Valuing The Environment
Biodiversity – the variety of plants, animals and micro-organisms in a region – delivers vital benefits to Victorians including clean air, fresh water and fertile soils.
Planned burning and bushfires can impact the health of the environment and also support plant and animals species that need fire for their survival.
We are charged with building the health of Victoria's biodiversity and this can sometimes involve the use of fire as a management tool. We balance this important obligation with a responsibility to manage bushfire risk to life, property and the environment.
To be successful we must reduce the risk of bushfire in a way that avoids unacceptable impacts.
Associate Professor Alan York of the School of Ecosystem and Forest Sciences from the University of Melbourne discusses the role of fire in ecosystem resilience at Science In Use, the DELWP Science symposium 2015
Vegetation Recovering After Fire
Many species have adapted to survive bushfires and some depend on fire to exist and develop. Planned burning can play a role in promoting essential ecological processes such as regeneration.
Healthy ecosystems provide us with clean air, water, carbon storage, forest products and diverse plants and animals, as well as opportunities for recreation and enjoyment. Maintaining ecosystems that are resilient to external shocks is important in ensuring healthy environments that continue providing these benefits.
Our management approach seeks to maintain or improve ecosystem resilience. We are taking a whole-of-system approach that builds on our management of threatened and vulnerable species, as required under the Environmental Protection and Biodiversity Conservation Act (Cth) and the Flora and Fauna Guarantee Act (Vic), to focus on ecosystem stability, diversity and disturbance as a whole. This involves developing ecological models and measures of ecosystem resilience under different fire regimes.
We base our environmental management approach around the concept of ecosystem resilience, which is defined as:
An ecosystem’s capacity to absorb both natural and management imposed disturbance but still retain its basic structure – in terms of species abundance and composition – function and identity over space and time.
How We’re Measuring Ecosystem Resilience
Understanding the impact of fire on ecosystems requires first being able to define and measure ecosystem resilience. This is complex and we can't directly measure all aspects of ecosystem resilience.
We use Tolerable Fire Interval (TFI) as a broad indicator of resilience at a landscape level. We have also developed additional measures – Geometric Mean Abundance and Vegetation Growth Stage Structure - to understand resilience and the impacts of fire. Other factors such as climate change, water availability and pest plants and animals also influence resilience.
We will continue to expand our understanding to develop more sophisticated measures of ecosystem resilience.
Tolerable Fire Interval (TFI)
Tolerable Fire Interval (TFI) is the amount of time recommended between fires for different types of plants (or vegetation communities). It's good for ecosystem resilience if vegetation is 'within TFI'. The larger the areas of our landscapes below minimum TFI and above maximum TFI, the less resilient ecosystems are likely to be.
The chart below shows the proportion of Victoria's vegetation that was below, within or above its TFI or had no history of fire impact, at various times over the past 25 years. Press the toggle button to see the TFI distribution by area across the state.
The recommended TFI for different types of plants is determined by some key features of a plant's life history including
- How it grows
- How it reproduces
- How it transitions between different phases of its life
If large areas of a landscape are younger than the minimum TFI, and the chance of bushfire is high, then a fire would be expected to have a large negative impact on biodiversity.
Geometric Mean Abundance Of Species In A Community (GMA)
This is defined as the relative abundance of all known species within a particular ecosystem, and provides a measure of the biodiversity of an ecosystem, which is a good indicator of resilience. It is used along with growth stage structure (described below).
GMA also allows us to consider the impact of different fire regimes on particular threatened species.
Vegetation Growth Stage Structure (GSS)
Groups of plants (vegetation communities) develop through growth stages that have distinguishing features, the same way humans do (e.g. juvenile, adolescent, mature).
The chart below shows the proportion of Victoria's vegetation within particular growth stages, at various times over the past 25 years.
Maintaining a diversity of growth stages (juvenile, adolescent, mature and old) in a particular ecosystem or landscape can help to improve ecosystem resilience. We can calculate a desired growth stage structure to maximise GMA for an ecosystem, so that a range of species occur.
DELWP sets a goal of having a diverse range of growth stages, which provide habitats for lots of different species. Planned burning can be used to manage a landscape so that overall, it is moving toward a desired growth stage structure. It can also be used to minimise the risk that bushfires remove all the older vegetation. This is important because it takes decades for juvenile vegetation to become old growth after a fire.
How We’re Managing Ecosystem Resilience
Our management approach seeks to balance the need to reduce impacts to life and property and maintain ecosystem resilience. We currently use thresholds around the proportion of the landscape below minimum TFI and above maximum TFI that act as triggers in bushfire management planning processes. We will use similar thresholds for species diversity (Geometric Mean Abundance) and Habitat/Growth Stages (Vegetation Growth Stage Structure).
How We're Improving
In the Barwon Otways Bushfire Risk Landscape we have trialled the use of GMA and GSS as measures of ecosystem resilience. Developing this approach has involved working with the University of Melbourne to determine what mix of growth stages would maximise the diversity of flora and fauna in the landscape. We then compared this ideal mix to the current distribution as well as proposed fire management strategies, to understand the impact of fire management.
By improving our understanding and ability to model how fire impacts ecosystem resilience, we can find the appropriate balance of fire in the landscape.
DELWP is also working with the University of Melbourne to develop tools to integrate measures of ecosystem resilience into bushfire management planning.
South-eastern Red Tailed Black Cockatoo Case Study
We work closely with communities and local environment groups to gather information about local plants and animals, particularly threatened or rare species.
The South-eastern Red-Tailed Black Cockatoo is an endangered species which lives in an area of South-West Victoria stretching from Portland to Horsham.
The Cockatoo lives on the seeds of Buloke and Stringybark trees. Bushfires and some planned burning activity can scorch these trees, reducing the seeds available for the birds.
In South-eastern Red-Tailed Black Cockatoo habitat we are trialling different kinds of planned burns that allow us to both manage fuel and preserve the bird's food source.
We are investigating options for protecting the cockatoo by compiling data and conducting burning trials designed to reduce crown scorch on trees. Our report on the results of these trials will inform bushfire risk management approaches in cockatoo habitats in the future.