How do reflective surfaces in urban environments affect tree health?

• A. Reflective surfaces reduce heat load on trees and improve growth.
• B. Reflective surfaces can increase drought stress and disease risk.
• C. Reflective surfaces have no effect on tree health.
• D. Reflective surfaces only affect soil moisture.

Answer: (B)

Reflective surfaces in cities change the local microclimate around trees by bouncing more solar radiation onto canopies, walls, and the surrounding air. That extra radiant heat raises leaf and bark temperatures and increases the amount of water the tree must transpire to stay cool. In urban settings, soil volume is often limited and soils are compacted, so the tree’s access to water is constrained. When the demand for water outpaces supply, drought stress sets in, weakening the tree’s growth and vigor. Stressed trees are more prone to disorders and pests, so disease risk can rise as well. That combination—higher heat and greater water loss with limited rooting space—explains why reflective urban surfaces more often contribute to drought stress and disease risk.

The other options aren’t as supportive of how this works: reflective surfaces don’t typically reduce heat load or improve growth, so that choice is misleading; there is a real effect on tree health in urban environments, so saying there’s no effect isn’t accurate; and the impact isn’t limited to soil moisture alone but includes changes in temperature and radiant energy that affect the canopy and overall vigor.