Karin's research
What drives the invasion of non-native plants? Phragmites australis in the Chesapeake Bay
The non-native haplotype of Phragmites australis (Saltonstall 2002) is an invasive species in many parts of North America including the Chesapeake Bay. We have been addressing a number of questions in our attempt to better understand the spread of this invasive plant.
The importance of land-use and genetics in Phragmites viable seed production (Collaborators: Dennis Whigham, Melissa McCormick, and undergraduate intern Heather Baron)
Phragmites can potentially spread by seeds or rhizomes. To evaluate the potential for spread by seed, we studied variation in viable seed production among Phragmites patches in nine subestuaries of the Chesapeake Bay.
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(1) Phragmites in the South River; (2) Karin collects Phragmites seeds; (3) seed packets after cold-stratification
We found large variation in viable seed production within and among Phragmites patches. Further investigation revealed that the patches that produced the greatest amount of viable seed occurred in subestuaries where the watershed had a lot of anthropogenic development. Plants in these areas are known to have higher levels of foliar nitrogen (King et al. 2007). In addition, we found a positive relationship between viable seed production and the number of genotypes per patch, indicating that both nutrient availability and genetics play an important role in Phragmites viable seed production.
Some initials findings were presented here:
Ecological Society of America meeting 2008: The potential for a seed-driven invasion of Phragmites australis in forested vs. developed watersheds of the Chesapeake Bay JPG
Society for Wetland Scientists meeting 2008: Variation in seed viability, genetic diversity, and foliar nutrients of non-native Phragmites australis in the Rhode River, a subestuary of the Chesapeake Bay JPG
Phragmites invasion across different plant communities - the importance of small-scale disturbances and propagule type (Collaborators: Dennis Whigham, and undergraduate interns Sally Gallagher and Heather Baron)
We conducted a field experiment where we placed seeds and rhizomes into artificially disturbed and undisturbed plots in four different brackish marsh plant communities (Typha latifolia, Spartina patens/Distichlis spicata, Scirpus americana, and Iva frutescens). We followed the fate of these seeds and rhizomes over the growing season and monitored differences in environmental conditions.
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(1) a belowground disturbance treatment with a seed packet; (2) Heather Baron installs a plot; (3) Phragmites invades by rhizome
In 2007, we found that seeds germinated to high percentages in disturbances in three of the four plant communities. In 2008, however, we had 100% mortality of seedlings. In both years, approximately 20% of all rhizomes sprouted and survived regardless of the presence of a disturbance or the type of plant community.
Findings from 2007 were presented here:
Ecological Society of America meeting 2008: The effect of small disturbances on germination and emergence of Phragmites australis in brackish wetlands (intern research) PDF
The seed banks of Phragmites-dominated brackish marshes (Collaborators: Dennis Whigham and Andy Baldwin)
We sampled the seed banks of Phragmites-dominated brackish marshes to determine:
(1) Does Phragmites form a seed bank? We specifically explored the hypothesis that Phragmites seed banks vary among Phragmites-dominated brackish wetlands and that this variation reflects differences in viable seed production of Phragmites stands.
(2) What is the potential for recruitment from the seed bank in Phragmites-dominated brackish marshes? We explored the hypothesis that seed banks of native species persist in brackish wetlands under dense stands of Phragmites.
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(1) Dennis Whigham collects a soil seed bank sample; (2) Karin checks on the greenhouse set-up; (3) a close-up of a seed bank sample
We found that Phragmites seedling emergence from seed bank samples was 25-60 times higher from patches known to produce viable Phragmites seed. We also found that the seed banks were much more diverse than the vegetation indicated (i.e., not dominated by Phragmites seeds), indicating the restoration potential of native plant communities after Phragmites control efforts.
What limits the restoration of wetland plant communities? Ecology and revegetation of Carex (sedge) species in prairie pothole wetlands
In the mid-continental U.S., plant recolonization in hydrologically restored wetlands occurs through natural processes; little emphasis has been placed on accelerating succession through seeding or planting of native species. While some plants recolonize quickly, Carex species (sedges), the dominant vegetation in natural prairie wetlands, are not returning readily to restorations in this highly fragmented landscape.
Seed dispersal and seed germination of Carex species in hydrologically restored prairie wetlands (Collaborator: Susan Galatowitsch)
We evaluated seed dispersal and seed germination limitation in hydrologically restored wetlands. We used seed traps in restored and natural wetlands to quantify seed rain - essentially how many seeds are landing on the ground. To evaluate seed germination limitation, we sowed seeds of five Carex species into restored and natural wetlands and monitored seedling establishment.
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(1) a soon-to-be wetland, after drainage tiles were dismantled; (2) Karin installs a seed trap; (3) germination plots in a restored wetland
We determined that sedge recolonization is limited by seed dispersal but not the availability of germination microsites. No Carex seeds were caught in the seed traps in restored wetlands but Carex seeds germinated readily in the restorations. These findings indicate that restoring wetland plant diversity requires active management, i.e., seed sowing.
Variation in seed dormancy and germination of Carex species (collaborator: Susan Galatowitsch)
To improve the success of revegetation efforts, we evaluated the seed dormancy and germination ecology of 14 Carex species. Prairie wetland sedges were notorious for having low seed production, low seed viability, confusing dormancy patterns, and strict germination requirements in addition to being dispersal limited in restorations.
(1) Karin collects Carex seeds; (2) seed heads of Carex hystericina; (3) seeds germinating in a growth chamber
We found enormous variability in the dormancy breaking and temperature germination requirements of Carex seeds. Some species will be easy to revegetate in wetlands while others will require special attention (e.g., seeding at higher rates to overcome low seed viability and cold treating seeds to break seed dormancy) from wetland managers hoping to restore the diversity characteristic of natural wetlands.
Citations:
King, R. S., W. V. DeLuca, D. F. Whigham, and P. P. Marra. 2007. Threshold effects of coastal urbanization on Phragmites australis (common reed) abundance and foliar nitrogen in Chesapeake Bay. Estuaries and Coasts 30:1-13.
Saltonstall, K. 2002. Cryptic invasion by a non-native genotype of the common reed, Phragmites australis, into North America. Proceedings of the National Academy of Science 99:2445-2449.