Modeling Hawaiian dryland (rainfed) agriculture has been an effective means for examining interactions between ecosystems and human behavior. Dryland agriculture in these discussions has often been treated as a homogenous farming system; however, this was in fact a dynamic system with distinct agroecological zones where specific mixes of crops were grown using different farming methods. We examine this variability by using historical depictions and ground surveys to estimate the extent of an agroecological zone represented by breadfruit plantations within Kona, Hawai'i Island. We estimate that the plantations produced 21,200–58,400 mt/yr of breadfruit on 3100–5900 ha with a likely canopy cover within the plantations of 38–73%. Our models suggest that yields per area in the plantation ranged from 1.96 to 3.61 dry mt/ha. Given the yield and labor requirements, breadfruit could have produced a caloric surplus for 15 people in contrast to 3.6 people under assumed requirements of sweet potato. This high surplus would have been vital for socio-political developments centered in the region, and highlights the importance of assessing variability of dryland field systems in discussion of their role in historical trajectories.