are required by plants and absorbed by the roots as divalent ions. , In some
instances, the low Ca concentration may result in a nutrient deficiency. In
other instances, the similar size of these ions results in.the plants not
being able to selectively absorb enough Ca without suffering Mg toxicity. One
of the proposed mechanisms by which plants may be able to adapt to serpentine
soils is an ability to preferentially absorb Ca over Mg (Walker et al., 1954).
Serpentine soils are also quite high in Cr, Ni, and Co. These
elements are not known to be required in plant nutrition, and in fact, rank as
among the most toxic of all elements to plants even though they are nearly
insoluble in soil solutions (Brooks, 1972). In addition, serpentine soils are
low in plant nutrients such as Nitrogen, potassium, and molybdenum (Walker,
1954). Finally, serpentine soils tend to be drier than adjacent non-serpentine
sites on account of shallow development and gravelly textures.
In most situations, it is likely that it is some combination of
these factors that accounts for the effect of serpentine on local vegetation.
Variation in the bulk composition of the parent material can likely result in
an increased or decreased effect on the vegetation. Where the content of
Cr, Ni, or Co is unusually high, for example, the adverse effect might be
expected to increase. Species compositional differences in the natural vegeta-
tion with serpentine areas may provide valuable clues in mineral exploration.
The authors are currently involved in an investigation of several
serpentine areas near the west coast of the United States. We are combining
ground based examination of vegetation, rock types, and soils with the use of
multispectral airborne scanner imagery. Our interest is to evaluate the
utility of such imagery to identify and map areas of serpentine and to detect
variations within the serpentine that may have exploration significance. This
paper describes preliminary results involving the delineation of serpentine
areas.
SOUTHWEST OREGON STUDY AREA
The southwest Oregon study area is located within the Siskiyou
Mountains adjacent to and north of the California and Oregon border and
approximately 40 km (on average) from the Pacific Ocean. The region is known
for its unique vegetation and geology. A wide diversity of vegetation types
has been recognized as occurring in relation to the steep climatic gradients
and diverse parent materials of the region. Elevations within the study area
range from 400m to over 1500m. The climate is strongly influenced by maritime
áir from the Pacific Ocean and has cool winters (mean January temperature is
5 degrees C) which are characterized by abundant precipitation (over 200. cm
annually) and mild dry summers (the mean July temperature is 20 degrees C).
The study area's vegetation follows the distribution of vegetation
zones as described by Franklin and Dyrness (in Mouat et al., in press). This
zonal outline follows:
Zone Dominant species or genera
Pine (Pinus sp.), Oak (Quercus sp.)
Douglas fir (Pseudotsuga menziesii)
Interior Valley Zone
Mixed-Evergreen Zone Douglas fir - sclerophyll shrubs
Mixed Conifer Zone Pine, Douglas fir, Incense cedar (Calocedrus
decurrens)
White fir Zone White fir (Abies concolor)
AM M MM t 9 À M M M a Ü—À IM Ó M nM M — —— MÀ m mm tl
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The study a:
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grassland.
