A lack of transparency and succession planning is impacting on diversity at board level, according to a report published by the Institute of Directors in Ireland.
The Diversity in the Boardroom 2019 report found increased support for gender targets rather than gender quotas - particularly among men.
However, it found that a high level of unplanned succession in Irish boardrooms ultimately undermines improving diversity.
Maura Quinn, the chief executive of the IOD, said the report found there is an "overwhelming recognition that board diversity in all its forms leads to enhanced board effectiveness and company performance".
Despite this, Ms Quinn said that almost half of respondents to the survey said their board does not have a rotation system in place for board tenure, with resignations and retirements the main reasons for boardroom changes.
"This lack of planned processes around succession planning militates against effective board diversity for good governance," she said.
39% of respondents to the survey believe gender targets, rather than mandatory quotas, should be introduced to increase the number of women on boards, an increase of 7% on a comparable survey in 2017.
The results show that 6% more women and 8% more men are in favour of gender targets, compared with 2017.
The survey also found that collectively 43% of men and women see unconscious bias as still the main barrier women face when being appointed to boards as directors in Ireland, but 54% of female respondents cite lack of access to the same networks as men as the main barrier.
Half of the respondents to the survey said they were directly or indirectly approached by the board or a member of the board.
"We need to resolve the fact that board appointments are made in an informal way and are not made transparently," she said.
"When you see there isn't an independent appointment process, except for 12% of appointments, gives an indication of how personal contacts are how boards are filled."
Ms Quinn said this leads to "reinforcement of the perception that board appointments are about 'who you know' and of accusations of it being a 'boys’ club'.
"We don't have diverse boards. People believe diversity is very important in terms of the quality of engagement and challenge and good for the bottom line," she concluded.