This thesis is an investigation of climate effects on radial growth of red pine (Pinus resinosa Ait) in northern Ontario over multiple spatio-temporal scales. In the context of climate change, these investigations provide insight about species survival, growth and range shift potential. In this thesis I investigate these three aspects of red pine dynamics using tree-ring width (TRW) data from 54 sites across northern Ontario. I first identified leading edge populations (16 No.) of red pine using climate data in hierarchical cluster analysis (HCA). I used various combinations of climatic variables as predictors in HCA, and evaluated their performance based on the compactness of formed clusters. These analyses reveal that leading edge populations of red pine in northern Ontario can be determined using three monthly climatic variables: mean minimum temperature (Tmin), mean maximum temperature (Tmax) and climate moisture index (CMI). I performed correlation and response function analyses to identify climatic controls on growth in these leading edge red pine populations. My results show that the effect of seasonal climate during prior summer was significant for growth in leading edge populations. Specifically, growth response was positive to prior summer precipitation (Prec) and negative to prior summer Tmax. This combined effect suggests the potential role of drought in controlling red pine northern range limit. My results question the validity of studies that predict large scale range shift potential of red pine under warming scenarios. My growth – climate analyses for the remaining red pine populations reveal a complex growth response of red pine in northern Ontario. In general, I observed four main results: (i) red pine populations in northwestern Ontario are more sensitive to climate than populations in northeastern Ontario, (ii) the growth-limiting effect of Prec is more significant than Tmax, (iii) growth – climate relationships follow a longitudinal gradient, and (iv) a shift in climatic controls of red pine temperature during first half of the 20th century to precipitation during recent decades. I also investigated age effects on red pine growth – climate relationships in an old-growth red pine forest at Wolf Lake Forest Reserve in northern Ontario. My analyses reveal that growth response to climate in young red pines is different from old red pines. Winter season Tmin positively influences growth in young red pine trees, whereas summer Prec (specifically July) positively influences growth in old red pine trees. I finally conclude that climate effects on red pine growth vary across space and time, and such variations must be considered in any decision-making process.