Response of riparian vegetation to drought and flood

April 20th, 2018

The Challenge

In the past, estimates of water requirements of floodplain trees were based on past hydrology and inundation trends rather than quantitative measurements to understand how trees use water (when, where from in the soil profile) and the drivers of tree condition. During the Millennium Drought, more than 70% of iconic red gum stands in the Murray-Darling Basin were in poor health or dead. Environmental flows were considered as a way to improve tree health however there was little information on how effective this would be and how much water would be required, what season and for how long.

The development of the Murray-Darling Plan, a Plan to equitably share water between users and the environment, required research to understand how to manage floodplain vegetation in the future with limited water resources, especially during drought periods. Information to inform delivery of environmental flows is critical to ensure that water is used to its maximum potential to benefit both users and the environment.

Flooded wetland covered in lemna and azolla with trees in the background — Flooded wetland in Yanga National Park, New South Wales. PHOTO: Tanya Doody

Our Response

Our capability

CSIRO provides experienced, demonstrated long-term expertise in vegetation water use and tree ecohydrology. It also has the ability to ensure that rigorous science in the fieldwork domain is undertaken by ensuring appropriate instrumentation sample size is used to provide the most robust results. Expertise crosses terrestrial, marine and riparian zones. Multi-disciplinary research is undertaken through collaboration with scientists in complimentary fields internal and external to CSIRO, to maximise research outcomes.

Science and Innovation

Project design and data collection in floodplain environments requires innovation to ensure success in the natural world. Often floodwater cannot be provided to high elevation vegetation and alternate ways to deliver water must be considered and trailed. New technology is applied when available to add value to existing techniques and push the boundary of what we currently understand in relation to vegetation water requirements and response to flooding to inform water resource management. Field installed sapflow sensors underpin the studies within this work package to determine tree water use and the response of vegetation to water made available through natural floods or via environmental watering methods.

Sapflow probes in a Coolabah tree — Tree water use is measured using sapflow probes that are installed into the tree trunk. PHOTO: Tanya Doody

Results

A collection of studies over several years has been completed by CSIRO to improve field understanding of vegetation condition, water use and water requirements and response of vegetation to various innovative watering techniques and overbank flooding. It is a package of work that aimed to provide quantified knowledge to inform water requirements of vegetation within the Murray-Darling Basin and tools to assist with monitoring of vegetation condition over time. The impact of this work continues to evolve but recognition is given to its value with invitations to CSIRO to provide expert knowledge to several committees involved in developing environmental water resource plans.

This rigorous work package has been important to continue the evolution of the Murray-Darling Basin Plan with respect to understanding vegetation water requirements and how much and when environmental water is required to prevent significant decline. Some key project outcomes include:

Past estimates of Red Gum water requirements have been based on spatial observations. A large field study, the first of its kind, conclusively quantified the water use and requirements of Red Gums.
Artificial flooding methods are required to ameliorate vegetation water stress during drought periods. Creation of an innovative freshwater lens was shown to be an effective method to improve vegetation condition.
Spatial analysis was important to show that floodplain vegetation respond positively to elevated weir pool levels related to flooding and delivery of irrigation water during summer months.
One study using drip irrigation, demonstrated the response of drought stressed Black Box to an environmental flow. New thresholds to water required to improve tree conditions were discovered.