Drought, Deluge and Diversity Decline

 

A novel experiment to examine how changing rainfall patterns combine with root herbivory to affect grassland ecosystems.

DRI-GRASS

Grasslands are an important type of ecosystem in Australia. Temperate grasslands now cover just one per cent of the area they covered prior to European settlement, and are threatened by changes in land use, climate and management practices.

Grassland productivity is closely aligned with climate conditions, with the volume and timing of rainfall directly linked to the composition and performance of grasslands. Future climate scenarios generally predict more extreme conditions in the future, which will likely result in reduced rainfall quantity, longer periods of drought and longer intervals between rainfall events.

Rainfall In Australia - Source: Bureau Of Meteorology
Rainfall In Australia - Source: Bureau Of Meteorology

Climate model projections - Source: Bureau Of Meteorology
Climate model projections - Source: Bureau Of Meteorology

In addition to these changes in climate, the impact of root herbivores needs to be factored into planning scenarios for grassland management because the stress imposed by drought events is likely to be exacerbated by damage to roots caused by these herbivores. This may mean that the combined effects of drought and root damage may push some ecosystems toward a 'tipping point' that results in loss of diversity, function and ecosystem health.

Temperate grasslands now cover just one per cent of the area they covered prior to European settlement...

Root Herbivores

These herbivores are typically the larval forms of beetles that normally reside in grasslands, often in significant numbers.

The adult beetles lay eggs during wet periods and prefer grasslands and moist soil over bare soils or legume-based pasture. The larvae feed belowground on plant roots and organic matter.

Other root herbivores include larvae of the Soldier Fly which prefer native grasses, and weevils which feed mostly on legume species.

Scarab Larvae. Image Credit - Kirk Barnett
Root herbivores - Image Credit: Kirk Barnett

The DRI-GRASS Experiment

This new research project aims to fill the knowledge gap about how predicted changes in rainfall combine with root herbivores to impact on grassland ecosystem functioning.

The experiment uses individual rainout shelters of the DRI-GRASS (Drought and Root-herbivore Impacts on GRASSlands) facility to exclude rainfall and reapply ambient, decreased or increased rainfall under a program of experimental treatments that simulate the various scenarios predicted under future rainfall regimes.

Rainfall treatments to date
Rainfall treatments to date

Additionally some plots have been inoculated with scarab beetles so that there will a known population of belowground beetle larvae to combine root herbivory with altered rainfall.

Experimental measures include:

  • above- and belowground biomass and composition of the plant community; plant physiological performance
  • root herbivore abundance and
  • nutrient cycling and stoichiometry.

In particular, researchers are working to understand how the combined impacts of biotic (root herbivores) and abiotic (drought, increased or reduced rainfall, or less frequent rainfall) stresses influence ecosystem responses to each factor on its own.

Outcomes

This project is the first in the world to examine the impacts of predicted changes in the frequency and amounts of rainfall on the interactions between grasslands and the root herbivores that feed on them, particularly under predicted future rainfall scenarios.

Scientists predict that there will be major effects on grassland ecosystems caused by the combined effects of increased soil water deficits and root herbivory that in turn increases plants' sensitivity to such droughts.

If irregular but heavy rainfall leads to increased egg production as beetles take advantage of high soil moisture following prolonged dry periods, some grassland systems may experience large numbers of root herbivores feeding at a time of water stress and this is when significant impacts on the ecosystem would likely emerge.

This project 'Drought, deluge and diversity decline – How do root herbivores affect grassland resilience to predicted changes in rainfall patterns?' is funded by the Hermon Slade Foundation [Project ID P00021516].

Related Links

Hermon Slade Foundation (opens in a new window)

CSIRO State Of The Climate Report (opens in a new window)

Bureau Of Meteorology State Of The Climate (opens in a new window)

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