Wilding Tree Risk Calculator

About the Wilding Tree Risk Calculator

The Wilding Tree Risk Calculator helps you assess the risk of planted conifer species spreading beyond a commercial forestry site.

Using the Wilding Tree Risk Calculator is a legal requirement under the National Environmental Standards for Commercial Forestry (NES-CF).

Find out more about the NES-CF

When to use the Wilding Tree Risk Calculator

You must use the Wilding Tree Risk Calculator to assess the risk of wilding conifers spreading if you are:

• planning to plant a new commercial forest (afforestation) with a conifer species
• replanting a forest with a conifer species.

You must get the assessment risk score:

• no more than 8 months before you give notice to your local council for afforestation, or
• no more than 8 months before replanting.

If your score is less than 12, planting or replanting is permitted. If it is 12 or higher, you need resource consent.

If you are replanting:

• you need resource consent if you replant with a conifer species that has a higher score than the one most recently harvested
• you do not need resource consent if you replant with a conifer species that has a score that is the same or lower than the one most recently harvested.

You’ll need to give the score and worksheets to the council to meet the NES-CF permitted activity conditions for afforestation and replanting on your site. There are other conditions you’ll need to meet for these activities.

Read more about this in the guidance:

National Environmental Standards for Plantation Forestry guidance

Who should use the calculator

If you’re using the calculator to comply with the NES-CF, a suitably competent person  must do the assessment. This means a person with:

• tertiary qualifications in silviculture and forest ecology and at least 2  years’ experience in the field of silviculture, or
• at least 5 years’ experience in silviculture that includes forest establishment.

Existing calculator

If your local council will receive your wilding tree risk assessment score before 25 June 2026, use the existing calculator in Appendix 1 of the Wilding Tree Risk Calculator guidelines.

Download the Wilding Tree Risk Calculator and guidelines [PDF, 1.7 MB]

Updated calculator 

If your local council will receive your wilding tree risk assessment score after 25 June 2026, use the updated calculator.

Updated Wilding Tree Risk Calculator and guidelines [PDF, 1.5 MB]

Wilding Tree Risk Calculator worksheet only [PDF, 226 KB]

Guidance and supporting material

The guide below helps you do a wilding tree risk assessment using the updated calculator. It explains how to use the different tools needed for each step. 

Wilding Tree Risk Calculator: Paper worksheet step-by-step guide [PDF, 3 MB]

The document below contains references to the published research used to support the updated calculator.

Supplementary information for Guidelines for the use of the Decision Support System "Calculating Wilding Spread Risk From New Plantings" [PDF, 1.6 MB]

Supporting tools

To help you use the updated Wilding Tree Risk Calculator, these tools are available.

Automated Excel spreadsheet

You can use the Excel spreadsheet below to calculate the risk score. 

Automated DSS1 Calculating Wilding Spread Risk From New Plantings [XLSX, 47 KB]

This guide helps you do a wilding tree risk assessment using the Excel spreadsheet.

Wilding Tree Risk Calculator: Excel step-by-step guide [PDF, 2.2 MB]

You’ll need to know how much of the land surrounding your planting site and the downwind land is covered by each land cover and land management type.

For the wilding tree risk assessment, the surrounding and downwind land is called the ‘receiving environment’. Downwind land refers to land in the direction the wind blows with the most force.

Find out how to get this information in the step-by-step guide.

R based assessment tool

You can use R script to identify the receiving environment for your site. There is guidance on how to do this in the step-by-step guide.

To use the R code, you’ll need RStudio. RStudio is a free, open-source Integrated Development Environment (IDE) designed for the R programming language.

Download RStudio here:

RStudio IDE – Posit

Download the R script:

R script for receiving environment [DOCX, 93 KB]

What has changed?

The main changes to the calculator are:

• it now uses both the tree species and the environment it could spread into to assess risk
• the science behind it has been updated to better reflect actual risk
• the assessment method has been updated to reduce reliance on judgement and increase transparency.

Other NES-CF tools

• Erosion Susceptibility Classification
• Slash Mobilisation Risk Assessment
• Fish Spawning Indicator