The National Arbor Day Foundation has challenged many cities to earn its "Tree City USA" flag by planting and protecting more trees.

国家植树节基金会向许多城市发起挑战，要求它们通过种植和保护更多的树木来赢得那面“美国树城”的旗帜。

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So it is quite useful of measuring tree-age in the fields of old-tree protecting and making use of some precious tree species.

通过年轮测量树龄在古树保护及珍贵树种开采利用等领域有着十分重要的意义。

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He has embarked on an ambitious plan to regrow stands of the imperiled Aspen tree, protecting them from elk with fortresslike structures made from forest slash.

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Dr. ELIZABETH MATSUI (Johns Hopkins University): We still need to be very vigilant about protecting the children who are still peanut and tree nut allergic.

NPR: Studies Predict Odds of Outgrowing Nut Allergies