Question

average thickness of annual rings by age of trees in forest a and forest b
forest a forest b
the thickness of the annual rings in the graph above indicates what type of environmental situation was occurring at the time of the trees development. a thin ring usually indicates a year of low growth caused by lack of water, forest fires, or insect infestation. on the other hand, a thick ring means a year of rapid growth when environmental conditions are favorable.
to collect the data in the graph above, scientists measured trees in forest a and forest b of the following ages: 10 years, 20 years, 30 years, 35 years, 50 years and 60 years.
based on the data shown in the graph above, what can be concluded about the comparative health of forest a & b and of the health of different ages of trees? choose all that apply.
forest b contains trees that have experienced more periods of rapid growth because the average thickness of rings is higher across all ages of trees.
there must have been more periods of rapid growth in recent years because trees in both forests that are younger than 50 years old have smaller ring thickness compared to older trees.
there must have been more periods of rapid growth 50 years ago because trees in both forests that are 50 years or older have much larger average ring thickness compared to younger trees.
forest a contains trees that have experienced more periods of rapid growth because the average thickness of rings is higher across all ages of trees.

Explanation:

• For the first option: Looking at the graph, the red line (Forest B) is above the blue line (Forest A) for all ages. Since a thicker ring means more rapid growth, Forest B has higher average ring thickness across all ages, so this option is correct.
• For the second option: The trees that are 50 years or older (e.g., 50 - year - old and 60 - year - old) have larger ring thickness. But we can't say "must" as there could be other factors. However, based on the data trend (older trees have thicker rings which imply more past rapid growth periods), this option is correct in terms of the data - driven conclusion (assuming the data is representative).
• For the third option: As explained above, the 50 - year - old and 60 - year - old trees have thicker rings. If we assume the tree's age corresponds to when it started growing (a 50 - year - old tree started growing 50 years ago), and since thicker rings mean more rapid growth, there is an indication (not a certainty, but based on the data) that there were more rapid growth periods 50 years ago (for the 50 - year - old tree's early growth) and even further back for the 60 - year - old tree.
• For the fourth option: The blue line (Forest A) is below the red line (Forest B) for all ages, so Forest A does not have higher average ring thickness across all ages. This option is incorrect.

Answer:

Forest B contains trees that have experienced more periods of rapid growth because the average thickness of rings is higher across all ages of trees; There must have been more periods of rapid growth in recent years because trees in both forests that are younger than 50 years old have smaller ring thickness compared to older trees; There must have been more periods of rapid growth 50 years ago because trees in both forests that are 50 years or older have much larger average ring thickness compared to younger trees.