Dendrochronology: Linking life and climate in the past

Kena Fox-Dobbs
University of Puget Sound
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In this exercise students explore; 1) how climate variables influence tree growth on historical and/or geological timescales, and 2) how climatic records are generated from biogenic chronologies. The exercise varies conceptually depending upon tree location (local and global), and type of tree records analyzed.

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Undergraduate majors course in paleontology

Skills and concepts that students must have mastered

Basic statistical and graphical methods for identifying correlation among datasets (Excel-based skills).

How the activity is situated in the course

This lab activity accompanies lecture(s) of paleoclimatological records, biogeography, and terrestrial ecosystems.


Content/concepts goals for this activity

- understand interaction between climate and tree growth
- understand how climatic information can be extracted from biogenic chronologies
- understand the importance of assumptions in paleoclimatological and biogeographical data analyses

Higher order thinking skills goals for this activity

- formulation of hypotheses and identification of assumptions
- analysis of data (test correlation between variables)
- place specific concepts from activity into broader paleo context

Other skills goals for this activity

Description of the activity/assignment

This is a basic exercise that can be expanded or modified any number of ways. I had access to wood slabs (tree cross sections) from several coastal and inland temperate trees, and slabs from a couple tropical trees, all of known age. The students worked in groups of 2-3 students; each group was assigned a slab and was given spreadsheets of annual and monthly climate data from a weather station near where their tree grew, and global average values. Each group was responsible for extracting data from the slab (eg. counting and aging rings, measuring ring widths), deciding what assumptions to make during data collection, graphing the data, and comparing the tree data to various climate data. The students managed/analyzed their data using Excel. Each group was also responsible for researching their tree species and location in order to understand how biology might influence climatic interpretations. In summary, the students looking at tropical slabs were generally unable to correlate ring width to any climate variable (local or global), and the students looking at temperate slabs were usually able to correlate ring width to various climate variables - with some interesting taxonomic differences. At the end of the exercise each group presented their findings to the rest of the class - we then discussed the pitfalls and practicalities of extracting paleoclimatic data from biogenic chronologies, and the importance of biogeography. From start to finish this exercise took a full 3hr lab section. Tree records can be generated from wood slabs collected opportunistically (eg. during campus construction projects), tree cores taken by the students (eg. from trees on campus, etc), or from high-resolution pictures of slabs or cores.

Determining whether students have met the goals

Participation during lab exercise, group presentation, individual written assignment

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