Memorial university of Newfoundland St. John's, Newfoundland and Labrador, Canada
Abstract: The boreal landscapes contain one third of the global forest and are experiencing the highest rates of warming due to climate change which may promote greater productivity. However, climate change in these environments is also impacting cold season dynamics, such as snowpack duration and timing and intensity of snowmelt events, with potential positive and negative cascading effects on ecosystem functioning. In balsam fir-dominated boreal forests along the Newfoundland and Labrador Boreal Ecosystem Latitudinal transect (NL-BELT) water is not a limiting factor on productivity, and previous studies indicate warming enhanced productivity supported by enhanced nitrogen availablity. We leveraged the climatic and geological differences in the NL-BELT to explore potential limits on warming-enhanced productivity and the extent at which shifts in cold season dynamics affect productivity under warming. We used the latest MODIS terra products for estimates of net annual primary productivity (NPP) and gross primary productivity (GPP) from 2001 to 2021 across the NL-BELT. To derive relevant indicators of climate change for these forests we obtained daily estimates of weather parameters for the same period from the Daymet meteorological model, in addition to the 8-day evapotranspiration data also from MODIS. We analyzed the data for significant monotonic patterns across time using the Mann-Kendall trend analysis for all productivity and climate variables and reported the rate of change using the Sen slope analysis. We also used a linear regression approach to test for temperature effects on productivity and to explore the extent to which changes in cold season dynamics affect warming-enhanced productivity. Preliminary results revealed a significant increasing trend GPP (p = 0.01, Sen’s Q = 3.21 gC m-2 y-1) across the NL-BELT but no significant increase or decrease in annual or seasonal temperatures for any region or across the NL-BELT, except for maximum temperatures during the winter for the entire NL-BELT (p = 0.03, Sen’s Q = 0.06 °C winter-1). Shifts in precipitation dynamics were observed over this 20-year period, with a decrease in precipitation intensity but an increase in the number of precipitation days. This appears to heighten the effect of warming on productivity particularly in the northernmost, colder regions of the NL-BELT, where there are greater geological reservoirs of phosphorus. Our results suggest that the effects of warming are altering precipitation patterns in significant ways during the cold season, strengthening the warming-enhancement of ecosystem productivity, especially at higher latitudes. This signifies potential regional controls on an important carbon-climate feedback.
