Hailstorm on 20 January 2020

Text and photos by Rosemary Purdie

In the early afternoon of Monday, 20 January 2020, a violent, 10-minute long hailstorm swept over the northern parts of Black Mountain Nature Reserve, pummelling the vegetation with hailstones up to 6 cm in diameter. Along the length of the storm's pathway tree canopies were stripped of their foliage, which formed a carpet on the ground.

Photo 1	Photo 2	Photo 3

Hailstones dumped on the edge of the storm, in O'Connor	Leaves carpeting the Callitris Track after the storm	View from the Forest Loop looking towards Belconnen Town Centre over stripped trees in the north-west part of the reserve

Was there any difference in storm damage between tree species?

Tree canopies

The canopies of Red Box (Eucalyptus polyanthemos) trees appeared to be more severely affected, mostly because of their rounder leaf shape. These leaves generally make Red Box canopies look denser under normal conditions (compared with the other eucalypt species that have narrower, more elongated leaves) and were bigger 'targets' for the hailstones to hit.

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Red Box tree canopies stripped of their foliage along the Callitris Track	Scribbly Gum and Brittle Gum trees along Little Black Mountain Track showing less canopy damage

Bark

The trunks of all the eucalypt species were severely bruised from the physical impact of hailstones. The bruising was most obvious on the pale, smooth bark of Red Box, Scribbly Gum (E. rossii), Brittle Gum (E. mannifera) and Yellow Box (E. melliodora) trees, but was also evident on the dark, rough bark of Red Stringybark (E. macrorhyncha) trees.

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Hailstone bruising on a Scribbly Gum	Hailstone bruising on a Brittle Gum	Hailstone bruising on a Red Stringybark

How quickly did the trees recover?

Young shoots started to develop from buds below the bark on the upper branches of many trees following around 60 mm of rainfall in the area on 10 February; by mid-March shoots were cloaking the stems. These epicormic shoots were also developing on some tree trunks in response to hailstone bruising.

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Dense shoots growing along a Scribbly Gum branch	Shoots developing from a hailstone bruise on the trunk of a Scribbly Gum

The following photos provide a visual record of the storm's impact on the trees and their subsequent recovery.

Series 1: southern Callitris Track

Photo 11a	Photo 11b	Photo 11c

24 Sept 2019 (four months before hailstorm)	23 Jan 2020 (three days after hailstorm)	17 Mar 2020 (two months after hailstorm)