Cervids eat leaves, fresh shoots, grasses, flowers, 'weeds', lichen(in the north of north), and in the dead of winter even the bark of willow, aspen, rowan: pretty much any softwood deciduous trees.
And of course mushrooms and berries when available.
Sadly, URW Cervids do not seem to eat mushrooms, nor berries. Grasses like flax go untouched in the open and when piled for fodder for the critters, as hoarding isn't fair and we should give back the excess, Spirits will remember.
I've not tried saplings, but anyway, when saplings are freshly growing, they're everywhere and the beasts have no need to go eat that one on the trap.
FWIF/IRL, kale in last few years has been trendy "super-food", we would plant kale and also cabbage, peas, radishes, turnips and oats, on fields that are scheduled for fallow. To increase the carrying capacity for hares, deer and moose. Maybe even attract doves, grouses and pheasants