Maple Syrup and Drought

Around this time of year, questions begin surfacing in some people’s minds about the expected conditions for maple tapping and for syrup production. Particularly in the last year or so, drought-like conditions have been an area of concern. This post specifically addresses concerns related to tapping maple trees that have been subject to drought, or drought-like conditions. Thank you! to those of you who shared your questions with us at My Minnesota Woods.

First of all, what is the state of the Minnesota drought? According to the Minnesota Climatology Working Group, large portions of northwest, west central, southwest, and south central Minnesota are classified as experiencing “Extreme Drought”.

Additionally, over 80% of Minnesota is classified as experiencing “Extreme Drought” or “Severe Drought”.

Minnesota drought regions as of January 2013. Source: drought
Minnesota drought regions as of January 2013. Source: drought

According to the Working Group, the overall drought situation is the result of abnormally dry weather in three, distinct time periods that affected particular regions and the state as a whole.

On the map to the right, yellow zones indicate abnormal dryness, pinkish indicates moderate drought, orange indicates severe drought, and red extreme drought. No part of the state is classified as being in exceptional drought.


The question remains, how do syrup producers determine whether or not drought conditions should affect production decisions. As is often the case, it depends.

Drought is one form of stress that trees experience. The 1990 publication, Sugarbush Management: a Guide to Maintaining Tree Health, offers the following advise for tapping stressed trees:

” It is unwise to tap trees that are under stress. Trees defoliated the previous summer, especially those defoliated…severely enough to trigger re-foliation, usually enter the dormant season with depleted energy reserves, such as starch and sugars. Such trees are unable to compartmentalize taphole wounds internally, produce vigorous callous (woody tissue) to close wounds externally, or manufacture the chemicals needed to thwart repeated invasions by opportunistic organisms.

Tapping stressed trees also is unwise economically. Sap from defoliated trees is lower in sugar content. More fuel and timem is required for evaporating the greater quantities of water.

 – Houston, D., Allen, D., and Lachance, D. 1990: p.9.

The 1996 publication, The North American Maple Syrup Producers’ Manual, offers a slightly different take:

Drought is commonly thought of as a major problem. If it occurs during the summer when trees are storing carbohydrates, it can reduce the health and vigor of the trees. With forest maples, there is commonly little that can be done to alleviate the effects of drought. Its severity, however should be evaluated together with other tree stresses [such as insect defoliation] to determine whether tapping should be reduced or suspended.

– Keeling, M., and Heiligmann, R. 1996: p.43 

Fortunately or unfortunately, there is no definitive answer for the entire state. The condition of the maple trees in the period prior and transitioning into into the dormancy  seems to be an important consideration, yet one that may have been overlooked at the appropriate time for observation. Individual tree age may also be an important consideration, as older and larger trees are likely to have more established and deeper root systems. Finally, site conditions may bear heavily on a stand’s drought related stress level.

In the end, close observation of stand conditions over time provide the best information for making decisions about weather or not to tap individual trees or stands. Limiting activity to more mature and seemingly healthy trees might be one way to mitigate additional stress or damage. A more conservative approach would be to refrain from tapping. The best decision is the one that is right for you and the immediate and long-term needs of you and your forest resource. If nothing else, this question provides a great example of how phenology and journaling about resource conditions can improve your ability to make good management decisions on the land you own or use.

Dave's work addresses forest livelihoods, focusing on Tribal traditions and uses. He's based in Cloquet, MN.

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  1. Because of the on-going drought conditions, this year I would recommend that people take it easy on their trees, only using one tap per tree.

    Hopefully the weather in 2013 will cooperate, and we will have ample freezing and thawing temperatures producing good sap flow!!

  2. My maple trees are producing very little sap. It started running very late, about March26. It is now April and they are producing very little sap, even though we’ve been having freezing nights and warm days (~45F). Is last summer’s drought, which was severe, a factor?

    Thank you.

  3. If you tap unstressed trees and the following season is very dry. Will that have an adverse effect on the overall health of the tree during the new season? Or does the tree need to struggle to start the next season due to lack of sap reserves?

  4. I have 90 taps about an hour straight north of Minneapolis, I have been collecting since first week of March…been getting 10-65 gallons of sap every day (minus about 4-5 day of no flow)…total of 900+ gallons of sap and 25 gallons of syrup so far….and still not bitter due to bud stage…all this snow it helping not only production, but allowing to keep stored sap in snow packed food grade barrels….been worried a couple times when ground snow is almost gone, it snows again = more sap & being able to keep my sap stash at approx 32-33 degrees!