Assessing the influence of climate on the growth rate of boreal tree species in northeastern Canada through long-term permanent sample plot data sets

Abstract

Climate has a considerable influence on tree growth. Forest managers benefit from the empirical study of the historic relationship between climatic variables and tree growth to support forest management frameworks which are to be applied under scenarios of climate change. Through this research, we have utilized long-term permanent sample plot records, historic climate datasets, and linear mixed modelling techniques to evaluate the historic influence of climatic variables on the growth rates of major boreal tree species in Newfoundland and Labrador, Canada. For the commercially significant spruce and fir forests of the province, we found growing degree days (GDD) to negatively correlate with tree productivity in warmer regions, such as much of Newfoundland (±1,350 GDD), but positively correlate with growth in cooler regions, such as those in Labrador (±750 GDD). With respect to precipitation, environmental moisture was not on average a limiting factor to species productivity in the province. These dynamics have implications for the productivity of the spruce-fir forests of the study area when considered alongside contemporary climate projections for the region, which generally entail both a warmer and wetter growing environment.

Mixed Regional Shifts in Conifer Productivity under 21st-Century Climate Projections in Canada’s Northeastern Boreal Forest

“…This characterization is not reflective of simulation outcomes for the province's southernmost forests (Figure 6), where conifer BA under RCPs 2.6, 4.5, and 8.5 was often found to either be generally consistent with, or slightly less than, BAs observed under the reference scenario (Figure 6). This observation corroborates a growing library of empirical studies that propose that increased conifer productivity at northerly latitudes may well be one "positive" socio-economic externality attributed to contemporary climate projections [15][16][17]. Other recent applications of PBM in Atlantic Canada, such as that completed by Taylor et al [14], have found that the transitional forests of the New England-Acadian forest region may begin to lose its boreal character as cornerstone boreal species fail to regenerate and survive beginning at the mid-point of the century under certain RCPs (i.e., RCP 8.5).…”

“…For most boreal species in NL, this parameterization presents neither a constraint, nor optimal conditions for growth [41]. The implicit assumption in the use of such a constant is that growing environment moisture is not, at present, a limiting condition to growth in most of the plots in NL's PSP inventory [17]. Further still, there would be an equal number of plots where surplus moisture is a limiting factor and moisture deficit is a limiting factor in a true census PSP inventory.…”

“…The impact of projected climatic change on forest growth and composition is expected to vary regionally, moderated by pre-existing growing conditions [10][11][12]. For instance, although it is often hypothesized that the New England-Acadian transitional forests of maritime North America may experience a reduction in the natural occurrence of some boreal conifers under higher concentration pathways [13,14], other studies relevant to more northerly latitudes forecast an increase in productivity for boreal species, such as the forests of Siberia and northern Canada [15][16][17]. Management practices can further complicate a forest's response to projected climatic shifts.…”

Conditional inference trees in the assessment of tree mortality rates in the transitional mixed forests of Atlantic Canada

“…In general, our results identify that climatic variables, including GDD, cumulative annual PCP, and INS had significant impact on tree mortality rates for some tree species. There is a wealth of scientific literature that support the significance of climate to tree growth [9,66,67].…”