices are applicable to all dry areas by illustrating that tied ridges are not effective at increasing soil water content in sandy soil due to its low water-holding capacity, thus implying the importance of contextual factors when designing specific agroforestry technologies. It is also important to note that there was a slight variation in perception between the villages, which aligns with this argument. A possible explanation for the observed variation in our case study villages might be due to the area's specific main staple food crops, soil type, or extent of farmers’ exposure to specific technologies. A study by Franzel and Scherr (2002) indicates that soil type, soil nutrient status, farmers’ wealth, and farm size might be factors for variation in the adoption potential of agroforestry practices in sub-Sahara Africa. For this reason, it is crucial to consider the area's local biophysical and socio-economic characteristics before promoting the scaling-up of a specific technology. Another highly accepted practice among most FGD participants was tree intercropping for its contribution to all sustainability factors (Figure 3). One possible explanation for these positive perceptions, e.g. indigenous knowledge integration, might be that traditional agroforestry has been practiced in the region for several years (Kitalyi et al., 2013). This is in line with a study by Tafere and Nigussie (2018), who note that rich experience in traditional experience agroforestry could impact the integration of tree intercropping with indigenous knowledge and promote positive perception among farmers. But most importantly, tree intercropping is known for its contribution to all sustainability factors though improving soil fertility, increasing productivity, mitigating land degradation, improving household income and food security, and improving access to biomass energy (Antwi-Agyei et al., 2023; Sawadogo, 2011). Additionally, farmers favour the adoption of tree intercropping alone as farmers do not perceive it to be labour intensive as long as they have secure land and can afford quality seeds.

The limited awareness of FMNR among farmers (Figure 4) might be due to its relatively recent introduction to the region, dating back to only 2015 (Moore et al., 2020). Using native trees in FMNR can decrease farmers’ reliance on external sources for foreign or exotic tree seed supplies. For example, the Baobab tree, abundant in Ilolo villages, is highly drought-tolerant and multipurpose. Farmers in dry areas with enough land should be encouraged to raise Baobab trees on their farms (Msalilwa et al., 2020). Participants did not emphasize the impact of boundary planting, except for its contribution to the social factor (Figure 3). The positive social impact was attributed to its role in mitigating land use conflict. This finding aligns with Kirabo et al., 2011 (2011), who stated that agroforestry practices like boundary planting can minimize conflicts arising from a shortage of grazing land and boundary conflict. Woodlots are positively perceived for its contribution to social and environmental outcomes. The environmental contribution of woodlots is associated with its potential to enhance of biodiversity and reduce land degradation, as highlighted by Tscharntke et al. (2010). Additionally, its social impact is linked to its impact to improve health status of local people. Medicinal plants play a vital role in the livelihoods of the local community, providing essential primary health care in Tanzania (Kitula, 2007).

4.2. Factors that influence farmers’ competency to practice sustainable agroforestry technologies

The study identifies that while farmers believe integrating tree intercropping with soil and water conservation technology would improve environmental and economic factors, the practical uptake of these practices remains low, implying a need to enhance the scaling-up of these technologies. Most farmers share a similar view that combining soil and water conservation technologies is too challenging to implement without external assistance, especially at the beginning. This might be due to the labour-intensive nature of these practices and substantial investment requirements, as highlighted by Adolph et al. (2021). These constraints are particularly evident among women, older farmers, and households with low socio-economic status. This finding aligns with the observation made by Kizito et al. (2022), who emphasizes the possible hindrance posed by high investment costs when adopting soil and water conservation practices like contour planting. Supporting this point, Nyamadzawo et al. (2013) show that implementing tied ridges requires about 33% more labour than conventional agriculture. To enhance widespread adoption, strategies aimed at alleviating the economic burden of high capital costs, such as enhancing access to credit, are crucial in the adoption of new agricultural technologies (Abdallah, 2016). However, access to credit institutions in the study villages is very limited. Research institutions working in the study area should pay close attention to capital resources and labour requirements to facilitate the widespread adoption of agroforestry and soil water conservation practice.

Dry climate and low soil moisture are the other main barriers to sustainable agroforestry practice. In regions where the scarcity of drought-tolerant seed is a concern, techniques such as Chololo-pit and tied ridges emerge as a potential solution. However, their suitability varies based on the specific soil condition of each location, as underlined by Nyamadzawo et al. (2013). For instance, Ilolo village is predominantly characterized by sandy soil (70%) (Kahimba et al., 2015), with limited water holding capacity, thus implying that Chololo-pit might not be the optimal approach. Conversely, practicing tree intercropping using drought-tolerant seeds can be a viable solution if the shortage of seed availability is addressed. To ensure the suitability of the chosen strategy, a thorough evaluation of the trade-offs associated with each practice remains vital, aligning with local biophysical and socio-economic characteristics (Antwi-Agyei et al., 2023). Another constraint highlighted by farmers is the intrusion of non-adopters, where unauthorized tree-cutting and trespassing occurs: some farmers see these conflicts as a means to inspire non-adopters to adopt agroforestry. This is in line with a study by Sanginga et al. (2007), who claim effectively managed conflicts could potentially drive adoption by raising awareness among non-adopters about tangible benefits through the experience of improved fuel wood and livestock supply on their farms. A contrasting observation is made by Hanif et al. (2018); their research in Bangladesh indicates that the planting of trees at farm boundaries led to the casting of shade on neighbouring farms, leading to boundary conflicts. This contradicting outcome shows the context-specific nature of the practices and highlights the importance of careful consideration before scaling up specific practices. The finding underlines the potential of strategically combining techniques such as tree intercropping, soil and water conservation, and boundary planting to enhance smallholder livelihood by improving production yield, overcoming the constraints of water stress, mitigating continued land degradation as well as boundary conflict, which is also supported by (Maré et al., 2022).

Furthermore, these finding stresses the vital role of local administration and institutional frameworks in supporting the sustainability of agroforestry practices. Local authorities could potentially reduce the likelihood of conflicts by addressing the needs of non-adopters, who may struggle to secure grazing areas for their livestock. Additionally, improving the enforcement of by-laws and regulations related to land use and trespassing can minimize the unauthorized activities on agroforestry farms, emphasizing the institutional aspects of sustainability. However, it is important to note that this study's scope centred on the perceptions of agroforestry adopters. Future research should aim to incorporate the perspective of non-adopters, who play a significant role in boundary conflicts related to agroforestry.

The overall finding from farmers’ sustainability perception and factors affecting their competency in practicing sustainable agroforestry suggests that a positive perception alone is insufficient to improve widespread and continued adoption. When introducing and scaling-up technology, contextual factors are also important factors that should be considered (Meijer et al., 2015). Given the varying acceptance, constraints, and contextual factors, along with the different synergies and trade-offs the practices have, it is crucial to combine strategies that complement each other (Antwi-Agyei et al., 2023).

4.3. Integrated assessment framework

We examine key attributes necessary for assessing the sustainability of agroecosystems, highlighting the importance of incorporating local perspectives into the selection of relevant indicators. Our study, using FGDs and KIIs, expounds on the important aspects that must be included in the integrated assessment framework for guiding future interventions. One aspect the study reveals pertains to the institutional dimension of sustainability, which is pivotal for evaluating agroecosystems. A study by Schindler et al. (2015), which reviews assessment frameworks in developing countries, similarly highlights the importance of incorporating an institutional dimension into sustainability assessment. This dimension can act as a bridge, connecting, synergizing, and narrowing the among the three pillars of sustainability (Stål, 2015). Another feature that is included in the adapted framework is the harmonization factor, represented by the ten elements of agroecology. Barrios et al. (2020) also affirm that integrating the ten elements of agroecology into an assessment framework facilitates a shift from thinking about specific and narrow problems to a more comprehensive consideration of broader systems. A comprehensive approach that effectively assists researchers and other stakeholders in the holistic designing, managing, and evaluating agroecosystems is developed by assimilating these elements into the framework. It is important to highlight the frameworks adaptability, serving as a fundamental reference for assessing agroecosystem practices in comparable settings.

5. Conclusion

The study introduces an integrated framework that evaluates agroecosystems’ sustainability, adoption, and scaling-up potential. By incorporating both local and expert knowledge, the study sheds light on key findings that have important implications for future research and practical applications. The finding underlines the potential of strategically combining different agroecosystem practices to enhance smallholder livelihood by improving production yield, overcoming water stress constraints, mitigating land degradation, and addressing boundary conflict. The study shows that farmers perceive combining different agroforestry practices with soil and water conservation practices as more effective and acceptable for achieving better social, economic, and environmental outcomes. However, the study's overall finding provides an important insight: while positive farmers’ perceptions are vital for promoting continued and widespread adoption, these perceptions alone are insufficient for successful adoption. It highlights the intersection of farmers’ perceptions with contextual factors, including biophysical and socio-economic factors, all of which play a significant role in successful adoption of agroecosystems. Furthermore, the institutional dimension emerges as a crucial factor, stressing its role in the successful outcome of agroforestry practice, particularly in managing land use conflicts between adopters and pastoralists in the study area. This study enriches our understanding of farmers’ sustainability perception of agroforestry and challenges faced by agroforestry adopters, offers implications for areas that require improvement to facilitate wider adoption while mitigating dis-adoption, and provides a stepping stone for future research. The findings also highlight the importance of non-adopters in successfully adopting agroforestry practices. It is, however, important to acknowledge the study's limitations, notably the absence of perspective from non-adopters. Therefore, future studies should encompass the perspective of both adopters and non-adopters through empirical investigation, given the study's qualitative approach. The adaptability of the proposed framework of this study across diverse contexts facilitates the systematic assessment of sustainability, adoption, and scaling-up potential of various agroecosystems in a participatory approach, either at a farm or regional level. The synergy of expert and local knowledge within this framework provides a valuable guide for farmers, researchers, and policymakers to make informed decisions. The broader application and testing of this framework in similar and comparable settings is encouraged.

Ethics approval

This research is part of the PhD project ‘Developing an Assessment Framework along the Agroforestry: Food security Nexus: Sustainable land Strategies for people-centred Land Restoration in Tanzania,’ which was reviewed and approved by the National research registration committee (NRCC) of the Tanzania Commission science and technology.

Availability of data and material

The data supporting this study's findings are available on request from the corresponding author. The data are not publicly available because it contains information that could compromise the privacy of research participants.

Authors contributions

Conceptualization: [all authors]; methodology—designing the work and collecting the data: [Mahlet Awoke]; formal data analysis and data interpretation: [Mahlet Awoke]; writing—original draft manuscrpit: [Mahlet Awoke]; writing—review and editing: [all authors]; supervision: [Anthony Kimaro, Katharina Löhr, Marcos Lana, Stefan Sieber]. All authors read and approve the final manuscript.

Consent

Informed consent was obtained from all individual participants included in the study.

Acknowledgments

The Authors thank those who participated in the focus group discussions and shared their perspectives. A special thanks to the Leibniz Centre for Agricultural Landscape Research (ZALF) in Müncheberg, Germany, and the staff of the Center for International Forestry Research-World Agroforestry Center (CIFOR-ICRAF) in Dar es Salaam, Tanzania, for their technical and logistical assistance.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was funded by the Academy for International Agricultural Research (ACINAR). ACINAR, commissioned by the German Federal Ministry for Economic Cooperation and Development (BMZ), is being carried out by ATSAF e.V. on behalf of the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH. Agroforestry technologies evaluated were introduced and validated by farmers with support from the USAID-funded Africa RISING program.