Eric Hazelton

ABSTRACT By formalizing reciprocal relationships between practitioners and researchers, both restoration and science can be advanced. We use large-scale experimental restorations of Phragmites australis-dominated wetlands on the Great Salt Lake to demonstrate how science and restoration practice can be improved by (1) collaborating with diverse wetland managers to evaluate questions related to P. australis control; (2) providing an interactive mapping website of current P. australis distribution to bring research results to practitioners; and (3) how recent research findings regarding mode of spread of P. australis is being used to reassess current control techniques.

Invasions are dynamic as both the invading organism and the invaded ecosystem change. Intrinsic changes to the invader (invasion process) can involve population level genetic and reproductive changes. Extrinsic changes (invasion effect) occur to the environment that is invaded (e.g., alterations to the physical environment), to the invaded plant community (e.g., changes in species diversity and composition or evolutionary changes), or to insect herbivory. To investigate how invasions change through time, we investigated both the process and effect of a Phragmites australis invasion by comparing young and old P. australis stands within two Chesapeake Bay subestuaries. We quantified clonal richness of P. australis stands, vigor of the invader, herbivore damage, and plant community composition. Our results indicate that only the population-scale genetics (clonal richness, genetic distance) changed over the course of 40 years. Clonal richness was lower in the old P. australis stands, likely due to intraspecific competition and/or initial colonization by fewer genotypes. The mean genetic distance among clones within old stands was lower than within young stands, suggesting that clones within old stands were mostly closely-related, while young stands were likely established by seeds from nearby stands and so were more representative of the local area. Clones in different old stands were genetically more distant from each other than those in young stands were from clones in other young stands. This pattern suggested that old stands were established by independent colonization events, while young patches were established by a mixture of seeds from local stands, which generated the lower average genetic distance between clones across young stands. We found that community composition, plant vigor, and herbivore damage to stems were similar across different age stands, which indicated that the effect of P. australis invasion becomes stable within a few decades. Over longer periods, the intrinsic invasion process may be more dynamic than the invasion effect.

Disturbance and biotic resistance are important factors driving plant invasions but how these factors interact for plants with different modes of colonization (i.e., sexual and asexual) is unclear. We evaluated factors influencing the invasion of non-native Phragmites australis that has been rapidly expanding in brackish tidal wetlands in Chesapeake Bay. We (1) conducted a survey of naturally occurring small-scale disturbances (removal of vegetation and/or sediment deposition) across four plant communities; (2) determined the effects of small-scale disturbance and biotic resistance on P. australis seedling and rhizome emergence; and (3) tested the effects of size and frequency of small-scale disturbances on seedling emergence and survival of transplanted seedlings. The results of our study demonstrate that the invasion window for seeds is in disturbed areas in high marsh plant communities that flood less frequently; seedling emergence in undisturbed areas was negligible. Establishment of shoots from rhizome segments was low in all plant communities. Disturbance size and frequency had no significant impact on seed germination and seedling survival. Our findings provide evidence that small-scale within-wetland disturbances are important for the invasion of the non-native lineage of P. australis by seeds in brackish tidal wetlands in Chesapeake Bay. Efforts to reduce disturbances - large and small - in wetlands can be used to limit P. australis invasion by seed but invasion by rhizome is still likely to occur across many plant communities irrespective of the presence of disturbance.


Read More: http://www.esajournals.org/doi/abs/10.1890/14-0434.1