Dendrochronology, the study of tree-ring records to glean information

For the first question, refer to the following portion: "In wet years rings are broad; during drought years they are narrow, since the trees grow less. Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions."

So if we look at the ring patterns of dead trees, we should be able to tell which years were dry and which years were wet based on the width of the rings. If we only have one tree, then we would obviously only be able to gather data for the years in which that tree was alive. But now imagine we have two trees. One of the trees died in 1960 at the age of 50, and the other was born in 1950 and lived for 60 years (a 10 year overlap). In that case, we would have ring data from 1910 - 2010 and could use that data to help figure out which years were wet and which were dry.

Now consider the 10-year overlap. Because we are talking about different trees, the actual widths of the rings from those years might not be exactly the same. However, during wet years, we would expect RELATIVELY broad rings. During dry years, we would expect relatively narrow rings. So even though the precise widths might not be exactly the same for both trees, the PATTERNS (i.e. narrow-narrow-broad-narrow-broad-broad-broad-etc) will likely be the same. Now the second paragraph does explain why this is not ALWAYS the case, but the passage suggests that the patterns will OFTEN exhibit similar patterns.

Hopefully that helps you arrive at the correct answer!


The highlighted portion specifically refers to trees that may go a year or two without adding rings. According to the first paragraph, it is often possible to determine a tree's age by counting the rings. Why? Because there is typically an annual boundary line at the end of the growing season. With a regular annual growth pattern, you can count the rings to determine the age.

But what if a tree goes a year or two without adding any rings? In that case, if you count the rings to determine the age, your number will be LESS than the tree's actual age. For example, if you count 40 rings, the tree could actually be 41, 42, 45, 50, or 60+ years old! We would have no way to determine the number of years in which rings were not added. This corresponds to choice (E).

As for choice (D), the highlighted portion refers to the uncertainty in ring count, not to the lack of variation in ring width in complacent trees. We are indeed told that trees with "complacent" rings show little variation in ring width from year to year. However, you should still be able to count rings to determine the AGE of complacent trees. You would not be able to tell which years were wet/dry, but you should still be able to determine the age.

Choice (E) is the best answer.