RIP Australian native trees – unprecedented death rates

For the first time ever, drought has claimed the lives of rare, centuries-old sandalwood trees in the South Australian outback. Ecologist John Read believes the situation is a real indicator of climate change. “Old trees don’t lie,” he says. “It really struck home when these trees that have been around for many centuries can no longer tolerate the conditions.”

It turns out it’s not just the sandalwoods. “We’ve noticed quite a significant die-off of wattles and long-lived pine trees,” he added.

Indeed, the words ‘unprecedented tree deaths’ are causing a lot of concern among the scientific community. Brendan Choat, Associate Professor at the Hawkesbury Institute for the Environment at Western Sydney University reports that the problem is not isolated to one or two tree deaths here and there. “Whole hillsides are dying,” he claims. "This drought seems to have pushed a lot of very resilient vegetation over the edge."

Thirsty trees

The main problem for trees during drought is the water transport system that sustains them. Water is pulled up under tension using energy from sunlight. During drought, this system falters. In hot weather, trees’ leaves lose more water through evaporation to stay cool but if there is not enough water, leaf temperatures can become so high that they effectively scorch.

Image credit: UNSW (2019)

Tree growth following drought

According to Phys.Org, how well forests recover from drought is largely unknown for most tree species. Using records from the International Tree Ring Data Bank, scientists measured the recovery of tree stem growth after severe droughts since 1948, at more than 1,300 forest sites across the globe. Tree rings provide a fairly accurate history of wood growth and show evidence of carbon uptake of the trees’ surrounding ecosystem.

A small number of forests displayed growth higher than predicted after drought, in parts of California and the Mediterranean. For the majority of the world’s forests, however, the data showed that trees struggled for years following a drought, with trunk growth taking on average two to four years to return to normal.

Dead Tree Detective

In 2018, scientists launched the Dead Tree Detectives project which crowd-sources information about tree deaths. Citizens are asked to take photos of dead trees and upload them to the Atlas of Living Australia website (www.ala.org.au). The entries are logged with data about location and species and ultimately, scientific experiments will be conducted to understand the physiological mechanisms that underpin tree mortality.

Honey production sours

Drought is also a very lean time for honey production as bees struggle to find nectar. Large Australian native trees, for example require rain many months before they’re meant to flower. The tree will produce a bud but if conditions aren’t conducive to flowering, the tree will conserve its energy and effectively go into ‘panic mode’. Ultimately, it will drop the bud without the flower ever having blossomed which of course means no pollen or nectar for bees.

Southeast Queensland beekeeper Jack Stone of Bee One Third tends to more than 150 hives in the region including on urban rooftops and out in country areas. “This year’s honey yield is noticeably and significantly down on last year’s,” he says. “I’m doing all I can to protect the health and wellbeing of my bee population to get them through the drought.”

Bushfire a part of the deal

As if drought weren’t bad enough, bushfires add insult to injury. In Western Australia, the timber industry has long complained about the risk of bushfire due to the cessation of timber harvesting in old growth forests in 2001. In 2016, a Forest Industries Federation of WA spokesperson said that “largely unmanaged fuel loads have built up to dangerous levels.”

Meanwhile , scientists reported in early 2019 that it takes up to 30 years for forest soils to recover after logging and 80 years after bushfires. David Lindenmayer, Professor of Ecology at the Australian National University said that soil determines the rate at which forests grow, the level of carbon there and how much carbon is fixed or released from the soil. He recommends that plantation feedstock be used instead of native forest timber.

Certainly, when discussing the effects of logging compared with bushfire, the figures are vastly different. In the last ten years in Victoria, around 3 million hectares of bush have been burnt. Logging has accounted for only 30,000 hectares, a mere 1 per cent of the total impact.

No matter where a person’s opinions lie on climate change, one thing is for certain; the timber industry is invested in protecting trees, not just for profit but in the noble pursuit of sustainability. Nature deals a pretty tough hand in our country. At the very least, our industry is acutely focused on doing its best to protect, preserve and nurture forests for the benefit of future generations.