Step 3: Generate sample plots

Earth Blox template: VM0047 Step 3: Generate sample plots

Now that you have delineated the donor pool area, you can use it to generate candidate control plots, and project plots from your project area.

For each plot, the UTM coordinates are added as an attribute (required by VM0047), as well as a stocking index value for three separate points in time. 

This template workflow generates two separate feature collections, one containing the control plots, and one containing the project plots, that can be matched in the next step of the process.

Selecting your stocking index

In this template, the ESA Above Ground Biomass is used as the stocking index, however we would recommend using a premium biomass dataset such as Chloris Geospatial: Aboveground Biomass Stock and Change (30m), as this:

1. Will produce the most robust results, anywhere in the world
2. Ensures you don’t have to worry about spatial gaps in the data (e.g. due to cloud cover)
3. Ensures you don’t have to worry about temporal gaps in the data (e.g. missing years).

You can save a lot of time in this way. Speak to us if you’d like to explore this option. 

Load the Donor Pool Area to Assets

Start by uploading the donor pool area to your Assets.

Learn more: Uploading a feature collection to Assets

Load in the donor pool area and project area

This template uses a sample donor pool area and a sample project area. To use your own project area and its corresponding donor pool area (that you created in the previous step), swap these out in the workflows.

1. Click on ‘View or change dataset’ in the workflow that uses the Example Project Dataset
2. Select the Assets tab, and select your Project area
3. Uncheck ‘Add recommended blocks’ before selecting Change dataset
4. Click on ‘View or change dataset’ in the workflow that uses the Example Donor Pool Area
5. Select the Assets tab, and select your Donor Pool area
6. Uncheck ‘Add recommended blocks’ before selecting Change dataset

Run the workflow

Click the ‘Run’ button on the workflow to generate your dataset. A popup in the bottom right corner will show you the progress of your export. You can leave the project workspace without interrupting the export process.

Download your exported dataset

1. Click on the Earth Blox logo in the top left hand corner to leave the project workspace. 
2. Click on the Exports page in the navigation menu
3. Click on the download icon to start the download to your device. Exported datasets are available to download for 48 hours.

Customising this template

Customising plot generation

Plot alignment and scale

The size of the sample plots are aligned to pixels of the Stocking Index. In this template, the AboveGroundBiomass band from the ESA Above Ground Biomass dataset. If you are using a different dataset, update the Generate sample plots block in each workflow to use the correct band.

VM0047 methodology requires plots to be between 0.09 hectares (30m × 30m) and 10 hectares.

Number of plots

You can adjust this number of plots that are generated for your needs. In this template, 35 sample plots are generated from the project area, and 3500 candidate control plots from the donor pool area. 

Project plots

A minimum of 30 project plots are required when calculating the performance benchmark. In case a project plot becomes invalid at a monitoring event, it is sensible to generate a few more than are needed (e.g. 5 extra). 

Control plots 

To provide 5 control plots (this is the “k” value) for each of the 35 project plots, 175 control plots are needed. 

We recommend creating 10-20 times the number of candidate control plots, as a number of control plots may become invalid at a monitoring event.

Minimum overlap

For project plots, at least 75% of each plot must be within the project area boundary. We recommend using the same threshold for control plots.

Learn more: Generate sample plots

Changing the stocking index points in time

Once the plots have been generated, the stocking index for each plot is calculated using the Calculate zonal statistics block at three different points in time. 

VM0047 requires you to calculate the stocking index at :

1. At the start of the project (t = 0)
2. 8–10 years before the project start date (i.e. not before t = −10 and no later than t = −8)
3. At least one other time point between those two.

To change the dates used, use the “Dates” dropdown in the Calculate zonal statistics block. 

Any changes you make must be consistent in both the control plots and project plots workflows. For matching to take place (in the next step) the attributes on each dataset must be identical.

Using a different stocking index

1. Add a new Use dataset block to the workspace 
2. Click “Search datasets” 
3. Choose the new stocking index dataset from the dataset catalogue
4. Select your project plots dataset as your area of interest
5. Click and drag the Save data for re-use block from the ESA Above Ground Biomass workflow block to the bottom of your workflow 
6.  Delete the ESA Above Ground Biomass workflow by dragging it to the bin icon in the bottom right of the workspace
7. Check the dates in the zonal statistics blocks are correct
8. Duplicate this workflow by right clicking on the Use dataset block and selecting Duplicate
9. Change the area of interest to the control plots dataset
10. Check that the attribute names and dates are identical for project plots and control plots.