Since deciduous trees lose their leaves in the winter and their ability to perform photosynthesis, do they have to store food to stay alive?

Question answered by Kristin Kaser, Plant Ecologist, INL ESER Program

Yes, deciduous trees must store food to stay alive in the winter. During the spring, deciduous trees begin creating food through photosynthesis; they are simultaneously preparing for their dormant period where they store extra nutrients as starches in underground structures like roots. As the growing season comes to an end, the tree responds to a shortening of the photoperiod which triggers the plant to drop leaves. Trees become dormant to protect themselves from freezing, as any water left inside their tissues, such as leaves, can turn into ice.

                Deciduous trees are adapted to prevent ice damage. First, the chemicals triggered by the decreasing photoperiod signals cell growth to stall. Second, the mechanics of water movement within a tree are stopped. Tree trunks have vascular tissues specifically designed to transport water. These tissues can have devastating cell damage from the formation of ice. This can be replicated at home by placing a full plastic water bottle in your freezer. Once the water has frozen, the bottle has bulged outward and sometimes cracks as the plastic becomes brittle from the extreme temperatures. If the vascular tissues of the trunk are cracked, it can break the capillary action of water movement and kill the tree because it cannot heal its self from within.

During the cold sub-freezing months, the tree has stored its food source far in the soil where it does not freeze or, in some cases, turns its starches into sugary antifreezes mixed with fatty acids to combat the damaging effects of ice. Try this with a second water bottle experiment. Obtain two 8 ounce water bottles. Warm up 2 cups of water. Pour 1 cup warm water into the first water bottle. Using the last cup of warm water, make a sugar water mixture by mixing 2 Tablespoons of sugar to the warm water and pour the remaining mixture into a new plastic water bottle. Watch which one freezes first.

As the photoperiod begins to change, trees respond to the shorter nights and warming temperatures. Trees begin to use their stored food by transporting nutrients with the newly melted water through their vascular tissues. The stored food grows spring flowers and leaves. Spring leaves begin photosynthesis, producing more leaves and food, thereby allowing the trees to store food for another winter dormancy.

Seed Dormancy

In the fall, many plants disperse their seeds far and wide. But what happens to these seeds during the wintertime when temperatures are cold? When the seeds land on the soil in the fall, they may absorb water, but most don’t germinate. They remain dormant during the cold winter months. Some seeds can survive lower temperatures than others. In this experiment, you will simulate harsh winter conditions and see which seeds are the heartiest.

Materials:  3 types of seeds, small plastic bags, marker, freezer, paper towels, water, small plastic plate, gallon-sized plastic bags

  1. Count out 25 of each type of seed.
  2. Place each group of 25 seeds in individual plastic bags.  Label the plastic bags with the name of the seeds and the word “Frozen.”
  3. Count out 25 more seeds of each type and place them in their own bags.  Label these bags with the name of the seeds in them.  Also add the word “Control.”
  4. Place the plastic bags labeled “frozen” into the freezer for five days (cold winter). 
  5. Wet a paper towel and wring it out to remove excess water.  Fold the paper towel into quarters and place on a small plate.
  6. Scatter the seeds from one of the “Frozen” bags onto the paper towel.  Place the entire plate into a gallon-sized plastic bag.  Label the bag with the same words that were on the original baggie.
  7. Repeat Step 6 for all Frozen and Control small baggies.
  8. Place all six bags in indirect sunlight.
  9. Every two days, add a bit of water to the paper towels and count the number of seeds on each plate that have already germinated.
  10. After 2 weeks, analyze your data.  How many seeds have germinated on each plate?  Which seeds best survived the “freezing winter”?

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