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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #88738
Title: SMALL-MAMMAL REGULATION OF VEGETATION STRUCTURE IN A TEMPERATE SAVANNA

Author
item WELTZIN, JAKE - TEXAS A&M UNIVERSITY
item ARCHER, STEVE - UNIVERSITY OF ARIZONA
item Heitschmidt, Rodney

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Study was designed to address potential role that prairie dogs may have played in regulating shifts in temperate grasslands to savanna woodlands. Results showed that such shifts can be dramatically affected by the presence of prairie dogs and associated fauna. Rate of disappearance of honey mesquite seeds and pods was up to 99 times greater on than off study colonies with ants being the primary seed removal agent and prairie dogs the primary pod removal agent. Likewise, survival of planted honey mesquite seedlings and saplings was 3-fold greater off than on colonies. However, it was found that prairie dogs do not eradicate honey mesquite; rather they simply reduce plant densities and subsequent expression. Results illustrate that wide spread eradication of prairie dogs probably dramatically increased the rate and extent of honey mesquite infestations into southwestern United States grasslands.

Technical Abstract: Times of documented increases in woody plant dominance in grasslands & savannas of North America coincide with the time of eradication of a once widespread native herbivore, the black-tailed prairie dog (Cynomys ludovicianus). We used field experiments and repeat aerial photography to demonstrate that prairie dogs, and the herbivores and granivores asso- ciated with their colonies, probably maintained grassland & savanna by preventing woody species such as Prosopis glandulosa (honey mesquite) from establishing or attaining dominance. Prosopis seed and pod disap- pearance was 3-99 times greater within prairie dog colonies. Ants were the primary agent of seed removal, whereas prairie dogs & associated vertebrates were the primary agents of pod removal. Survival of Prosopis seedlings protected from vertebrate herbivory was similar on and off prairie dog colonies (-60%), whereas survival of unprotected seedlings was 3 times greater off- than on-colony. On-colony, prairie dogs and associated herbivores girdled & destroyed all Prosopis saplings within 2 d of planting; survival of 1-yr-old seedlings was reduced by 50% after 3 mo of exposure to on-colony herbivores. Despite high levels of woody plant seed disappearance and seedling herbivory, on-colony "seedling" reserves were substantial (950 plants/ha). Thus, prairie dogs & the fauna that occur on their colonies suppressed rather than eliminated Prosopis from the colony site. Removal of prairie dogs led to rapid development of Prosopis stands. Repeat aerial photography showed that Prosopis canopy cover on a colony eradicated in 1950 (27%) increased to a level (61%) comparable to that of off-colony Prosopis stands (65%) within 23 yr.