Environmental disclosure on mandatory and voluntary reporting of Portuguese listed firms: the role of environmental certification, lucratively and corporate governance

Purpose This study aims to construct two environmental disclosure indices (EDI), one obtained from the mandatory reporting (annual report) and the other from the voluntary reporting (sustainability report), to compare their evolution. In addition, the authors developed and evaluated a conceptual model that aims to analyse if the two EDI are affected by industry, environmental certification, lucratively and corporate governance attributes. The legitimacy, signalling and voluntary disclosure theories are used to support the theoretical relationship between the company's characteristics, corporate governance and environmental disclosure. Design/methodology/approach Using the content analysis technique, the authors have developed two indices to assess the level of environmental disclosure in the companies' mandatory and voluntary reporting. In addition, to analyse the determinants of EDI, the authors applied the technique of multiple linear regression using panel data. Findings Based on Portuguese listed companies (Euronext-Lisbon), the results, from 2015 to 2017, exhibited an increase of 14.6% and 25.8% for the EDI obtained from the annual reports and for EDI obtained from the sustainability reporting, respectively. In addition, the results revealed that the environmental certification, lucratively, number of members on board and number and proportion of women of the board directors tend to affect the annual reporting EDI. Regarding the sustainability reporting EDI, the results showed that the environmental certification, lucratively and proportion of independent members of the board of directors have an impact on it. Research limitations/implications The study focuses on quantitative rather than qualitative disclosures and it brings some insights to the theoretical field. Practical implications The results obtained can assist corporate decision-making processes regarding the improvement of environmental disclosure, both on the mandatory annual report and on voluntary sustainability reports. Originality/value This study brings new perspectives to this topical issue in accounting. Originally, this study is applied to Portuguese listed companies and it shows different trends and determinants of environmental disclosure when included in the annual reporting or sustainability reporting.