Publication Date

1-2023

Publisher

CSIRO and Department of Primary Industries and Regional Development

Abstract

The Kimberley region in north-west Western Australia is covered by extensive savanna woodlands and tussock grasslands. Approximately half the region is under pastoral leases predominately used for beef production. The Western Australian (WA) government Department of Primary Industries and Regional Development (DPIRD) undertakes lease assessment and inspection to ensure the maintenance of pastoral land condition (maintenance of perennial grass cover that supports livestock grazing and soil condition). This presents several challenges around defining land condition and practices that support and improve long-term ecological sustainability of pastoral lands. The objective of this project was to develop state and transition models (S&TMs) for tussock grasslands and woodlands of the Kimberley as a tool to support DPIRD led monitoring and compliance programs in the Kimberley. The models were developed to meet three key outcomes:

  1. A shared understanding (across a range of Departmental staff, scientists and land management experts) of grassland dynamics in the Kimberley, including when observed changes in tussock grasslands and woodlands are driven by natural disturbance cycles or management.
  2. Informing management and regulation of grassland ecosystems, including the relationship between pasture types and where they should be grouped or separated for developing quantitative measures of pasture condition, what should be measured to identify a change in ecosystem state, what management actions might result in a transition to an ecosystem state with greater biomass of palatable pasture species, and over what time frame those changes might occur.
  3. Options to link information in S&TMs to remote sensing information, including the description of a set of rules that could be used to interpret remotely sensed information for on-ground management.

Two S&TMs were developed for Wet-dry tropical eucalypt woodlands (red soil) ecosystems and Rainfall-pulse driven arid and semi-arid tussock grasslands (black soil) ecosystems, that occur across the west and east Kimberley. The models were developed in a two-day expert elicitation workshop using the Australian Ecosystem Models framework archetype models as templates. Nineteen states were described, including two reference states and 17 modified states, across both ecosystem types. Each state included information about within-state variability, driven by natural disturbance and recovery processes, captured through descriptions of ecosystem expressions. The S&TMs also described 58 transitions between modified states (38 for the red soil S&TM and 20 for the black soil S&TM). Transitions included information on drivers, pre-conditions and timeframe for transitions, and likelihood of transitions driven by management actions that aim to recover pasture condition. Expert-elicited information on the characteristics (structure, function and composition) of each ecosystem state (and its expressions) was combined with quantitative measurements of species frequency and cover taken from the Western Australian Rangeland Monitoring System (WARMS) dataset and satellite imagery. S&TM information was captured in conceptual diagrams, text, tables and spreadsheets.

Overall, the S&TMs have organised information about tussock grassland and woodland dynamics across the Kimberley that:

  1. complement existing classification schemes for pasture type and condition
  2. provide a basis for interpretation of landscape change that is due to transitions between ecosystem states that impact landscape values (e.g. cattle production, ecological integrity), versus change driven by endogenous disturbances (e.g. fire, drought, flood)
  3. provide a structured way to assess pasture condition and a guide to management actions that might be implemented to reverse undesirable changes
  4. articulate a method for organising and cataloguing ecosystem dynamics that is transferable to other regions of the WA rangelands.

Several knowledge gaps remain, and next steps should focus on developing quantified measures of ecosystem states (condition), mapping the spatial location of ecosystem states, and shaping the S&TMs into decision trees for informing practical land management, monitoring and evaluation.

Number of Pages

106

Keywords

tussock grassland, savanna woodland, state and transition model, pastoral rangelands, Kimberley

Disciplines

Agricultural Science | Agriculture | Environmental Indicators and Impact Assessment | Natural Resources and Conservation

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