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The tree people in the Lord of the Rings--the Ents--can get around by walking. But for real trees, it's harder to uproot. Because they're literally rooted into the ground, they are unable to leave and go __26__.
When a tree first starts growing in a certain area, it's likely that the __27__ envelope--the temperature, humidity, rainfall patterns and so on--suits it. Otherwise, it would be unable to grow from a seedling. But as it __28__ , these conditions may change and the area around it may no longer be suitable for its __29__.
When that happens, many trees like walnuts, oaks and pines, rely __30__ on so-called "scatter hoarders," such as birds, to move their seeds to new localities. Many birds like to store food for the winter, which they __31__ retrieve.
When the birds forget to retrieve their food--and they do sometimes--a seedling has a chance to grow. The bird Clark's nutcracker, for example, hides up to 100,000 seeds per year, up to 30 kilometers away from the seed source, and has a very close symbiotic (共生的) relationship with several pine species, most __32__ the whitebark pine.
As trees outgrow their ideal __33__ in the face of climate change, these flying ecosystem engineers could be a big help in __34__ trees. It's a solution for us--getting birds to do the work is cheap and effective--and it could give __35__ oaks and pines the option to truly "make like a tree and leave."
A. ages
B. breathing
C. climatic
D. elsewhere
E. exclusively
F. forever
G. fruitful
H. habitats
I. legacy
J. notably
K. offspring
L. replanting
M. subsequently
N. vulnerable
O. withdraws
