COS 52-2 - A rare tree, a rattlin’ tree: climate and deposition effects on growth of boreal tree species at their southern lowland range limits.

Background/Question/Methods

Boreal peatlands at their southern range limits in the Boreal Temperate Ecotone (BTE) of eastern North America provide distinct habitat and ecosystem services compared to surrounding uplands. These peatlands also serve as refugia for disjunct boreal tree species, providing the only suitable habitat for these species at, or near, their lowland southern range limits. In this study we examined growth rates in four tree species – Picea mariana (Black Spruce), Abies balsamea (Balsam Fir), Larix laracina (Eastern Larch), and Thuja occidentalis (Northern White Cedar) – growing at, or near, their lowland southern range-limits in a large ( > 400 ha) boreal peatland at Shingle Shanty Preserve and Research Station, located in the west-central Adirondacks in upstate New York. The objectives of this study were to 1) quantify annual growth trends in the four species; and 2) determine relationships between growth trends, climate and hydrochemistry. We obtained increment cores from 134 trees in the peatland (71 Black Spruce, 25 Balsam Fir, 21 Larch and 17 Northern White Cedar). Annual ring widths were measured and crossdated. Annual growth was modelled against current and previous year monthly temperature and precipitation, North Atlantic Oscillation and atmospheric deposition and pH data from 1980 to 2018.

Results/Conclusions

Tree ages ranged from 13 to 251 years old, however most trees established in the second half of the 20^th century. All four species showed a period of high growth in the 1950’s. Following that, Black Spruce growth has continuously declined, while the other three species have fluctuated, but all showed declines since 2000. Model results showed highly significant relationships between growth and the tested variables (R² values from 0.33 to 0.49 and p< 0.001 for all models). Models are highly species specific, but all models included some combination of deposition and previous year monthly temperature variables. Models suggest that declines in atmospheric inputs since the 1980’s has been detrimental to growth, while spring, fall, and winter temperature increases over the same period have generally had a positive influence. Interestingly however, Black Spruce and Balsam Fir’s negative response to summer temperatures suggests growing season temperatures may be becoming too warm for these species.