In a new study published in Human Ecology, I took on the daunting but important task of integrating quantitative field data with qualitative interview data to advance a novel, socio-ecological understanding of intrinsic crop yield fluctuations. Let me first introduce my motivation for this research, and why a socio-ecological approach was so important.
A growing number of global initiatives aim to support farm resilience against environmental threats, yet often overlook alternate bearing—inherent yield fluctuations in long-lived crops (e.g., apple, olive, pistachio, avocado). Because many of the components and interactions in contemporary agricultural ecosystems are under farmer control (e.g., nutrient and water availability, species composition, genetic variability), human influence is generally thought to outweigh ecological processes, such as those that might induce synchronous seeding. Yet media and trade reports have cited alternate bearing in discussions of national yields, a pattern I confirmed in a global analysis published in Philosophical Transactions of the Royal Society B. The fact that synchronous fluctuations often persist suggests that alternate bearing poses an important, and poorly examined, threat to farming livelihoods and supply chains. The bulk of existing research on alternate bearing has examined plant level mechanisms through isolated agronomic experiments, with little attention to patterns or drivers of synchrony. Less studied still is how farmers understand, experience, and cope with alternate bearing, which ultimately determines their resilience capacity to this persistent stressor. My goal with this research was to advance an integrated, socio-ecological understanding of alternate bearing across scales grounded in farmer experience.
To do so, I conducted a study on the patterns and perceptions of alternate bearing across Costa Rican coffee farms using a socio-ecological approach. The study was conducted in collaboration with coffee farmers in Santa María de Dota, Costa Rica. Data consisted of 10 years of farm-level production data paired with semi-structured interviews and 2 years of plant-level monitoring which together capture observed patterns of farm-level alternate bearing, farmer experience with alternate bearing, typical management practices, and relationships between alternate bearing, management, and physical farm features. We found evidence of alternate bearing in farm-level data, indicative of synchrony among plants across farms. Farmers possessed detailed knowledge of alternate bearing, including the role of intrinsic and extrinsic drivers operating at differing scales, and alternate bearing played an important role in management decision-making. Interestingly, farmer-reported management strategies for alternate bearing differed based on their perception of the underlying drivers. Those seeing alternate bearing as externally driven are more likely to employ management practices that mitigate the effects of bad weather and pests, while those viewing it as intrinsic to the plant, consistent with ecological theory, instead use management strategies intended to mitigate the underlying resource tradeoffs. Quantitative analysis of farm-level alternate bearing revealed no significant relationships between alternate bearing and variability in management choices, though higher elevation farms tended to have steadier yields. Plant-level analyses demonstrated tradeoffs in the number of initial fruits per node between years, as well as an association between high initial fruit load and subsequent branch death, consistent with the hypothesis that intrinsic resource dynamics are the underlying cause of individual alternate bearing. We again found no evidence that plant-level tradeoffs were mitigated by any of the focal management practices; to the contrary, increased fertilizer led to a marginally greater alternate bearing index at this scale. Coping mechanisms for low-yielding years included taking out loans, supplementing with other income streams, and limiting household spending. Notably, farmers were more willing to cut back their household expenses than they were to limit farm management following a low-yielding year, citing fears that doing so would lead to a downward spiral of farm health. This strategy may prove maladaptive given other sources of uncertainty. Potential opportunities to support more adaptive responses to low-yielding years include further expanding income diversification and securing plant health and vigor with less reliance on agrochemical inputs.
A socio-ecological, case-study approach was essential to be able to ground the quantitative analysis in farmer experiences. The factors influencing farmer decision-making are highly subject to the cultural, political, and institutional structures of a particular place. The lack of a management effect here is significant, as interviews revealed that alternate bearing plays an important role in farm management decision-making. Farmers viewed fertilizer intensity as especially effective at mitigating alternate bearing, though we found no evidence to support this claim. Ecological theory suggests increased resource availability could instead exacerbate fluctuations. Furthermore, fertilizer is among the greatest on-farm expenses for this community and fertilization rates far exceed those employed in other coffee farming regions. Yet farmers were reluctant to limit fertilizer application even when farm income was limited following a poor harvest, instead opting to cut back on household spending. Their reports highlight the consequences of alternate bearing for farmer households and offer valuable context for the quantitative results. the factors influencing farmer decision-making, which are highly subject to the cultural, political, and institutional structures of a particular place. The lack of a management effect here is significant, as interviews revealed that alternate bearing plays an important role in farm management decision-making. Farmers viewed fertilizer intensity as especially effective at mitigating alternate bearing, though we found no evidence to support this claim. Ecological theory suggests increased resource availability could instead exacerbate fluctuations. Furthermore, fertilizer is among the greatest on-farm expenses for this community and fertilization rates far exceed those employed in other coffee farming regions. Yet farmers were reluctant to limit fertilizer application even when farm income was limited following a poor harvest, instead opting to cut back on household spending. Their reports highlight the consequences of alternate bearing for farmer households and offer valuable context for the quantitative results.
My hope is that this research serves as a catalyst for further inquiry into the mechanisms of alternate bearing and its links to ecological dynamics and socio-ecological resilience. I am currently building on the study described above to examine patterns of alternate bearing and yield synchrony within and among coffee-growing regions. There is ample opportunity, and a pressing need, to advance a socio-ecological understanding of alternate bearing across spatial and temporal scales and across perennial crop taxa. An empirical understanding of the phenomenon grounded in farmer experiences is key to supporting farmer capacity to manage and cope with fluctuations amidst mounting environmental pressures.