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ForestGALES is a computer-based decision support system that assesses the risk of wind damage to conifer forests in Britain and compares the impacts of different silvicultural practices. ForestGALES is recommended for use at forest scales, rather than for individual stands, because of inherent variability in predictions.


How ForestGALES works

Calculating wind risk

ForestGALES calculates the probability of wind damage to a stand in two stages by looking at information from the trees and the site.

Using information from the trees:

  • species
  • height
  • diameter
  • age

and then the site:

  • soil type
  • rooting depth
  • spacing
  • thinning

ForestGALES then calculates the critical wind speed at which trees will be damaged, either by uprooting or stem breakage, and its likely return period based on stand location.

Detailed Aspect Method of Scoring (DAMS)

The probability of damaging winds occurring is then calculated using information on the wind climate throughout Britain as classified in the DAMS scoring system. DAMS is a modelled windiness score calculated from tatter flag observations, elevation, aspect, topographical exposure, valley shape and direction.
DAMS values can be:

  • Calculated for a specific location directly; or
  • Looked up from the DAMS scores for the whole of Britain.

DAMS scores are available to download

This information can be used to assist stand management decisions, for example felling age, silvicultural practice and cultivation.

Using ForestGALES

Throughout its development, ForestGALES was designed in consultation with representatives of both private and state forestry organisations and is designed to be easy to use and includes extensive on-line help.

Latest version ForestGALES

ForestGALES 2.5 is now available for download.

The current version is ForestGALES 2.5, which is the upgrade to ForestGALES 2.1 and replaces all previous versions of the ForestGALES software, incorporating research done since the last upgrade. The main changes are:

Damage is less likely to be predicted

Users’ experience indicated that ForestGALES 2.1 tended to predict more damage than was observed. A comparison with actual storm damage, and ongoing research into the science of wind risk in forests, has supported this. As a result, in ForestGALES 2.5 the estimated critical wind speeds for damage are higher, and stands are now predicted to be less at risk of damage.

Change to inputs

In ForestGALES 2.5, the effects of cultivation and drainage on anchorage have been combined and replaced by rooting depth. A Soil and Rooting Helper is provided to help users decide on the correct combination of soil and rooting for a given site.

Crown size calculations

The calculations of crown size within ForestGALES have been revised and are now based on a much larger data set than before. For most species this makes little difference. Crown size calculations are substantially improved for western hemlock, Douglas-fir and lodgepole pine.

Research capability

ForestGALES 2.5 has a Research mode which has added features that make ForestGALES more flexible for research users. Species-specific external parameter files make it easier to alter parameters such as crown relationships or anchorage coefficients. New species can also be added. Weibull parameters describing the wind regime can be entered directly rather than being calculated from DAMS. A wide range of outputs is now optionally saved to a file.

fgr – the ForestGALES R package

A version of the ForestGALES wind risk model is available for use by forestry and land-use change scientists and specialists, ecologists and meteorologists, in a format that is flexible and fully customisable. This is designed to meet the needs of users for application in any forested landscape, and to encourage international collaboration on forest wind risk research.

Since the release of ForestGALES version 2.5, the tree stability team at Forest Research have used the R programming language for all further model development. The model fgr, the ForestGALES R package, is the product of the latest research and development.

R is widely used in the forestry and land-use change research sectors in Britain and throughout the rest of the world. Many models and utilities are available as R packages, thus providing the opportunity for relatively straightforward integration between tools within a common platform. R packages can also be used as a plugin within the QGIS software, as we have done with fgr in the FOSPREF-Wind project.  

What’s new in fgr?

This latest version of ForestGALES, fgr, features a series of modifications and improvements from ForestGALES 2.5, and as such fgr represents the cutting edge of forest wind risk modelling.  Two sets of changes have been made:

  • Firstly, improvements have been made to the ‘roughness’ method which underpins calculations of wind loading in uniform forest stands.
  • Secondly, we have introduced the “’turning moment coefficient’ (TMC) method for calculating risk to individual trees in mixed forest stands.

These changes are described in more detail:

Stand-level calculations

fgr represents an improvement on the traditional stand-level approach used in previous ForestGALES releases.  Several scientific advances have been incorporated into the calculations of critical wind speed in uniform stands:

  • We use new equations for more precise calculation of stem volume, based on the work of Fonweban et al. (2012);
  • The calculations of the effects of wind gusts, upwind gaps, and newly formed (brown) edges have been improved;
  • We have revised the method of calculating the contribution of the mass of canopy to the critical bending moment of the tree;
  • We have improved how the distribution of drag across the forest canopy is represented;
  • We have added more species to the ForestGALES parameterisation, including alternative conifers species (jack pine, white spruce, black spruce, balsam fir, maritime pine, radiata pine) and some broadleaves species (beech, birch, oak, and Eucalyptus globulus).

Individual-tree calculations

The traditional roughness method of ForestGALES calculates vulnerability and risk of the average tree in a stand.  Based on the innovative work published in Hale et al. (2012) and Hale et al. (2015), fgr allows the calculation of individual-tree vulnerability, and the associated risk of wind damage, in stands of mixed-species and irregular structure. This allows easier and more confident risk and vulnerability assessments in complex stands. The effect of complex stand dynamics on wind risk can be accounted for with the TMC method if tree-level competition indices are available. While still in a developmental stage, provisional tests have shown that results are consistent with observed damage.

Where can I download fgr?

The first release of fgr can only be downloaded from the Forest Research website.

This online form will capture your contact details. Terms and conditions must be accepted.

Once the form is complete, an email with four attachments will be sent to the email provided in the form. All personal data are treated in compliance with GDPR regulations.

What’s in the package

Once the form has been submitted, you will receive an email with four attachments:

  1. The Windows binary fgr package in a compressed archive (in .zip format)
  2. The fgr package User Manual in a PDF file
  3. A PDF file containing a copy of the fgr package Licence terms
  4. A text file with simple instructions to install the fgr package within your R library.

The fgr package is built in a modular way, so that not only wrapper functions for the two methods (‘roughness’ and ‘TMC’) are available for standard use, but all the individual functions are also available for advanced users. The simulations are fully customisable: all species parameters can be changed (including mechanical properties of wood, wood density, etc.), parameter sets for new species can be added and stored, and the values of physical constants (e.g. air density, snow density amongst many others) can be changed and stored for future use.

Model outputs can be produced in a compact form that is suitable for most standard use and contains calculated vulnerabilities and risks of uprooting and stem breakage, or in an extended format reporting the outputs of all advanced calculations. Example datasets are provided to help users familiarise with the functionality of fgr. All functions and datasets are documented. Working in batch mode in fgr is easy, since it takes advantage of all standard R practices for vectorised functions.

The fgr manual is a PDF document that details and explains the functionalities of the package and provides extensive background to the numerous aspects of wind damage risk research that went into the creation of fgr. Worked examples based on the provided datasets are included in the manual to provide further assistance, together with an extensive bibliography.

DAMS scores: a measure of windiness for the UK

As a hybrid-mechanistic model, fgr is designed to be able to simulate most forestry conditions, anywhere in the world. The windiness of a site is typically described with the scale and shape parameters of a Weibull distribution of mean wind speeds, as per standard meteorological practice.

In the UK, information on the wind climate throughout Britain is classified in the DAMS scoring system. DAMS scores in raster format (as GeoTiff) are available to download in a coordinate reference system (CRS) compatible with Ordnance Survey data (EPSG: 27700), or alternatively in a CRS compatible with Google Maps, OpenStreetMap, etc. (EPSG: 3857).

Assistance with fgr

For technical support and enquiries relating to fgr, please contact Forest Research at:

How to Access ForestGALES

ForestGales can be installed on your computer (installation version) or run directly from the internet (web-based version).

Download ForestGales

To download ForestGALES you need an access code. New users of ForestGALES will need to purchase an access code which costs £50 + VAT.

To purchase an access code, contact:

Forestry Commission Publications (CST)
Chetham House, Bird Hall Lane, Cheadle Heath, Cheshire, SK3 0Z3.

0161 495 4845 

Current users of FG will be sent an access code. If you have not received your code, please contact ForestGALES support:

Download ForestGALES now with your access code

By downloading ForestGALES 2.5, you agree to the terms of our licence agreement.

Web-based ForestGALES

ForestGales is also available as software that you operate through your web browser. The web-based version calculates the probability of wind damage for a single stand.

The web-based version of ForestGales is free

If you encounter any problems during registration or whilst logging in, please email us at:


If you encounter any problems please email us at:


Does ForestGALES work with mixtures?

The current version of ForestGALES models the effect of the wind on stands that are assumed to consist of identical trees. It’s suggested that in mixtures that the risk of wind damage to each component is calculated separately, using the top height and mean diameter of the component, and the average spacing based on the whole crop (i.e. all components of the mixture). The risk to the stand as a whole can be considered to be highest risk for any component, since if one species is damaged then the resulting gaps will increase the risk of damage to the remaining trees.

Does ForestGALES work outside Britain?

The mechanisms by which trees are damaged by the wind are similar throughout the world. However the relationships between diameter and crown size, the resistance of trees to overturning and the wind climate will differ from country to country.

The current version of ForestGALES was designed for British conditions, but it has been successfully adapted for use in New Zealand, south-west France, Denmark, Canada (Quebec and British Columbia), and Japan. ForestGALES 2.5 includes a research mode that allows input parameters and wind climate to be easily modified for other countries.

What does ForestGALES calculate?

ForestGALES calculates the probability of average trees being damaged within a stand. Damage to the average tree will by implication mean that the stand as a whole will be substantially damaged.

How does ForestGALES compare to the Windthrow Hazard Classification (WHC)?

ForestGALES estimates the chance (or probability) of windthrow or stem breakage, rather than stating a precise height at which damage will occur as in the WHC. Probabilistic predictions are more realistic than precise heights since the occurrence of damaging winds varies from year to year, which has a powerful influence on the occurrence and spread of damage. The risk of damage is dependent on the windiness of the site. In the WHC the measure of windiness is much coarser than is used in ForestGALES. This allows ForestGALES to discriminate several levels of risk for trees in similar WHC classes. A study of actual storm damage indicated that stands can be grown for longer than if they were managed using the WHC.

ForestGALES – Technical support

For technical support and enquiries relating to ForestGALES, please contact Forest Research at the following address or email

Bruce Nicoll

Forest Research, Northern Research Station, Roslin, Midlothian, EH25 9SY

Tel: 0300 067 5287
Fax: 0131 445 5124

ForestGALES further reading

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Belcher, S.E., Harman, I.N. and Finnigan, J.J. (2012). TheWind in the Willows: Flows in Forest Canopies in Complex Terrain. Annual Review of Fluid Mechanics 44: 479–504

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Blennow, K., Persson, J., Wallin, A., Vareman, N. and Persson, E. (2014). Understanding risk in forest ecosystem services: implications for effective risk management, communication and planning. Forestry 87: 219–228.

Cook, N.J. (1985). The designer’s guide to wind loading of building structures. Part 1: Background, damage survey, wind data and structural classification. Butterworths, London pp 371.

Coutts, M.P. (1986). Components of tree stability in Sitka spruce on peaty gley soil. Forestry 59: 173-197.

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Dobbertin, M. (2002). Influence of stand structure and site factors on wind damage comparing the storms Vivian and Lothar. Forest, Snow and Landscape Research 77:187–205

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