Elm Morphology

Student: Daniel Delatte
Mentor: Leila Pinchot (Forest Service Northern Research Lab)

Total Leaf Area increases with light while Specific Leaf Area decreases with light. This study aimed to observe the structure of leaves as they grew positioned differently on different trees where some were shaded more than others in order to see if they would build up more of a tolerance to the Dutch Elm Disease. We believed the trees with smaller leaf sizes spent more of their energy into producing a defense system strong enough to combat the disease making it tolerant. We also wanted to create a formula from the information gathered in the process to be able to in the future gather leaf mass in a non-destructive manner after gathering the midrib length of a leaf.

Dutch Elm Disease (DED; Ophiostoma novo-ulmi) is an invasive fungus that attacks several species of elm (Ulmus sp.) native to the United States and Canada, including American elm (Ulmus americana). To examine the potential trade-off between growth and DED-tolerance, we evaluated leaf morphology 1. between American elms tolerant and susceptible to DED, and 2. among three tree canopy positions: high, intermediate, and low. We hypothesized that elms with tolerance to DED would allocate less energy to leaf growth, which we assessed using leaf area, dry mass, and specific leaf area (SLA). Leaf area and dry weight were greater in the high canopy than low canopy position in the DED-tolerant cultivars, but not for the susceptible cultivar. Differences in dry mass and leaf area between tolerant- and susceptible elm- may be explained by tree form of the cultivars rather than tolerance. Across cultivars, SLA of low-canopy leaves was 20% greater than that of high-canopy leaves. In our study American elm, a fast-growing species, allocates more energy to upper canopy than lower canopy leaves, suggesting that elm has a flexible growth strategy. This study will inform future studies evaluating trade-offs between growth and DED-tolerance.