These pine trees have so much English ivy growing on them that they are not getting enough sunlight to make new shoots to support growth. Thus the roots are being starved and dying. The trees will soon blow over or die if the vines are not cut.
Sheep will clear the leaves off the trees so sawing through the vines is quick and easy (and kills all the English ivy above). The sheep also nearly kill the vines on the ground by defoliating them.