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Woodland grazing toolbox banner showing a wild boar eat bracken at Glen Affric and a Highland cow in Glengarry beside birch trees

6.2.3 Determining stocking density and duration of grazing

Determining an appropriate stocking density and the length of time the wood will be grazed is the key stage in setting your grazing regime.

Stocking density is the number of livestock that graze a woodland or woodland management unit. There is more than one way of deciding on stocking density and the input of a grazier who knows the area can be invaluable.

The stocking density calculation template (xls 43k) is a spreadsheet that will give you grazing options that should allow you to select an appropriate grazing regime. When you have completed the template, append it to your Woodland Grazing Plan and summarise the conclusions in section 6b.   

The spreadsheet is set up to carry out most of the calculations for you. The links and comments below should help you to complete it but you may also find it helpful to refer to the worked example (xls 43k). This is in the same Excel file as the stocking density calculation template.

1. Calculating forage availability

Your woodland types and open ground habitats will have been defined and mapped in section 3 of the Grazing Management Plan. Enter the habitats and woodland types and their areas in box 1 of your calculation template. Then enter a figure for annual production per hectare of ‘dry matter’ for each habitat, using the tables of forage availability for each habitat type. From this, the template will calculate the total annual productivity for each of your habitats.

2. Determining an appropriate level of grazing intensity

In section 4 of your woodland grazing plan you will have decided on the range of herbivore impacts that might meet your biodiversity and/or cultural heritage objectives. The impact of herbivores on the woodland depends in part on the grazing intensity. A measure of this is the proportion of the available forage that they eat (utilise).

Convert the desired level of grazing impact that you recorded in section 4 into target utilisation rates. Note that habitats within the same management unit can have different target utilisation rates, provided that the anticipated impacts on each habitat are compatible with your objectives.

The spreadsheet can now calculate the total annual target for dry matter removal for each habitat and for the wood as a whole.

3. Calculating forage intake by domestic and wild grazing animals

To complete this section of your template satisfactorily, you must have some idea of how many deer will be present in your woodland. You will find information on wild herbivores in section 5 of the Toolbox. You may also have a deer management plan with information on target deer populations over the lifetime of the grazing management plan. From this information and the table of forage intake for different species and breeds of grazing animal, you should be able to calculate the number of deer likely to be present in the woodland area and their daily dry matter intake. In the spreadsheet, enter these figures in column 1 of box 2.

The spreadsheet can now calculate the estimated annual intake by deer and the amount that remains available for removal by stock at the target utilisation rate.

Using the Toolbox information on selecting species and breed of grazing animal, enter the type of grazing animal you will be using for your conservation grazing and the daily intake of dry matter for that animal. From this information the spreadsheet will calculate the total number of stock grazing days required in a year to achieve your target utilisation rate.

Note that the figure for dry matter intake will vary according to season as shown in the forage intake table. In addition, supplementary feeding, especially during the winter months, will reduce the overall figure. The amount of the reduction will depend on how much supplementary feeding is required.

4. Arriving at your preferred gazing regime

The template now allows you two options. You can either decide on an optimal number of livestock animals and the spreadsheet will calculate the number of grazing days needed with that number of animals; or you can decide on the ideal number of grazing days and the spreadsheet will show the number of animals needed for that period.

You may be limited by the number of animals available, in which case you would want to follow the first option. If the biodiversity /cultural heritage objectives show a preference for the season of grazing or the duration of grazing you would want to go for the second option.

Box 2 of the template has room for three different grazing regime options. You can use columns 2 and 3 to try different combinations of animal type, number of animals and duration and season of grazing.

Once you have decided on a preferred grazing regime enter the details in box 3 at the foot of the template.