Treesponsibility - which has planted more than a quarter of a million trees in the Calder Valley - is trying to raise the £6,000 needed to buy a new vehicle after its bus was stolen in March.
The group says it has received an insurance settlement but it is seriously short of what is needed to buy another minibus, even one that is second hand.
"We try to encourage volunteers to use public transport where possible, with the minibus to take them the final leg of the journey from the railway station to the tree planting sites," said the group.
"Volunteer days continue outside of the tree planting season when we carry out maintenance on sites.
"We were devastated when we discovered our minibus had been stolen.
"With the price of second hand vehicles rocketing in the last two years, the settlement is somewhat short of what is required for a decent replacement, so we are asking for help to raise the additional £6,000 we need."
Treesponsibility has been raising awareness of the need for action on climate change since 1998.
To donate, visit https://www.crowdfunder.co.uk/p/keep-treesponsibility-moving