Tag: responses | Data Nuggets

A plot in the experimental treatment after the tarp was removed. The tarp caused the snow to melt faster.

The activities are as follows:

Climate change is causing Earth’s average temperature to rise, but warming is not the only change happening. Climate change can affect many parts of an ecosystem at the same time. For example, in the Rocky Mountains, temperatures are getting warmer, and the climate is also getting drier. This means that summers have more hot and dry periods, while winters are bringing less snow. Warmer temperatures and less snowfall cause the snow to melt earlier in the spring.

Amy and Dylan are two scientists working in the Rocky Mountains. They are studying plant phenology, or seasonal timing of events related to growth and reproduction. Visiting year after year, Amy and Dylan noticed dramatic springtime changes. They were able to observe these differences with their own eyes, before they took a scientific approach.

Dylan in the field. Photo Credit: Kelby Anderson.

To support their observations, they turned to historic long-term datasets. They confirmed three important patterns. First, since the 1970s, plants are flowering earlier. Second, over the same time frame, snow is melting earlier and exposing bare ground. Finally, the date that plants are flowering is strongly related to snowmelt date. This suggests that snowmelt date might be a cause of earlier flowering. However, these datasets were also a collection of observations over time. Observations alone cannot prove snow melt is causing earlier flowering. There are too many factors that are changing at the same time.

To tease apart what is going on, Amy and Dylan needed to design an experiment. A carefully designed experiment can isolate factors that may be affecting a variable while controlling other conditions. Amy and Dylan thought that plants rely on the timing of snowmelt as a cue for their phenology.

To test their hypothesis, Amy and Dylan set up an experiment that manipulated the timing of snowmelt. They chose a field site in a Rocky Mountain meadow. This site contained a mix of many plant species, and they focused on three: two-lobe larkspur (Delphinium nuttallianum), tall larkspur (D. barbeyi), and Lewis flax (Linum lewisii).

Like the surrounding landscape, the meadow was covered in snow over the winter. Amy and Dylan established 16 plots within the meadow. In the spring of 2025, they placed black tarps on half the plots. The tarp warmed in the sun and melted the snow under it. The tarps are removed as soon as bare ground is visible below the tarp. The snow in these ‘experimental’ plots melted two weeks earlier than the ‘control’ plots without tarps.

Amy and Dylan then tracked the development and flowering of plants in both plots. They recorded the first flowering date of each individual plant. For their data they converted calendar dates to day of year. They started with January 1 as Day 1 and continued to count up by one for each day. They predicted that plants in the experimental plots will flower earlier than plants in the control plots.

Featured scientists: Amy Iler (she/her) and Dylan Simpson (he/him) from the Chicago Botanic Garden

Flesch–Kincaid Reading Grade Level = 8.5

Additional Teacher Resources:

There is an additional Data Nugget, “Flowers chasing spring” about this research.

Flowers chasing spring

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?

Dylan and a field technician, Mairin Boshoven, observing plants in the Rocky Mountains.

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

Flesch–Kincaid Reading Grade Level = 8.6

Additional Teacher Resources:

There is an additional Data Nugget, “Bringing the heat” about this research.