UNDER STRESS: The lack of rain is seeing the normally vibrant green of the Northern Rivers turn to a dusty brown.
UNDER STRESS: The lack of rain is seeing the normally vibrant green of the Northern Rivers turn to a dusty brown. Marc Stapelberg

The cool reason why plants turn brown during a drought

You may have noticed the lush vegetation along our country roads starting to look singed, brown and crispy.

In fact, whether they are palm trees, pine trees or shrubs there are more and more brown and yellow spots forming across the vegetation as the sustained drought puts pressure on our flora and fauna.

Southern Cross University Plant Science director Professor Bronwyn Barkla said it was a typical stress response by vegetation in order to survive the lack of water.

She said rather than what looks like an early autumn, it was actually plants trying to minimise the need for water through either shedding leaves or directing water to other parts of the plant so they could keep the nutrients and the water in the youngest part of the tree.

 

Professor Bronwyn Barkla (left) said we would see plants utitlising a stress response as the drought continues.
Professor Bronwyn Barkla (left) said we would see plants utitlising a stress response as the drought continues. Marc Stapelberg

Professor Barkla said people may also see trees and plants start to flower in an attempt to save their genetics.

"Another stress response that people could be seeing is that the vegetation may flower at unusual times which is indication that the plant is under stress.

"It produces seeds and then survives through those seeds."

She said there was a likely hood that we would start to lose trees due to the sustained lack of rain.

"Trees are resilient, and they have mechanism to withstand this but at some point, those mechanism will break down if there is not water," she said.

The science behind water conservation in plants sees a delicate interplay between Stomata on the leaves to collect CO2, and transpiration where the leaves lose water through evaporation through those very same stomata.

"In times of drought the drought tolerant plants can regulate how much those pores open, so the less time they are open at the hottest time of day the better because they won't lose so much water," she said.

She added some plants may even store CO2 and use sugars so they don't have to open their Stomata during the day at all, and only transpire in the evening.

Professor Barkla said rainforest areas in and around Mt Nardi may appear more lush still as they have huge root systems that could access water from underground water sources.

She said wind in open areas could play a huge factor in how much water plants lose, while plants in Lismore and urban areas would face increased heat stress from concrete and building surfaces reflecting heat.

 

The lack of rain is seeing the normally vibrant green of the Northern Rivers turn to a dusty brown.
The lack of rain is seeing the normally vibrant green of the Northern Rivers turn to a dusty brown. Marc Stapelberg

Daleys Fruit Tree Nursery spokesperson said the heat of this summer was putting enormous stress on gardens and orchards.

"One way to help stressed fruit trees cope is to cut them back hard. Mix up some diluted, white, acrylic paint and then paint the exposed branches with this to protect them from sunburn," they said.

"This method will reduce the stress on the tree and it will encourage strong new growth once the rains come.

"Water in the cool of the evening or early in the day and recycle water where ever possible.

"Mulch will retain this precious moisture and is most effective if applied around the drip line of your trees.

They said if trees were stressed and had fruit on them it would reduce the stress on the tree to remove the fruit.

"Selecting plants that are well adapted to dry periods will also help you get them through the dry times, and plants that are native to a Mediterranean climate will cope much better in times of drought than trees native to the wet tropics," they said.

Lismore Garden Centre owner Cameron said people would start to really notice the deterioration in their trees and plants by the end of the month as the dry weather continued to have an effect on the soil and private residences.

He said those on tank water would be suffering the most, but those with a reliable supply of water were still purchasing plants in normal consumer patterns.

He added that drought resistant plants offered a solution for the future as they were adapted for the harsher conditions in the way many tropical plants weren't.

He warned that it would take more than a few patchy storms to save the vegetation as the hydrophobic ground would mean high runoff which in turn was good for catchments, but not necessarily for root systems.

He said a slow gentle sustained period of rainfall would be needed for any real plant regeneration to occur.