Reaching new heights: Chemical signatures of lodgepole pine trees change with elevation, but not with latitude

Melanie Mullin
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, the mountain pine beetle is expanding its range facilitated, in part, by climate change, and has invaded areas that were historically climatically unsuitable for its survival. As a result of this range expansion, novel
more » ... pole pine stands in Alberta are being invaded. Thus, it is timely to predict if the vulnerability of lodgepole pine trees varies across the province's elevational and latitudinal gradients. Elevational and latitudinal gradients 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, and 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 1,251 m, and a latitudinal gradient of 736 km. I also determined age, growth rates, 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 on the chemical signatures of trees. 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 stress the importance of considering plant defenses against range expanding insect herbivores in forest pest management. iii
doi:10.7939/r3-5bhb-6e97 fatcat:4bef3wvsqbhi5o65rx3epsqbdi