- Teacher Guide
- Student activity, Graph Type A, Level 3
- Student activity, Graph Type B, Level 3
- Student activity, Graph Type C, Level 3
- Grading Rubric
How does a plant know when to make a flower? Their phenology, or seasonal timing of growth and reproduction, can be driven by many things. When the weather warms in the spring, many plants start to make flowers when temperatures are just right. Other plants follow the number of hours with sunlight. In one very particular system, plants might actually be following the timing of snow.
High up in the Rocky Mountains, scientists are studying plants at elevations where snow covers the ground for six months of the year. In the spring, when the ground is still covered in snow. Plants under the snow are unable to sense the temperature of the air or sunlight hours. This means that plants may have to use a different cue, such as the timing of snowmelt, to know when to flower.
Amy and Dylan are two scientists who love and have spent a lot of time in the Rocky Mountains. While there, they noticed the springs were changing and wanted to document what they were observing. They wondered whether the date of snowmelt was changing over time. If so, were the plants responding by shifting their flower timing?
To answer their question, they looked to the work of two additional scientists. The first is David Inouye, a retired plant ecologist from the University of Maryland. David has been observing flowers at the Rocky Mountain Biological Laboratory for the last 50 years. David and his team measured phenology of 163 plant species across 36 plots in the Rocky Mountains. From early spring through summer, they surveyed their plots every two days, recording every plant species flowering in each plot. They measured first flowering date as the day they observed the first flower for each species. His records show, over time plants have been flowering earlier and earlier each year.
Another scientist, billy barr (who doesn’t capitalize his name), has been living and working at the Rocky Mountain Biological Laboratory since the 1970s. Initially for his own curiosity, billy started recording the weather at the Lab. He then built a weather station outside his cabin. His records have become important to many areas of research at the station.
These records include billy’s observations for the first date that snow was completely melted in the area, called the date of bare ground. billy used Julian dates, which start with January 1 as Day 1 and continue to count up by one for each day. And just like David noticed plants are flowering earlier than they used to, billy noticed that snow has been melting earlier than it used to.
Hearing about these changes in flowering date and snowmelt timing, Amy and Dylan wanted to know if changes in snowmelt timing itself could explain changes in flower timing. They thought that snowmelt triggers plant growth by exposing the ground to light, warmth, and soil moisture from melting snow. If plants start to grow earlier, they thought they will also flower earlier. This led them to predict that years with earlier snowmelt would have earlier flowering. Fortunately, David’s and billy barr’s datasets already include all the information needed to test this hypothesis! All they had to do was bring the two datasets together in a new way. They started with one species of plant with a purple flower, Linum lewisii.
Featured scientists: Amy Iler (she/her) and Dylan Simpson (he/him) from the Chicago Botanic Garden
