Some of the oldest living things on our remarkable planet are trees. The record holders are bristlecone pines (狐尾松) of the western United States, quite a few of which are known to be more than 3,000 years old. One individual, discovered in 2012, is estimated to be more than 5,060 years old, making it the oldest known non-clonal tree in the world! : individuals across a number of other tree species have also been around for thousands of years.
So, how do trees survive for thousands of years? . Undoubtedly, part of the answer lies in luck. Ancient trees have obviously not submitted to deadly diseases, pests, fires, droughts, windstorms, landslides, or the human axe in the centuries and centuries that they have quietly endured.
The other part of the answer has to do with how trees age. In fact, there is quite a debate about whether ancient trees can be considered "immortal (永生的)". That is, will such trees ever die if they are not killed by an outside force? We may never know the answer to that, but, at the very least, . While cell death is an important factor in the aging of humans and other animals, one study found little evidence of cell death in the ginkgo tree vascular cambium (银杏树维管形成层). In addition, a study of bristlecone pine pollen (花粉) found no significant increase in mutation (变异) rates with age, which is another factor associated with animal aging. .
Older trees benefit greatly from having bodies made mostly of dead woody tissue. In fact, an old tree might be as much as 95 percent dead tissue! Given that it isn't alive, wood does not require metabolic (新陈代谢的) activity to maintain it, .
A．so an old tree doesn't really need to do much to keep living
B．This is a question that has something to do with the good luck of trees
C．However, bristlecones are certainly not alone in terms of the oldest creatures
D．This is a fascinating question for biologists that does not yet have a settled answer
E．What's more, some ancient trees have superior chemical defenses against pests and diseases
F．which means that trees can survive everywhere without being limited by external and internal conditions
G．we know that ancient trees age in ways that are dramatically different from the ways that most animals and even other plants age
