Abstract
th , 2012; revised July 10 th , 2012; accepted July 25 th , 2012 Ecosystems in Mediterranean climate regions are projected to undergo considerable changes as a result of shifting climate, including from extreme drought and heat events. A severe and sudden dieback event, occurring in regionally significant Eucalyptus gomphocephala woodland in Western Australia, coincided with extreme drought and heat conditions in early 2011. Using a combination of remote sensing and fieldbased approaches, we characterized the extent and severity of canopy dieback following the event, as well as highlighted potential predisposing site factors. An estimated 500 ha of woodland was severely affected between February and March 2011. Tree foliage rapidly discolored and died over this period. In the affected portion of the woodland, approximately 90% of trees greater than 20 cm DBH were impacted, while in the adjacent unaffected woodland 6% showed signs of damage. Tree density in the unaffected area had approximately 4.5 times more trees than the affected woodland. Precipitation drainage patterns are thought to explain the difference between affected and unaffected woodland. Dropping groundwater levels, a relatively shallow soil profile, and extreme drought and heat in 2010-2011 are thought to predispose water-shedding sites to drought-triggered canopy dieback during extended periods of dryness. Tracking forest health changes in response to severe disturbance is an important key to deciphering past and future vegetation change.
Highlights
In Mediterranean climate regions, drought is one of the key selection pressures on forest distribution and growth (Damesin et al, 1998)
We conclude that a severe and sudden dieback event in E. gomphocephala woodland coincided with extreme drought and heat conditions in early 2011
A similar, though more severe, dieback event of Eucalyptus marginata-dominated forest in the south-west of Western Australia (SWWA) occurred during the same time; affecting an estimated 16,500 ha (Matusick et al, unpublished data)
Summary
In Mediterranean climate regions, drought is one of the key selection pressures on forest distribution and growth (Damesin et al, 1998). Despite a range of adaptations to disturbance events, trees in Mediterranean ecosystems can be vulnerable to drought and heat-induced canopy dieback (Lloret et al, 2004) and associated declines in growth (Jump et al, 2006) and carbon storage (Galiano et al, 2012). These forests will be further challenged if drought periods become more frequent, as predicted by climate change projections (Giorgi & Lionello, 2008). The average temperatures have risen at a rate of
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