Selecting proper species for successful restoration has been a major task for ecologists. Many times, seed availability and commonly used practices prevail over the use of locally adapted native species, emerging trends, and even regulations. Butte, Montana has a long history of mining and, unlike most mining towns, Butte’s urban landscape included mining operations and waste dumps that are located within the residential areas. Arsenic and other heavy metals, such as lead, can be found in high concentrations on several sites, and for that reason, the area was declared a Federal Superfund site in 1983. In order to preserve human health, a relatively quick remedial action was taken, whereby waste was capped in place and “stabilized” by agronomic grasses. The ultimate goal in this process is to restore these sites. For this reason, different trials have been performed, including establishing diversity islands to enhance native plant species within the non-native grasslands. Monitoring these islands showed that natives are not spreading out into the reclaimed areas. In our current research, we studied how the reclamation grasses influence the establishment and spread of native species. Our monitoring included, evaluating changing environmental conditions, including bare ground and litter, along transects that ran 25 meters from the center of the dispersal islands in each of the cardinal directions. We also performed greenhouse experiments with the most common reclamation grass, Agropyron cristatum, to investigate possible allelopathic effects.
Results/Conclusions
Our results show that plant species richness decreased significantly when moving away about 6 meters from the center of the diversity islands. On the other hand bare ground cover decreased and litter depth increased significantly along the transect. We found an average 7.3 cm litter depth in the reclamation grass stands, while litter depth in native control sites averaged only 2.1 cm.
Further, we found supporting evidence in our greenhouse experiments that A. cristatum is a severe limiting factor for the establishment of desired native species by creating not only a thick physical barrier but also a chemical barrier through its allelopathic potential. Leaf litter from A. cristatum had a negative effect on the growth and germination of native species. Based on our findings, traditional reclamation performed in the Butte area has had a long term negative effect on future restoration success.
Acknowledgements: The research was supported by the Butte Natural Resource Damage Restoration Council.