Melanie Mullin | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Melanie Mullin. This seminar is open to the general public to attend.
Thesis Topic: Reaching new heights: Chemical signatures of lodgepole pine trees change with elevation, but not with latitude

MSc with Dr. Nadir Erbilgin.

Seminar Abstract:

The lodgepole pine (Pinus contorta var. latifolia) is Alberta’s provincial tree and critical to the forest industry. This pine species is the historical host for mountain pine beetle (Dendroctonus ponderosae Hopkins, Coleoptera: Curculionidae, Scolytinae). In western Canada, mountain pine beetle is expanding its range facilitated in part by climate-change, and has invaded areas that were historically climatically unsuitable to their survival. As a result, novel lodgepole pine stands in Alberta have being invaded. Thus, it is timely to predict if the vulnerability of lodgepole pine trees varies across the province’s elevational and latitudinal gradients. Elevation or latitude can be used as space-for-time gradients in climate change studies. Host susceptibility to bark beetles is usually assessed via tree defenses. The primary defenses of lodgepole pine against bark beetles are the constitutive concentration of oleoresin terpenoids. Production of these defense chemicals relies in part on tree reserves, non-structural carbohydrates (sum of total sugars and starch). I investigated whether the concentration of monoterpenes, diterpene resin acids, and non-structural carbohydrates of lodgepole pine trees change as a function of elevation or latitude. I characterized the chemical profile of trees along an elevational gradient of 1,251m, and a latitudinal gradient of 736 km. I also determined age, growth rates, and basal area index values, stand density, and basal area. I found that concentrations of terpenes increased with elevation while soluble sugars decreased. Latitude had no effect. Overall, this project shows that pine trees occurring at higher elevations have a greater concentration of constitutive defense compounds, and a lower concentration of glucose and sucrose. These findings call for future research to determine inducibility of the same defense compounds at high elevations, and also stress the importance of considering plant defenses against range expanding insect herbivores in forest pest management.