Calculate the area of aspen in the harvest area

Aspen is an important timber resource used to produce commodities such as paper, pallets, boxboard, and plywood. As the GIS specialist for a natural resource agency, you've been given a timber harvest proposal and have been asked to answer the following questions:

  • How many acres of aspen exist in the harvest area?
  • How many acres of land will be cut in the proposed timber harvest?
  • How much timber is the harvest expected to yield?

Calculate the acreage of each forest stand

First, you've been tasked to answer how many acres of aspen exist in the harvest area.

  1. Download the Timber Harvest Planning project package.
  2. Locate the downloaded file on your computer. Double-click TimberHarvestPlanning.ppkx to open it in ArcGIS Pro. If prompted, sign in to your ArcGIS account.
    Note:

    If you don't have ArcGIS Pro or an ArcGIS account, you can sign up for an ArcGIS free trial.

    Map of forest stands polygons and river lines

    The white lines are rivers and streams and the green polygons are forest stands.

  3. In the Contents pane, right-click ForestStands and choose Attribute Table.

    The attribute table opens. This layer contains information about each forest stand, including soil type, age class, ownership, and vegetation type.

    Tip:

    To learn more about Age_class, Veg_type, and the other attributes, view the layer's metadata.

    There is also a field named Shape_Area, which is automatically generated. However, the values are in square meters, and the forestry manager has requested values in acres. You'll add a new field to calculate the area in acres.

  4. On the ribbon of the attribute table, click the Add Field button.

    Add field button directly above the attribute table

    The Fields view appears.

  5. For Field Name and Alias, type Acres. For Data Type, choose Double.

    New Acres field shown in the Fields table with Double chosen for Data Type

  6. On the ribbon, on the Fields tab, in the Changes group, click Save.
  7. Close the Fields table.

    The attribute table now has an empty field for storing area values in acres. Next, you'll calculate those values.

  8. In the attribute table, right-click the header for the Acres field and choose Calculate Geometry.

    Calculate Geometry in the context menu of the Acres field in the attribute table

  9. For the Calculate Geometry Attributes tool, enter the following parameters:

    • For Property, choose Area.
    • For Area Unit, choose Acres.
    • For Coordinate System, choose Current Map [Map].

    Calculate Geometry Attributes tool

  10. Click Run.

    The Acres field in the attribute table fills with values. Now you know the acreage of each stand.

  11. Close the attribute table.

Find the acreage of aspen stands

Next, you'll create a bar chart to find out how many acres of aspen stands exist in the study area.

  1. In the Contents pane, right-click ForestStands, point to Create Chart, and choose Bar Chart.

    A chart view and Chart Properties pane appear.

  2. In the Chart Properties pane, for Category or Date, choose Veg_type.
  3. In the Fields list, choose Acres. Confirm that Aggregation is set to Sum.
  4. Under Data Labels, check the Label bars box.

    Chart Properties pane set to Veg_type, Sum, and Acres, with Label bars checked

    The chart shows a green bar for each vegetation type, labeled with the sum of its acres. There are 65,219 acres of aspen stands in the study area.

    Part of the bar chart showing the acreage of each vegetation type, with the tallest bar for lowland forest

    However, you know that not all stands in the study should be included in the count. The harvest plan will be applied to state-owned public forests and private industrial forests. Little to no harvesting will occur on private, nonindustrial lands. You can apply a definition query to filter the dataset to only the appropriate land ownership types.

  5. In the Contents pane, double-click ForestStands to open the Layer Properties window.
  6. Click the Definition Query tab and click New definition query.

    New definition query button on the Layer Properties window

  7. Construct the clause Where Ownership is not equal to non-industrial private and click Add.

    Add button below the only clause in the Definition Query builder

  8. Click Apply, and on the Layer Properties window, click OK.

    The map now has some gaps in it. Nonindustrial private lands are no longer shown.

    Gaps in the map where private nonindustrial lands have been removed

    The bar chart has also changed. Now the number above the Aspen bar reads 55,333. This is the answer to the forest manager's first question.

  9. On the Quick Access Toolbar, click Save to save your project.

    Save button on the Quick Access Toolbar

There are 55,333 acres of aspen in the harvest area. But not all of this land will be harvested. In the next lesson, you'll answer the next question: How many acres of land will be cut in the proposed timber harvest?


Calculate the area of land to be harvested

In the previous lesson, you calculated the area of existing aspen on public and industrial lands. Now that you know how many acres of aspen exist, you can determine which stands will be harvested. The forest manager has provided you with some criteria about where trees can be cut. The first criterion is that no harvesting can take place within a 100-foot buffer along rivers and streams. Logging too close to water can cause harmful erosion and sedimentation, so it is important to leave trees standing around waterways.

Create buffers around waterways

First, you'll create a polygon layer to represent the 100-foot buffer around all watercourses.

  1. If necessary, open TimberHarvestPlanning.ppkx and close the Chart view.
  2. In the Contents pane, select ForestStands. On the ribbon, on the Data tab, in the Definition Query group, change the active query to <None>.

    Active Definition Query set to <None> on the Data tab of the ribbon

  3. On the ribbon, on the Analysis tab, in the Geoprocessing group, click Tools.
  4. In the Geoprocessing pane, search for and open the Buffer tool.
  5. For the Buffer tool, enter the following parameters:

    • For Input Features, choose Waterways.
    • If necessary, for Output Feature Class, type Waterways_Buffer.
    • For Distance, type 100 and choose Feet.
    • For Dissolve Type, choose Dissolve all output features into a single feature.

    Buffer tool with all parameters set

  6. Click Run.

    A new layer is added to the map.

  7. Zoom in on the map to see the buffer layer.

    Transparent polygon buffer surrounding the rivers on the map

    This polygon represents the 100-foot protective zone around rivers and streams where timber cannot be harvested.

Erase waterways buffer from forest stand polygons

Next, you'll remove this area from the ForestStands layer using the Erase tool.

  1. In the Geoprocessing pane, click the Back button.

    Back button on the Geoprocessing pane

  2. Search for and open the Erase tool.
  3. Run the Erase tool with the following parameters:

    • For Input Features, choose ForestStands.
    • For Erase Features, choose Waterways_Buffer.
    • For Output Feature Class, type ForestStands_NoRivers.

    Erase tool with parameters filled in

    The tool runs and a new layer is added to the map.

  4. In the Contents pane, turn off ForestStands.
  5. Right-click Waterways and choose Remove.
  6. Remove Waterways_Buffer.

    The basemap now shows through in the buffer zone around rivers.

    ForestStands polygons with a buffer around waterways removed

  7. Open the attribute table for ForestStands_NoRivers.

    Because you removed some area from the polygons, you need to recalculate the values in the Acres field.

  8. Right-click the Acres field and choose Calculate Geometry.

    The Calculate Geometry Attributes tool appears in the Geoprocessing pane.

  9. For Property, choose Area, and for Area Unit, choose Acres. For Coordinate System, choose Current Map [Map].
  10. Click Run.

    The Acres field is updated to reflect only the land that does not border rivers or streams.

  11. Close the attribute table.

Identify stands for harvesting on industrial lands

Now that you've removed the buffer around rivers and streams, you need to identify the aspen stands that meet the rest of the forest manager's criteria. Cutting trees that are too young is a waste. And while aspen can grow on a variety of soil types, production varies between these types. More timber can be produced on rich, loamy soils than on dry, sandy soils.

The forest manager has provided you with different harvesting criteria for different land ownership types. First, you'll consider the criteria for logging on industrial lands: Only harvest stands that are at least 40 years old.

  1. In the Contents pane, double-click the ForestStands_NoRivers layer to open the Layer Properties window.
  2. On the Definition Query tab, click New definition query.
  3. Construct the clause Where Veg_type is equal to aspen and click Add.
  4. Click Add Clause to expand the query to multiple clauses.

    Add Clause button on Definition Query 1

  5. Construct the clause And Ownership is equal to industrial and click Add.

    Constructing the second clause And Ownership is equal to industrial

  6. Click Add Clause again. Construct the clause And Age_class is greater than or equal to 40 and click Add.
  7. At the top of the query, click Definition Query 1 (the query name) and type Industrial Harvest.

    Definition query name changed to Industrial Harvest

  8. Click Apply and click OK.
  9. Zoom and pan on the map until you can find some of the remaining forest stands.

    Very few of the original forest stand polygons meet the criteria for harvesting on industrial lands. Next, you'll make a new field so you can flag these areas for harvesting.

  10. Open the attribute table for ForestStands_NoRivers.
  11. Click Add to add a new field.
  12. For Field Name and Alias, type TimberHarvest. For Data Type, choose Text.
  13. On the ribbon, on the Fields tab, in the Changes group, click Save.
  14. Close the Fields table.
  15. In the attribute table, right-click the header for the TimberHarvest field and choose Calculate Field.
  16. In the Geoprocessing pane, in the TimberHarvest = box, type 'Industrial'. (Be sure to include the single quotation marks.)

    'Industrial' entered in the Calculate Field tool for the TimberHarvest field

  17. Click Run.

    The TimberHarvest field in the attribute table updates.

    Attribute table with Industrial in all rows for the TimberHarvest field

    Only those polygons that meet the criteria of the definition query have been updated. The others continue to have a value of <Null> for the TimberHarvest field. Next, you'll create a definition query to identify those stands that will be harvested on public lands.

Identify stands for harvesting on public lands

There are more publicly owned forest stands in your study area than industrial lands. There are also more criteria for harvesting these lands:

  • Only harvest stands that are at least 50 years old.
  • Only harvest stands that are at least 20 acres in size.
  • Only harvest on soil types containing well-drained loam.

  1. Open the Layer Properties window for ForestStands_NoRivers.
  2. On the Definition Query tab, click New definition query.

    New definition query button at the bottom of the window

  3. Rename Definition Query 2 as Public Harvest.
  4. Add five clauses:
    • Where Veg_type is equal to aspen
    • And Ownership is equal to state-owned public
    • And Age_class is greater than or equal to 50
    • And Acres is greater than or equal to 20
    • And Soil includes the value(s) well-drained loam, well-drained loamy sand, well-drained sandy loam

    Public Harvest definition query with five clauses

  5. Click Apply.
  6. Next to Public Harvest, click the Set as Active button to choose it as the active query.

    A brighter green check mark indicates the active query.

  7. Click OK.

    The map updates to show different forest stands. The attribute table indicates that 78 stands meet the criteria for harvesting on public lands.

    Attribute table showing 0 of 78 selected at the bottom

  8. Use the Calculate Field tool on the TimberHarvest field to label the filtered features as 'Public'.

    'Public' entered in the Calculate Field tool for the TimberHarvest field

  9. Close the attribute table.

Find the total acres that will be harvested

You've now located which aspen stands will be harvested. Next, you'll create a chart to find out how much land they cover.

  1. In the Contents pane, click ForestStands_NoRivers to select it.
  2. On the ribbon, on the Data tab, in the Definition Query group, change the active query to <None>.

    All forest stands draw again on the map.

  3. On the ribbon, on the Appearance tab, in the Drawing group, click Import.

    Import button on the Appearance tab of the ribbon

    The Apply Symbology From Layer tool appears.

  4. For Symbology Layer, click the Browse button.
  5. In the Symbology Layer window, click Folders and double-click the TimberHarvestPlanning folder connection.

    TimberHarvestPlanning home folder connection in Project > Folders

  6. Open the commondata folder and then the userdata folder. Double-click AspenHarvest.lyrx.

    Apply Symbology From Layer tool with parameters

    Note:

    A layer file (.lyrx) allows you to save and reapply symbology properties. It will only work if you used the same spelling for the field name and values as defined in this lesson. If you did not, you can create your own symbology or skip to step 8.

  7. Click Run.

    The map is symbolized to show where aspen will be harvested on both public and industrial lands.

    Map showing aspen harvest areas in bright greens with the rest of the forest area in transparent gray

  8. In the Contents pane, right-click the ForestStands_NoRivers layer, point to Create Chart, and choose Bar Chart.
  9. In the Chart Properties pane, for Category or Date, choose TimberHarvest. For Fields, choose Acres and check the Label Bars box.

    The bar chart is color-coded to match the symbology on the map. The bars are also labeled with the total number of acres that will be harvested for each land ownership type.

    Bar chart showing 355 acres of industrial lands and 5,582 acres of public lands

  10. Close the chart view and save the project.

You can now inform the forestry manager that a total of 5,937 acres of aspen will be harvested; 355 acres on industrial lands, and 5,582 acres on state-owned public lands. In the next lesson, you'll calculate the volume of this harvest.


Calculate the expected volume of the timber harvest

In the previous lesson, you calculated the area of land to be logged. The forest manager also needs to know how much timber to expect from the harvest. She provided you with the following chart for calculating the volume of timber:

Soil typeVolume equation

Excessively drained sand

y = 14.318 * ln(x) - 36.695

Well-drained sand

y = 17.373 * ln(x) - 49.959

Well-drained loamy sand

y = 14.378 * ln(x) - 36.808

Well-drained sandy loam

y = 24.572 * ln(x) - 75.969

Well-drained loam

y = 15.319 * ln(x) - 41.775

Moderately drained loam

y = 17.109 * ln(x) - 48.980

Poorly drained silt

No harvest

Volume (y) is a function of age class (x) on various soil types. Volume is determined in cords per acre.

Calculate cords per acre

To calculate how many cords of wood will be harvested, you'll need to add one more field. Then, you'll populate it based on the above equations.

  1. If necessary, open TimberHarvestPlanning.ppkx.
  2. Open the attribute table for ForestStands_NoRivers and click Add to create a new field.
  3. For Field Name and Alias, type Cords. For Data Type, choose Double.
  4. Save your changes and close the Fields table.

    The new Cords field is added to the end of the attribute table. You don't need to calculate the volume for all records, only for those stands that will be harvested.

  5. On the ribbon, on the Map tab, in the Selection group, click Select By Attributes.
  6. In the Select Layer By Attribute tool, click Add Clause and construct the clause Where TimberHarvest is not null.

    Constructing the clause Where TimberHarvest is not null in the Select Layer By Attribute tool

  7. Click Add and click Run.

    A total of 113 features are selected. Next, you'll calculate their volumes.

  8. In the Geoprocessing pane, click Back.
  9. Search for and open the Calculate Field tool.
  10. For Input Table, choose ForestStands_NoRivers. For FieldName, choose Cords. For Expression Type, choose Arcade.

    Because the equation for calculating volume is different for each soil type, you'll use a conditional expression.

  11. For Cords =, copy and paste the following code:
    if ($feature.stand_data_csv_Soil  == "well-drained loamy sand") {
    return 14.378 * Log($feature.stand_data_csv_Age_class) - 36.808
    }
    else if ($feature.stand_data_csv_Soil  == "well-drained sandy loam") {
    return 24.572 * Log($feature.stand_data_csv_Age_class) - 75.969
    }
    else if ($feature.stand_data_csv_Soil  == "well-drained loam") {
    return 15.319 * Log($feature.stand_data_csv_Age_class) - 41.775
    }
    else if ($feature.stand_data_csv_Soil  == "moderately-drained loam") {
    return 17.109 * Log($feature.stand_data_csv_Age_class) - 48.980
    }
    else {
    return 0
    }

    This expression calculates the cords per acres of each selected forest stand based on its soil type.

  12. Click Verify and click Run.

    Verify and Run buttons on the Calculate Field tool with the Cords= box populated with the conditional expression

    Values are added to the attribute table for the selected rows.

    Part of the attribute table showing one Industrial row with a value of 24.28 in the Cords field

Calculate volume

One more calculation is required. The numbers that you just calculated represent the number of cords per acre that can be expected from the harvest, based on the soil type of each forest stand. But some of these stands are larger than others. Next, you'll multiply the number of cords per acre by the number of acres to find the expected timber harvest yield.

  1. In the Calculate Field tool, clear the expression from the Cords= box.
  2. In the Cords= box, type, or copy and paste $feature.Cords * $feature.Acres.
  3. Click Run.

    In the attribute table, values in the Cords field update again for the selected rows.

    Part of the attribute table showing one Industrial row with a value of 139.23 in the Cords field

  4. At the top of the attribute table, click Clear to clear the selection.
  5. Right-click the header of the Cords field and choose Statistics.

    A new chart appears, along with a Chart Properties pane.

  6. In the Chart Properties pane, find the Sum value.

    Sum value (131,535) in a list of statistics in the Chart Properties pane

  7. Save the project.

The total yield of the planned aspen harvest is expected to be 131,535 cords of wood. The plan is to cut 5,937 acres of forest from a total of 55,333 acres of aspen in the harvest area. To find these values, you created three new fields: Acres, TimberHarvest, and Cords. You then used a variety of tools to populate those fields with the correct values, including Buffer, Erase, Calculate Field, and Calculate Geometry Attributes.

While the forest manager knew the criteria for the planned timber harvest, she needed you, as the GIS specialist, to provide answers to some basic questions: Which lands will be harvested? How much of the forest will be cut? How much wood will the harvest produce? Now that you both have these numbers, you can begin to assess the viability of the harvest plan with relation to your agency's conservation and business goals.

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