| deciduous | refers to trees or shrubs that shed leaves completely at the end of the annual growth period. |
| defoliation | the loss of needles or leaves due to pest activity, disease, or negative environmental response. |
| delayed dormant | time of year when dormancy is about to end; characterized by the beginning of bud swell. |
| desiccation | the drying or loss of moisture from a leaf or plant part. |
| dieback | progressive death of shoots, branches, and roots generally starting at the tip. |
| dioecious | having unisexual flowers, each sex confined to a separate plant, said of species. |
| distorted | taking on a shape that is unnatural. |
| distortion | taking on a shape that is unnatural. |
| drought | periods or conditions that demonstrate the lack of moisture or rain. |