PS 65-89
Ecological regular pattern formation of Alpine Avens (Geum rossii) and the Northern Pocket Gopher (Thomomys talpoides) disturbance on Pikes Peak, Colorado
Regular pattern formation of strikingly tall, dense tundra vegetation patches primarily composed of Alpine Avens (Geum rossii) has been observed in aerial photographs on the tundra of Pikes Peak. We focused on understanding which processes contribute to the patch formation and maintenance. According to the theory of regular patch formation, patches are formed and maintained by a combination of short-distance facilitation and long-distance inhibition. First, we wanted to describe the vegetation composition of the patches and open-tundra. Then our questions were “Are these patches created and maintained by activities of Northern Pocket Gophers (Thomomys talpoides) or are they determined by biogeochemical mechanisms?”
To address these questions we examined the vegetation composition, height, and soil chemistry along 15m transects through 8 randomly chosen patches. Data on species composition, vegetation height, microtopography, and soil parameters such as soil moisture, plant and soil carbon-to-nitrogen ratios, and nitrogen (N) mineralization rates were collected along each transect. Each parameter was compared in areas within the patches to the open tundra. To examine the effect of gophers, we examined the large-scale spatial distribution of the avens patches relative to each other, surface gopher disturbance in relation to individual avens patches, and the underground characteristics of the tundra below the patches.
Results/Conclusions
The species composition of the patch compared to the outside tundra significantly differed. The patches were dominated by forbs (Geum rossii and Bistorta bistortoides) while grasses and lichens characterized the open tundra. Interestingly, all dominant patch species were subdominant in the open tundra, and open tundra species were subdominant in patches.
The dominant patch species were taller within the patch (8.21cm) compared to the open tundra (4.24cm), approximately 2 times higher (t=-15.78; df=556.499; p<0.0005). Open tundra-dominant species were shorter inside the patch compared to the outside. The microtopography showed that the elevation within the patch was significantly higher, between 5-20cm (t=14.256; df=693.156; p<0.0005). Soil inside of the mat was found to be on average 0.0375ml/g soil drier than soil outside the mat when using a paired t-test for all 8 transects (t=-4.160; df=7; p=0.004). Soil C: N ratios were significantly lower inside the mat compared to the outside (t=-3.040; df=4; p=0.038), suggesting a more fertile environment. Plant C:N ratios had no significant difference between individuals inside and outside of the mat (t=-0.159; df=2; p=0.888). Based on Ripley’s K analysis, the gopher disturbance was significantly clumped into and around the patches.