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Photo points


Uses:

Monitoring the growth, condition, and survival of individual trees or groups of trees over extended time intervals.

Materials needed:

For ground-level plots: For aerial plots:

Notes:

A photo point is a location from which a specific field of view can be relocated and rephotographed repeatedly. Changes in the tree population at a given site are easily seen by examining a series of photographs taken from a photo point over a period of years. If images are digitized, graphics software can be used to scale photos to match and even produce animated "time lapse" presentations.

Ground level photo point

There are two major considerations in establishing an effective photo point. First, trees and other features which are to be documented should be clearly visible at the time the original photo is taken as well as in future photographs. Try to situate the camera well away from vegetation that might subsequently block the view. Also, avoid views across vacant lots or areas where subsequent construction would interfere with the image. Perspective should also be considered in composing photos. For example, empty planting spaces along a street are easier to see in a view that looks across rather than down a street.

Second, it is desirable to duplicate the original camera view in later photographs as precisely as possible. The best match will be obtained if the camera location and angle, and the time of day and time of year are duplicated in later photographs. Take careful notes at the time that the original photo is taken. The location of the camera can be referenced to permanent landmarks, such as property lines, intersections, fire hydrants, and the like. A survey marker or other permanent monument may be installed at the camera location to facilitate relocation. A compass bearing should be taken to establish the direction of the photo in the horizontal plane (be sure to note whether the bearing is corrected for declination). Information about the height of the camera and its angle above or below level should be noted. The type of lens, focal length setting (if a zoom lens is used), date, and photographer should also be noted for future reference.

In some cases, historical photographs may already be available, but the actual location of the camera is unknown. With a copy of the photo in hand, it is often possible to establish a new photo point that closely matches the original angle. This may be easier to accomplish using a camera with a zoom lens. Once the new point is established, the data described above for new points should be noted so that subsequent photos can be taken from the same point. Ground level photo points are limited by the area that can be effectively shown in each photo. They are likely to be less effective for dense stands of trees and areas with many tall buildings. In some cases, these limitations can be overcome by getting a higher vantage point, such as from the top of a hill or building. In other situations, aerial photo points may be necessary to allow adequate monitoring.

One application of this technique would be for monitoring the effectiveness of tree protection and preservation during development or new construction. Well-situated photographs taken before, during, and after construction can be used to document and monitor both short and long-term impacts. Trees damaged during construction and development may not show serious symptoms until five or ten years later. Strategically situated photo points can clearly show whether protected trees have subsequently declined or been removed.

Pope Valley, CA 1989.

 

Pope Valley, CA 1995. Note hillside clearing, decline of large valley oaks on valley floor at left, and growth of oak seedlings protected from grazing.

 

Aerial photo points

An aerial photo point is simply a variation of the use of aerial photography described under Photogrammetry and remote sensing techniques. Permanent plots are established based on easily recognizable features such as roads, buildings, utility corridors, or landforms, so that the same area can be compared in successive photographs. Photographs should be printed at the same scale to facilitate direct comparisons. Transparent overlays can then be used to pinpoint the location of specific trees in different photographs.


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