Flowering times: Are they a -changin'?

Lesson Objectives:

By the end of the lesson, all students will:

1.      Engage in a class-wide discussion introducing the topics of global warming and climate change.

2.      Investigate, organize, and interpret evidence extracted from the UConn Virtual Herbarium and NOAA's Earth System Research Laboratory.

3.      Construct graphs in Microsoft Excel that relate temperature trends in Connecticut with flowering dates of plant specimens.

4.      Share their conclusions in a classwide discussion about their findings and their implications for Connecticut.

Related Connecticut State DOE Core Science Curricular Standards:
Grades 9-10

      D INQ. 2 – Read, interpret, and examine credibility and validity.
      D INQ. 5 – Identify independent and dependent variables, including those that are kept constant and those used as controls.
      D INQ. 6 – Use appropriate tools and techniques to make observations and gather data.
      D INQ. 9 – Articulate conclusions and explanations based on research data, and assess results based on the design of the investigation
      D INQ. 10 – Communicate about science in different formats, using relevant science   vocabulary, supporting evidence, and clear logic.

Estimated Time to Complete Lesson:
Two to three 50-minute class periods.  Depending upon internet and computer availability in the students' homes and students' levels of independence, much of the graphing and researching can done at home, allowing more classroom time for discussions.

Materials needed:
Computers with internet and printer access, and Microsoft Excel (or similar spreadsheet program)
Student worksheets

Background for Teachers:
It is accepted throughout the scientific community that the Earth is not static. The earth’s climate changes because of plate tectonics, variation in solar output, cycles in the earth’s orbit, vulcanism, and bombardment of extraterrestrial debris, among other factors. These changes usually are experienced over the periods of tens to hundreds to thousands of years. In recent decades, however, climatologists have seen rapid changes in conditions as a result of human activity. These changes include rising global temperature as a result of the burning of fossil fuels, which increases the level of “greenhouse gases” such as methane and carbon dioxide in the atmosphere. Changes in climatic conditions such as the mean temperature are likely to affect us and the other organism living in Southern New England.

Cameron Wake, a scientist with the University of New Hampshire’s Climate Change Research Center, warns that changes in temperature can affect “the ski industry, tourism, transportation, agriculture, emergency management, health, and fuel consumption for heating and cooling.”

In fact, the effects of warming already are evident. Previous research (Primack et al., 2004) has shown that plants in southern New England now flower 6 – 10 days earlier than they did a century ago, and this change is correlated with warmer mean temperatures. Plant collections have been important in identifying this trend, and students can use online collections information to verify this change.

Assumed Student Prior Knowledge:
Students should be familiar with the terms “global warming,” “climate change” and “herbarium.”  They should have basic knowledge of computer use, including general functionality of the internet and spreadsheet programs (such as Microsoft Excel).  Students should have a background in first-year algebra; they need to have a foundational comprehension of the various parts of a graph and linear functions, including being able to make real-world analyses of the coefficient of x, and independent and dependent variables. Simple tutorials can be given if needed to ensure that all students have at minimum the base level of skill.

PART I: Introduction to climate change and herbaria

25-30 minutes

To start the lesson, begin by asking students to take a minute to write down a few things they think of when they hear the terms “global warming” and “climate change.” Then open the floor to a classwide student-led discussion on the terms.  Allow students to share their knowledge, opinions and questions on the subjects, and feel free to write on the board any key topics, terms, or interpretations that are brought up.  Try to initiate discussion and introduce the lesson plan with such questions as:

      “In your opinion, is climate change occurring?”
      “What might be some ways in which we could determine if climate change is occurring?”

PART II: Investigation of Connecticut temperature trends

25-30 minutes

Students start by investigating whether there is evidence that the climate is changing.  Many conditions may be changing, and there are many ways to investigate these changes. Measuring the amount and intensity of precipitation, measuring whether glaciers are growing or shrinking, and measuring ocean surface levels are a few of these ways.  Students will focus in this exercise on Connecticut temperature trends over the past century.

 Introduce students to the NOAA website (http://www.esrl.noaa.gov/psd/data/timeseries/) where they will download and evaluate temperature trends in Connecticut for the past 100 years.  The NOAA website is easy to negotiate and has vast amounts of information.  For this lesson:

1.      From the page that's loaded with the link, select the fourth option titled “US Climate Division.”

2.      Under “State,” select Connecticut, and under “Division” choose to show data for the “State area averaged.”

3.      Set the “Year Range” to span the period from 1900 to 2009.

You then can choose to obtain data from every month, January through December, during the range of years, or you can pick “seasons.”  The NOAA website defines a “season” as the period between any two months, so for spring, you can select “Seasonal average” and set the “First month of season” as March or April and the “second month” (technically the last month of the season) to June.  To determine the average annual temperature, simply select “Seasonal average” and set the “First month of season” to January and the “second month” to December, essentially averaging every month together to produce a yearly mean temperature.

The output format must be “Raw data values” so students may copy-and-paste it into an associated Excel file called AverageTemperatureGraphs.

Every student (or pair) should be able to access the NOAA website and pull up data on the annual (January through December) mean temperature.  Students should copy-and-paste this data into Column A of the Excel file named AverageTemperatureGraphs. This Excel file can be found on the Virtual Herbarium.  The file has been formated to display the data so it can be graphed (in its raw form, the data paste in a single column).  Columns E and F (not C and D) contain the graphable forms of the data. Create an XY Scatterplot and include a “best-fit line,” which displays the general trend in the data. Do this by right-clicking on a data point and select “Insert Best Fit Line” (which must be linear).  Make sure the R2 value (which represents the strength of the relationship between the X and Y coordinates) is included.   The long series of more than 100 data points do not need to be printed.

If students are not strong in algebra, take the time to explain what the linear equation means in terms of real-world application (also explaining the meaning of the “independent” and “dependent” variables).  For example, the function for the changing mean annual temperature in Connecticut over the past century should be:

      y = 0.0152x + 18.825

The dependent variable is the variable that we are investigating. It is the variable that is responding to the independent variable. It is the “response” variable and is displayed on the Y axis. In this case, Mean Temperature is the dependent variable. In the linear equation, the Y-intercept (the value of Y when X is the Year 0) is of little relevance. The coefficient of X has more meaning and importance in this exercise. It is the slope of the trend line, and it tells us that the annual temperature in Connecticut has increased 0.0152 degrees Fahrenheit per year on average during the period studied.  Over the course of a century, the average annual temperature has risen 1.52 degrees Fahrenheit

Students then will be able to investigate a specific season or month of their choice (or your assignment) and determine if there has been, for example, a stronger warming trend in the fall than the spring, or in April than in November.  Students would compare their one or two seasonal graphs with those of other students in the class.

An Excel file for teachers on the UConn Herbarium website contains data and graphs for annual, seasonal, and several monthly mean temperatures for the past century.  Access these beforehand and familiarize yourself especially with the strong warming trends (almost 3.3 degrees over the past century) that have occurred during the spring and early flowering/budding season (February-April).

PART III: Herbarium data extraction and graphing

15-20 minutes

Now that all students have been able to observe the temperature trend in Connecticut over the past 100 years, they will investigate whether plants are responding to the changing temperatures.

Explain to students that an herbarium is a collection of preserved plants used for research and education – something like a library of pressed plant specimens, some of them very old. An herbarium typically has thousands of specimens (some have millions), each with information on when and where it was collected. If a projector is available and connected to a computer, pull up the UConn Virtual Herbarium (http://bgbaseserver.eeb.uconn.edu/index.htm) and show students how they can search for, organize, and download data.  Show them where they can access the Excel spreadsheets for individual species (the choices are listed below).

Depending on class size, students may work independently or in pairs. Each student (or pair) should select one species to investigate. Most of the species are flowering earlier, but a few are not, which illustrates that organisms are  responding differently to environmental change.

These are the species for which good database information is available:

Acer pensylvanicum
Amaranthus cannabinus
Lilaeopis chinensis
Aster laterifloris
Bidens laevis
Conyza canadensis
Erigeron philadelphicus
Heracium aurantiacum
Solidago gigantea
Silene antirrhina
Arabidopsis thaliana
Barbarea vulgaris
Draba verna
Hesperis matronalis
Panax trifolius

Students should access files on the Virtual Herbarium for their particular species.  These small prepared Excel files contain information on their species, including specimen number; scientific name; UConn Herbarium barcode number; phenology (though all specimens are flowering); collector's name and associated specimen's collection number; specimens' location including state, county, town, and locality; collection month, day, and year; and the approximate Julian Date of collection.  The last value was determined with the following simplified equation to alleviate student confusion in trying to extract this data:

Once the appropriate spreadsheet is downloaded, each student can create a graph.  To do so, a student  should highlight columns L and M (Collection Year and Julian Day) and insert an XY Scatter plot.  Students need to label each axis and use appropriate scales.  Then a “best fit” line needs to be added to show the general trend in flowering time. Students can print out their tables and the graphs and submit them with the associated worksheet.
If you would like to create a classroom display showing all the graphs plotted by the class, noting any conclusions, and what can be done in reaction to noticed trends, make sure the graphs are appropriately sized and well-presented (labeled axes and titles, “best fit” lines with R2 values). A file with the graphs for each of the species is available if teachers want to compare students' results.

PART IV: Drawing conclusions, analyzing, and making predictions from data.

15-20 minutes

Bring the class back together so each group can quickly present its findings.  Allow students to compare their results.

 Discuss the consequences of continued warming and earlier flowering. Students should be able to predict future problems for agriculture. Possible questions to lead the discussion include:

1.      Could earlier flowering times be problematic for agriculture? Would they be beneficial at all?

2.      If warming continues, how might it influence the amount of time between flowering and fruiting, and why might that matter?

3.      What could we do to prevent plants from flowering even earlier?

4.      What could we do to slow the rate of warming? Would we be able to to stop warming?

 The possible consequencies of earlier flowering in plants are many. These are a few:

This could be a good moment to discuss the concepts of correlation and causation.  In this exercise, students have found evidence that flowering time in some plant species has changed in in response to a changing climate in the past century.  They have not found proof that this is the case. Science works through the accumulation of evidence. Nothing is proved. Additional analyses would be needed to rule out the possibility that some other condition is responsible for the earlier flowering. The connection between earlier flowering and warming temperatures is a good working theory, but much has changed in the past 100 years and any of those changes could play a role. As scientists investigate other possible causes and rule them out, our confidence in the connection between warming and flowering time will become greater.

It also is important that students understand the difficulty in slowing the pace of global climate change. Even if greenhouse gas emissions were reduced immediately (and no one is even talking seriously about this), global warming would continue for many decades because of the fossil fuels we already have burned in the past 150 years. Failure to reduce greenhouse gas emissions will only make the warming more extreme.

If the students are more advanced, the discussion could be shifted to focus on the benefits and handicaps of using herbarium data.  Let them comment on use of the online database and exercise.  How else could we use herbaria? What sort of questions might online specimen data be able to answer? What are the strengths and weakness of online herbaria data?

Related Resources:


      Contains scientific articles that address the issues of climate change in the Northeastern United States and how the agricultural industry is struggling with these issues and addressing them. Some provide a well-rounded introduction into climate change science.

      Outlines the impact of climate change on agriculture, including evidence of shorter developmental time in crops.


      Provides graphs and evidence of earlier budding times from data obtained from herbaria by researchers at Boston University and Harvard.  The paper also has information on warming temperature trends in New England and graphs displaying recorded annual temperatures, which could be used directly in the lesson.

http://www.niu.edu/PubAffairs/RELEASES/2007/sept/maples.shtml  and  http://www.edf.org/page.cfm?tagID=42708
      These two sites provide brief overviews of the impact of warming temperatures on the sugar maple industry in New England.