Surveys of the condition of river red gum communities in the mid-north of South Australia from 2008 to 2016 have returned alarming findings. Not only are the mature trees declining in condition, but there is no regeneration occurring to replace them and the age gap in red gum populations is widening. Without active intervention, the Northern & Yorke region could lose its classic red gum landscapes in 30-50 years. The results of these surveys, carried out for the Northern & Yorke Natural Resources Management Board, were presented at the Goyder Water Forum in July 2017.
Severe die-back was noted in river red gum communities in the Northern & Yorke region in 2005. From 2008-2015, over 60 sites were monitored annually in Broughton, Mambray Coast, Wakefield and Willochra catchments. The overall cause of die-back was found to be reduced water availability, with declining regional rainfall and increased extraction from catchments.
From stressed condition in 2008, red gum communities partially recovered in 2010-11, following good rainfall. Site condition deteriorated again in 2012-13, coupled with heavy insect attack. Levels of insect attack in 2014-15 were insignificant, and canopy condition improved as epicormic growth converted to normal tip growth. Recovery continued in mature trees in 2015, but with lower scores than 2008. All catchments had trees with dual crops, indicating healthy seed volumes available.
However, no regeneration of red gum seedlings has been found at any monitoring sites from 2008 to 2016. The primary factors preventing regeneration appear to be competition from dense spring weeds in riparian zones and from early annual growth of reedbeds in watercourses due to declining flows.
Active intervention will be required to sustain red gum communities in the long term. Otherwise, there is an increasing risk that aging and water-stressed river red gum communities will gradually disappear from regional landscapes. A proposal presented to the NRM Board in 2016 recommended a target of 20% multi-layered native vegetation in regional landscapes, and a citizen science program is being developed in 2017 to encourage landholders and community groups to promote germination and survival of red gum seedlings.
The presentation can be viewed here: http://www.goyderinstitute.org/_r721/media/system/attrib/file/448/Jensen%20NY%20red%20gums.pdf