ISA Certified Arborist Practice Exam

Wilting leaves and leaf drop are clear indicators of water stress in a tree. When a tree does not receive enough water, it struggles to maintain its physiological functions, leading to visible signs of stress. Wilting occurs as the tree's inability to uptake water affects the turgor pressure within cells, causing leaves to droop. Additionally, trees may drop leaves as a survival mechanism to reduce transpiration and further conserve water, which helps them to endure periods of drought or limited water availability.

In contrast, bright green foliage typically suggests that a tree is healthy and adequately hydrated, while rapid growth and thick branches indicate sufficient resources, including water, sunlight, and nutrients. Increased fruit production is generally associated with favorable growing conditions, including ample moisture, rather than a stress response. Therefore, the presence of wilting leaves and leaf drop is a strong sign that the tree is experiencing water stress, making it the correct answer.