This is an indicative list of what trees maybe in flower or bearing fruits throughout the year. It is not an exhaustive list, but an informative listing to encourage readers to explore further, and I suggest the Collins Book of British trees as a starting place.
The following is a list of trees that will carry fruit or berries during March as food for birds and ground feeding animals. The only deciduous trees that will carry leaves are oak and beech, all coniferous trees will bear leaves.
There is very little change from the February listing, except that you will notice, especially in severe weather, that the Ivy plant will bear vast amounts of fruit, this being the only seed that carries nectar throughout the winter. The same plant also harbours smaller birds such as Robin, Wren and Tits, since it is both waterproof and windproof, plus bearing fruit.
Numerous trees/bushes however will start to show signs of leaf/blossom formation.
This second list contains a selection of berry/fruit bearing bushes plus taller seed plants found in hedgerows, all of which providing food for winter birds.
The additional listing for this month however shows which trees may well - given favourable conditions, commence early blossom flowering: