Characterizing long-term tree species dynamics in Canada’s forested ecosystems using annual time series remote sensing data

Mapping tree species and changes in species distribution over time enables monitoring of successional dynamics and linking of realized species distributions to regional, climatic, and disturbance processes. Such knowledge is valuable for informing forest management activities regarding the role of climate change and various types of forest disturbances on tree species distributions and successional processes. In this study, we used time-series Landsat imagery to produce annual maps of dominant tree species (n = 37 tree species classes) from 1984 to 2022 at a 30-m spatial resolution for the 650 Mha of Canada’s forested ecosystems. The classification approach was based on spectral, geographic, climatic, and topographic descriptive metrics and was independently calibrated and validated with data from Canada’s National Forest Inventory. Preliminary results were informed by disturbance events and post-processed to ensure consistency of the annual species maps. Assessment of the resulting annual species maps using independent validation data resulted in an overall accuracy of 86.1 % ± 0.14 % (95 %-confidence interval). Over the study period, Canada’s treed area increased from 335 to 359 Mha. The area dominated by conifers increased in absolute terms but decreased in relative terms (from 86 % to 84.9 %), especially in western ecozones where wildfire is the main agent of disturbance. The area dominated by black spruce ( Picea mariana ), the most common tree species in Canada, remained stable, but its relative area decreased by 4.6 %. The area dominated by balsam fir ( Abies balsamea , 1.5 %), trembling aspen ( Populus tremuloides , 0.9 %), jack pine (0.5 %), and sugar maple ( Acer saccharum , 0.4 %) increased. In burned areas, the prevalence of black spruce (74.7 %) and jack pine ( Pinus banksiana , 14.6 %) was greater than their prevalence in Canada’s forested ecosystems overall (58.7 % and 3.8 %, respectively), while trembling aspen (2.4 % vs. 10 %) and subalpine fir (1.1 % vs. 4.6 %; Abies lasiocarpa ) were underrepresented in burned areas. The area dominated by black spruce was underrepresented in harvested areas (46.8 % vs. 58.7 %) whereas balsam fir (6.9 % vs. 3 %), Engelmann spruce (5.5 % vs. 2 %; Picea engelmannii ), red spruce (1.8 % vs. 0.4 %; Picea rubens ), lodgepole pine (11.2 % vs. 5.6 %; Pinus contorta ), Douglas-fir (2.7 % vs. 1.3 %; Pseudotsuga menziesii ), and western hemlock (4.8 % vs. 2 %; Tsuga heterophylla ) were found to be overrepresented. Both post-fire and post-harvest dynamics indicated a general trend of regeneration to the same pre-disturbance tree species, with post-harvest landscapes exhibiting a greater variety of different dominant tree species. These results provide valuable information for sustainable forest management and can inform conservation strategies by helping to better understand the short- and long-term effects of forest disturbances on species presence and distribution. • Tree species mapped annually (1984–2022) using Landsat imagery and ancillary data. • Overall accuracy assessed with independent validation data was 86.1 % ± 0.14 %. • Canada’s forest area increased as did the relative prevalence of broadleaf species. • Post-disturbance regeneration rates and species composition varied by change type. • Species shifts more common after harvesting than after wildfire disturbances.

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