Leaf Longevity at the Arnold Arboretum

Posted by Linnea Smith and Sarah Pardo

Hi! We are two new members of the Primack lab: Linnea Smith (yes, like Carolus Linnaeus), an undergraduate at Boston University who’s joined the Primack lab for the summer with funding from the BU UROP program; and Sarah Pardo, a rising senior at BU Academy.

Linnea and Professor Primack doing fieldwork at the Arnold Arboretum

We are investigating how many years evergreen plants at Harvard University’s Arnold Arboretum retain their leaves, and why. Ecological theory suggests that a leaf stays on the branch, photosynthesizing, until it’s made a profit on the energy that went into making it. We want to determine if the amount of time a leaf remains on a plant is more influenced by the original environment in which the plants grow, or their evolutionary history.

Professor Primack and Sarah examining pine needles in the field

When tree branches begin growing in the spring, a scar is formed on each twig where bud growth had halted the previous winter. By counting the number of scars, we can determine the number of years of twig growth and leaf formation on a tree branch. For example, say a twig has leaves on seven scar-separated segments and no leaves on the eighth segment or beyond. This tells us that leaves stay on that twig for seven years. So far we have evaluated 173 species including conifers such as pines, firs, spruces and hemlocks and other evergreens like rhododendrons and hollies.

Showing seven years of growth on tiger tail spruce at Arnold Arboretum

We’ve both really enjoyed our work in the Primack lab so far and appreciate the warm welcome we’ve been given!