Pocket gophers are burrowing
rodents named for their external fur-lined cheek pouches. They prefer
roots and stems of herbaceous plants, especially those found in the
early stages of forest growth and succession. Because of this preference,
seedlings become a very tempting target. Commonly gophers will prune
seedling roots and often pull the entire seedling into their burrow.
Stem clipping at ground level and girdling are also common with seedlings
less than half an inch in diameter—the most vulnerable. Damage
by pocket gophers to root systems may go unnoticed until seedlings become
discolored or tip over. Several factors have been noted that predispose
a stand to pocket gopher damage:
- current pocket gopher density
- soil suitability for burrowing
- herbaceous understory
- amount of adjacent border with preferred forage
- site preparation
Management practices to reduce pocket gopher damage include
silvicultural practices, such as minimizing disturbance of an area,
habitat manipulation, trapping, repellents, fumigation, and seedling
barriers such as Vexar tubing. However, strychnine baiting is the most
widely used method to reduce pocket gopher populations prior to planting
Baits are applied below ground to minimize impacts on
nontarget species. Scientists at the field station have conducted
several tests to determine risks to nontarget animals, such as golden-mantled
ground squirrels,yellow pine chipmunks, and weasels, that may occur
while strychnine-baiting pocket gophers. Population responses of nontarget
species, were monitored on two reforested sites in Oregon. Immediately
after baiting, ground squirrel numbers declined, however, the following
spring the population had recovered. Yellow pine chipmunk populations
were not reduced by strychnine baiting, but in fact increased in the
treated plots the following spring. This increase may reflect an invasion
of chipmunks in the absence of ground squirrels.
Predator-prey interactions are largely unknown since subterranean
predator activity is difficult to observe. Thus, artificial burrow systems
were established to investigate interactions of weasels and pocket gophers
at the field station. Weasels readily killed and consumed healthy
pocket gophers. All weasels ate strychnine-baited gopher carcasses after
72 hours, but no weasels died from secondary poisoning. Although caching
behavior of weasels may increase their exposure to secondary poisoning
of strychnine, this in turn may be minimized by the fact that the majority
of weasels only sampled carcasses
In addition, scientists sampled several insect species
to determine strychnine concentration levels and any potential risks
to insectivore species. Fly larvae and ants were found to contain high
levels of strychnine, however, little risk is posed to insectivores
due to the quantity of insects that would have to be consumed to acquire
a lethal dose. Studies by the field station have shown that
the current method of controlling pocket gopher populations, strychnine
baiting, poses relatively little risk to nontarget species.
*the above discussion is summarized from the following article
by Wendy M. Arjo. Click on the link to see the full-text of the article.
ARJO, W. M. 2003. Is it a pocket gopher or mole? Western Forester
Additional NWRC Resources
EL HANI , A., D. L. NOLTE, J. R. MASON, AND S. BULKIN. 2002. Response
of nontarget species to underground strychnine baiting for pocket gophers
in southwest Oregon. Western Journal of Applied Forestry 17:9-13. 341K
NOLTE, D. L., AND K. WAGNER. 2001. Non-target impacts of strychnine
baiting to reduce pocket gopher populations on forest lands in the United
States. Pages 59-70 in H. J. Pelz et al., editors. Advances in vertebrate
pest management. Volume 2. Filander Verlag, Furth, Germany. 505K
ENGEMAN, R. M,. AND G. W. WITMER. 2000. Integrated management tactics
for predicting and alleviating pocket gopher (Thomomys spp.)
damage to conifer reforestation plantings. Integrated Pest Management
Reviews 5:41-55. 2,041K
99-19 ENGEMAN, R. M., AND D.
L. CAMPBELL. 1999. Pocket gopher reoccupation of burrow systems following
population reduction. Crop protection 18:523-525. 443K
ENGEMAN, R. M., JR. V. G. BARNES, R. M. ANTHONY, AND H. W. KRUPA. 1998.
Damage reduction to ponderosa pine seedlings from northern pocket gophers
by vegetatoin management through grass seeding and herbicide treatment.
International Biodeterioration & Biodegradation 42(2-3):115-121.
97-25 ENGEMAN, R. E., V. G. JR. BARNES, R. M. ANTHONY, AND H. W. KRUPA.
1997. Effect of vegetation management for reducing damage to lodgepole
pine seedlings from northern pocket gophers. Crop Protection 16(5):407-410.
92-33 CAMPBELL, D. L., J. P. FARLEY, P. L. HEGDAL, R. M. ENGEMAN, AND
H. W. KRUPA. 1992. Field efficacy evaluation of diphacinone paraffin
bait blocks and strychnine oat groats for control of forest pocket gophers
(Thomomys spp.). Proceedings of the Vertebrate Pest Conference
91-59 FARLEY, J. P., AND D. L. CAMPBELL. 1991. ABSTRACT. Movement of
radio transmittered paraffin diphacinone bait blocks by forest pocket
gophers (Thomomys spp.). Northwest Science 65(2):34.
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