Understanding boreal/hemi-boreal forest growth sensitivity to seasonal variations in temperature and water availability provides important basis for projecting the potential impacts of climate change on the productivity of these ecosystems. Our best available information currently comes from a limited number of field experiments and terrestrial biosphere model (TBM) simulations of varying predictive accuracy. Here, we assessed the sensitivity of annual boreal/hemi-boreal forest growth in Canada to yearly fluctuations in seasonal climate variables using a large tree-ring dataset and compared this to the climate sensitivity of annual net primary productivity (NPP) estimates obtained from fourteen TBMs. We found that boreal/hemi-boreal forest growth sensitivity to fluctuations in seasonal temperature and precipitation variables changed along a southwestern to northeastern gradient, with growth limited almost entirely by temperature in the northeast and west and by water availability in the southwest. We also found a lag in growth climate sensitivity, with growth largely determined by the climate during the summer prior to ring formation. Analyses of NPP sensitivity to the same climate variables produced a similar southwest to northeast gradient in growth climate sensitivity for NPP estimates from all but three TBMs. However, analyses of growth from tree-ring data and analyses of NPP from TBMs produced contrasting evidence concerning the key climate variables limiting growth. While analyses of NPP primarily indicated a positive relationship between growth and seasonal temperature, tree-ring analyses indicated negative growth relationships to temperature. Also, the positive effect of precipitation on NPP derived from most TBMs was weaker than the positive effect of precipitation on tree-ring based growth: temperature had a more important limiting effect on NPP than tree-ring data indicated. These mismatches regarding the key climate variables limiting growth suggested that characterization of tree growth in TBMs might need revision, particularly regarding the effects of stomatal conductance and carbohydrate reserve dynamics.
Bibliographical noteFunding Information:
We thank Deborah Huntzinger, Associate Professor at School of Earth and Sustainability from Northern Arizona University for proof reading on an earlier version of the manuscript. This research was funded by a Strategic and Discovery Grant of the Natural Sciences and Engineering Research Council of Canada (D. Way, M.P. Girardin) and Canadian Forest Service funds (M.P. Girardin, E. M. Campbell, J. Metsaranta, A. Arseneault). D. Way is also partially supported through the United States Department of Energy contract no. DE-SC0012704 to Brookhaven National Laboratory. P. Reich is supported by the U.S. National Science Foundation Biological Integration Institutes Grant NSF-DBI-2021898.We would like to thank all the people, as well as the funding agencies, who contributed to the development and applications of the different models and data used in this work. Tree-ring datasets assembled during this study have been deposited in the TreeSource repository, https://treesource.rncan.gc.ca/en. Restrictions may apply to the availability of third-party raw data (e.g. Canada's NFI, ABMI, MFFPQ), which were used under agreements, and so are not yet publicly available. Reasonable requests for accessing such data can be made to authors and with permission of the data contributors (contact names are included in the TreeSource repository). Annual NPP simulations were retrieved from the MsTMIP v1 ensemble of terrestrial biosphere model simulations generated by the North American Carbon Program (NACP, https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=1225). Weather data are freely accessible through Environment Canada's portal (https://climate.weather.gc.ca/) and the BioSIM server (https://cfs.nrcan.gc.ca/projects/133). No custom code or mathematical algorithms were used in the analyses of these data. The R code for our statistical analyses is available from the authors upon request, and each of the R packages used is referenced in the Methods.
This research was funded by a Strategic and Discovery Grant of the Natural Sciences and Engineering Research Council of Canada (D. Way, M.P. Girardin) and Canadian Forest Service funds (M.P. Girardin, E. M. Campbell, J. Metsaranta, A. Arseneault). D. Way is also partially supported through the United States Department of Energy contract no. DE-SC0012704 to Brookhaven National Laboratory. P. Reich is supported by the U.S. National Science Foundation Biological Integration Institutes Grant NSF-DBI-2021898 .We would like to thank all the people, as well as the funding agencies, who contributed to the development and applications of the different models and data used in this work.
© 2022 Elsevier B.V.
- Boreal/hemi-boreal forests
- Forest productivity
- Multi-scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP)
- Climate Change
PubMed: MeSH publication types
- Journal Article