1. What can a lilac tell us about national climate change?
Erin Posthumus
USA-NPN National Coordinating Office
November 7, 2017

2. Headlines like these are becoming common in recent years – the hottest month on record, the hottest year on record, the earliest spring…

3. But what does this really mean for local plants and animals
But what does this really mean for local plants and animals? How are they responding?

4. Phenology Drivers:
Phenology is the science of life cycle events – when leaves appear on trees in the spring, when birds migrate, when insects emerge. Many of these life cycle events have close ties to climate variables like temperature, precipitation, or the amount of cold that accumulates in a winter.

5. Lilacs, though ornamental in the United States, are one of the earliest plants to leaf out in the spring time. You could say that early spring activity is associated with the timing of lilac leaf out.

6. This was recognized by researchers back in the 1950s
This was recognized by researchers back in the 1950s. Joe Caprio, a professor at the University of Montana, started a project to distribute cloned lilacs to observers across the country. By using cloned lilacs, Caprio took out the variable of genetics, so that the environmental response of lilacs to their local environment could be studied.
Many of these lilacs have been monitored for decades. Observers send in their reports of when the lilacs leaf out and bloom in the spring. This has resulted in a dataset over 50 years in length of how the plants respond each year to local weather and accumulated temperature.
Schwartz et al 2012

7. First leaf date Extended Spring Indices (SI-x) First bloom date
Heat accumu-lation
Warm Spells
First leaf date
First leaf and first bloom dates are average of cloned and common lilac, and two species of honeysuckle.
First leaf date
More heat
More Warm Spells
First bloom date
More recently, researchers such as Mark Schwartz at the University of Wisconsin, Milwaukee, have taken these decades of lilac observations and turned them into models to predict when lilacs will leaf out and Bloom given a set of temperature and weather variables for that year.
Schwartz 1997
Schwartz et al 2006

8. The USA National Phenology Network has taken these models and turned them into maps that show when first leaf and first bloom will occur in each year for locations across the country.

9. The USA-NPN also makes available anomaly maps that compare the current year to a 30-year average ( ). For each location, you can see how early or late spring is compared to the long-term average.