When it comes to climate change, the evergreens are ever ready.
Associate Professor Pedram Daneshgar and a team of student researchers conducted a battery of saltwater exposure tests this summer on young trees that are native to New Jersey’s coastal forests. The experiments were designed to provide a glimpse at what the increased contact with wind-borne ocean spray and floodwaters—brought on by more frequent and intense coastal storms—will mean for trees along the region’s waterfront areas.
Working with a large sample of American hollies, sassafras, black cherries, red maples, and cedars, the researchers found that the deciduous trees were decidedly less salt-resistant. The results point to a future in which climate change will tilt natural selection in favor of the hollies and cedars, and begin to eliminate the others near beaches, estuaries, and other brackish water bodies.
“They’ll try to survive, but if there’s no more seed source from parent trees, they won’t,” says Daneshgar.
The team conducted two types of experiments on the trees. In the first, the roots were submerged in a tank of saltwater for intervals of one, six, and 12 hours to simulate flooding according to tide cycles. In the second set of tests, the trees were sprayed with concentrations of saltwater running from zero parts per 1,000 (a control) to 25 parts per 1,000 (comparable to levels in lower Barnegat Bay). Half of the trees were placed beneath a mesh sheet to emulate the shaded conditions young trees see at the bottom of a forest.
Across the board, the evergreens fared better after their exposure to both the spray bottles and the flood tank (although none of the trees survived the 12-hour flood).
“The results showed that deciduous, broad-leaf species are starting to die off,” says Jeff Dudek, a student who worked on the project. “We saw leaf loss, curling of leaves, stunted growth. The prediction there is that we’ll start to see a more evergreen-dominated forest.”
This fall, the researchers removed the trees’ leaves and weighed them. They are now analyzing which species had the strongest growth and maintained the strongest root systems in the face of the saltwater exposure.
The research was conducted in the campus greenhouse by Daneshgar, Dudek and students Kelsey Connelly and Matthew Francis.
Daneshgar says the study results offer clear guidance for those planting near the shore: “Use salt-tolerant evergreens that have very waxy leaves.”
A version of this article originally appeared on Monmouth University’s Urban Coast Institute blog.