Gravel mine reclamation on the shortgrass steppe: Current status and assessment of competition

Background/Question/Methods

Restoration of degraded landscapes is an important process to return ecosystems disturbed by human caused activities such as agriculture, oil extraction, mining and road building back to a level of health, sustainability and integrity.  The State of Colorado does not evaluate restoration success based on community function or compare a reclaimed site to an intact functional ecosystem of similar type, but such comparisons are recommended.  This study compares the vegetation community structure of the Poudre Learning Center, a site being reclaimed from gravel mining, to two reference sites on the Pawnee National Grasslands.  A consequence of gravel mining is susceptibility to invasion by noxious weeds, and invasibility may be affected by functionally similar species or resident and invading species.  Of special interest were the noxious weeds Bromus tectorum, found predominantly on the mined site, and Cirsium arvensis, ubiquitous on both sites.  To investigate if native plants are efficacious in mitigating the prolific growth of noxious weeds when functionally similar, a greenhouse study was conducted targeting Cirsium arvensis and Bromus tectorum.  Plants were grown with functionally equivalent native plants, with functionally different native plants and with themselves at three density levels (1X1, 2X2, and 3X3).

Results/Conclusions

Initial analysis using MRPP comparing species composition indicates statistical differences between the mined site and the reference sites.  The mined site had the following as significant indicator species: Bromus tectorum, Convolvulus arvensis, and Elymus smithii as significant indicator species while the reference sites were indicated by Bouteloua gracilis, Carex stenophylla, Equisetum leavigatum, and Ratibida columnifera. For the greenhouse experiment, an ANOVA comparing number of leaves, longest leaf, plant height and above and below ground biomass indicated no significant competition or density effects for either Bromus tectorum or Cirsium arvensis.  Thus, competition from functionally equivalent species was not different than competition from functionally different species and cannot help explain the invasibility of reclaimed shortgrass steppe communities.