Australian mistletoe distribution is increasing, and recent studies established clear links between mistletoe infection and tree mortality (Griebel et al., 2017). However, our mechanistic understanding behind increased tree mortality is rare, since we are typically lacking direct observations about how mistletoes affect their host’s physiology.

We address this gap by continuously monitoring stem and branch sap flow and a range of leaf and sapwood traits of infected and uninfected trees of two co-occurring eucalypt species within the Cumberland Plain woodland in south-eastern Australia.

We recorded that the eucalypt leaves use stomatal regulation to reduce water loss, which was generally lacking for mistletoe leaves. Sap flow rates of stems and branches of both infected eucalypt species remained unregulated even under extreme atmospheric dryness during a hot summer heatwave. This indicates that the excessive water use of mistletoes likely increases xylem cavitation rates in hosts and supports that hydraulic failure contributes to increased mortality of infected trees.

You can read more about how mistletoe influences tree mortality in a press-release from the American Geophysical Union or on environmentalresearchweb.

The publication is open-access and can be downloaded here: Anne Griebel et al 2017 Environ. Res. Lett. 12 115012