Initial Publication Date: July 5, 2011

Climate, Weather, and Trees

Part D: What Makes the Sap Flow?

As discussed in the Sugaring Wisconsin video (shown in Lab 1B), the supply of the precious maple sap in the spring of each year relies upon a unique combination of climatic conditions including: a summer of sufficient rain and moderate temperatures followed by a winter that produces a generous blanket of protective snow over the trees roots.

With the changing of the seasons from winter to spring, which produces a cycle of warm days and freezing nights, the maple sap begins to move up the stem of the trees. In trees that have been tapped for collection, the sap then flows from the taps in the trees into buckets (pictured right) or plastic tubing. Maple syrup producers collect the sap and boil it to concentrate it into maple syrup and sugar. The sap flow ends when night time temperatures no longer fall below freezing. Typical sugaring seasons last up to eight weeks, generally from late January until early April.

Get a sense of average winter temperatures in the Northeast

Examine the graphic below. Observe how the average winter temperatures change as you move from south to north across the map. This variation is important to the timing and duration of the sap flow season. Click on the image for a larger, clearer view. Note: North is up on this map.

Checking In

Check your understanding of the map graphic above by using the questions below. Select all the answers that are correct, and then click the Check Answers button at the bottom of the list.

  1. Which state(s) have average winter temperatures below 30ËšF ?
    [INCORRECT] Virgina has the warmest average winter temperatures. The temperatures are generally above 30ËšF.
  2. Which state has the coldest average winter temperatures?
    [CORRECT] Maine has the coldest average winter temperatures because it is the farthest north.
  3. Based on winter temperatures, which state(s) would normally have the latest start to the sap flow season?
    [INCORRECT] Virginia does warm up the earliest in the spring. However, since the average winter temperatures in Virginia are generally above freezing, it is not a major producer of maple syrup. Pennsylvania is at the southern end of the maple syrup producing range.


When will the sap flow begin?

Use your knowledge of maple sugaring (Lab 1B), and average temperatures in Vermont (Lab 1C) to predict when you think the sugaring season should begin. Write down the approximate date range that you think is most likely to be the start of the sugaring season. You will need to get your buckets washed and your taps sterilized before this date!

  1. Now that you have investigated Vermont's typical climate patterns, examine monthly temperature graphs for Burlington, VT, pictured below. Click the "show me" window to access the graphs from January to April 2009 and 2010. On the graphs, locate the dates where the daily temperatures begin to fluctuate above and below freezing (32 degrees F) for several days in a row. These are the conditions that trigger the start of the sugaring season. Note: the temperature scales vary on these graphs.
    • Record the first date of fluctuation above and below freezing on a piece of paper or in your notebook.
      2009 _______ , 2010 __________
  2. Next, look at the monthly graphs of March and April. Locate the dates when the daily temperatures no longer fall below freezing for a period of several days. These temperatures trigger the end dates for the season, when the sap flow tapers to an end. Additionally, the sap also becomes of lower quality as the night time temperatures rise.

    • Record the last date.
      2009 _______ , 2010 __________
    • Use these numbers to calculate the number of days in the sugaring season. Check your answers below.

Checking In

  1. During what date range do the temperatures begin to fluctuate above and below freezing, triggering the flow of the sap in the maple tree?
  2. During what date range do the temperatures no longer fluctuate, slowing the flow of the sap in the maple tree?
  3. Use the dates that you recorded to calculate the number of days in the sugaring season.

Temperature trends that could affect the maple syrup production

Now that you have examined an average climate as well as daily, monthly, and annual weather patterns, you will take a look at a much longer climate record, 120 years. Scientists, who study climate, use a minimum of 17 years of data to view trends in climatethis record is over 100 years longer.

Examine the very long-term temperature trends for the state of Vermont. To access the data go to Southern Climate Impacts Planning Program (SCIPP) data products page and select the historical climate trends tool (scroll down the list). On the page that loads, set the following parameters:

  • State: Vermont
  • Climate Division: Entire State
  • Season: Annual
  • Variable: Temperature

The SCIPP site will generate a graph of historical climate data for you to observe. Click the "Chart Info" button to read more about the data on the graph. Once you have a graph to observe, complete the following:

  1. Look at the trend of temperatures over this period of time. Notice how the temperatures vary above and below the long-term average annual temperature of 42.6ËšF, represented by the horizontal line, and are gradually becoming generally warmer with time. Recall that an annual average temperature would be the average of all the daily temperatures for an entire year!
  2. Roll your mouse or cursor over the graph to see specific data points. A red curve indicates a warmer period than the historical average, while a blue curve is a period that is cooler than the historical average.
  3. Finally, switch the "Season" from Annual to Winter. Recall that for meteorological meteorology: the science concerned with the processes and phenomena of the atmosphere; especially as applies to forecasting the weather. record keeping, winter is defined as the months of December, January, and February. Look for similarities and differences in the temperature trends.
  4. While viewing the graph, answer the Stop and Think questions, below.

Stop and Think

10. How have the average annual temperatures (gray line with dots) changed from year to year over this time period? Use a ruler or straight edge to draw a best-fit line through the points on the trends graph.

11. In the winter (D, J, F) season graph what patterns do you observe? How might warmer winters change the precipitation and sap flow patterns in Vermont?


In this lab, you were introduced to a seasonal event, maple sugaring, which is linked to climate. Are there similar events in your own region? For example, in some climates there is an "ice-out" date when the lakes and rivers thaw in the spring. Other seasonal events of note are the start of the "monsoon season" in the Southwest and autumn leaves changing color in New England. 

Research and discuss local seasonal events with your classmates. When do they begin and end? Are they connected to agricultural practices or celebrations? Have their average dates of occurrence changed over the past 50 years? 

You will return to this maple syrup case study later in the module. In the next few labs, you will learn a little more about the factors that drive weather and climate as well as climate's impact on ecological regions, or biomes.

Optional Extensions

Use the Southern Climate Impacts Planning Program (SCIPP) data products website to research other climate trends, such as precipitation, or climate trends in other regions or states.

Explore more regional climate data, including average temperatures and precipitation, as well as departures from normal, for both monthly and annual data. Northeast Regional Climate Center. This site also includes data from other regions. 

Read about climates impact on other agricultural products including:

  • Climate and Peanut Butter explains how climate change is affecting one of America's favorite food staples.
  • You probably haven't thought of your comfy clothes as made of a crop, potentially impacted by changing temperature patterns. Read Climate & Your Comfy Clothes to learn more.
  • All around the world crops depend on the right climate conditions in order to thrive. These crops include: grapes, cherries, and almonds grown in California. Read more about warming climates effects on these food crops in this article: Global Warming and California Agriculture (Acrobat (PDF) 491kB Apr7 15).

More maple syrup links:

Citizen science opportunities:
Students and teachers may want to look into other impacts of climate change on the United States. There are many citizen science opportunities available for students to become involved in monitoring how the climate is changing life in their own backyard. Several examples are listed below.

  • Project Budburstincludes materials for teachers and students, additional resources, and even a mobile phone application.
  • Journey Northis another citizen science project that students can become involved in. Students track seasonal animal migration, spring leaf-out, and other phenological events.
  • Picture Postshows you how you can get started recording change in your own backyard ecosystem.
  • Nature's Notebookoffers many opportunities to become an observer.