flesh, and are kept there by the barbs (Kings- 
bury 1964). The long, barbed awns of Hor- 
deum jubatum make it one of the worst plants 
for causing mechanical injury to the eyes and 
mouth of range livestock as well as of elk, 
deer, and antelope (USDA Forest Service 
1937). Occasionally, the awns of the ubiquitous 
Bromus tectorum work into the tongue and 
soft mouth tissue to cause inflammation (Dur- 
rell et al. 1950). 
The spiny covering around the seeds of Cen- 
chrus pauciflorus has caused hoof irritation 
(Durrell et al. 1950), and the spiny fruits 
of Tribulus terrestris can cause external and 
internal injuries if inadvertently fed in hay 
(Muenscher 1947). 
The stiff spines and barbs on the stems of 
certain range plants are at least potentially in- 
jurious to livestock. Such plants include Opun- 
tia spp. (Muenscher 1947) and Rubus macrope- 
talus (Kingsbury 1964). The latter species is 
considered good browse for stock in western 
Washington and Oregon (U.S. Forest Service 
1937), but the thorny stems occasionally be- 
come lodged in the nasal passages of cattle 
(Kingsbury 1964). 
A few range plants have fibrous or hairy 
characteristics that sometimes cause trouble 
when eaten. Verbascum thapsus and Eremo- 
carpus setigerus, for example, are covered with 
dense mats of hair that can form solid, indiges- 
tible balls in the digestive tract, particularly of 
sheep (Muenscher 1947). The fibers in Yucca 
spp. occasionally cause the same _ problem 
(Stoddart and Smith 1955). 
Deterrents 
Whereas some structural features actually in- 
jure grazing animals, others merely discourage 
use. Various species of Opunita are usually 
avoided because of their numerous’ sharp 
spines. When these are removed, the fleshy 
stems are readily eaten by both sheep and cat- 
tle (U.S. Forest Serv. 1937). On large areas, 
such species as Opuntia arborescens also form 
a barrier to the use of palatable forage grow- 
ing with it. Spines and barbs of other range 
plants no doubt serve equally as barriers to 
livestock grazing. 
The overall coarseness of plants and a high 
proportion of stems to leaves are two more 
structural deterrents to use that might be con- 
sidered. If given the opportunity, grazing ani- 
mals are highly selective of what they eat. 
Rank, harsh vegetation, as well as that with a 
high crude fiber content, is generally avoided 
(Stoddart and Smith 1955; Joint Committee 
A.S.A. et al. 1962). Sheep are known to prefer 
leaves over stems (Cook et al. 1948). Grasses 
that tend to retain dry flower stalks from the 
previous growing season are preferred less 
than those that do not. Livestock will avoid 
this coarse, dry material as long as other more 
desirable forage is available. 
PHYSIOLOGICAL ATTRIBUTES 
A number of physiological attributes of 
plants are considered undesirable from the 
standpoint of range management. These are 
not usually considered as being in the same 
realm as poisonous or physically damaging 
properties. Their influence is more indirect and 
more subtle. However, the value of range 
plants for forage production is greatly affected 
by their physiological characteristics. 
As an example, much of our western range 
is subject to summer drought so intense that 
many of the species become dormant and dry. 
The inability of a species to become summer- 
dormant may decrease its resistance to damage 
from grazing. Stipa comata, which does not be- 
come dormant during the hot summer months 
in southern Idaho, is more susceptible to her- 
bage removal in the summer than is Sitanion 
hystrix, which does become dormant (Wright 
1967). Regrowth in late summer and fall fol- 
lowing summer dormancy depends not only 
upon rainfall but upon the plant’s ability to 
break dormancy and to produce new leaves. 
Species physiologically unable to do this are 
probably less desirable on such ranges than 
those that do have substantial regrowth. In 
this regard, perennial grasses appear superior 
to forbs. 
Changes in nutrient content of herbage dur- 
ing the growing season and during dormancy 
are important considerations in evaluating 
range species. Nutrient content generally de- 
creases as the growing season advances and 
plants mature. Some range grasses in North 
Dakota lose more than 70 percent of their pro- 
tein by the end of summer (Whitman et al. 
1951). However, the amount of decrease is at 
least partly an inherent characteristic that 
varies among species. At a time when other 
prairiegrasses become very low in protein, the 
protein content of Boutelouwa gracilis has been 
known to increase (Williams 1953). Usually 
the nutrient decrease is most pronounced in 
forbs and is least noticeable in shrubs. Al- 
though the nutrient content of shrubs is gener- 
ally less than that of grasses and forbs early in 
the growing season, by fall the reverse is true 
—especially with regard to protein level be- 
cause of the differences in rate of loss (Blais- 
dell et al. 1952; Oecelberg 1956). Seasonal 
changes of nutrient content in shrubs are 
greater in deciduous species than in evergreen 
species (Short et al. 1966). 
Nutrient content, then, varies not only be- 
tween species, but species differ in their ability 
to retain nutrients. Physiological characteris- 
tics that cause plants to rapidly lose nutrients 
are undesirable. Attributes that permit plants 
67 
