Background: With the declining state of biodiversity, it is important that available literature is utilised to its full potential to mitigate environmental issues. Systematic reviews and systematic maps are considered the top tier of available knowledge in conservation science but often neglect non-English-language literature. Non-English-language literature can provide unique evidence, especially in ecological studies, which may influence findings and alter conclusions. In order to mitigate any barriers which may limit authors’ ability or intent to include non-English-language literature, we assessed factors that may predict the inclusion of non-English language literature in ecological systematic reviews and maps, as well as the authors' perspectives. Methods: We assessed all systematic reviews and maps published in the journal Environmental Evidence (n=72) prior to January 2022, extracting data related to the study's level of language inclusiveness and its potential predictors. We also surveyed the corresponding author from each paper (n=32 responses), gathering information on the barriers to the inclusion of non-English language literature. Results: 32 (44%) of the 72 assessed reviews did not search or screen for languages in any non-English languages. The most common justifications for this were resource and time constraints. Regression analysis showed that systematic reviews and maps involving authors from a greater number of countries, and author teams that spoke more languages searched significantly more non-English languages. Our survey identified that the most common barriers to higher levels of language inclusion were the lack of relevant language skills within the review team and limited funding. Conclusion: Our study suggests that greater diversity in the review team is the most effective method for increased language inclusion and thus more comprehensive and unbiased systematic reviews and maps. Alternatively, machine translation combined with the utilisation of the review team’s knowledge may reduce the financial and resource burden of translation. The cost of translation could also be included in funding applications to alleviate the financial burden of translation. The implementation of the methods described may allow for use of the full breadth of conservation literature to achieve better environmental outcomes.
