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Tree rings provide a record of local climate during the life of the tree. Many trees are hundreds of years old, and a few live thousands of years. Thus the rings provide information that is not available from scientific records.
In a tree the cambium, the cells that will become wood or bark, grows in a light layer during late spring/early summer changing to a dark layer in later summer/early fall. The light layer is early wood, formed when the tree is growing rapidly. The dark layer is late wood and is grown more slowly. The growth occurs at the outside of the trunk, just under the bark, so that a light and dark ring pair represents one year.
These annual rings can be counted to tell the age of the tree, and because there is more growth under good conditions, the growth patterns can be studied to determine the conditions a tree lived through such as forest fires, drought, insect attack, floods, or slopes. The study of tree rings and climate is called dendroclimatology. (The study of data from tree rings is called dendrochronology.)
You can read the rings of a tree in either a cross section of the trunk or a core taken from the trunk. Cross sections are most often used to read trees that are already dead or to read tree stumps.
Cores are used to read living trees. An instrument called an increment borer is drilled into the tree. This extracts a piece of wood about the size of a drinking straw that shows the growth rings. Using this method, the rings can be read without killing the tree. The growth of a tree's annual rings is related to the weather in the area. If it has been a dry summer a tree does not grow very much during that and the following year or two. If it was a wet summer than there is more growth.
Annual Rings: The rings of growth on a tree that marks a year of growth.
Cambium: The layer of cells in a woody plant that will become wood or bark.
Climate Change: Changes in climate over time. One area of global change.
Core Sample: Piece of a tree, about the size of a drinking straw, pulled out by an increment borer.
Cross Section: A horizontal slice of a tree used to age the rings.
Dendrochronologist: A person who studies tree ring growth.
Dendrochronology: The science of dating events and environmental changes by studying growth rings in trees and aged wood.
Dendroclimatology: The science of analyzing tree ring growth to reconstruct year-to-year, seasonal, and yearly climatic variations. This science is used to determine climatic change.
Enhanced Greenhouse Effect: An increase in greenhouse gases.
Global Change: Changes in the global environment that may alter the capacity of the Earth to sustain life including changes in climate, atmospheric chemistry, land productivity, oceans and fresh water resources, and ecosystems.
Greenhouse Effect: Greenhouse gases act like a blanket, trapping rays of the sun between the Earth and atmosphere causing higher temperatures (much like a plant greenhouse).
Greenhouse Gases: The gases in the atmosphere which can stop the Sun's radiation reflected from the Earth's surface from escaping back into space. These gases include water vapor, carbon dioxide, CFC's (chlorofluorocarbons), nitrous oxide, methane and ozone.
Increment borer: An instrument used to take a core sample from a tree.
Written By Ava Rose.