Evergreen Trees Through the Seasons

As the earth orbits around the sun, most climates experience some fluctuations that separate the year into seasons. These changes affect almost all living beings - plants and animals alike! When it gets cold outside, we bundle up to keep warm while some other animals go into hibernation. Annual plants will grow and bloom when it’s warm and there’s plenty of sunlight, and they’ll die in the winter. Perennials are similar, but the rootstock (underground part of the plant) will regenerate new growth in the following spring and summer.

Trees are much larger plants, and are generally divided into two groups: deciduous trees and evergreen trees. Deciduous trees lose their leaves in the fall and enter a state of hibernation for the winter before regrowing their leaves from buds. The leaves of evergreen trees will stay green all year long, and are constantly being replaced as the cells age and die. While deciduous trees have evolved and adapted to better survive in cool/dry periods, evergreens were already pretty hardy and could withstand more harsh conditions without changing. This is why they stay green all year. For more information on leaves, check out our blog post about them from this May!

The largest subgroup of evergreen trees are conifers, which is Latin for “cone-bearer”. Not all evergreens are conifers, because in some climates (such as a tropical rainforest) plants like palm trees and shrubs shed and regrow leaves year-round. There are seven coniferous families, all of which have needle leaves and reproduce via cones.

Cones come in all different shapes and sizes, ranging all the way from the coulter pine’s 11 lbs to the Canadian hemlock’s one centimeter long cone. In order to reproduce, conifers have both male and female cones. The male cones are the only ones that release pollen, and thus are smaller than female cones and reside on the tree’s lower branches.

​When it’s time to reproduce, the male cones release millions of tiny grains of pollen, which the wind carries up toward the female cones. Coniferous trees can be self-pollinated to create genetically identical offspring, or the wind could carry pollen from one tree to another. After pollen is released, the male cones don’t have any further purpose so they fall off and die. In the image below, cloud of pollen grains are released by the male cones of an evergreen!

The first step of fertilization begins with the pollination of a female cone. Next comes the appearance of pine seeds growing among the female cone’s scales; iIt can take up to two years after pollination for the cone to produce seeds! Some pine cones even have spines on the scales to dissuade birds from eating their seeds.

Test Your Knowledge!

The most common type of conifer in North America is the pine family (Pinaceae). This family include pines, spruces, firs, hemlocks, larches, and true cedars. You can go outside to collect random cones and try to find which type of tree they belong to!

Here are a few key differences:

• Spruce cones grow from the center of a stem. The overlapping scales are paper-like and thin.
  
• Pine cones also grow from a central stem. Some have spiny scales. The overlapping scales are woody and thick. Seeds are located at the scales’ base.
  
• Fir cones grow upwards from closer to the tip of the stem. Scales overlap and feel papery and flexible. They often fall apart while still connected to the tree.
  
• Hemlock cones are very small; only about one inch long. They grow from the tips of the branch and have thin, flexible scales.
  

For more information and helpful images, we recommend “Simple Keys for Identifying Conifers” by Playful Learning.  Click here to visit their website!


References:


“Simple Keys for Identifying Conifers”. Playful Learning, playfullearning.net . Accessed on 12/6/17. https://home.playfullearning.net/resource/simple-keys-identifying-conifers-pine-family/

“Pollination by the Wind”. Newton’s Apple, newtonsapple.org.uk. Accessed on 12/7/17. http://www.newtonsapple.org.uk/pollination-by-the-wind/





Image Credits:


Hodan, George. “Evergreen”. Released into the public domain. Uploaded on 12/7/17 from publicdomainpictures.net

Kratochvil, Petr. “Christmas Garland”. Released into the public domain. Uploaded on 12/7/17 from publicdomainpictures.net

Moisset, Beatriz. “Pollen Flowing From a Pine Tree”. Released into the public domain under the Creative Commons Attribution-Share Alike 3.0 Unported license. Uploaded on 12/6/17 from commons.wikimedia.org

Kratochvil, Petr. “Cone and Needles Background”. Released into the public domain. Uploaded on 12/7/17 from publicdomainpictures.net

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