Introduction

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Periodic aerial surveys of the pine timberlands of the South provide the primary means for early detection of southern pine beetle (SPB) outbreaks. During warm months, beetle-infested trees become visible from the air within 3-6 weeks after attack as their crowns turn from green to yellow and eventually to orange, red, and brown (see cover). Early detection of new infestations is the first step in controlling SPB and in reducing timber losses.

This handbook explains how to plan and conduct an aerial sketchmap survey to detect new SPB infestations (spots) throughout the beetle's range in the southern United States. It is designed to supplement USDA Agriculture Handbook 560 entitled "An Aerial Observer's Guide to Recognizing and Reporting Southern Pine Beetle Spots" (Billings and Doggett 1980).

Purpose of an Aerial Detection Survey

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The purpose of an aerial detection survey is to accurately locate infestations, to determine their relative size and number, and to evaluate the need for control. This is accomplished for SPB by conducting periodic flights over pine forests in small, fixed-wing aircraft and plotting suspected SPB spots (groups of dead and dying pine trees) onto maps or aerial photographs. Once detected from the air, suspected spots are visited on the ground to confirm the causal agent and assess the need and priority for control (Billings and Pase 1979).

In most commercial forest situations, expanding SPB spots should be controlled to avoid additional timber losses, using one of the approved control methods of salvage, cut-and-leave, chemical sprays, or pile-and-burn (Swain and Remion 1981).

Planning an Aerial Detection Survey

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Aircraft

Figure1. Cessna 182, a four place, high-wing monoplane commonly used for aerial detection surveys. (Texas Forest Service photo)

The success of an aerial detection survey depends largely on preflight preparation and planning as well as the skill and dedication of the aerial observers.

Single-engine, high-wing aircraft are commonly used for aerial detection surveys. High-wing aircraft offer better visibility than low-wing airplanes. Four and six-place aircraft are preferred to two-place airplanes. Survey aircraft should be capable of slow flight since most detection surveys are flown at 90-100 mph. Survey aircraft should be able to take off and land on relatively short runways and carry sufficient fuel for at least 5 hours of flight. The most common survey aircraft are Cessna Aircraft Corporation² models 172, 182, 185, 206, and 210 (fig. 1).

Equipment

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Equipment used in aerial detection surveys should be assembled in kit form and taken on every flight. Suggested equipment includes the following:

Necessary

1. Maps (or photos) of area to be flown
2. Colored pencils or grease pencils
3. Air sickness sack or canister (coffee can)

Optional

1. 35 mm camera with color film
2. Small tape recorder
3. Radio for ground communications
4. Electronic navigational unit
5. Sunglasses (yellow lenses preferred)
6. Motion sickness remedy

Flight Maps and Plans

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Appropriately scaled flight maps should be chosen to completely cover the area to be flown. Aerial photographs, photo index maps, or photo mosaics also may be used. Choosing an adequate scale is particularly important. A large-scale map such as a 7 1/2-minute quadrangle map (scale = 1:24,000) will allow more accurate plotting but will cover a smaller area than a 15-minute quadrangle map (scale = 1:62,500). Thus, four 7 1/2-minute quadrangle maps will be required for the same size area covered by one 15-minute quadrangle map. Many large scale maps, however, may present a handling problem in the plane.

Up-to-date maps that show identifiable landmarks (roads, lakes, power lines, etc.), as well as current features such as forest plantations and agricultural fields, are particularly helpful for accurate plotting.

Figure 2. Portion of a 15-minute quadrangle map showing parallel 2 1/2-mile flight lines and locations of suspected SPB infestations. The symbol 20/1 indicates a newly detected spot having 20 visibly infested trees and a priority 1 for ground checking. (Texas Forest Service photo)

Parallel flight lines (except for very mountainous terrain) should be drawn on maps prior to the detection flight (fig. 2). Each flight line should start and end at a recognizable landmark, such as a road intersection, river, or power line. Depending on the intensity of the survey, flight lines should be drawn at 1-, 2 1/2-, or 5-mile intervals in either a north/ south (N/S) or east/west (E/W) direction. The distance between flight lines and maximum scanning distance per observer will determine the percent coverage (table I, page 8). If flight lines are set at intervals of 2 1/2 miles, each observer would be responsible for detecting infestations out to a lateral distance of 1 1/4 miles to obtain 100 percent coverage of the survey area.

If aerial photographs (scale = 1:15,840 or 1:20,000) are used, no flight lines need to be drawn. The plane simply flies down the center of each sequential photo as the observers scan up to 1 1/4 miles (or half the photo width) on each side of the plane.

The accuracy of sketchmapping surveys (number of spots overlooked) will depend on various factors, including visibility, size of spots to be detected, flying altitude, aircraft speed, and flight line interval. When detecting small spots (one to four trees), the width of strip each observer scans should be restricted to 1/2 mile (flight lines 1 mile apart). If only spots with five or more trees are plotted, a 1- or 1 1/4-mile-wide strip can be observed from each side of the plane (flight lines 2 to 2 1/2 miles apart) (table 1). During periods of poor visibility or when beetle infestation levels are high, it is best to fly lines 1 to 2 miles apart to assure complete coverage. In mountainous terrain, it may be best to fly along contours rather than to follow parallel flight lines.

The space in survey aircraft is limited. Thus, an efficient way to handle bulky survey maps or aerial photo files should be developed in advance of the survey flight. Large maps can be folded once parallel to the flight lines and then fanfolded into smaller sections perpendicular to the flight lines. This method has certain disadvantages, however. Flight lines laid out near the lengthwise fold are difficult to follow unless the maps are refolded. Also, if used for numerous surveys, maps may become worn and information lost at each fold.

Another approach is to cut the survey maps into strips of a convenient size. Strips covering the planned flight route are pasted end-to-end and deployed on a map-rolling device (fig. 3). The observer winds the roller knobs to advance the strip and plots the desired information on the flat writing surface.

Prior to the second and for subsequent detection flights in a given year, flight maps should be updated to show the current status of all previously detected spots. By marking which spots have recently been reported as controlled or inactive, the observer can check these spots during the aerial survey to determine whether there are any reinfestations (breakouts). Suggested symbols for use on SPB flight maps are listed in table 2, shown on page 10.

Visual orientation over flat, poorly defined terrain can be difficult. Accurate navigation can be assured by installing and using electronic navigation systems in the survey aircraft. The most dependable and useful of these systems is portable and can be easily installed in different aircraft (Dull 1980).

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Figure 3. A map-rolling device, specifically designed for long straight flight lines over flat terrain, aids the handling of survey maps during aerial detection surveys (Texas Forest Service photo).

Frequency of Flights

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The frequency and timing of aerial detection flights will depend upon several factors, including the season of the year, level of SPB activity, and geographic location. In the western gulf coastal States, SPB may be active throughout the year, but the rate of crown discoloration and the abundance of new spots vary seasonally. Most new infestations become visible to aerial observers between April and September (fig. 4A). Accordingly, detection flights may begin as early as April and continue at intervals of 4 to 6 weeks until hardwood foliage begins to change color in the fall.

The detection of new spots is hampered during early spring months when hardwood trees are leafing out and again in the fall when the foliage of hardwood and cypress trees discolors. Also, new spots are small, scattered, and difficult to detect from December through March. Thus, peak detection typically occurs during May, June, and July. During outbreak years, however, a midwinter detection flight may be useful to locate large overwintering infestations or new spots that were initiated during the previous fall.

In the Atlantic Coastal Plain and Piedmont regions of North Carolina, South Carolina, Virginia, and Tennessee, peak detection occurs in late summer. In these States, one summer detection flight near the end of June and a second in late September are usually sufficient (fig. 4B, page 11). A midwinter flight also is useful during outbreak years to pinpoint the location of overwintering beetle populations. Spots detected in this winter flight should be controlled prior to beetle dispersal in the spring.

Table 2. - Suggested symbols to use on SPB flight maps

¹Some organizations prefer to use a square symbol to indicate that a spot's location may not be accurately plotted.

Figure 4. Seasonal detection patterns for southern pine beetle infestations in gulf coastal areas (A) and southeastern, Piedmont and mountain areas (B). Arrows indicate recommended (I) and optional (I) flight dates for aerial surveys.

Attributes of an Effective Aerial Observer

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A trained aerial observer is the key to a successful SPB detection survey. Attributes of an aerial observer should include:

1. A working knowledge of SPB and its infestation characteristics at different seasons.
2. An ability to recognize SPB infestations from the air and to distinguish them from damage due to other causes (see Billings and Doggett 1980).
3. A willingness to fly and not be abnormally subject to motion sickness.
4. Good eyesight and normal color perception (not color blind).
5. An ability to read maps and to orient between air and ground. Local knowledge of the area to be flown is particularly useful for accurate plotting.
6. At least 50 hours in the air and similar experience on the ground participating in routine detection and evaluation surveys.

Training is essential to prepare new workers to be effective aerial observers. Training sessions should include instructions on how to use maps and how to recognize and evaluate SPB spots from the air. Color slides showing examples of SPB spots at different times of the year and in different stages of development provide effective training aids. But proficiency at aerial detection must ultimately come from actual experience in the air.

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The number of observers required for a detection survey may vary from one to three. Over flat terrain, a common arrangement is to use three observers. One observer sits in the right front seat of the plane and acts as a navigator to keep the pilot on course. From the rear seat, the other two observers detect and map those infestations visible on their respective sides of the aircraft. If only two observers are used, either observer can inform the pilot if the plane strays from the designated flight line. For training purposes, a trainee/observer may be seated in the right rear seat behind an experienced navigator/observer. In this manner, comparisons can be made of plotting accuracy between an experienced observer and a trainee.

Scheduling Detection Flights

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Weather can greatly affect survey efficiency and accuracy. Cloudy, overcast conditions reduce visibility. Turbulent conditions cause physical discomfort, often resulting in disorientation. The pilot should avoid flying through clouds and during thunderstorms.

Surveys should be scheduled for clear days with low wind velocities and minimal haze, if possible. They should be conducted between 9:00 a.m. and 3:00 p.m. to avoid long shadows. To reduce observer fatigue, survey flights should last no more than 4 consecutive hours without landing. Two shorter flights on consecutive days, for example, are likely to be more effective than one long, uninterrupted flight.

Flight Altitude

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For SPB detection surveys, the altitude of flight above ground will depend on weather conditions and the size of infestations to be reported. If visibility is good, an altitude of 1500-3000 feet is preferred for detecting and evaluating multiple-tree infestations containing 10 or more trees. Under overcast or partially cloudy conditions or if smaller infestations (less than 10 trees) are to be recorded, flight altitudes will need to range from 1000-1500 feet above the ground.

Lower flight altitudes, however, make it more difficult to pick out key landmarks and maintain orientation. Also, historical records in Texas show that small infestations (one to five trees) are soon vacated by SPB or are caused by agents other than SPB. In contrast, spots most likely to expand and require control tend to have 10 or more trees at detection, particularly in mid- to late summer months. Therefore, the lower size limit of infestations to be plotted (detection threshold) is often set at 10 trees. These "high priority" spots are detectable from higher altitudes.

Plotting SPB Infestations

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When areas of dead or dying pine trees are located from the air, the observer should:

1. decide whether or not the infestation is likely to be an SPB spot.
2. check the map to see whether it has been plotted on an earlier flight.
3. look for signs of recent beetle activity (yellow-crowned trees except during winter months).
4. estimate the relative size of the spot (total number of dead and/or infested trees) and record this estimate on the map next to the spot location.
5. assign a ground check priority to the spot and record this on the map.

If the spot appears to be an SPB infestation, meets the minimum spot size to be recorded (detection threshold), and contains signs of recent attacks, the location of the spot should be plotted on the map as accurately as possible using an appropriate symbol (table 2, page 10). The observer should take note of visible landmarks (road intersections, clearings, powerlines, etc.) to assure accurate plotting. During spring, summer, and fall surveys, the presence of pines with fading (yellow) crowns indicates spots with recent beetle activity and those most likely to expand. During winter and early spring months, yellow-crowned trees may not be visible and a large portion of the beetle population will reside in red or bare-crowned trees.

An estimate of the relative size of the spot should be listed next to the spot location on the map (fig. 2). Two methods exist for estimating spot size. One is to record the total number of dead and dying trees which is indicative of the amount of salvageable timber. The other method is to note only those trees with red and yellow crowns but not those having lost most or all of their foliage. This latter method provides a better measure of trees that still contain beetles. (Admittedly, during summer months most beetles will have emerged from trees with red crowns. However, inclusion of red-crowned trees in the spot size estimate will help to compensate for those recently infested trees that still may have green crowns. Such green-crowned trees may harbor a sizeable portion of the beetle population in the spot, but are indistinguishable from unattached trees to the aerial observer.)

Before selecting one method for estimating spot size over the other, check the survey policy of your organization. And be sure to inform the ground crews of which system you use. Finally, a priority for ground checking is assigned to the spot (fig. 2, page 7). Details on how to recognize SPB spots and set ground check priorities from the air are given in USDA Agriculture Handbook 560 (Billings and Doggett 1980).

To accurately determine the location of the spot, it often is necessary to depart from the N/S or F/W flight line and circle the spot. Once the spot is mapped correctly, the aircraft should be returned to the flight line and the survey resumed. The need for accurate plotting cannot be overemphasized. A misplotted spot can cause ground crews to waste many hours searching for a spot in the wrong area.

The same set of maps should be used throughout the season. This way, previously detected spots will not be reported more than once. Furthermore, spots reported as controlled or inactive can be observed for signs of renewed beetle activity (breakouts) in later flights. Also, spots plotted on maps from previous flights may serve as landmarks in large roadless areas.

A pencil with a different color lead should be used for each flight to avoid confusion among different detection flights. For each survey flight, the flight map should be noted to indicate flight date, color of pencil used to plot spots, names of observers, and any unusual conditions (bumpy, hazy, etc.).

Reporting and Evaluating Detection Information

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Once a detection flight has been completed, the spot locations, numbers of affected trees in each spot, and other pertinent information should be provided to ground crews. It is recommended that inexperienced aerial observers also participate in ground check activities to share in the frustrations associated with poorly plotted spots.

To aid interpretation and evaluation, survey results should be summarized in table form by spot size for each area flown. The summary should show number of spots in increasing spot size classes, as shown in table 3. If a 10-tree detection threshold is used, common spot size categories would be 10, 11-20, 21-50, 51 + trees. Particular attention should be paid to spots with more than 20 actively infested trees, since these are likely to account for a majority of the timber losses if left uncontrolled. One significant statistic obtained from the aerial survey is the number of spots (or infested trees) per 1000 acres of host type. This statistic is useful for evaluation of the level of SPB activity in an area, for comparison between areas, or for comparison of number of spots between detection flights over the same area. In general, when the SPB population level exceeds one spot per 1000 acres of host type, beetle activity is considered to have reached an outbreak level.

Table 3.—Suggested format for summarizing aerial survey data from a single SPB defection flight

Late Season Evaluation Flight

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During years when beetle populations are high, it may be useful to conduct a late season evaluation flight just prior to hardwood foliage fade. The main purpose of this survey is to revisit all previously detected spots that have yet to be reported as inactive or controlled. Each spot should be reevaluated for evidence of recent beetle activity. If needed, a new spot size estimate and ground check priority should be assigned to each spot.

In many cases, spots which appeared active at first detection may no longer contain yellow-crowned trees by the end of the summer. Such spots can be assigned a low ground check priority, or considered as inactive. In contrast, other spots that appeared small in early summer may have expanded to considerable size by September, requiring urgent attention (Billings 1979). Methods for updating spot size and priority data on flight maps are shown in table 2.

Checklist

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1. Decide on area to be flown.
2. Delineate parallel flight lines at equidistant intervals (N/S or E/W) on maps of appropriate scale and prepare maps for convenient use in the aircraft.
3. Prior to each flight, update flight maps to show previously detected spots that have recently been controlled or found to be inactive.
4. Schedule flight for good, clear weather during the appropriate season.
5. Request an experienced pilot and proper aircraft and schedule a preflight briefing so the pilot and navigator clearly understand where to go and what will be done.
6. Limit duration of each flight to no more than 4 hours.
7. Stay on flight lines, except to circle suspected spots when needed to assure accurate plotting.
8. Record location of detected spots on map, together with estimate of spot size and priority for ground checking.
9. Take advantage of flight to inspect previously controlled spots for breakouts or to reevaluate uncontrolled spots; also, replot any spots from previous flight that ground crews were unable to locate.
10. Report detection information to ground crews promptly.

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Selected References

Issued June 1984

Modified for Internet August 1998