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Breadfruit (Artocarpus altilis (Parkinson) Fosberg) is a prolific tropical tree producing highly nutritious and voluminous carbohydrate-rich fruits. Already recognized as an underutilized crop of high potential, breadfruit could ameliorate food insecurity and protect against climate-related productivity shocks in undernourished equatorial regions. However, a lack of fundamental knowledge impedes widespread agricultural adoption, from modern agroforestry to plantation schemes. Here, we used a multi-environment breadfruit variety trial across the Hawaiian Islands to determine photosynthetic limitations, understand the role of site conditions or varietal features, and define their contributions to agronomic efficiency. Photosynthetic rates were dependent on location and variety, and strongly correlated with fruit yield (r2 = 0.80, P < 0.001). Photochemistry was suitable to full-sunlight conditions, with a saturation point of 1545 photosynthetically active radiation, Vcmax of 151 μmol m-2 s-1 and Jmax of 128 μmol m-2 s-1, which are high-end compared with other tropical and temperate tree crops. However, limitations on CO2 assimilation were imposed by stomatal characteristics, including stomatal density (P < 0.05) and diurnal oscillations of stomatal conductance (>50% reductions from daily maxima). These constraints on CO2 diffusion are likely to limit maximum productivity more than photochemistry. Our results comprise the first comprehensive analysis of breadfruit photosynthesis, successfully link ecophysiology with fruit yield, and identify vital traits for future research and management optimization., (© The Author(s) 2025. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

In this research we identify the processes leading to hierarchical society in a region of Sāmoa, the often-labelled 'birthplace' of the Polynesian chiefdoms. Our analyses in the Falefa Valley on 'Upolu island combine lidar mapping and ground survey to reveal an extensive system of archaeological features: rock walls, ditches, and platforms. Excavation and radiocarbon dating underpin a feature chronology and characterize feature variation. Soil nutrient analyses and geoarchaeological coring indicate spatial differences in the agricultural potentional of the valley and human modification of the environment over time. Our results demonstrate that the construction of large rock walls, some several hundred meters long, began approximately 900-600 years ago, shortly after rapid population rise in Sāmoa. This was followed by the building of small rock walls, often enclosing rectilinear fields or platforms. Both rock wall types are concentrated in the western and northern regions of the valley and greater rock wall densities are associated with areas of higher agricultural potential. The earliest wall construction was penecontemporaneous with partial forest removal that created a more productive wetland environment in the southeastern region of the valley, an area later a focus of agricultural ditching. We propose that with population rise the variable fertility of agricultural land became a significant resource gradient, influencing the population in two ways. First, areas of more fertile agricultural land promoted territorial behaviour, including large rock walls, and led to a collective action problem. Second, niche construction in the form of human-induced environmental change created a productive wetland agricultural system that was enhanced with a reticulate ditch network, the maintenance of which also led to a collective action problem. We conclude that in the Falefa Valley, the second largest catchment in Sāmoa, collective action problems were the cause of increased social hierarchy and may underlie the origins of chiefdoms throughout Polynesia., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Cochrane et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)