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Figure 2.11. Comparison between the instrumented precipitation record and the
tree-ring record, California, USA. The solid line represents the instrumented record
and the dashed line represents the reconstructed (tree-ring) record (after Hughes
and Graumlich, 1996).
individual tree rings. However, other biological and environmental conditions
can affect inter-annual fluctuations in ring width, and current ring growth.
Because of this, ecological conditions such as soil fertility, plant competition,
forest stand development, diseases and insect pests, wildfire incidents, environ-
mental pollution and sunlight availability that affect tree growth must also
be considered when undertaking dendrohydrological studies (Loagicia et al .,
1993).
Tree-ring analysis is usually better suited for the reconstruction of past
drought events rather than past events of high precipitation. This is because
conditions such as plant competition and soil fertility act as limiting factors
in years with high precipitation and obscure the hydro-climatic signal in the
tree-ring records. Lag effects after severe conditions can also obscure tree-ring
analysis as individual events can affect forced responses in the tree-ring width
for several years. Despite these issues, however, tree-ring analysis can provide
accurate descriptions of past precipitation regimes. Figure 2.11 shows a compar-
ison between the instrumented precipitation record and a tree-ring record in the
USA. The tree-ring record follows the general trend of precipitation variations;
however, in places there are slight differences in the magnitude of events or sea-
sonal rainfall. Despite the departures in magnitude, the comparison shows that
tree rings can provide a true reflection of precipitation changes. The main limi-
tations preventing tree-ring analysis from becoming a more commonly used tool
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