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Pemba (Zanzibar, Tanzania)

all pictures: © Monique Borgerhoff Mulder


  • Principle investigator: Monique Borgerhoff Mulder

  • Team members:
    Jeff Andrews, Tim Caro, Matt Clark, Emmanuel Maliti

  • Previous members: Amy Collins, Helle Goldman

  • Research since: 2015

Site Details

Pemba (1,014 km2) is one of the two main islands of the Zanzibar archipelago, and lies 50 km off the coast of Tanzania. Inhabited for over 20,000 years, its fertility allowed it to play a central role in the development of the Swahili culture of the East African coast for well over a millennium. Pemba became part of the Omani Sultanate and (starting in the early 1800s) pivotal to global clove production. Clove production has shaped much of the island‘s ecology and society, and persisted throughout the British colonial period. Since the Revolution (1964), and particularly the crash in global clove prices, the island has reverted to being an agricultural hinterland. Principal livelihood occupations entail agroforestry (covering 44.1% of the island), with the production of rice, cassava, peanuts, coconuts, pineapples, mangos and many other species. Fishing (pelagic, reef and inshore) is also central to livelihoods, as well as livestock raising, seaweed cultivation, and small-scale marketing. Pembans‘ historical dependency on cloves created a cosmopolitan society with considerable ethnic diversity, politically dominated by Omanis. The islanders fall under the Revolutionary Government of Zanzibar, and Islam is the predominant faith. 


Our research primarily addresses the evolutionary dynamics underlying the social-ecological systems that characterize the island. Our initial focus was on the evolution of cooperation across the island in relation to an initiative to reward communities for desisting from deforestation (Reducing Emissions from Deforestation and Forest Degradation, REDD+). In order to study how cooperative communal institutions for natural resources emerge, the first step was composing a quantitative ethnography of forest dependence across the island, the first and only islandwide analysis of the interactions between the island‘s forests and its economy (Andrews & Borgerhoff Mulder 2022). Despite the project‘s ultimate failure (due to external implementers), we performed one of the first investigations into the effects of a conservation project‘s failure on the willingness for future participation (Andrews & Borgerhoff Mulder 2023a). Despite the failure to deliver on its promises, exposed residents are more likely to participate in future programming, highlighting the possibility for positive cumulative institutional growth from even failed projects. 

Building on this foundation, we have developed a set of formal analytic and agent-based models to study the economic and evolutionary forces driving the emergence and stabilization of collective property rights regimes over common pool resources (Andrews et al. 2023b). Our results show that borders are a necessary but insufficient precondition for the evolution of sustainable management institutions and that information exchange between groups is crucial in helping groups determine optimal harvesting policies. The discovery that borders are a necessary precondition for sustainable management led us to investigate the role of inter-group competition over natural resources using experimental games and community resource mapping across Pemba (Andrews et al. 2023c, Clark et al. 2023). 

From this research, we found that in the absence of borders, support for natural resource management is adversely affected by inter-group resource theft – highlighting that inter-group conflict does not always lead to high levels of cooperation, as suggested by many proponents of cultural multilevel selection. To further understand how technological and institutional innovations spread, we have developed the first application of a statistical technique using ordinary differential equation modelling to track the diffusion of conservation innovations (Clark et al. 2022). Furthermore, as it is clear that natural resource management is affected by the number of users, since 2022, Dr. Andrews has begun an extensive high-resolution, longitudinal research program studying how people switch from subsistence production to participating in the broader market economy on the island. 

Our methods rely heavily on the co-production of knowledge of importance to forest managers and communities, household and individual level surveys, social network analysis, participatory mapping, econometric analysis, experimental games, remote sensing and spatial analyses, all guided by theoretical modeling. With the establishment of the Ngezi-Vumawimbi Cultural and Biological Heritage Centre we aim to strengthen community and citizen science, and integrate our Pemban research assistants and collaborators into the scientific process.

Selected Publications

Andrews, J. B., & Borgerhoff Mulder, M. (2018). Cultural group selection and the design of REDD+: insights from Pemba. Sustainability Science, 13: 93-107.

Andrews, J. B., Borgerhoff Mulder, M. (2022). Forest income and livelihoods on Pemba: A quantitative ethnography. World Development, 153: 105817.

Andrews, J. B., et al. (2020). Does REDD+ Have a Chance? Implications from Pemba Tanza-nia. Oryx, 1-7.

Clark, M. (in progress). Community mapping to parameterize a model for the evolution of conservation institutions.

Borgerhoff Mulder, M., et al. (2021). A silver lining to REDD: Institutional growth despite programmatic failure. Conservation Science and Practice, e312.

Caro, T. (2022). Upgrading Birgus: lessons for invertebrate conservation. Biodiversity and Conservation. doi: 10.1007/s10531-022-02480-z

Caro, T., et al. (2022). Practical guide to coproduction in conservation science. Conservation Biology, e14011.

Clark, M., et al. (2022). A quantitative application of diffusion of innovations for modeling the spread of conservation behaviors. Ecological Modelling, 473: 110145.

Clark, M., & Andrews, J. B. (2021). A game of spillovers: Conservation strategies in Pemba and their unintended consequences. Anthroposphere: The Oxford Climate Review, 7.

Collins, A., et al. (2022). How community forest management performs when REDD+ pay-ments fail. Environmental Research Letters, 17(3), 034019.

Davidson, D. J., Andrews, J. B., & Pauly, D. (2014). The effort factor: Evaluating the increasing marginal impact of resource extraction over time. Global Environmental Change, 25, 63-68.

Davidson, D. J., & Andrews, J. B. (2013). Not all about consumption. Science, 339(6125), 1286-1287.

Goldman H. V. (1996). A comparative study of Swahili in two rural communities in Pemba, Zanzibar, Tanzania. PhD New York University.