1.  The challenge of no net loss: a framework for evaluating biodiversity offset policies
National Biodiversity Offsets Conference
Canberra 26th Aug 2019
Ascelin Gordon, Isaac Peterson
ICON Science
School of Global, Urban and Social Studies
RMIT University, Melbourne
@ascelin

2. Biodiversity value
Time

3. Development occurs
Biodiversity value bi t1
Time

4. Development occurs
Biodiversity value bi t1 t2
Time

5. bi t1 t2 t1 t2 Biodiversity value Time Time Development occurs
Offset implemented
Biodiversity value bi bo
Counterfactaul 1 t1 t2 t1 t2
Time
Time

6. bi t1 t2 t1 t2 Biodiversity value Time Time Development occurs
Offset implemented
Biodiversity value bi bo
Counterfactual 2 t1 t2 t1 t2
Time
Time

7. bi t1 t2 t1 t2 Offsets: objective of achieving
no-net-loss (or better) of biodiversity
How to measure gains is critical
Development occurs
Offset implemented
Biodiversity value bi bo
Future 2
Counterfactual 3 t1 t2 t1 t2
Time
Time

8. bi t1 t2 t1 t2 Offsets: objective of achieving
no-net-loss (or better) of biodiversity
How to measure gains is critical
Restoration gain
Development occurs
Avoided condition decline
Biodiversity value bi bo
Future 2 t1 t2 t1 t2
Time
Time
Avoided clearing

9. bi t1 t2 t1 t2 Offsets: objective of achieving
no-net-loss (or better) of biodiversity
How to measure gains is critical
Restoration gain
Development occurs
Avoided condition decline
Prioritizes
Low condition
areas
Biodiversity value bi bo
High condition
areas
Future 2
Areas with high
risk of clearing
(also high
condition) t1 t2 t1 t2
Time
Time
Avoided clearing

10. Important considerations for calculating impact
To determine whether NNL is achieved, we need
Net impact of both interventions to be ≥ 0
i.e. <negative impact of development> + <positive impact of offset> ≥ 0
Be explicit about time horizons
Requires the impact of the development be commensurate with the impact calculated for offset (else adding 🍏+🍊’s!)
Thus need a consistent set of assumptions in calculating both impacts, which also means consistent assumptions underpinning counterfactuals

11. Scales of evaluation
The scale of what is being evaluated is very important. The next few slides illustrate the different possible scale.
Assume each square is a parcel of land that can either be developed or offset

12. Scales of evaluation 1. Site: Individual development/offset pair
Site scale meaning evaluating a single development offset pair for NNL

13. Scales of evaluation 1. Site: Individual development/offset pair
Site scale meaning evaluating a single development offset pair for NNL

14. Scales of evaluation 2. Program: All developments/offsets
Program scale meaning the longer term sequence of development offset pairs or all development offset combinations under the policy

15. Scales of evaluation
2. Program: All developments/offsets

16. Scales of evaluation 3. Landscape: Whole area where policy is applied
Here include both all areas impacted, all areas where offset activities occur as well as everything in between.
So can include biodiversity values not impacted by the offsetting or development
Useful for understanding the impact that an offset policy has on broader trajectories of biodiversity.
Factors being directly impacted, or contribution of a policy to wider ecological objectives?

17. `Offsetsim’ Developed as an R package
Open source, available on github: github.com/ascelin/offset_simulator
Allows you to simulate:
ecological dynamics
development
different kinds of offset policies
evaluate their performance

18. Example simulation 2500 parcels
Each assigned initial ecological condition, declines through time
Logistic curve to model improvement from management as offset
Loop (50 years, 250 developments)
Parcel developed
Calculated development impact
Determine offset impact requirements
Implement offset

19. Site scale results Restoration + avoided condition decline
Offset must
accrue gains
In 30 years
biodiversity value
Fig 1a and Firg 1b
time
time

20. Site scale results Restoration + avoided condition decline
Offset must
accrue gains
In 15 years
biodiversity value
Fig 1a and Firg 1b
time
time

21. Program and landscape scales
Restoration gains
Offset must
accrue gains
In 30 years
biodiversity value
Fig 1a and Firg 1b
time
time

22. Program and landscape scales
Restoration gains
Offset must
accrue gains
In 30 years
biodiversity value
Fig 1a and Firg 1b
time
time

23. Program and landscape scales
Restoration gains
Offset must
accrue gains
In 15 years
biodiversity value
Fig 1a and Firg 1b
time
time

24. Case study: Cumberland Plain
Western Sydney Strategic Sustainability Plan
Future tends in extent and condition of native vegetation, focus on Cumberland Plain Woodland Ecological community
Model development within the Priority Growth areas and a range of offset scenarios
Expert-elicited model of ecological condition change under do nothing and management as an offset (Vegetation Integrity Score)

26. What does all this mean for offsetting
In real world, offsets often determined through a process of negotiation.
Can use these approaches to evaluate what has or could happened under different policies. Some policies require estimation of counterfactuals.
Estimating counterfactuals are tricky and fraught with uncertainty; however, we need them to determine impact, as outcome can be meaningless.
The scale we evaluate at is important.

27. Thank you Acknowledgments ascelin.gordon@rmit.edu.au @ascelin
Sarah Bekessy, Atte Moilanen
Cumberland Plain Woodland
Photo: Greg Steenbeeke