Monday, August 6, 2007 - 1:30 PMOOS 3-1: Key factors and constraints in restoration of native plant communities in arid, monotypic infestations of saltcedar (Tamarix spp.)
Kenneth D. Lair, Bureau of Reclamation
Critical knowledge gaps exist regarding vegetative recovery in aridic, monotypic saltcedar (Tamarix spp.) stands with no desirable understory. Formulation of revegetation strategies that provide site stabilization, resistance to further saltcedar and secondary weed infestation, and acceptable habitat values for affected wildlife species becomes particularly problematic in monotypic saltcedar stands under biological, pyric and herbicidal (i.e., non-mechanical) control scenarios. Undisturbed soil surfaces impacted by long-term saltcedar leaf litter accumulation, salinity, and standing woody biomass restrict potential for successful revegetation. Co-dominance of saltcedar and understory herbaceous invasives [e.g., Russian knapweed, Acroptilon repens (L.) DC.; perennial pepperweed, Lepidium latifolium L.; cheatgrass, Bromus tectorum L.], or replacement of saltcedar through release of these secondary invasives that become monotypic, is becoming much more prevalent across western riparian areas as narrowly-focused, saltcedar-oriented herbicidal treatments are more frequently applied. Long duration of saltcedar occupation may deplete desirable microbial communities, particularly arbuscular mycorrhizae. In research conducted on the Rio Grande, Pecos River, Colorado River and in California’s San Joaquin Valley, innovative revegetation strategies and techniques were used to address these challenges, including soil surface and rhizosphere manipulation to increase precipitation capture and retention, create micro-sites exhibiting lower salinity, and restore mycorrhizal associations; seed delivery and protection methodologies, including use of seed coating and seed safening using activated charcoal under broadcast herbicide applications. Results will be reviewed that demonstrate utility and effectiveness of techniques and materials used in meeting four primary requisites for successful restoration on these site types: a) moisture capture and conservation; b) salinity management; c) growth medium augmentation; and d) integrated approaches for saltcedar regrowth and secondary weed management.