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Q94 - How Many DBH Categories Are Needed to Accurately Age a Tree?

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Secondary Growth & Wood Anatomy

Scientists constructed models for four threatened tree species in sub-tropical forests in Vietnam, and used these models to estimate tree ages (figure Q.94). Tree age is measured by ring count and trunk diameter at breast height (DBH). Rates of growth were categorised using changes in DBH from 10 to 1000, with 1000 at the finest- grain measure of change.

Figure Q.94. Estimated (lines, for the 10-, 100-, and 1000-category DBH models) and observed (circles, from ring counts) ages for the four tree species Annamocarya sinensis, Calocedrus macrolepis, Dacrydium elatum, and Pinus kwangtungensis.

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. Using the smallest category gives the most accurate information of tree age of P. kwangtungenesis.
B. Age estimates increase particularly strongly from 100 to 10-category model in D.elatum.
C. Model with just 10 DBH categories underestimate the observed ages for three species.
D. For D.elatum, measuring DBH using either 100 or 1000 will give an accurate estimate of tree age, whereas to estimate the age of C. macrolepis, only 100 gives a reliable estimate.
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Question reproduced from IBO 2016, Theoretical Paper B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)