Trees are able to defend themselves against diseases. They have both protective structures and protective processes. Thanks in large part to research done by Dr. Alex Shigo, we now know a great deal more about the way trees protect themselves than we did 50 years ago.
Just as our skin keeps harmful bacteria on the outside, bark (树皮) keeps out tree diseases. Since they can’t move around to avoid dangers, trees need thicker “skin” than we do. Living and non-living tissues protect tree trunks, roots, and branches from mechanical injury, drying out, and diseases.
But when something destroys this first line of defense — tears through the bark — what happens internally is interesting. When an injury occurs, a tree will transform some of its stored sugars to make masses of defensive chemicals, which are then distributed in a specific pattern internally around the wound. Dr. Shigo was the first to document this pattern, which he called CODIT — Compartmentalization (分室化) of Decay (腐烂) in Trees.
In making these CODIT compartments, trees form chemical walls to protect themselves from infection. The success of this walling-off process depends a lot on the species. Hard maple, for instance, can generate a strong CODIT response while species like soft maple achieve only an average level. Some, on the other hand, barely manage to form any chemical walls.
Overall tree vitality is another important factor. Even a hard maple may not be able to form strong chemical walls if it’s in a weak state. By definition, landscape trees are stressed as compared to their forest-living cousins. A street tree is worse off, faced with limited root space, air pollution, and more. The size of the injury also makes a difference. Even a healthy tree can have its defenses destroyed by a large wound.
Humans can help maximize trees’ defense capability by watering during dry seasons, keeping things out of the root zone, etc. In return, trees will help keep us in good health by offering shade, beauty, and companionship.
7. What will happen first if diseases come close to trees?
A.Infection will occur internally. | B.Bark will provide protection |
C.Chemical walls will take effect. | D.Defense chemicals will be formed. |
8. What does the author think of Dr. Shigo’s research?
A.Groundbreaking. | B.Conservative. | C.Ambiguous. | D.Straightforward. |
9. What does the author want to convey by mentioning hard maple in Paragraph 4?
A.Trees can form chemical walls |
B.The size of the injury affects CODIT. |
C.Trees cannot protect themselves if weakened. |
D.The effectiveness of CODIT varies among species. |
10. What can most likely be the best title of the passage?
A.The gift of the trees. | B.The magic of CODIT. |
C.The function of the bark. | D.The self-preservation of the trees. |