Outbreak of Phoracantha semipunctata in Response to Severe Drought in a Mediterranean Eucalyptus Forest

Abstract

Extreme climatic events, including droughts and heatwaves, can trigger outbreaks of woodboring beetles by compromising host defenses and creating habitat conducive for beetle development. As the frequency, intensity, and duration of droughts are likely to increase in the future, beetle outbreaks are expected to become more common. The combination of drought and beetle outbreaks has the potential to alter ecosystem structure, composition, and function. Our aim was to investigate a potential outbreak of the native Eucalyptus longhorned borer, Phoracantha semipunctata (P. semipunctata), following one of the most severe droughts on record in the Northern Jarrah Forest of Southwestern Australia. Beetle damage and tissue moisture were examined in trees ranging from healthy to recently killed. Additionally, beetle population levels were examined in adjacent forest areas exhibiting severe and minimal canopy dieback. Severely drought-affected forest was associated with an unprecedented outbreak of P. semipunctata, with densities 80 times higher than those observed in surrounding healthier forest. Trees recently killed by drought had significantly lower tissue moisture and higher feeding damage and infestation levels than those trees considered healthy or in the process of OPEN ACCESSForests 2015, 6 3869 dying. These results confirm the outbreak potential of P. semipunctata in its native Mediterranean-climate Eucalyptus forest under severe water stress, and indicate that continued drying will increase the likelihood of outbreaks.

Chronic historical drought legacy exacerbates tree mortality and crown dieback during acute heatwave-compounded drought

“…Ecosystems may change most rapidly and profoundly in regions experiencing compound events or multiple stress periods, occurring concurrently, or in quick succession . In the Northern Jarrah Forest, and elsewhere, the combination of drought and warming has corresponded with beetle outbreaks (Seaton et al 2015), forest fires (Gouveia et al 2016), and associated widespread terrestrial carbon losses (Berner et al 2017). Not only do these processes have an impact on forest structure and functioning, but also the potential to profoundly alter our future atmosphere and climate (Zemp et al 2017).…”

A thirteen‐year study on the impact of a severe canker disease of Corymbia calophylla, a keystone tree in Mediterranean‐type forests

“…A sudden and unprecedented forest collapse was observed in the Northern Jarrah Forest (NJF) of SWWA following record dry and heat conditions in 2010/2011, with the death and collapse of midstorey and overstorey jarrah and marri crowns observed following this period of sudden and severe drought (Matusick et al, 2013). The four tree deaths at the Brunswick Junction forest site that were not associated with canker were attributed to drought induced mortality, with high feeding damage and infestation levels by the native Eucalyptus longhorned borer (Phorocantha semipunctata Fabricius) providing further evidence that these deaths resulted from water stress (Seaton, Matusick, Ruthrof, & Hardy, 2015). under severe water stress, B. mediterranea develops rapidly within the xylem with the potential to kill the entire host (Desprez-Loustau et al, 2006;Vannini & Valentini, 1994).…”

“…The SWWA has experienced a persistent trend of declining annual rainfall and increasing temperatures since the 1970s (Bates, Hope, Ryan, Smith, & Charles, 2008), which is projected to continue into the future (CSIRO & BOM 2007, IPCC 2013. The four tree deaths at the Brunswick Junction forest site that were not associated with canker were attributed to drought induced mortality, with high feeding damage and infestation levels by the native Eucalyptus longhorned borer (Phorocantha semipunctata Fabricius) providing further evidence that these deaths resulted from water stress (Seaton, Matusick, Ruthrof, & Hardy, 2015). A sudden and unprecedented forest collapse was observed in the Northern Jarrah Forest (NJF) of SWWA following record dry and heat conditions in 2010/2011, with the death and collapse of midstorey and overstorey jarrah and marri crowns observed following this period of sudden and severe drought (Matusick et al, 2013).…”

Within-Tree Distribution and Survival of the Eucalyptus Longhorned Borer Phoracantha semipunctata (Coleoptera: Cerambycidae) in a Mediterranean-Type Ecosystem

“…Large areas of stressed and dying trees associated with a drought event, leading to widespread attack by P. semipunctata in Southwestern Australia jarrah forest, showed that tree health was critical for determining the intensity of borer emergence [36]. To estimate the borer's population size and better understand its behaviour, these drought-stressed trees in the Northern Jarrah Forest (NJF) provided an opportunity to determine how tree characteristics shaped the within-tree distribution and affected the survival of P. semipunctata in Australia.…”