Climate change has the potential to shift plant ranges upslope and poleward. If a plant population grows on a patch of suitable habitat, and that patch moves at a constant speed due to climate change, the population will be able to persist and shift with climate via growth and dispersal processes if the speed of climate change is slow enough. In long-lived plant species, individuals that get left behind at the trailing end of the traveling patch do not necessarily die. They can persist for years or decades, producing a reduced amount of seeds, some of which disperse to areas optimal for growth. We develop an integrodifference equation model of tree range shifts in response to climate change, modeling a structured population, where mature individuals can persist to some degree outside of the moving habitat patch. We measure the contributions of individuals from different age classes to population growth, and compare the critical speed of climate change, which is the maximum speed of climate change a population can endure, in populations with and without relic individuals left behind the moving patch.
Results/Conclusions
Populations left behind the traveling habitat patch can contribute significantly to the population in the patch via dispersal of propagules to the patch. In some cases, these relic populations contribute more to population growth than the younger, less fecund individuals within the patch. Populations with mature individuals left behind can withstand higher speeds of climate change than those without. Models that assume all individuals outside of the patch die may underestimate the critical speed of climate change. Additionally, allowing some population persistence outside of the shifting habitat patch in the model produces population distributions that “lean” poleward (i.e. are skewed away from the direction of the range shift). This skew is especially strong when the speed of climate change is high, and high amounts of skew are often followed by extirpation. Changes in the shape of a population’s distribution, specifically increases in the degree of leaning poleward or upslope, may be evidence of stress induced by climate-driven range shifts.