Print PageThe extent to which climate determines species’ range limits is a classic ecological question that has become particularly relevant as many organisms on Earth experience rapid rates of anthropogenic warming. We ask how climate and competitive interactions influence the growth of trees at upper and lower range limits of three Pacific Northwestern conifers (Abies amabilis, Tsuga heterophylla, Tsuga mertensiana) on Mt. Rainier, Washington, USA. Recently, we have shown that climate controls adult tree growth in tree species with upper limits at high elevations on Mt. Rainier: near treeline, individuals showed low growth in cold and high snowpack years, and annual growth was synchronized, further suggesting that stand-level effects such as climate constrain growth. However, annual growth was not strongly affected by climate in trees growing in closed-canopy forests at low elevations and individual growth in these trees was poorly synchronized. These results suggest that climate controls growth in adult trees growing at treeline, while local drivers (perhaps biotic interactions) influence growth in closed-canopy forests. We expand on these results by examining the growth response of sapling trees relative to climate and competitive environments (canopy gaps versus closed-canopy) across the same altitudinal gradient on Mt. Rainier.
Results/Conclusions
Growth in saplings was not strongly affected by climate at any elevation, indicating that climate does not limit sapling growth at range limits. However, sapling growth differed between saplings growing in canopy gaps versus under closed-canopy forest, and the sign of this difference varied with elevation. Our results demonstrate that responses to climate can vary dramatically between life history stages within a species, with some stages more sensitive to climate than others. Climate change induced range shifts in closed-canopy forests will therefore be difficult to accurately predict, particularly with common current approaches such as climate envelope models.
