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REPORT OF COMMISSION VII 35 
States for the determination of kinds and areas of croplands by various federal 
agencies. They may be used as contact prints or as enlargements. In areas of 
relatively flat topography, the photos may be used as maps, and approximate 
acreages of various ownerships and various kinds of crops are determined from 
them by direct measurement. No extensive reliance can be put on interpretation 
of annual or short rotation crops, because kinds and acreages of crops can change 
radically in a short period of time. Periodic repeat photography is required in 
any event to keep agricultural data more or less current, and field inspection is 
required to obtain much of therequired information. Even when current photog- 
raphy is available field inspection, rather than photo-interpretation usually 
is relied upon to determine the type of crop. 
Aerial photos can reveal reliable information on patterns of agricultural 
land use. Newly cleared areas can be identified by windrowed brush, or residual 
stumps, or other evidence. Abandoned fields show invasions of trees or shrubs 
or weedy growths. The practice of clearing, cropping for a few years, and then 
abandoning—which is so common on the infertile tropical soils—leaves a dis- 
tinctive pattern of rectangular areas of different age classes of re-invading 
natural vegetation. 
Seaweed is an unusual crop which is harvested throughout the world. As 
with cultivated agricultural crops, seaweed can be inventoried with the aid of 
aerial photographs. Work done in Nova Scotia (Cameron 1950) showed that 
rapid and economical surveys could be made of seaweed beds. Interpretation 
of certain weed species was possible, but detailed differentiation of weed types, 
and determination of tonnage per square mile had to be done by sampling of 
the photo types from a boat. Both standard and color Sonne photography were 
used, and the color was considered superior. 
Range inventories determine the kinds and amounts of forage available to 
livestock on non-cultivated range and pasture lands. Forage generally consists 
of native grasses and other herbaceous plants, but also includes browse provided 
by shrubs and trees. Range surveyors make estimates of the carrying capacities 
of fields or other management units by inspecting, on the ground, the species 
and densities of distinctive vegetation types. The palatability of each kind of 
vegetation to a given class of livestock is considered, as well as the percentage of 
each kind which can be safely utilized without deteriorating the range. The 
primary end result of the inventory is a summary, by units of area, of the num- 
ber of animals of a given kind or kinds which can be grazed over a certain period 
of time. 
Because range survey techniques require information on species and densities 
of herbaceous vegetation, aerial photos must be supplemented by considerable 
ground work. The photos, however, can be of great assistance by permitting 
preparation of an accurate vegetation type map. Grassland and other types 
obviously capable of providing forage can be identified and classified to any 
desired intensity within the limitations of the photographs and the interpreter's 
skill. Some standard types, for example, might include grassland (annual); 
grassland (perennial); weeds; woodland-grass (savannah); desert browse; wet 
meadow; etc. Likewise, waste areas incapable of producing forage can be sepa- 
rated out from consideration of the range resource. Such unproductive types 
might include barren areas, such as sand dunes or talus slopes and inaccessible 
or extremely rocky or precipitous areas. After the photos have been classified 
as to range types, the range surveyor can visit the types on the ground to obtain 
species and density information. 
Range types may be delineated directly on contact prints, or on enlarge- 
ments. Many boundaries can be drawn without the aid of a stereoscope, espe-