ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Detrimental Effects
Harmful effects of small mammals on forest regeneration include the harvest and
caching of cones by red squirrels (Schmidt and Shearer 1971). Unlike the seed caches
of golden-mantled ground squirrels and chipmunks, the probability of conifer seed
germination from undisturbed red squirrel cone caches is very low. However, these
cone caches are frequently a seed source for restocking programs.
Small mammals and birds consume a large percentage of conifer seed before it
germinates. Schmidt and Shearer (1971) found that small forest animals consumed 24
out of 25 mature ponderosa pine seeds. Red squirrels harvested 66 percent of the
mature cones. After seeds were dispersed, deer mice, chipmunks, and birds consumed
the equivalent of an additional 30 percent. Gashwiler (1967) found that only 12 per-
cent of Douglas-fir seed survived until the end of the germination period in Oregon.
Small mammal s continue to affect conifer regeneration after germination. Tree
seed1 ings are eaten by small mammals, birds, and ungulates (Saigo 1968). Although
pocket gophers expose the mineral soil necessary for the germination of some conifer
seed, they may eat root systems of young trees. They a1 so girdle and eat seed1 ings
below the snow surface during the winter. Tevis (1956b) found that the greatest loss
of red fir (~bies rnagnifica) seed1 in s resulted from root exposure to the air inside
pocket gopher tunnels, Hooven (1971 3 reported similar effects on ponderosa pine in
Oregon.
Young trees are subject to girdling by mice and rabbits. Red squirrels in
northwestern Montana gird1 e the tops of western larch (Lurix occidentaZis) . '
Porcupines can be very destructive to trees of all ages.
SMALL MAMMAL MANAGEMENT
Trapping, Poi sons, Insecticides, and Herbicides
Trapping and poisoning are temporary measures for reducing small mammal popu-
lations that retard conifer regeneration. These measures are not generally considered
practical, long-term solutions (Tevis 1 %6b, Hooven 1971, Smith and Aldous 1947). The
effects of these treatments persist only as long as the effort is sustained
(Tevis 1956~).
Insecticides, in sufficient concentrations, will cause martal ity in small mammals
(Morris 1970). Unfortunately, small mammals which eat insects receive disproportion-
ately high concentrations of these poisons.
The effects of herbicides on small mammal populations are generally indirect.
The kill ing of vegetation may el iminate essential food or cover required by certain
species. In a Colorado study, range treatment with 2,4-D improved the growth of
grasses and killed the forbs. This resulted in a sharp reduction in pocket gophers
that fed on forbs, and an increase in montane voles (~icrotus montanus), which prefer
close-canopied grass cover (Johnson and Hansen 1969).
'personal Communication: Curtis Halvorson, USDI, Fish and Wild1 ife Service,
Ft. Collins, Colo.; George Wilson, Glacier View Ranger Station, Columbia Falls, Mont.