When the bark of a tree is removed in a circular fashion, a process known as girdling occurs, which disrupts the flow of nutrients and water between the roots and the leaves. The bark contains phloem tissue, responsible for transporting photosynthates, primarily sugars produced in the leaves, down to the roots. Consequently, the roots become starved of energy, leading to a depletion of stored resources and ultimately causing the tree to dry up and die. This illustrates the critical role of the vascular system in plants, emphasizing the interconnectedness of various plant parts in nutrient transport and overall vitality, a concept essential for understanding plant physiology in UPSC examinations.