Climatic Inferences from Dendroecological Reconstructions - Dendroclimatology - page 268

Small Fire Years (<4 sites recording fire)

WET Large Fire Years (>20 sites recording fire)

4

2

0

− 2

DRY

− 4

1600 1650 1700 1750 1800 1850 1900

1.5

El Nino

1.0

0.5

0.0

− 0.5

− 1.0

La Nina

− 1.5

1600 1650 1700 1750 1800 1850 1900

Year

Fig. 9.3 ( Upper plot ) Tree-ring-reconstructed summer (July-August) Palmer Drought Severity
Index (PDSI; solid line ) (from Cook et al. 2004 ) , shown with the largest and smallest regional fire
years identified from the 120-site fire-scar network from the southwestern United States ( lower
plot ). Tree-ring reconstructed Niño-3 index of sea surface temperatures (SSTs; Cook 2000 ) , shown
with the same set of largest and smallest regional fire years

during years prior to fire years to assess antecedent conditions that may have been
important for fire occurrence. Significant climate anomalies are assessed by using
bootstrapped confidence intervals based on distributions of annual climate values.
Results of SEA from the Southwest regional data confirm that, on average, the larger
fire years occurred during drought years and La Niña events, and that the small fire
years occurred during the opposite patterns of pluvial years and El Niño events
(Fig. 9.4 ) . Interestingly, SEA also often shows that there were significant lagging
relationships in climate/ecosystem dynamics, with fire years typically following