Notes on Forestry Uses in Aerial Photo Interpretation

21.1 Timber-Type Mapping


21.1.1 Preliminary Considerations

Timber type mapping -- delineation and identification of homogenous stands of timber or other vegetation cover on aerial photographs


Now often fits into larger ecological classification schemes

See Figure 21.1 for a typed photograph


Decisions to make:

  1. selecting the legend system to use
  2. deciding on the level or degree of refinement wanted
  3. establishing minimum area and width standards


Relates to objectives, photo scale, and scale of the final map desired

21.1.2 Typing Methods

Can map without field verification but it is risky

Field verification done to:

  1. to establish an initial identification base for the interpreter new to an area
  2. to give continual training to the interpreter familiar with an area
  3. to pick up certain classes that cannot be recognized on the photos
  4. to correct errors


Combining field checking with photo interpretation:

        Pre-typing, make type lines on the photos before going into the field. Questionable areas can be checked after typing a small area, and then type larger areas as experience gained.

        Post-typing, field reconnaissance first. Travel as many roads and paths as possible, then type the map


Critical to take advantage of local experience.

21.1.3 Systems Used in the Pacific Northwest by the U.S. Forest Service (an example)


The PNW Ecoclass Identification System

Computer compatible, links into a larger ecosystem classification system. Based on climax vegetation, not necessarily what is there.


The U.S. Forest Service PNW Forest Type Mapping System

Used for many years. Not originally computer compatible, but has been modified. Based on current use, not climax vegetation.

Forest versus Nonforest

Usually easy to distinguish. Can be some difficult cases such as grown in farmland


Commercial versus Noncommercial Forest

How to define commercial vs. noncommercial: forest characteristics, ownership, intention, etc.


Commercial Forestland Classes and Symbols

Type classifications based on species composition, tree size, age class, degree of stocking, understory conditions, and stand history. System uses a six part symbol


Species Type

Predominant species type.

On smaller scale photos need to know where various types are likely to be located.

Can have species combinations.

Requires knowledge of the forest ecology of the region.

Figures 24.5, 24.6, and 24.7 show coniferous species identification on large-scale photos in western Canada.

Figures 21.2 and 21.3 show drawings of silhouettes and aerial view of selected hardwoods and conifers.


Stand-Size Class

Tree diameter is the most common basis.

Can relate crown diameter to tree diameter. Not always a straight line relationship.

Need distinct category delineations: seedlings & saplings, pole timber, small saw timber, large mature timber, and large over-mature timber.

Good forest inventory data critical.

In stands with two distinct classes can indicate that too. See Figure 21.1 and Table 21.1


Stocking Class

Crown closure (the proportion of the area covered by tree crowns) is best measure of stocking See Figure 24.2 for scale.

Can also use a broad classification system.

For regeneration can also make a classification of stocking


Species Composition Symbols

Can recognize the composition of the stands according to agreed upon rules such as:

  1. No secondary species recognized unless it comprises at least 20% of the total existing stand.
  2. Species composition symbols follow the stocking symbol and are listed in decreasing order of abundance. Not more than three species recognized.
  3. Omit symbol when there is only one species and no associated species.



Data of Stand Origin

System shows date of origin of young stands to the nearest decade, rounding up if greater than five.


Forest Type Prefix and Condition Symbols

Used to indicate some condition describing the origination of a stand of management.

21.1 Aerial Photos and Timber Sales

Aerial photos provide input to an ongoing information management system that would be used for timber sale planning and execution. A geographic information systems (GIS) is critical for forest management. Timber sales need to be part of the overall planning process.

21.2.1 Presale

Photos previously taken can help locate sales in the off-season. Especially when field recon difficult or impossible.

Development of a cutting priority map. Part of a GIS.


Topographic features visible in stereo viewing can influence location of sales.


Initial sale compartment delineations can be made on photos.

The overview of a photo view reduces the possibility of illogical sales compartments.


Final sales boundaries must be made surveyed on the ground since photos donít show enough details.

Rough estimates of sales volume can be made from photos.

The type of logging practiced can be evaluated on photos.

Photos can be used in selective cutting operations.

Salvage sales can be estimated from photos, both in pre-damage and post-damage photos. Color infrared photos can be helpful.

21.2.2 Road Planning

Stereo views give more detail than topographic maps for planning roads.

21.2.3 During Sale

Photos can help keep the timber harvesting on track.

Photos can document progress of a sale. See Figure 21.6

21.2.4 Post-sale

Often used for small-scale coverage flown after the completion of the sale to map the cutting units and the new road system.

Sometimes special oblique photos of cutting units to plan slash-burning are done in Canada.

21.3 Forest Fire Protection

An overview


Includes fire prevention and detection. Also planning, preparation, and training activities.

Thermal scanning can penetrate smoke and is used (not the same as IR photography). See Figure 21.7

Panchromatic and regular color vertical and oblique photos used for planning.

Can also use photo mosaics

Fuel mapping another procedure using aerial photos. Fuel maps prepared from photos, ground recon, and air recon.

21.3.2 Suppression

Aerial recon including photos essential to fire fighting. Photos canít penetrate smoke. Need to use thermal imaging in combination with pre-existing aerial photos.

21.3.3 Post-Fire Analysis

Aerial photos used for damage assessment. Can do aerial photo timber inventories.

21.4 Forest Insect and Disease Detection

Canít detect all insect and disease problems from the ground. Photos can:

  1. detect the presence of damage
  2. locate the damage
  3. estimate the amount of damage
  4. Estimate relative population sizes of insects.


Color infrared film very important in this process.


Murthaís classification system foridentification and detection of damage based on the physiological changes in the foliage as detected from aerial photos:


Type I: Trees that are completely or almost completely defoliated

Type II: Trees that show some defoliation through the presence of bare branches or malformation

Type III: Trees that show the foliage as some other color that is not consistent with normal foliage color of the species involved

Type IV: Trees that show no visible sign of damage but have a deviation from the normal reflectance pattern in the nonvisible light range.