SHORT-TERM AND LONG-TERM EFFECTS OF GOPHERS (THOMOMYS-TALPOIDES) ON SOIL ORGANIC-MATTER DYNAMICS IN ALPINE TUNDRA

Mounding activities of a burrowing rodent, the northern pocket gopher (Thomomys talpoides) on litter decomposition and soil carbon storage i n alpine tundra were studied in the Front Range of Colorado, USA. Plan t litter buried in gopher mounds lost 45% of initial mass during the f irst three months versus only 13% mass loss for surface litter. Surfac e litter decayed more rapidly during the non-growing season, and after 15 months values were 58% and 45% loss for buried and surface litter, respectively. Cumulative losses were greater for buried litter for al l dates. Placement of litter on north- or south-facing slopes did not affect decay rates. The long-term impact of chronic gopher disturbance on soil carbon storage was assessed by measuring soil carbon amounts beneath undisturbed and disturbed vegetation types. Undisturbed vegeta tion had lower bulk densities, and significantly greater depth of surf ace horizons. Amounts of soil carbon were not significantly different beneath gopher-impacted and non-impacted vegetated areas on modest slo pes. However, in areas chronically disturbed by gophers that lacked ve getation, carbon storage in the top 15 cm of soil was reduced from 8.5 kg C . m(-2) to 5.5 kg C . m(-2). Thus, chronic, frequent disturbance by gophers appears to lower the carbon content and perhaps the fertil ity of mesic and xeric alpine meadows.