Reducing harvest fragmentation with patch objectives

Without any specific spatial direction, Patchworks will chose polygons for harvest based on their contribution to broad forest level goals (these are harvest quotas and transportation expenditures so far in our example). A typical result is that the model will 'cherry pick' stands all over the landscape in order to meet these goals exactly as would be implied by an aspatial model. This will likely result in a large number of small blocks that increase road densities, increase the overall fragmentation and drive up costs.

In our sample, harvest patches have been defined for the C5 to achieve the desired distribution of harvest pattern. The harvest patch tracks the blocks that have been harvested in a single period; after that period they are no longer considered part of the patch. For more detailed information on defining patch criteria and patch accounts see the section called “Patch Accounts”.

Although we have not yet run the scheduler (don't do this yet, wait until after the next section), if we did we would see the scheduler adjust the pattern of harvest, the distribution of products, and the choice of road segments in order to find a suitable balance between all objectives.

We have harvested a single block already, making this block eligible for a patch in fourth period. Let's zoom back into our original Block 13352 in period 4 and examine some of the patch statistics.

[Note]Note

Be sure that the block layer is selected in the Legend panel so we can access some of the block properties.

  1. Zoom into our block using the tool or the from the toolbar.

  2. Right click on the block to access the pop up menu and select 'Show patch statistics for patch.harvest'

Figure 29. Viewing patch statistics for a single block

Right clicking on a block when the layer is selected will access a menu of block specific items; including the patch statistics dialog.


Table 1. Patch statistic field description

FieldDescription
Patch typeThe name of the patch criteria being used for this patch
Block contentThe amount of area within the block that satisfies the patch criteria
Block areaThe gross area of the block
Patch contentThe area within the patch boundary that satisfies the patch criteria
Patch areaThe gross area within the patch boundary
EdgeThe length of the perimeter of the patch
Area ratioThe perimeter of the patch divided by the perimeter of a circle with the same area.

The patch statistics for Block 13352 shows that the block gross area is 30.941ha and that all 30.941ha is contributing to the patch area (the only patch area at this point!). From these simple patch statistics we can't determine if this patch size is meeting some of the distribution goals of the planning area. To see the patch size objectives we can return to the target charts for patches.

[Note]Note
  1. Close the patch statistics window by clicking 'OK'.

  2. Choose the 'Targets' tab to access the target directory.

  3. Navigate to the 'patch' folder and expand the harvest sub-folder to view the size classes available.

Three size classes have been defined for the harvest patches:

If you expand the patch size folders further you will notice that each size class contains five sub accounts. For more detailed information on these patches and the sub accounts see the section called “Patch Accounts”. The targets we are interested in are those that are active and are represented by a green dot.

[Note]Note

Open the active patch target charts by clicking on the targets represented by a green dot.

  • patch.harvest.0_10.size

  • patch.harvest.10_50.size

  • patch.harvest.50+.size

  • patch.harvest.50+.attractor

Arrange the charts so that you can see the Map Viewer and the three size target charts.

That familiar single black bar appears in the fourth period of the patch.harvest.10_50.size target chart. If you hold your mouse over this black bar the value in the grey box will read 100. The size patch accounts represent the percentage of the total disturbance that falls into the defined categories. In our case, 100% of the harvest falls into the 10-50ha size class. What would happen if we made the patch bigger? Let's find out...

[Note]Note

To expand the harvest patch we will harvest the neighbouring block of block 13352.

  1. Open the Query Tool again and form the following expression: GRIDCODE = 13389

  2. Zoom to the select block and right click to access the pop up menu and select 'View and Edit Treatments'.

  3. Apply another 'CC' treatment to this block at 20 years into the future by right clicking in the line chart.

  4. Return to the Map Viewer and unselect any blocks and the scroll bar is at period 4.

You can now see both blocks have received harvest treatments in the same period and are neighbours. This makes them part of the same patch.

[Note]Note
  1. Open the patch.harvest.10_50.size target chart and notice the black bar in the fourth period has disappeared.

  2. Open the patch.harvest.50+.size chart to find black bar again. 100% of the harvest patches are now within the 50+ha size class.

By scheduling an additional block beside the original block we have increased the size of the patch enough to have it jump size classes. An easy way to see the actual size of the new patch is to view the Patch Statistics again (right click on the block and chose 'View patch statistics for patch.harvest'). Block 13389 is 30.48ha making the new patch area 61.429ha.

[Tip]Tip

Patch information for blocks is also available in the block attribute table the section called “The Block Attribute Table” or by displaying the individual block records.

Now that we have looked at the features and accounts for the transportation and patching of one block we need to look at the overall goals of the forest and how all of the objectives work towards the desired management solution for the Crowsnest Pass.