Eucalyptus ovata tree growth
The TASVEG community DOV “Eucalyptus ovata forest and woodland” is a threatened plant community that, on Rubicon, is competing for space with SHW “Wet heathland”.
When we bought Rubicon in 2007 there was a scattering of adult E. ovata trees in some areas but few juveniles or seedlings, perhaps due to the previous frequent fire regime. Since then we have we have kept fire out of most of the E. ovata areas (DOV) and burnt patches of Wet heathland (SHW) that could potentially convert naturally to E. ovata woodland.
We have been monitoring an area that is potentially in transition from SHW to DOV because immature Eucalyptus ovata trees are growing on the site. The aim of the monitoring is to better understand the population dynamics of the immature trees, including what happens when the area is disturbed by burning. In 2015 we burnt part of the monitored area.
On 1 Oct 2012 and 4 Oct 2012 all the E. ovata trees over 2 meters tall within a defined DOV area were numbered with degradable paper tape. A random sample of twenty of these trees was selected for long term monitoring using randomly generated numbers in Microsoft Excel. These twenty trees were labelled with numbered aluminum tags. On October 1 the following measurements were taken for each tree:
- The circumference of the trunk of each of the 20 selected trees over 2 meters tall was measured at breast height over bark (DBH) using the Australian conventional measurement height of 1.3 metres above the ground. The diameter was then calculated using the formula: Diameter = circumference/pi (3.142)
- The canopy health (the average proportion of healthy foliage that is present was measured i.e. deduct from 100% the per cent of the crown with leaf damage). This measurement does not include the lower limbs that do not form part of the canopy. Large dead trees are measured for DBH but have 0% canopy cover.
This Juvenile E. ovata tree is one of twenty trees whose circumference measured annually.
The crown of this Juvenile E. ovata tree was partially burnt in the 2015 burning program.
On 4 October 2015 the annual measurement of the circumference at 1.3m and the percentage of damage to the foliage through burning or insect damage was made. The figure below shows the change in diameter at breast height (DBH) in each of the 19 trees measured over four years. One tree had died in that time and was removed from the data set. All the remaining trees had grown in diameter over the three year period – some more than others. The trees with smaller starting DBH in 2012 had, on the whole, a higher percentage increase in DBH than those with larger starting DBH.
There does not appear to be a relationship between the average amount of leaf damage from insects that a tree had sustained in 2012, 2013 and 2014 and the percentage change in DBH between 2012 and 2015. In 2016 it will be interesting to see the effect that burning has had on the DBH of the six trees involved.