EPOW - Ecology Picture of the Week

     Gopher Tunnels Aren't Simple   --->

Valley Pocket Gopher (Thomomys bottae), Family Geomyidae
Coconino National Forest, Arizona

Explanation:  Scroll right to view the full panorama of this pocket gopher family's home ... at least the array of tunnels and burrows that intersect the surface of the ground.

We are in the meadows of Hoxworth Springs, on Coconino National Forest in northern Arizona outside Flagstaff.  Elk browse here.  Plants with terrible names bloom here.  And gophers dig here.

Gopher's are one of nature's amazing ecosystem engineers.  In digging their burrows, they incorporate plant seeds into the soil, mix in organic matter, defecate and fertilize the soil, disperse seeds and spores, aerate the soil, and provide tunnels as habitats for many other species vertebrate and invertebrate alike (Stromberg and Griffin 1996).  

Their soil mounds -- characterized by an asymmetric dirt plug, unlike the symmetric shape and centrally-located plug of moles -- have been shown to have lower soil moisture and slow nitrogen mineralization rates compared to the surrounding soil, that serve to create stressful conditions for native plant establishment and growth (Kyle et al. 2008, Jones et al. 2008, Eviner and Chapin 2005, Coggins and Canover 2005b, Canals et al. 2003, Wolfe-Bellin and Maloney 2000).  This helps maintain the mounds plant-free and usable by the little rascals.  However other research has shown that pocket gophers have little to no effect on regeneration of aspen trees (Coggins and Conover 2005a).

In other studies, gopher mounds have been found to also have little effect on water infiltration rates into the soil ... but they seem to foster higher densities of earthworms (Zaitlin et al. 2007), which are another ecosystem engineer with key ecological functions that are similar to those of the gophers.

Pocket gopher burrows dug by adults tend to be longer than those dug by juveniles.  In areas of denser plant cover or more clay content of the soil, pocket gopher burrows tend to be shorter and cover less area.  I guess it's harder (more energetically costly) to dig through plant root wads and into clay than through softer soil lacking plants.  

But the overall geometry of burrow systems tends to be similar among different species of pocket gophers (Romanach et al. 2005).  

Go figure.  

Information:
     Canals, R. M., D. J. Herman, and M. K. Firestone. 2003. How disturbance by fossorial mammals alters N cycling in a California annual grassland. Ecology 84(4):875-881.
     Coggins, S. T., and M. R. Conover. 2005a. Effect of pocket gophers on aspen regeneration. Journal of Wildlife Management 69(2):752-759.
     Coggins, S. T., and M. R. Canover. 2005b. Effects of pocket gophers on the herbaceous vegetation growing in aspen meadows. Wildlife Society Bulletin 33(4):1210-1215.
     Eviner, V. T., and F. S. Chapin, III. 2005. Selective gopher disturbance influences plant species effects on nitrogen cycling. Oikos 109(1):154-166.
     Jones, C. C., C. B. Halpern, and J. Niederer. 2008. Plant succession on gopher mounds in western Cascade meadows: Consequences for species diversity and heterogeneity. American Midland Naturalist 159(2):275-286.
    Kyle, G. P., A. Kulmatiski, and K. H. Beard. 2008. Influence of pocket gopher mounds on nonnative plant establishment in a shrubsteppe ecosystem. Western North American Naturalist 68(3):374-381.
     Romanach, S. S., E. W. Seabloom, O. J. Reichman, W. E. Rogers, and G. N. Cameron. 2005. Effects of species, sex, age, and habitat on geometry of pocket gopher foraging tunnels. Journal of Mammalogy 86(4):750-756.
     Stromberg, M. R., and J. R. Griffin. 1996. Long-term patterns in coastal California grasslands in relation to cultivation, gophers, and grazing. Ecological Applications 6(4):1189-1211.
     Wolfe-Bellin, K. S., and K. A. Moloney. 2000. The effect of gopher mounds and fire on the spatial distribution and demography of a short-lived legume in tallgrass prairie. Canadian Journal of Botany 78:1299-1308.
     Zaitlin, B., M. Hayashi, and J. Clapperton. 2007. Distribution of northern pocket gopher burrows, and effects on earthworms and infiltration in a prairie landscape in Alberta, Canada. Applied Soil Ecology 37(1-2):88-94.