How Trees Provide Evidence about Past Climate
Short explanation of Dendrochronology
 Trees grow in both height and width.
 Trees growing in environments with distinct growing
seasons produce annual growth rings.
 Trees growing in environments with little seasonal
variation – (such as tropical rainforests) often do not
have visibly distinct growth rings.
 Annual Growth Rings are formed in the Xylem layer
 The xylem tissue in trees conducts water and dissolved
nutrients from the soil throughout the entire tree
 New xylem tissue is produced during periods of active
growth
 In general cells are larger and more numerous during
periods with abundant moisture
 In northern environments each Annual Growth Ring is
composed of two rings
 a Spring Ring
 Thicker because there is more water present and growing
conditions are ideal
 Summer Ring
 Thinner and darker in colour because there is less water and
the growing xylem cells are smaller
There are no fall or winter rings because trees in northern
environments are not actively growing during those
seasons
 The thickness of the rings is affected by weather
conditions during that growing year.
 Rings are thicker when growing conditions are ideal –
warm and wet.
 Rings are thicker when growing conditions are poor typically hot and dry.
 Note: unusual weather conditions can occasionally
result in the production of additional growth rings in a
single year
 these are called “false growth rings”
Build your own Climate Tree
Discovered in Norway in 1906, the Oseberg
ship, the best preserved Viking ship ever
found, reveals its Norse shipbuilders'
graceful construction style.
Photo credit: © Svergies TV
The analysis of the
oak planks making
up one Viking
Longship (found in
Norway) showed
that the wood was
from trees cut
down near Dublin,
Ireland some time
between AD 10601070.
1. Tree Ring Detective
2. Dendrochronology and Climate Change Lab
3. Trees: Recorders of Climate Change