Theme 1 - Winter Survival: Trees
What a wacky winter we are having this year! Rain, snow, sleet–we saw it all this afternoon. The wet weather was the perfect recipe for throwing snowballs. We spent some time writing, drawing, and stickering in our journals before it was time to learn how trees survive winter.
We gathered around and first talked about the difference between trees with leaves and trees with needles. Trees with leaves are deciduous. We listed examples like maple, oak, beech, and aspen. Trees with needles are coniferous (or evergreen), like pine, hemlock, tamarack, and cedar. We can remember this word because coniferous trees have cones! All of these examples are around us here on the Natural Education Reserve. Because most deciduous trees drop their leaves in the fall, we can only identify them by their buds (look at the tips of the branches) and bark right now. Their buds are where new leaves are forming for spring. Some trees, like oak and beech, hold onto their dead leaves until spring–they are marcescent. Scientists have not pinpointed the reason for this. Perhaps it is to provide shelter for wildlife or to protect the trees’ buds from browsing animals, like deer. The dead leaves might also provide additional nutrients for the trees in spring when they fall and act as mulch.
Oak leaves in winter.
Two ways trees prepare for winter are: slowing down to save energy and handling below-freezing temperatures. Trees produce their food (and oxygen for us) through the process of photosynthesis. The green pigment in their leaves, chlorophyll, captures energy from the sun to make their food. Chlorophyll breaks down in the fall as the amount of sunlight decreases, revealing beautiful fall colors as other pigments begin to show through. When trees are ready to drop their leaves, they send all their vital nutrients to their roots for the winter. This is their energy-saving mode, called dormancy. Another reason trees drop their leaves is because water expands when it freezes. Has anyone ever left a closed can of pop in the car during winter? You would know firsthand what I am talking about! Coniferous trees hold less water in their needles and also have a wax-like coating to protect themselves during the freezing temperatures. Here’s a question to think about–if coniferous trees keep their needles, do they still go through photosynthesis in winter? (The answer is: Yes!)
We also learned about tree growth by investigating tree cookies today! Every year, trees add one ring of growth just under their bark. When the amount of sunlight, water, and nutrients are ideal, a tree will have a great year and more wood will form than in years when conditions are not ideal. Trees have the most growth in spring and early summer, which forms a light-colored ring. As growth slows in late summer and fall, a thinner, dark ring is produced.
We can identify these varying years of growth by looking at cross sections of trees. Starting from either the center circle to the bark, or vice versa, we count either the light or dark rings. This will tell us how old the tree was when the cross section was cut. We put our heads together and determined that one of our tree cookies was 52 years old and the other was 138 years old! We also discussed that trees do not like to be overcrowded, which can affect their growth and overall shape of their trunk. Before heading out for our hike, we each made our own tree cookies on paper plates. We placed a star on each ring (year) that was significant to us–birth of our siblings, years we got pets, etc. We then braved the weather for a quick hike to the Pine Forest before heading home!
