What condition may be damaged by digging trenches?

Digging trenches can significantly impact the roots of ornamental plants. The roots are essential for a plant's stability and nutrient uptake, as they anchor the plant in the soil and absorb water and essential minerals. When trenches are dug, especially in close proximity to ornamental plants, the digging can sever or damage the root system. This can lead to a variety of problems for the plant, including reduced access to nutrients and water, which may cause stress or even lead to the plant's decline or death if a substantial portion of the root system is affected.

While stems, flowers, and leaves are also important parts of a plant, they are generally less impacted by trenching compared to the roots. Damage to the roots can have a more immediate and severe impact on the overall health and survival of the plant. Thus, the correct choice identifies the part of the plant that is most adversely affected by the activity of digging trenches.