[13] In 2013, she was appointed Director of Science at the Royal Botanic Gardens, Kew,[9] on a 5-year secondment from the University of Oxford.

[14] On 1 October 2018, Willis succeeded Keith Gull as Principal of St Edmund Hall, Oxford.

Many scientific studies are limited to short-term datasets that rarely span more than 40 to 50 years, although many larger organisms, including trees and large mammals, have an average generation time which exceeds this timescale.

Short-term records therefore are unable to reconstruct natural variability over time, or the rates of migration as a result of environmental change.

She also argues that a short-term approach gives a static view of ecosystems, and leads to the conceptual formation of an unrealistic "norm" which must be maintained or restored and protected.

She has argued that the impacts of contemporary climate change on plant biota is uncertain and potentially not as severe as researchers envision,[17] and challenged assumptions made in the interpretation of spatially constrained temperature records.

[19] Willis's research has been published in Nature,[20] Science,[21][22][23][24][25] Philosophical Transactions of the Royal Society B,[26] Biological Conservation.