If at some point in time your daughters were to inherit this land from you, then at the time that occurs they would receive a "stepped up" basis in the land. That means that their new basis would be the fair market value of the land on the day they inherit it. If they then decide to sell the land, they owe tax on any gain they realize from the sale. Since their gain would be figured by taking the selling price less their basis, it is a big advantage to them to receive the stepped up basis through inheritance, as this will minimize any taxable sale they have if the property is ever sold.
If you just simply sign the property over to your daughters at this time and take your name off the deed, this would be considered a gift to them and they would not benefit from receiving a stepped up basis in the property.
Instead, you should leave your name on the deed and then also add your daughters names to the deed, and title the deed as "joint owners with rights of survivorship". By doing it this way, then if the day comes that something happens to you, your daughters will still receive the stepped up basis on the value of the land.
Please refer to the following IRS publication for determining Basis of Assets - See the section starting on page 9 for basis of inherited property. It discusses and example of how joint tenancy works.
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