The QEII National Trust says more farmers are signing up to permanently protect significant areas of their land with covenants.
About a tenth of New Zealand's farming businesses are now protecting land under QEII covenants.
Chairman James Guild says that's putting pressure on the limited funding which the trust has available to run the scheme and help with costs such as fencing.
He says the number of farmers and other rural landowners with sites of environmental, ecological or cultural significance already under covenant or approved, has doubled in the past 10 years to more than 4000.
Mr Guild says about 10% of farming businesses now have covenants in place which protect 120,000 hectares of land.
He says the trust provides some money to help with legal and other costs such as fencing, but increased support from the Government's conservation budget, and funding from other sources, hasn't kept pace with the demand.
That means the trust will need to look at sponsorship because the more land it takes on the higher the costs that go with it.
Mr Guild says the trust needs strong relationships with its convenant holders.
He says the trust also needs to look at its relationships with other stakeholders which are also interested in looking after and protecting New Zealand's biodiversity.
Mr Guild says the trust also needs to look at commercial relationships which may assist with funding and allow the trust to continue to grow without compromising the quality of the land it's looking after.
He says the QEII Trust receives some funding from district and regional councils and operates on an income of about $4 million a year.