How variable from year to year is sap production by maple trees in the U.S?

How variable from year to year is sap production by maple trees in the U.S?

Background: When spring days get warm and the nights stay cool, it means one thing in the north woods: syrup season. Northern states from Minnesota to Maine produce maple syrup commercially each spring, but conditions must be just right for the sap to keep flowing. Sap flows fastest and longest when the days get above 40°F and nights get down below freezing. If spring weather warms up too quickly, it will be a bad year for syrup producers.

The graph shows the number of gallons of syrup produced per tap for the top 10 syrup producers in the country from 2007 to 2014.

Data Source: http://www.nass.usda.gov/nh/0605mpl.pdf; http://www.nass.usda.gov/Statistics _by_State/New_England_includes/Publications/Special_Reports/maple12.pdf; http://www.nass.usda.gov/Statistics_by_State/New_England_includes/Public...

Questions: 

1.  What does this graph show about the variability in productivity of maple tree taps from year to year?

2. What could you say about the spring weather in 2007 and 2013? 

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