Final answer:
The tree dies after the bark is removed in a circular fashion because the disruption of the bark prevents the movement of water and nutrients between the roots and leaves. The primary cause is the interruption of water and nutrient transportation, not just the roots being starved of energy.
Step-by-step explanation:
When the bark of a tree is removed in a circular fashion around its base, known as girdling or ring-barking, the tree gradually dries up and dies. The main reason is that the removal of bark disrupts the flow of essential nutrients and water between the roots and the aerial parts of the tree. Specifically, reason number 1, "Water from soil cannot rise to aerial parts," is the most accurate. The bark contains the phloem and the xylem, which are crucial for transporting water, minerals from the soil to the leaves, and sugars from the leaves to the roots. Without this connection, the roots are indeed starved of energy (reason 2), affecting the tree’s overall ability to survive. However, the primary cause of death in this case is the interruption of water and nutrient transportation.
Some other factors that can affect a plant's survival are environmental conditions such as drought, cold, disease susceptibility, and competition for nutrients. Plants, through processes like nutrient recycling, can manage and conserve resources during stressful conditions. This involves relocating nutrients from non-essential or old parts (like older leaves) to more vital areas such as seeds or storage tissues.
In a drought scenario, plants will attempt to conserve water by closing their stomata, which can lead to a reduction in transpiration. This mechanism helps the plant to survive temporary water shortages but if drought conditions persist, it may have to shed leaves. This response to drought aligns with the understanding that the water will move from the soil to the plant as long as the plant can exert a strong enough pull to remove water from medium-sized pore spaces in the soil (as described in Fig. 4).