Harnessing foresters' engagement for climate change adaptation: the emerging tool of next-generation citizen science

Citizen science is an increasingly common approach for collecting large amounts of data across extensive spatial and temporal scales in ecology and environmental sciences. To facilitate participation, the majority of citizen science projects are based on opportunistic smartphone-based tasks that can be completed in just a few minutes. We reviewed 639 citizen science projects and coordinated distributed experiments, assessing the level of engagement expected from participants, and found that citizens can also perform highly engaging tasks, including conducting experiments, similar to those expected from collaborating scientists. We coined the term "next-generation citizen science" for experiments conducted by citizens with specialized knowledge and addressed the benefits and risks of such projects using the example of MyGardenOfTrees. This unprecedented continent-wide transplant experiment involves over 300 forester-citizens who dedicate their time and expertise to testing different seed origins in their forests over a five-year period, and co-develop a prediction tool with researchers for selecting suitable species and provenances for assisted migration. We used marketing analysis of recruitment data to identify strategies for participant recruitment and retention across the multi-cultural landscape of Europe, thereby expanding the boundaries of citizen science beyond its traditional use. Furthermore, we present the development of the experimental design and protocols aimed at optimizing logistical feasibility, scientific rigor, and social acceptance. Our findings highlight the untapped potential of such experimental citizen science approaches to increase the scale of ecological experiments and ultimately obtain generalizable findings, thereby overcoming context dependence.