Charlotte Hemingway

Hubert Cochet

François Mialhe

Gunnell

_____________________________________

livelihood dynamics in Amboseli, Why pastoralists grow tomatoes: Maasai southern Kenya

Keywords: comparative agriculture, pastoralism, cash crops, Maasai, Amboseli

This study documents the causes and processes behind the uptake of crop cultivation by a Maasai community of southern Kenya which, until recently, was still devoted to full-time mobile livestock keeping. Based on the methods of comparative agriculture and a detailed quantification of household income from livestock and cash crops, a classification of farm units (n = 38) into nine production systems reveals that agro-pastoralism on the Mbirikani group ranch, which is situated between Amboseli and Chyulu Hills national parks, is now mainstream, and that crops can exceed 70% of household income. Microeconomic analysis also documents large disparities in household income, with irrigated tomato farms benefiting from access to a pipeline ranking highest in profitability.

Overall, the pastoralist-peasant dichotomy ingrained in portrayals of East-African rural life has outlived its relevance, with the tomato currently being a key game changer. This growing appeal for agriculture, however, is threatening the wildlife conservation because the profitability of tomato cropping has begun to outcompete those employment alternatives. By promoting landscape fragmentation and water extraction, however, irrigated agriculture also undermines free movement of wild animals outside the parks, restricts access to the key resources they require, and exacerbates human-wildlife conflicts.

Introduction

African pastoralism: trends and challenges in the 21st century

Pastoralism involves living with, but also from, uncertainty [START_REF] Catley | The futures of pastoralism in the Horn of Africa: pathways of growth and change[END_REF][START_REF] Davies | The economics of mobile pastoralism: a global summary[END_REF][START_REF] Krätli | Living off uncertainty: the intelligent animal production of dryland pastoralists[END_REF][START_REF] Scoones | Living with uncertainty: new directions in pastoral development in Africa[END_REF]. This arises largely because climatic variability is a key characteristic of semi-arid rangeland ecosystems [START_REF] Ellis | Climate patterns and land-use practices in the dry zones of Africa: comparative regional analysis provides insight into the effects of climate variations[END_REF], which are typically too dry for reliable crop cultivation and thus primarily used for various forms of livestock production.

Pastoralists have developed time-tested adaptations to variability in water, fodder, or disease through flexible strategies of land control, diverse tenure arrangements in mosaic landscapes (Swallow and

The pastoralism-agriculture nexus

This study focuses on a semi-arid rangeland in southern Kenya located between Amboseli National Park, Mt. Kilimanjaro, and the Chyulu Hills National Park, and populated by Maasai communities. The option of practising full-time pastoralism here is understood to have been made possible over the last 2000 to 3000 years because of a bimodal rainfall regime, which allows for a longer birthing season than in comparatively drier parts of East Africa and thus secures year-round milk production [START_REF] Mccabe | Adopting cultivation to remain pastoralists: the diversification of Maasai livelihoods in Northern Tanzania[END_REF]. Although the Maasai commonly specialise in pastoralism, depending on time and place they have nonetheless been known to also practice farming and hunting [START_REF] Spear | Being Maasai: Ethnicity & Identity in East Africa[END_REF]. The Maasai are divided into various categories defined by geographical, age, clan, sub-clan and gender criteria. The category relevant to territory is known as a section, and the Kisongo section is one among several devoted to full-time pastoralism [START_REF] Mccabe | Adopting cultivation to remain pastoralists: the diversification of Maasai livelihoods in Northern Tanzania[END_REF]. It is also the largest, currently dominant between Lake Manyara in the west (Tanzania), the Pangani River in the east, and the Amboseli area in the north, where the Kisongo are also known as Loitokitok [START_REF] Lewis | Amboseli landscapes : maasaï pastoralism, wildlife conservation and natural resource management in Kenya, 1944-present[END_REF][START_REF] Ndagala | Territory, pastoralists, and livestock : resource control among the Kisongo Maasai[END_REF].

Economic diversification of Maasai pastoral economies typically involves an intensification of livestock husbandry (e.g., cattle cross-breeding, adoption of veterinary drugs, raising of animals for niche markets [START_REF] Morris | Interventions for African pastoral development under adverse production trends[END_REF]Bekure et al., 1991;[START_REF] Rutten | Selling wealth to buy poverty: The process of the individualization of landownership among the Maasai pastoralists of Kajiado District, Kenya[END_REF] and/or an adoption of agriculture and other non-pastoral activities [START_REF] Coast | Maasai socioeconomic conditions: a cross-border comparison[END_REF][START_REF] Homewood | Policy and practice in Kenya rangelands: impacts on livelihoods and wildlife[END_REF][START_REF] Little | Challenging orthodoxies: understanding poverty in pastoral areas of East Africa[END_REF][START_REF] Little | Avoiding disaster: diversification and risk ranagement among East African herders[END_REF]. Some Maasai pastoralists are thus becoming 'agro-pastoralists'. An operational definition of agro-pastoral systems is that farmers engage in grazing-based livestock production as well as cropping activities [START_REF] Aryal | Transhumance, livestock mobility and mutual benefits between crop and livestock production[END_REF], with livestock predominantly fed on natural pasture (sometimes also crop residue) and crops grown mostly for cash or for direct household subsistence [START_REF] Tolera | Livestock production in pastoral and agro-pastoral production systems of southern Ethiopia[END_REF].

The number of Maasai who have entirely abandoned mobile livestock keeping and/or become fulltime farmers is currently not well documented, but the stereotype of the one-dimensional Maasai herdsman as an obligate pastoralist is unravelling fast in this region. Pastoralist 'dropouts' have been anecdotally reported [START_REF] Little | Challenging orthodoxies: understanding poverty in pastoral areas of East Africa[END_REF], but patterns of diversification over time have been most of all context-specific. In northern Tanzania, the uptake of cropping occurred in two stages: household horticulture to generate food supplements, followed by commercial agriculture [START_REF] Mccabe | Adopting cultivation to remain pastoralists: the diversification of Maasai livelihoods in Northern Tanzania[END_REF].

Agriculture and livestock are thus not two separate, parralell activities. Among the Kisongo Maasai, documented causes of conversion to part-time agriculture include drought-related livestock losses [START_REF] Western | Cattle and pastoralism: Survival and production in arid lands[END_REF], loss of access to forage and water caused by the expansion of wildlife protection areas [START_REF] Fratkin | Pastoralism: governance and development issues[END_REF][START_REF] West | Parks and peoples: the social impact of protected areas[END_REF], and the recurrence of cattle-related diseases [START_REF] Mccabe | Adopting cultivation to remain pastoralists: the diversification of Maasai livelihoods in Northern Tanzania[END_REF]. National governments and multilateral agencies such as the World Bank have acted as catalysts in these diversification patterns, for example by promoting infrastructure and land policies aimed at avoiding a 'Tragedy of the Commons'. In Kenya, these have typically involved sedentarisation, commercial ranching, and land privatisation through various land rights reforms [START_REF] Fratkin | Pastoralism: governance and development issues[END_REF]. The disintegration of customary institutions is thus both a cause and a consequence of economic diversification among full-time pastoralists.

Individual decisions to diversify occur either by choice or by necessity. The impetus for choice is to reduce nutrition-related risks (with dietary improvements especially benefiting children: [START_REF] Galvin | Nutritional status of Maasai pastoralists under change[END_REF][START_REF] Mccabe | Adopting cultivation to remain pastoralists: the diversification of Maasai livelihoods in Northern Tanzania[END_REF][START_REF] Stavi | Food security among dryland pastoralists and agropastoralists: The climate, land-use change, and population dynamics nexus[END_REF], but also reflects changes in social and cultural norms through co-existence and interaction with more recently settled, non-Maasai agricultural populations [START_REF] Mccabe | Adopting cultivation to remain pastoralists: the diversification of Maasai livelihoods in Northern Tanzania[END_REF]. Whether or not poverty among pastoralists is a cause of livelihood diversification is less clear-cut: [START_REF] Little | Avoiding disaster: diversification and risk ranagement among East African herders[END_REF] have argued that only the wealthiest and poorest were driven to livelihood diversification, and [START_REF] Homewood | Policy and practice in Kenya rangelands: impacts on livelihoods and wildlife[END_REF] reported instead that all socioeconomic categories of pastoralists were concerned. There is little evidence that women benefit much from either livestock keeping or from agriculture [START_REF] Hodgson | Women as children : culture, political economy and gender inequality among Kisongo Maasai[END_REF], but it would appear overall that (i) human population growth, with the average reduction of cattle per capita that this entails; and

(ii) Kenya's market economy, which exerts constraints but also generates opportunities, are the two key drivers currently pushing all socioeconomic categories of pastoralists towards diversification.

Livestock-related activities have sometimes gained from diversification. Revenue from agriculture, for example, can be reinvested in herd restocking or livestock healthcare, and can contribute to avoid selling animals when cash is required for domestic expenditure or for bridging food deficit periods [START_REF] Landais | Des rizières et des vaches[END_REF][START_REF] Zaal | Pastoral integration in East African livestock markets: linkages to the livestock value chain for Maasai pastoral subsistence and accumulation[END_REF]. The expansion of agriculture on East-African rangelands, however, has been detrimental in other respects by reducing access to key resources for livestock and wildlife (forage, water), and by fragmenting the landscape and impeding the mass dispersal of herbivores and their predators [START_REF] Fratkin | Pastoralism: governance and development issues[END_REF]Hobbs et al. 2008;[START_REF] Mccabe | Adopting cultivation to remain pastoralists: the diversification of Maasai livelihoods in Northern Tanzania[END_REF].

The pastoralist-peasant dichotomy having thus mostly outlived its relevance in many parts of the world [START_REF] Scoones | Pastoralists and peasants: perspectives on agrarian change[END_REF], here we go beyond idealised anthropological categories or simplistic models about rangeland management by recognising that mixed livelihood strategies exist among the Kisongo Maasai. This generates landscape dynamics where the coexistence of, and interaction between, agriculture and livestock call for being investigated at face value, with potential for conclusions being fed back into decision-making about the future of the pastoralism-agriculture-wildlife nexus in East Africa's savanna ecosystems. Based on the methods of comparative agriculture, which in the present case include a microeconomic analysis of household income from a combination of livestock and crops (including tomatoes), we document the uptake of crop cultivation by a Maasai group-ranch community that, until recently, was still devoted to full-time livestock keeping. We reconstruct the 20th century context leading up to this step change in Maasai livelihood strategies, and characterise the current diversity of production systems that has arisen from this new dynamic.

Field setting

Physical landscape

The study area is a savanna extending east of the Great African Rift at an elevation of ~1200 m (Fig. 1). The vegetation mosaics are chiefly controlled by climate, water availability, herbivory patterns, and soil types, and consist of woodland savanna dominated by Commiphora, Balanites and Acacia spp. [START_REF] Western | The status of the Amboseli rhino population[END_REF], and grassland savanna dominated by C4 plants. The climate is semi-arid, with a bimodal rainfall regime. Aridity-related uncertainty is exacerbated by a recurrence of droughts (Fig. 2) and by large interannual rainfall variation [START_REF] Altmann | Dramatic change in local climate patterns in the Amboseli basin, Kenya[END_REF]. Droughts typically occur after failure of the short rains (Ogutu et al., 2014), and years of drought are followed by above-normal rainfall, such as in 1998 and 2018. Water is available for wildlife from spring-fed perennial swamps (e.g., Isinet, Ilchalai, Fig. 1), from their outflowing, low-discharge streams, and a from few lakes (Fig. 3). Accordingly, agriculture has also concentrated around these small areas with direct access to water (Fig. 3), the rest of the group ranch being only suitable for pastoralism. The springs are supplied by subterranean water flowing out of the volcanic lava structures along the foothills of Mt. Kilimanjaro, thereby making this savanna environment somewhat unique. The ecosystem functions as a major wildlife dispersal area for large mammals (e.g., gnu, zebra, gazelles, elephants;[START_REF] Ojwang | Wildlife migratory corridors and dispersal areas: Kenya rangelands and coastal terrestrial ecosystems (Kenya vision 2030), Kenya Rangelands and Coastal Terrestrial Ecosystems[END_REF][START_REF] Okello | Agricultural expansion within Kimana electric fences and implications for natural resource conservation around Amboseli National Park, Kenya[END_REF], with an alternating pattern of high dry-season concentrations around perennial swamps in Amboseli National Park (392 km², a game reserve in 1948 gazetted as a national park in 1974), and rainy-season dispersal throughout the Greater Amboseli Ecosystem, which extends between Mt. Kilimanjaro and the Amboseli and Chyulu national parks and hosts a number of Maasai group ranches and farming settlements (Fig. 1).

Social and political context in historical perspective

The Kisongo Maasai are the oldest recorded occupants of the area [START_REF] Boles | Historical ecologies of pastoralist overgrazing in Kenya: long-term perspectives on cause and effect[END_REF], which was maintained as a pastoral 'homeland' (Maasailand) with vast game reserves by British rulers. Since Kenya's independence in 1963, however, the area has also become an agricultural frontier, attracting pioneer migrants among ethnic groups who are primarily farmers (e.g., Kikuyu) and who harness the water resources provided by the Kilimanjaro spring line and the swamps. From 78% in 1960, the Maasai population of Kajiado District had thus fallen to a proportion of 60% in 1984 [START_REF] Fratkin | Pastoralism: governance and development issues[END_REF]. This is an ongoing process.

We focus here on Mbirikani group ranch (1258 km²), created in 1975 and today hosting 4636 members. With support from USAID and the World Bank [START_REF] Fratkin | Pastoralism: governance and development issues[END_REF], group ranches were established in the Maasai rangelands by the government of Kenya following the Land Adjudication Act of 1968 [START_REF] Kibugi | A failed land use legal and policy framework for the African Commons? Reviewing rangeland governance in Kenya[END_REF][START_REF] Veit | Rise and fall of group ranches in Kenya[END_REF]. Ranching was deemed an improvement on traditional mobile livestock keeping because it would encourage optimal pasture management and more marketoriented output [START_REF] Woodhouse | African enclosures: a default mode of development[END_REF]. As such, it was a continuation, now enshrined in Kenyan law, of the colonial 'Konza' and 'Il Kisongo' grazing schemes set up after 1945 by the colonial African Land Development Organisation [START_REF] Kibugi | A failed land use legal and policy framework for the African Commons? Reviewing rangeland governance in Kenya[END_REF]. Although these failed and were soon abandoned, grazing schemes of this kind were aimed at creating large ranches (up to 20,000 acres) for extended families as a means of replacing nomadic pastoralism with supposedly sound ranching techniques, of encouraging settled agriculture, and eventually of opening up land ownership to private companies and cooperatives [START_REF] Kibugi | A failed land use legal and policy framework for the African Commons? Reviewing rangeland governance in Kenya[END_REF].

Under the group ranch concept, a 'group' refers to individuals who are recognised as members. The ranches are governed by an elected committee and the land is held collectively under private title [START_REF] Kibugi | A failed land use legal and policy framework for the African Commons? Reviewing rangeland governance in Kenya[END_REF]. The original design of the reform was to pursue the land privatisation process that had begun during the colonial era [START_REF] Peron | L'occidentalisation des Maasaï du Kenya : Privatisation foncière et déstructuration sociale[END_REF]. The group ranch settlement was initially accepted by the Maasai community as a means of preventing further agricultural encroachment from outsiders onto their ancestral rangelands, and was instrumental in acquiring exclusive legal ownership of the landproperty deeds being the only document guaranteeing access to bank loans (with the land mortgaged as collateral) for funding boreholes or cattle dips [START_REF] Fratkin | Pastoralism: governance and development issues[END_REF], and for investing in forms of enterprise other than livestock keeping.

Many group ranches, however, were not self-sufficient because the land could not provide its members with sufficient access to water and forage [START_REF] Peron | L'occidentalisation des Maasaï du Kenya : Privatisation foncière et déstructuration sociale[END_REF]. This accelerated a transfer of capital from cattle (the highest-ranking resource in Maasai culture) to land [START_REF] Galaty | The land is yours": social and economic factors in the privatization, sub-division and sale of Maasai ranches[END_REF]. The neighbouring Kimana group ranch, for example (Fig. 1), has already achieved full land subdivision. Of the initial 51 incorporated group ranches of Kajiado County, no fewer than 46 have already been subdivided in this way. The Rombo, Olgulului, Mbirikani and Eselenkei ranches (Fig. 1) have been engaged in an on-off process of subdivision for nearly 20 years, with Kuku being the only ranch to not yet have begun a subdivision process. The belt formed by those four group ranches (Fig. 1) still represents in 2021 the last continuum of undivided rangeland between the Tanzanian border and Nairobi [START_REF] Burnsilver | Beyond Group Ranch subdivision: collective action for livestock mobility, ecological viability and livelihoods[END_REF][START_REF] Galaty | Grounding pastoralists: law, politics, and dispossession in East Africa[END_REF]Ntiati, 2002).

From the 1950s, the colonial authorities also developed water harnessing infrastructure [START_REF] Swynnerton | A plan to intensify the development of African agriculture in Kenya[END_REF]. Isinet swamp, for example (Fig. 3), was reclaimed for irrigated agriculture, which also took off around Loitokitok and Kimana [START_REF] Githumbi | Pollen, people and place: multidisciplinary perspectives on ecosystem change at Amboseli, Kenya[END_REF][START_REF] Rutten | Selling wealth to buy poverty: The process of the individualization of landownership among the Maasai pastoralists of Kajiado District, Kenya[END_REF]. A pipeline was laid down in 1954-1956, parallel to the north-south all-weather road. In 1982, decisions were taken during an informal meeting to restrict human settlement to a corridor along the pipeline and thus to avoid residential scatter across the rangeland [START_REF] Peacock | Herd movement on a Maasai group ranch in relation to traditional organisation and livestock development[END_REF]. That pipeline captures the high-discharge (17 L/s) underground spring of Nolturesh in the foothills of Mt. Kilimanjaro, situated on Loitokitok group ranch.

The pipeline was completed in 1992, conveying water to the urban areas of Kajiado, Machakos and Athi River [START_REF] Rutten | Shallow wells: A sustainable and inexpensive alternative to boreholes in Kenya[END_REF]. Water tanks along the pipeline are dedicated to supplying neighbouring communities, but numerous illegal connections also provide free and unregulated access for households and businesses. The farmed landscape at Mbirikani is thus overall controlled by opportunities of access to water, and currently forms three clusters: one on deep silt-and clay-rich red soils irrigated by pipeline water; another on clay-rich, shrink-swell black soils (Vertisols) irrigated by stream-and springwater; and a third, rainfed outlier located on young volcanic soils in the Chyulu Hills, where annual rainfall totals are higher (locally up to ~1000 mm) than in the lower-lying rangelands of the ranch (Fig. 3). Protected areas devoted to wildlife conservation in and around Mbirikani include Chyulu Hills National Park (Fig. 1), Kimana Sanctuary (adjacent to Isineti swamp), and Endonyo Wuas (Fig. 3). Agriculture is forbidden in these areas, and access to livestock is regulated.

Development policies in Kenya's group ranches today largely focus on the promotion of improved livestock systems based on more productive breeds and on enhancing milk and meat output, thereby maximising feed and fodder inputs, reducing the use of pasture, and supporting market integration into a commodity chain [START_REF] Kuria | Adapting dryland livestock production to meet climate change challenges in Kenya[END_REF]. Maasai pastoralists are commonly receptive to some of these modern incentives. For example, while maintaining herd mobility as a key feature, they use veterinarian products and acquire improved cattle breeds.

Maasai pastoralism

Pastoralism in the area today is based on the small East African shorthorn Zebu, Red Maasai Sheep, and Small East African Goat [START_REF] Scarpa | Valuing indigenous cattle breeds in Kenya: an empirical comparison of stated and revealed preference value estimates[END_REF]. Livestock is kept in a corral called a boma, which can also be broadly defined as the homestead (corral and house) (see Suppl. Fig. 1). Female livestock comprise the majority of the herd because the Maasai pastoral system prioritises dairy production over meat. Male calves will thus typically compose 20% of a Maasai herd but the number rapidly declines after they have reached finishing weight. Only a few mature bulls and steers are kept thereafter [START_REF] King | Maasai herd and flock structures in relation to livestock wealth, climate and development[END_REF]. Zebu cattle subsist on short grasses and forbs and have limited milk yields, but their tolerance to heat and aridity and to forage deficiencies is outstanding. They are nonetheless obligate drinkers and require ~60 L/day [START_REF] Blackie | Rangeland management and ecology in East Africa[END_REF]. Mixed-breed and mixed-species herds overall allow pastoralists to harness a greater range of natural resources, access a greater diversity of habitats, and thus better withstand different types of shock [START_REF] Scoones | New directions for pastoral development in Africa[END_REF].

Livestock is living capital [START_REF] Ridder | Modelling of extensive livestock production systems[END_REF]. It provides goods consumed by the household, liquidities from sales, or gifts (a currency in social capital). The overarching economic rationale of the system consists in maximising milk production and herd size in order to cushion the impacts of periodic mortality hazards caused by drought and disease [START_REF] Bierschenk | Rational herdsmen. Economic strategies of the agropastoral Fulani of Northern Benin[END_REF]. The herd is thus managed as a savings bank account 'on legs'. Livestock accumulation is itself also a drought-adaptation strategy aimed at maintaining stock after losses in order to bounce back. One of the worst droughts in living memory occurred in 1961 (the 'Year of powdered milk'), during which food was delivered by helicopter for 18 months. Other droughts with severe effets for pastoralists occurred in 1980,2009 and 2017 (Fig. 2). These events played a decisive role in the choices made thereafter by some pastoralists to diversify, in particular by practicing agriculture [START_REF] Western | Cattle and pastoralism: Survival and production in arid lands[END_REF].

Materials and methods

Comparative agriculture: a methodological framework

The methodology is based on comparative agriculture, a standardised framework of mixed methods (e.g., semi-structured interviews, participant observation) aimed at characterising and comparing farm-level production systems situated in different social, cultural and environmental settings around the world (see Suppl. Material, sections 2 to 7). Investigations aim to understand farm trajectories and farm differentiation within small territories, each defined by specific socioeconomic and agroecological conditions [START_REF] Cochet | Comparative Agriculture[END_REF]. Comparative agriculture is particularly useful for characterising agrarian diversity on a regional scale through farm profiling and classification [START_REF] Lacoste | Assessing regional farming system diversity using a mixed methods typology: the value of comparative agriculture tested in broadacre Australia[END_REF], and for gaining a dynamic understanding of the socio-economic processes playing out in the rural economy. Comparative agriculture focuses on access to essential factors of production such as land, labour, and capital in order to understand the system's historical trajectory and structural diversity [START_REF] Aubron | Poverty and inequality in rural India. Reflections based on two agrarian system analyses in the state of Gujarat[END_REF]. Its four core concepts are the agrarian system, production system, cropping system and livestock farming system. An agrarian system is an assemblage of several production systems in a particular region. Production systems encompass farms that share similar production factors and economic orientation [START_REF] Aubron | Labor as a driver of changes in herd feeding patterns: evidence from a diachronic approach in Mediterranean France and lessons for agroecology[END_REF][START_REF] Cochet | The systeme agraire concept in francophone peasant studies[END_REF]. A production system consists of one or several cropping systems (plot level) and livestock farming systems (herd level). This nested approach is synthesised in Figure 4 and detailed in the Supplementary Material.

Documentation of landscape units and historical transformations (steps 1 and 2)

Given that biophysical constraints determine a spectrum of potential agronomic activities, step 1 (Fig. 4) consisted in defining broad landscape units based on criteria such as water availability, topography, vegetation, soil, and land use. This was achieved using Google Earth, and complemented by direct field observations. The aim of step 2 (Fig. 4) was to document an event chronology of the production systems in the area before and since the group ranch reform. Reconstructing these trajectories required piecing together information about livestock and farming practices from scientific and grey literature, and from narratives by Maasai elders. Fifty elders known to have reared livestock in Mbirikani were randomly selected among the landscape units identified during step 1. These included Endonyo Wuas, Lemasusu and Center (Chyulu foothills landscape unit); Orbili and Oltiasika (plains); Ilchalai, Esambu, Isinet and Kaliserua (swamp area); and Irmabateni, Inkoisuk, Mbirikani, Nasipa and Orng'osua for the pipeline corridor (see Fig. 3). A preliminary typology of production systems was established based on the information collected at this stage.

Modelling agricultural diversity (steps 3 and 4)

In comparative agriculture, 'modelling' consists in profiling different production systems by grouping farms that share similar characteristics in terms of historical trajectory, farm size, herd size and composition, land-use affinities, farming equipment, livestock migration pattern, origin of labour, etc. This facilitates comparisons, ranking, and the assessment of complex situations [START_REF] Lacoste | Assessing regional farming system diversity using a mixed methods typology: the value of comparative agriculture tested in broadacre Australia[END_REF].

In step 3 (Fig. 4), thirty-eight working Maasai agro-pastoralists were selected using a purposive sampling strategy based on the preliminary typology established after step 2. The technical and socioeconomic aspects of their activities were documented. As Maasai men were usually ill-informed about the details of milking and cropping, which are conducted by Maasai women and non-Maasai sharecroppers, respectively, six interviews with Maasai women, and a further nine with sharecroppers working for Maasai landowners, were also carried out. The final classification of production systems is generated in Step 4. It is a simplified representation of reality (a model) based on a finite number of observed individuals [START_REF] Couty | Qualitatif et quantitatif : deux modes d'investigation complèmentaires[END_REF][START_REF] Delarue | Systemic impact evaluation: a methodology for complex agricultural development projects. The case of a contract farming project in Guinea[END_REF].

3.5 Microeconomic analysis of the production systems (step 5) Final step 5 (Fig. 4) focused on the estimation of household income. The balance-sheet approach to this task presents components of uncertainty because Maasai pastoralism (i) is not fully marketoriented, (ii) does not involve scrupulous book-keeping, and (iii) involves nested cycles of herd building, destocking and restocking over many years. A precise appreciation of household economies in agro-pastoral systems would thus ideally require taking account of social as well as financial capital afforded by livestock [START_REF] Alary | Livestock's contribution to poverty alleviation: how to measure it?[END_REF]. Given further that animal-related produce is very rarely estimated in the same way as crop-related produce [START_REF] Alary | Livestock's contribution to poverty alleviation: how to measure it?[END_REF], an additional challenge thus arises in the estimation of household income when considering livestock and cropping activities together. [START_REF] Behnke | Measuring the benefits of subsistence versus commercial livestock production in Africa[END_REF] has nonetheless shown that the benefits of subsistence production in African pastoral economies are often underestimated, whereas commercial assets, instead, are commonly overestimated.

Household income, i.e., what remains in a household's budget for consumption, investment or capitalisation over a defined period, was estimated for each of the production systems arising from the classification obtained in step 4. Microeconomic variables entering the calculation of household income are (i) gross product, (ii) intermediary costs, and (iii) external labour costs [START_REF] Cochet | Comparative Agriculture[END_REF].

Those variables can be tailored to context (Cochet and Devienne, 2006) instead of being pre-ordained before the interviews [START_REF] Lacoste | Assessing regional farming system diversity using a mixed methods typology: the value of comparative agriculture tested in broadacre Australia[END_REF]. The values were calculated using data collected during step 3 and product prices obtained at the livestock market. Due to fluctuations in market prices, the calculated values provided in this study are valid for the year 2018.

Gross product (GP)

GP is the annual wealth produced at farm level from cropping-and livestock-related activities (Eq. 1).

The production values were calibrated on local market prices, thereby providing a price that farmers would have to pay for the product if they had not produced it. GP = GPcrops + GPlivestock (Eq. 1)

GPcrops is a function of crop yield (kg/acre) (Eq. 2). As food prices vary throughout the year, we chose for each cropping season the average price (KES/kg) at peak sales time (KES: Kenyan shilling):

GPcrops = ∑ 𝑌𝑖𝑒𝑙𝑑 𝑐𝑟𝑜𝑝 𝑖 𝑖 * 𝑆𝑎𝑙𝑒 𝑝𝑟𝑖𝑐𝑒 𝑐𝑟𝑜𝑝 𝑖 (Eq. 2)
GPlivestock accounting cannot just rely on estimations of the animals sold or gifted because this approach (better suited to meat-oriented livestocking) only considers residual stock as a result of offtake and purchase rate. GPlivestock was thus estimated by adding the average annual growth of herd value to the value of the milk produced for human consumption (Eq. 3, in KES/CEqU1 ).

GPlivestock = GPmilk consumed + GPmean annual growth of herd value (Eq. 3)

GPmilk equals a woman's milk harvest multiplied by the number of women in the household. There are no outlets (e.g., dairy cooperatives) for selling milk locally. Household size thus sets a ceiling on production needs. Maasai women use a calabash (empokori) to collect milk. One empokori has an average capacity of 4 L. During the rainy season, daily milk harvest is typically 16 L/woman. In the dry season, most of the cattle have been driven to pasture, and daily harvest from the remaining cows at the boma decreases to 4 L/woman. Small stock are milked year round but the milk harvest is only 0.6 L/woman/day (i.e., two 30 cl cups) (see Suppl. Material for further details on the Maasai dairy economy). The estimation of GPmean annual growth of herd value requires several steps and involves an annual estimate of a cow's progeny aggregated over the duration of the cow's life (Fig. 5).

The estimated number of offspring per cow is then divided by average cow lifespan to obtain unit mean annual herd growth per female cow. In line with the literature and confirmed by interviewees, age at first calving is three. Heifers will thus contribute to increase herd size when their mothers are six years old. Male calves are also valued but do not contribute to herd growth. The average annual growth of herd value, 9240 KES/year/cow is calculated using a model assuming a drought impacting herd demographics once every 6 years and using 2018 prices (held constant) (see Suppl. Material, Section 3, for details about the herd growth model). Similar calculations were made for small stock.

Intermediary costs

Intermediary costs (IC) are goods and services used as inputs in the production process; they also encompass the depreciation of assets (Table 1). IC are deducted from the gross product to estimate the value added (VA, Eq. 4). VA at the scale of the cropping system (in KES/acre) and at the scale of the livestock farming system (in KES/CEqU) correspond to the total wealth created respectively for one acre of cropping system and one CEqU of a livestock farming system. The combined VA at the scale of the production system thus corresponds to the total wealth produced by the work force (e.g., family labour and external labour). Given that land on Mbirikani group ranch has not yet undergone subdivision and is still communally owned (grazing is not limited by a ceiling in available pasture surface area); and given further that any production system is characterised by a range of herd sizes but by a fixed cropland acreage, expressing economic indicators for each farm unit per acre would be unsuitable. The value added of the farm unit is thus standardised to animal units, and thus expressed in KES/CEqU. VA = GP -IC (Eq. 4)

External labour

The need for external labour is greater than before because school attendance in Kenya curtails the family workforce. Livestock left to wander unattended entails a higher vulnerability to predators and diminishes observance of grazing rules. The wages for external labour were deducted from the VA for calculating household income (HI, Eq. 5). Where relevant, land rent and/or food for sharecroppers were also deducted. HI = VA -Wages -Land rent (Eq. 5)

Two categories of external labour, one engaged in herd management and the other in crop harvesting, were considered. The household income of each production system was compared against a survival threshold, which was calculated while taking account of expenses for food (2000 KES and 1000 KES/month, respectively for an adult and for a child) and school fees (~4000 KES/quarter/child) for a standard household (most frequently encountered pattern: one husband, two wives, eight children).

The minimum monthly earnings one adult requires for him-/herself and their children, i.e., the survival threshold, is approximately 88,000 KES/year/person. By comparison, the official overall rural and urban poverty lines in 2015 were 39,024 KES/year/person and 71,940 KES/year/person, respectively (KNBS, 2018).

Results

Differentiation processes among the production systems over time

Table 2 is a chronology of locally important historical events harvested from the history-focused interviews. Trends show that changes in access to natural resources essential to pastoralism were the main drivers of production system transformation, and that these were specifically spurred by wildlife conservation policies [START_REF] Unks | People should also look after the people": relational values of wildlife and collectively titled land in Ilkisongo Maasai group ranches in Southern Kenya[END_REF]. The creation of Amboseli National Park in 1974 is primarily what deprived herders of key access to water and pasture during the dry season. Migratory routes were adjusted under this new, overarching constraint, but difficulties in accessing water entailed a cascade of other quantitative and qualitative adaptations, such as a reduction in herd sizes and a gradual increase in the number of shoats (which are better adapted to water scarcity and feeding on woody perennials). The eviction of farmers from the Chyulu Hills in 1983, and again in 2018 (Table 2), has continued to drive the wedge deeper between pastoralists on the one hand, and conservationists and wildlife on the other.

Infrastructures aimed at improving access to water multiplied after World War II. They played a central role in establishing permanent bomas near these new water access points and thus on fixing transhumance routes. The pipeline had a particularly important effect on patterns of population settlement within Mbirikani group ranch (Fig. 3). Pastoralism was also strongly impacted by successive droughts:

• The 1961 drought precipitated collective adhesion to the group ranch as a land tenure arrangement.

• The successive droughts of the early 1980s further led to the allotment of two acres of swamp land per male ranch member. This process, however, was not a legally valid group ranch land subdivision because the issued allotment letters were not recognised by the Kenyan state.

Cropping and water-access potential of these lands nonetheless vary from one plot to another.

The informal nature of the operation thus benefited some households more than others.

• The 2009 drought entailed major livestock losses, compounded by a frenzied rush to rumoured greener pastures around Mombasa. This event accelerated the urge to convert from livestock to crops. The 2009 drought entailed a 65% decline of livestock [START_REF] Gichohi | Long-term monitoring of livestock depredation in Amboseli ecosystem, Kenya[END_REF]. Numbers of smaller livestock, particularly goats, also increased after the 2009 drought because of their resistance to water stress.

• A great drought occurred in 2017 and also had a strong impact on herd sizes, but at a time in the regional chronology when livestock mobility had already become much less prevalent than in 1961. The largest breeders called on fodder and food supplements more than ever before, thus revealing strong inequalities in economic resilience to drought hazards within the community.

The interviews also revealed that conversion to agriculture among the Mbirikani Maasai first occurred in the mid-1970s, initially among poorer livestock owners. Spurred by necessity, the smallest livestock owners were thus first to adopt subsistence agriculture under sharecropping agreements with other ethnic groups (Table 2). Other categories followed suit thereafter. Possession of a larger herd is clearly 'Mombasa drought', where ~75% of herders lost more than 50% of their cattle. Drought: ~50% of herders again lost more than 50% of their cattle. Ministerial executive order forbids farming in the Chyulu Hills. Farmers are evicted.

Note. 1 According to Peron (1995, p. 56), the low milk yields of East African Zebu cows imply that Maasai families required large herds to survive: one adult Maasai required approximately 2 to 3 cows for his own consumption needs in the rainy season, 10 to 15 in the dry season, and more than in times of drought.

a major economic buffer against drought hazards and an insurance policy against milk shortages. A critical illustration of this is that larger breeders were able to invest in water transport trucks after the 1980s droughts by decapitalising their stock (i.e., selling cows). This operation provided access to pastures devoid of natural water reserves, resulting in opening up a new pastoral frontier in the Chyulu Hills. This form of intensification through mechanisation was the exclusive preserve of owners of the largest herds. Two types of pastoral systems thus co-exist depending on capacity for motorised water transport: one has maintained longer-range transhumance between the upland plains and the Chyulu Hills, and the other moves herds between the upland plains and their swamp enclaves in the south (Fig. 6). The gradual expansion of agriculture in these swamps, however, is restricting access to this shorter-range option. The differences between those two systems seem to be increasing. The largest breeders (≥ 100 heads)

fatten their adult males (3-4 years) and sell them in the rainy season (April, time of peak body mass).

Mature females are not sold because they ensure herd growth and milk for household consumption.

At the opposite end of the spectrum, herders owning less than 10 cows cannot settle for the same strategies and are sometimes forced to sell females and calves. This slows herd growth and reduces milk output. Such production systems rely more heavily on small ruminants for meat and milk, although larger livestock farmers may also lend cows to smaller livestock farmers so they can meet their household dairy needs.

A critical development in the historical timeline of Mbirikani is that farmers endowed with sufficient financial capital invested in tomato cultivation from the mid-1990s. This cash crop requires intermediary costs and manual labour. Some outlay is also needed for establishing a connexion to the pipeline. In the swamps, those who cannot afford tomatoes continue to grow maize and beans as subsistence crops. Tomatoes are sold primarily for the urban markets of Nairobi and Mombasa, but also locally. In the early 21st century, numbers of improved livestock breeds (Borana cattle, Galla goats, Dorper sheep) began to increase. Their massive build makes them profitable but they require more frequent watering than hardy breeds, more fodder, and have a faster metabolism. Crop calendars must adapt to these needs. Some herders owning at least 50 heads have also started to build small runoff-harvesting ponds (eselanke) (see Suppl. Fig. 2) aimed at extending the period of water availability, and for growing one or two additional acres of tomatoes over one or two crop cycles. The reservoirs are built on collective ranchland but are privately managed. This informal infrastructure ensures a form of intensification while modifying the surface hydrology of the savanna ecosystem.

Classification criteria of the group ranch production systems

Based on the sample analysed for this study (n = 38), nine different production systems labelled PS1 to PS9, and eight subsystems within those categories, were identified on Mbirikani group ranch in 2018. The production systems differ according to a number of criteria (Table 3; see Suppl. Table 1 for a full version). Notes. 1 Number of sampled farms belonging to the production systems: PS1 (n = 5), PS2 (n = 4), PS3a (n = 4), PS3b (n = 5), PS3c (n = 3), PS4 (n = 1), PS5 (n = 1), PS6 (n = 3), PS7a (n = 4), PS7b (n = 0 because this represents the scenario where PS7a respects the prohibition to farm in the Chyulu Hills), PS8 (n = 3), PS9a (n = 2), PS9b (n = 2), PS9c (n = 1).

2 See Fig. 6 Results highlight sharp inequalities in herd ownership, especially PS1 and PS2, which hold respectively 30 and 10 times more livestock than PS9. Another key finding is that nearly all the PS are jointly involved in agriculture and pastoralism. Individuals still relying exclusively on pastoralism belong to PS5, PS7b or PS9b, respectively because they were renting their farmland but gave it up, they stopped farming after forced eviction from the Chyulu Hills National Park, or could no longer afford the inputs.

The cropping calendar varies as a function of location, because of variability in access to water (Fig. 7).

This calendar highligths an important advantage of pipeline irrigation, which is the possibility to sustain production throughout the year (three crop cycles). This contrasts with the swamp environments (where drainage ditches would also be required to evacuate excess water during the rainy season -hence only one annual crop) and with the rainfed settings (seasonal water shortages).

We supposed that the Chyulu Hills have the same precipitation regime as in the plains but with approximately 20% more monthly rainfall because of greater elevations (summit: ~2000 m). Cropping systems located in the swamp areas usually farm the two acres allocated in the 1980s (see Section 4.1 and Table 2), or more if additional acreage is rented (PS9c). Pipeline-irrigated tomato farmers manage between two and four acres of land along the pipeline because there is no de facto limitation of land along the pipeline. In the Chyulu Hills, Maasai settlers who evaded eviction may farm up to 10 acres of purely rainfed crops (the 10-acre ceiling in the Chyulu Hills is a consequence of land allocation policies in the 1990s). Maize is usually harvested by the sharecroppers, or by Maasai family labour.

Herds are traditionally kept by unpaid family labour (children, women, young men), but increasing rates of school attendance among the Maasai entail the employment of additional labour. Some households, however, cannot afford these costs and herd pooling remains common practice. At boma level, some Maasai maintain the enclosure fence themselves, while others pay annually for servicing and repair. If the boma is shared, the cost of boma maintenance is shared between the household members.

Herd size and composition

Mixed herds of cattle and shoats are suited to harnessing a greater array of natural resources, to enduring different types of hazard, and also provide a diversity of products (milk, meat, animal fat, livestock offspring, manure for building huts, cash when sold). In terms of herd size, results reveal the wide gap between the wealthiest (PS1, more than 400 heads) and poorest pastoralists (PS7, less than 15 heads). Most production systems have mixed breed herds, but some have fully adopted improved breeds (PS1 and PS2). A few herds still consist almost entirely of Zebu (PS7).

Herd migration pattern

A total of seven migration patterns were identified (Table 3; Fig. 6), among which cost of livestock watering is a key discriminating factor. Despite being attractive during the dry season because forage abundance declines on the plain, the Chyulu Hills pastures require particularly costly water conveyance to the livestock. The migration pattern 'to north Chyulu' and 'from south plains to Chyulu' (Table 3) is characterised by the highest watering costs because agro-pastoralists have to pay for the transport of water and for access to a borehole in the latter case. Some agro-pastoralists (e.g., from PS1) also own a truck: they thus do not pay for transport of water (water is free) but bear the cost of the annual depreciation of the vehicle (Table 1). The watering costs of the migration pattern 'towards Amboseli' are zero because livestock can drink from the wetlands they encounter along the way.

Economic performance of the production systems

The microeconomic analysis reveals large economic disparities in household income, especially between the higher-ranking production systems involving pipeline-irrigated tomato farming and the others (Fig. 8). Just below the top earners are tomato growers based in the swamps and those enjoying a minimum of six rainfed acres in the Chyulu Hills. The income of families that do not grow tomatoes or cultivate less than three acres of rainfed crops in the Chyulu Hills lies below, or close to, the survival threshold. The tomato is thus the game changer. We also assessed the relative weight of crop revenue in total household income under each production system (Fig. 9). Agriculture, and particularly tomatoes (Fig. 10), shows up as very lucrative despite its high intermediary costs (domestic animals, often small stock, consequently have to be sold to purchase those inputs). Seven production systems obtain more than 70% of their income from crops, and all of them include tomatoes. PS7a involves only three acres of rainfed hillside crops, but the relative weight of crops on overall income is ascribable to the very low CEqU score. Two production systems record a range of 35-60% of household income deriving from crops: thus PS1, with two acres of pipeline-irrigated tomatoes but a large herd (400-600 CEqU); and PS3b, which farms two acres of tomatoes in the wetlands (but only one crop cycle). PS1 members often also grow crops on rented land from other group ranches (not documented here). Crops contribute more revenue to PS1 household incomes, therefore, than in the balance sheet presented here, which is restricted to the territory of Mbirikani ranch and calibrated on 2 acres of pipeline-irrigated tomatoes. When restricted to maize (PS9a, PS3c), harvest revenue contributes to less than 5% of the total. Lastly, crops contribute no income in three cases: PS5, because the land is leased3 to others; and PS9b and PS7b, because its members have no financial capacity to farm, or because farming is forbidden where they reside (e.g., Chyulu Hills).

Economic performance of crops

The value added generated by one acre of pipeline-irrigated tomato crops is overall four times greater than one acre of mixed rainfed crops that include tomatoes, and double the value generated by one acre of swamp-irrigated tomato and maize crops (Fig. 10). Even though outlay is much greater in the pipeline-irrigated tomato system than in the swamp-irrigated tomato and maize or in the mixed crops systems, surpluses generated by the pipeline-irrigated tomato system arise because (i) three cropping cycles are possible, and (ii) production can occur out-of-season when prices are high, i.e., December to July (Suppl. Fig. 5).

Discussion and outlook

Evidence of socio-economic inequalities on the ranch

The identification of nine production systems reveals a large diversity of microeconomic situations within the Maasai community, corresponding to as many levels of relative socioeconomic vulnerability. The 2017 drought showed that the economic resilience of richer pastoralists hinged on acquiring fodder and cattle feed supplements, thus emulating input-intensive farming methods until now mostly alien to the local livestock management practices. [START_REF] Homewood | Policy and practice in Kenya rangelands: impacts on livelihoods and wildlife[END_REF] previously revealed that 10% of households around Amboseli owned 45% of the livestock. It was difficult to establish why some herders possessed larger herds in the first place, and respondents were evasive about this issue. It is highly likely that other factors relating to institutional power (political capital) would explain initial livestock accumulation. None of the economic disparities detected, however, appear to have arisen from dramatic forms of oppression or from rags-to-riches success stories in the last 70 years. Transformations were essentially circuitous, piecemeal and incremental, with advantages -once gained through herd size and political power -maintained and cumulative. The weight of these assets has played an important role in the ability to cope with future shocks, with disparities always magnified in the context of droughts.

The Maasai community is nonetheless well known for its moral economy based on reciprocity and mutual aid (e.g., [START_REF] Aktipis | Risk-pooling and herd survival: an agent-based model of a Maasai gift-giving system[END_REF]Western and Finch, 1986;[START_REF] Western | Environmental change and the vulnerability of pastoralists to drought: a case study of the Maasai in Amboseli, Kenya[END_REF]. Lactating cows, for example, are loaned to the needy to secure milk for the family, although at the same time generating a form of social dependency. These favours are returned in the form of services (e.g., cattle dipping, herding chores). In a setting where the most remunerative production system generates twenty times more income per capita than the lowest (Fig. 8), this trading of social capital throws a thin veil of traditional ethnic solidarity (see Section 2.3) over the growing economic disparities otherwise highlighted by the data.

Revenue from crops in Maasai household income: threats and opportunities

Crops today are clearly more profitable than livestock in Mbirikani, as likewise documented in Ethiopia (62 to 71% of household income; [START_REF] Adunga | Factors influencing income level of agro-pastoral communities[END_REF] and in Kenya, Tanzania and Uganda (60 to 90%; [START_REF] Rufino | Transitions in agro-pastoralist systems of East Africa: Impacts on food security and poverty[END_REF]. The profitability of tomato cropping is often advertised online in Kenya (e.g., "how to become a millionaire through tomato farming", etc.). At Mbirikani, only owners of large herds manage to derive substantial income from pastoral activities.

Agriculture, however, may not be profitable in the longer term because revenue from tomatoes is fundamentally conditioned by access to (i) a favorable market (volatility of tomato prices notwithstanding), (ii) labour (the sharecroppers), and (iii) water. Furthermore, pipeline-irrigated crop cultivation cannot occur more than ~3 km from the pipeline for the water to reach the fields. It requires supervision and thus cannot occur far from its attendant bomas. The economic rent associated with the revenue from pipeline-irrigated tomatoes (Fig. 10) is also not necessarily a secure asset in the longer term because the original purpose of the Nolturesh pipeline was first and foremost to provide drinking water to remote urban residents. From an economics perspective, pipeline irrigation therefore incurs an opportunity cost measured by the forgone benefit of allocating water to tomato crops instead of satisfying the intended urban demand. Water supply is ranked as the top development priority in Nairobi, Mombasa and Kakamega and concerns all social categories [START_REF] Gulyani | Water for the urban poor: water markets, household demand and service preferences in Kenya[END_REF]; as a result, conflicts (recounted in interviews and documented in Kenyan media) arose in 2018 over access rights between Mbirikani group ranch members and the Nolturesh Pipeline company. Irrigation is usually a high-volume, low-value use of water, so when it competes with urban uses the opportunity costs are high [START_REF] Briscoe | Water as an economic good : the idea and what it means in practice[END_REF]. Such conflicts could multiply in the future, raising the stakes and drawing local agriculture and livestock issues at Mbirikani into a national or even global minefield. Little is known about hydrological discharges, aquifer recharge rates, and overall dependability of water for planning purposes in the Greater Amboseli Ecosystem. Such key information, however, should in the future determine the scope for agricultural expansion in Amboseli's group ranches, where water is currently being used as an unregulated, open-access resource.

A further threat to the steadiness and viability of cash-crop expansion is that Maasai institutions have functioned until now under a regime exclusively focused on pastoralism [START_REF] Fratkin | Pastoralism: governance and development issues[END_REF]. Maasai institutions must therefore adapt to the ongoing processes of livelihood diversification and are experiencing unprecedented difficulties more widely in the context of group ranch subdivision.

Maintenance of traditional forms of pastoralism may also eventually require external support from the state and/or third-sector organisations to counterbalance the amputation of roaming space by 'fortress' wildlife conservation policies in the last 40 years (see Table 2).

The unlikely disappearance of mobile livestock keeping at Mbirikani

The importance of tomato crops in total household income is only valid for Maasai residents with access to irrigation. Furthermore, there was no record in the sample of anyone having entirely abandoned livestock keeping in order to embrace full-time crop farming. Although reliable data on total crop acreage were unavailable, values at Mbirikani are small in comparison to rangeland acreage.

Livestock is thus foreseeably the only viable resource for this territory in its majority. In the rainfed Chyulu Hills, crops rank high in household income only because of the very low CEqU score (PS7a) or because of larger acreage (10 acres in the case of PS8). As shown in Figure 10, the economic importance of crops in the rainfed region is not a function of crop type.

Crucially, whereas cash revenue from livestock can be replaced by cash revenue from crops, milk is a non-substitutable resource. This is particularly true for remote areas like Mbirikani, where no dairy market exists. As well as being culturally ingrained in Maasai society and cosmology (the Maasai defined themselves as 'iltung'anak loonkisho', meaning 'people of the cattle'), milk is the staple food and its long-term consumption has allowed the group to maintain unique biological features such as low cholesterol levels [START_REF] Biss | Some unique biologic characteristics of the Masai of East Africa[END_REF]. What the Maasai eat defines them quite literally as pastoralists who live off the food of their livestock; their status as predators, hunters or farmers is subsidiary (Århem, 1989).

There is thus little to indicate that recent rural dynamics driven by tomato cultivation are either unidirectional or irreversible [START_REF] Babiker | Introduction (from decline to survival in East African drylands)[END_REF]. Cash crop cultivation elsewhere in Kenya, for example, is far from having deterred the Maasai community from livestock husbandry. At Naroosura group ranch in Kenya's southern rift valley, for example, Maasai livestock remains an essential safety net in contexts of low yields or crop market collapse. Crop residue is fed to the cattle, and farming income allows herd restocking in the wake of drought-related mortality [START_REF] Pollini | Resilience through adaptation: innovations in Maasai livelihood strategies[END_REF]. In Laikipia, even though families own far less livestock than twenty years ago, livestock is still the most important fallback in periods of food scarcity [START_REF] Ulrich | Small-scale farming in semi-arid areas: Livelihood dynamics between 1997 and 2010 in Laikipia, Kenya[END_REF].

Examples of strong integration between agriculture and livestock were scarce. One occurrence consisted in selling sheep or goats in order to buy farm inputs. Another consisted in letting livestock graze in the fields after harvest, but only in times of drought. No systematic use of animal manure to fertilize the fields was reported. Re-investment of crop revenue (including revenue from land leases) into livestock production, and vice versa, was not, however, systematically explored in this reconnaissance study. Future research may nonetheless reveal further intricacies in the agricultural economics and ongoing agrarian transformations of Mbirikani ranch.

Impact of wildlife conservation policies on cropping and livestock activities

Transhumant pastoralism in southern Kenya has been strongly affected by 20th century wildlife conservation policies [START_REF] Unks | People should also look after the people": relational values of wildlife and collectively titled land in Ilkisongo Maasai group ranches in Southern Kenya[END_REF]. The creation of Amboseli and Chyulu national parks in 1974 and 1983, respectively, has amputated the eastern and western extremities of the Amboseli wildlife dispersion and livestock transhumance corridors, with the Kisongo Maasai thus falling victim to (i) loss of access to water (Amboseli) and pasture (Chyulu), but also to (ii) unfair compensation for herd predation in a context of intensified human-wildlife conflict within shrinking rangeland territory (e.g., raids from elephants on crops). The creation of group ranches has further constrained the extent of grazing areas and reduced the flexibility of Maasai pastoralism, which was a key dimension of its adaptive capacity. Resentment over policies to protect biodiversity, therefore, has reached a high tidermark [START_REF] Unks | People should also look after the people": relational values of wildlife and collectively titled land in Ilkisongo Maasai group ranches in Southern Kenya[END_REF]. 'Fortress' conservation attitudes initially pointed the finger at herding practices and large herd sizes, thereby perpetuating the colonial trope about the Maasai livestock economy being inefficient and motivated by a taste for prestige rather by a sound sense of ecosystem management [START_REF] Homewood | Pastoralism and conservation[END_REF]. In other pastoral areas, contraction of rangelands has in fact led to a 'reproductive squeeze' where pastoralists overgraze remaining pastures [START_REF] Zhang | Marketization induced overgrazing: The political ecology of neoliberal pastoral policies in Inner Mongolia[END_REF]. At Mbirikani today, however, conservation organisations are now attempting new forms of alliance with the Maasai against the expansion of agriculture. The prospect of fields crowding out rangeland habitat, or at least impeding the free movement of wildlife around critical water access points and through dispersal corridors -with alarming precedents in the Kitengela area, south of Nairobi National Park -are providing vivid warnings of unwanted outcomes [START_REF] Nkedianye | Livestock-wealth inequalities and uptake of crop cultivation among the Maasai of Kenya and Tanzania[END_REF][START_REF] Said | Effects of extreme land fragmentation on wildlife and livestock population abundance and distribution[END_REF].

The intrinsic profitability of agriculture nonetheless poses a strong threat to conservationists because the strategy for winning over Maasai pastoralists to the cause of wildlife habitat preservation is partly based on opportunity costs -i.e., attracting Maasai residents to conservation-and tourism-related jobs with wages that exceed income from livestock and crops. While it is difficult to predict how long the Amboseli tomato boom is set to endure, conservation NGOs may struggle for some time to outbid the profitability of tomato cropping. Additionally, while agriculture in Amboseli has until now rarely been in direct competition with wildlife conservation because the expansion of cash crops is hampered by access to water, (i) grabbing of water resources by powerful individuals for agriculture and (ii) landscape fragmentation by fencing both have insidious impacts on key components of wildlife survival. Strategies for furthering conservation goals are thus limited to finding ways of restricting the expansion of agriculture, or to re-incentivising cattle transhumance while seeking to reduce shoat loads, which exacerbate soil degradation. Emphasis on the positive effects of cattle loads on savanna biodiversity and ecosystem services is one of the evidence-based narratives that can achieve this (reported by a conservationist working for one of the main NGOs; see also [START_REF] Reid | Savannas of our birth: People, Wildlife, and Change in East Africa[END_REF].

Approaching the microeconomics of farming on Mbirikani goup ranch from a historical perspective (Table 2) has shown how the government's push in favour of ranching as a solution to rangeland management (1968), followed by 'fortress' conservation (1974,1983), ended up amputating land use options for Kisongo Maasai pastoralists and driving them into an accelerated transition from full-time pastoralism to agro-pastoralism. They are now facing some unforeseen consequences of those policy choices made barely 50 years ago. Steering the pastoralism-agriculture-wildlife nexus out of this impasse and towards new viable trajectories is an acute challenge for the near future, with few easy options beyond reopening the national parks to a negotiated coexistence between wildlife and pastoralism, and perhaps steering subdivision of the four remaining, unsubdivided group ranches of the area (Fig. 1) towards imaginative and flexible negotiated solutions. Pastoral producers in Kenya thus continue to face the dilemma of "being caught between new land tenure rules associated with the dissolution of group ranches and subdivision of communal rangelands, and the unchanged ecological exigencies of their dryland systems" [START_REF] Burnsilver | Beyond Group Ranch subdivision: collective action for livestock mobility, ecological viability and livelihoods[END_REF]. The pull of agriculture is a relatively new component to that dilemma, adding to the acuteness and complexity of the issues facing the sustainability of East-African pastoralism and wildlife conservation.

Conclusion

Maasai pastoralism is continually evolving and is currently integrating cash-crop agriculture. Pastoral production not only intersects with crop farmers, commodity traders, and other components of the rural economy, but in southern Kenya it is evolving into a mosaic of agro-pastoral production systems in which full-time pastoralism is diversifying. While mobile livestock herding is unlikely to disappear, and while the ongoing transition does not foreshadow any easily predictable or pre-ordained endpoint, tomato cultivation is transformative because it raises household revenue to much higher levels than pastoralism. It also undermines conservationist agendas, which commonly endeavour to make employment in wildlife conservation profitable so that pastoralists continue to engage in conservation-related strategies [START_REF] Norton-Griffiths | The opportunity costs of biodiversity conservation in Kenya[END_REF]. Conservation NGOs, however, often cannot outcompete irrigated agriculture. This partly explains why Kenya -and Africa more widely as a result of the park tourism crash during the Covid-19 pandemic years of 2020-2021 -is seeking new ways of funding conservation through international strategies (pan-African and beyond) rather than by relying on local but volatile differentials in rural livelihood diversification opportunities.

Fig. 1 .

 1 Fig. 1. Study area location map. Topography generated from the ALOS World 3D Digital Elevation

Fig. 3 .

 3 Fig. 3. Location of bomas and water sources on Mbirikani group ranch. Topography generated from

Fig. 4 .

 4 Fig. 4. Steps of agrarian diagnosis in comparative agriculture

Fig. 5 .

 5 Fig. 5. Herd-value growth model. See Supplementary Material for further details.

Fig. 6 .

 6 Fig. 6. Mobile livestock seasonal migration patterns between settlements on Mbirikani group ranch

Fig. 7 .

 7 Fig. 7. Climate diagram and cropping system (CS) calendar. A. Walter-Lieth diagram: rainfall and

Fig. 8 .

 8 Fig. 8. Annual income of production systems on Mbirikani group ranch according to herd size.

Fig. 9 .

 9 Fig. 9. Annual income of production systems on Mbirikani group ranch by source of revenue (crops or

Fig. 10 .

 10 Fig. 10. Comparison of gross product, intermediary costs, and value added per unit acre for each

Table 1 .

 1 List of intermediary costs and costs linked to depreciation of fixed capital

		Intermediary costs	Annual depreciation of fixed
			capital (wear and tear)
	Livestock system	Watering of livestock	Truck (for livestock watering)
		Veterinary costs	Maintenance of boma fence
	Cropping system	Fertilisers, Seeds	None (tractors used for ploughing
		Water for pipeline irrigation (connection to pipeline)	belong to the labourers who are payed for this task)
		Ploughing (outsourced to labourers)

Table 2 .

 2 Chronology of events at Mbirikani since 1880, with impacts on production systems

Table 3 .

 3 Characteristics of the nine production systems (PS) and their variants

	Production system	Sub-	No. of	Cattle	Migration pattern 2	Cropping system
	code name	system 1	CEqU	herd type (breed)		(no. of acres)
	PS1	-	240-360	Improved To north Chyulu,	Pipeline tomatoes (2)

Given that the livestock subsystems are multi-species, we combined bovine gross product and shoat (sheep + goat) gross product by reference to a standardised female unit, typically an Animal Equivalent Unit. Given that females are responsible for the growth of the herd (the living capital), we opted for a Cow Equivalent Unit (CEqU) because cows are iconic to the social identity of the Maasai and provide the staples of their economy.

On Mbirikani ranch, all the farming chores are done by the sharecroppers. The only daily labourers are the tomato pickers (usually carried out by groups of Maasai women, who receive 200 KES for a 70 kg crate). This regime is not necessarily identical on all ranches in the area.

Additional revenue received from land leases was not documented and thus not quantified in total income calculations. Only revenue from crop and livestock production was considered.

Acknowledgements

We thank two anonymous reviewers for their detailed, thoughtful and constructive comments. We acknowledge the Agence Nationale de la Recherche (ANR, France) for supporting the research program ANR-16-CE03-0004 MaGNUM.