P.PSH.1222 - Impact of bushfires on soils, pasture and the microbiome

Summary

Bushfires are a natural agent of disturbance often resulting in multifactorial damaging impacts. On farms, along with health and wellbeing of producers and stock being affected, the health of the soil that forms the foundation of farming is also influenced. Heat from unplanned fire has capacity to sterilise soil, kill pasture seeds, remove soil nutrients, and temporarily decimate the soil microbiome.

Prior to this project, comparatively little was known about the long-term recovery of soil, or growth of nutritionally rich vegetation tolerant to post-fire conditions. A tool box of strategies and recommended courses of action have been developed for producers to manage post fire recovery of soil and vegetation.

Objectives

• A literature review is delivered summarising the possible direct and indirect consequences of fire on the recovery of soils, pastures, and other vegetation, and options for their management from similarly affected areas in Australia, North and South America, Africa, Russia, and Europe.
• Results and summary regarding the consequences of bushfire on soil quality as measured by assessment of soil microbiota and biogeochemistry is delivered.
• Insight is reported on the effect of bushfires and planned burns on nutrient values of collected pastures, the growth patterns of seed banks of pasture vegetation, and the effect of fire on pasture growth, normalised difference vegetation index and biomass accumulation as determined by remote sensing.
• Insights to any interrelationships between nutrient content and the soil microbiome, vegetation and grazing livestock in pasture systems are discussed within individual summaries.
• An interdisciplinary toolkit for post-fire impacts and recovery to inform future post-fire pasture recovery and management was planned as an objective. Over the intervening years several excellent manuals, factsheets and web-based information portals have been generated. We have collated these resources and sought to add value through added content with regards to soil and pasture recovery post fire to complement the existing Bushfire recovery manual generated by the MLA.

Key findings

• Post bushfire, primary producers should put in place weed management systems and maintain vigilance to ensure that new invasive and possibly damaging (poisonous) species do not gain a foothold in the fire affected paddocks.
• Use of satellite imagery is an important and useful method for gaining a broader overview of property status and puts into context a range of factors including biomass estimations however, satellite imagery needs to be matched with biological sampling as it is susceptible to geographic conditions.
• Biochemical analysis of soil samples collected in bushfire exposed and unexposed paddocks as well as soils exposed to a planned burn has revealed persistent variation in extractable phosphorus (P), nitrate (NO3+), and available nitrogen (N) indicative of a soil with improved nutrient content for pasture growth in severely burnt pastures in comparison to unburnt sites. This finding suggests a positive aspect to bushfire exposure in the context of grassland fires however it must be stressed that this finding may be confounded by properties closely adjoined with forests since the predicted temperatures of these soils may be higher.
• Exposure to fire has no apparent detrimental effect on seed germination in the short term (six months post burn) as measured in the planned burn site and the long term (eighteen and thirty-months post bushfire event).
• Verbal reports from all the producers in this study and biological evidence in the plant matter growth in the seed bank analysis from soils collected 18 months post bushfire suggest that an unexpected issue faced by producers post bushfire was rapid and vigorous overgrowth of previously unseen weed species.
• Analysis of the microbiota (bacteria) and mycobiota (fungi) in soil collected from planned burn at six months post fire event, and bushfire exposed/unexposed soils at 18- and 30-months post fire exposure, found no consistent differences between burnt and unburnt soils at the community-level.

Benefits to industry

Reported insights to pasture and soil viability following the 2019/2020 bushfires and subsequent rainfall and flood events in livestock producing properties located in NSW provides a unique understanding to producers of the measured consequences of bushfire relevant to the Australian setting. The review of literature revealed a paucity in similar analysis of the consequences of bushfires to Australian livestock producers. These findings will serve as reference for producers and feedback from producers has been utilised to generate an informative factsheet containing links to tools for recovery post-fire.

MLA action

Discussion under to develop a management guide for producers.

Future research

• A web-based toolkit be developed providing easy access to updated national and regional information.
• Research has shown that satellite imagery is an important and useful method for gaining a broader overview of property status, further extensive research is required to assess value and specificity of the method in relation to agricultural land and in as a complement of biological sampling.
• There is a paucity in published data relevant to soil biochemistry post bushfire in Australian agriculture settings. Development of a repository of such data that included variables such as soil type, and microbial and nutrient content variations.
• A comprehensive study of the efficacy of mulching in bushfire recovery through use of planned burn simulations may provide producers with increased confidence.