Negative and positive effects of climate change on the demography of a subalpine perennial plant

Background/Question/Methods

Climate change may affect plant demography through both direct and indirect pathways. Advancement of spring snowmelt is an important dimension of climate change in high altitude ecosystems. Early snowmelt is associated with reduced floral abundance of several subalpine plant species at our study site in the Colorado Rocky Mountains, including our study species, Helianthella quinquenervis (aspen sunflower). Early initiation of flower buds increases their susceptibility to damaging spring frosts; over 90% of H. quinquenervis flowers are lost to frost in some years. While this indicates a negative effect of climate change on reproduction, compensatory responses because of reduced costs of reproduction may allow frost-damaged plants to redirect resources to growth and survival. In addition, the longer growing seasons associated with earlier snowmelt may further enhance vegetative growth and development. Thus, climate change could impose a complex combination of positive and negative demographic effects on H. quinquenervis and other long-lived perennial plant species. Using 15 years (1998-2012) of H. quinquenervis demographic data, we evaluated how the timing of snowmelt affects growth, survival, and regeneration. We then combined these demographic effects in an integral projection model to assess how climate change is affecting the population dynamics of this plant species.

Results/Conclusions

Earlier snowmelt was associated with increased plant size (number of meristems) in the following year, supporting the hypothesis that longer growing seasons associated with climate change have a positive effect on plant growth. There was no evidence for a direct effect of the timing of snowmelt on plant mortality. A positive relationship between floral abortion and plant size in the following year supports the hypothesis that floral abortion in response to frost damage enhances plant growth, via reallocation of resources. Costs of reproduction may therefore impose a trade-off between growth and reproduction, and plants may be able to redirect resources to other structures in the event of frost damage. Here we provide evidence for two positive effects of climate change on plant growth, directly via longer growing seasons and indirectly via reallocation of resources from developing flower buds lost to frost damage. This study highlights the value of long-term demographic data for generating insights into the ecological effects of climate change.