Why does tree phenology (spring leaf out and autumn leaf drop) vary across space and time? Most explanations focus on the role of climate on immediate physiology. However not all genotypes within a species might respond the same way to climate, and phenological effects may occur several years after a stressful weather event. In our new study, we explore these questions in the charismatic species, quaking aspen. You can read the study at New Phytologist or download a PDF.

We first use remote sensing datasets to show that phenology in this species varies by multiple months in southwestern Colorado, and that spatial patterns in one year change across multiple years.

We then quantify this variation with respect to two genetic factors (cytotype and sex) measured in field studies, and show strong differentiation with respect to both, indicating that different genotypes may take more or less risky canopy deployment strategies.

We then couple these patterns to additional DNA sequence data and show that the phenological variation is genetically heritable.

Then using numerous other spatial datasets, we show that the phenological responses are driven by responses to climate variables in previous years (up to three years in the past), indicating that current-year phenology may be a lagged response to multiple prior years of stressors.

Please give the study a read – it opens a lot of interesting questions about carbon and water economics in trees, and shows the extra insights we can gain by coupling genetic and remotely sensed datasets.