Using marsh organs to test seed recruitment in tidal freshwater marshes

Premise: Seed recruitment niches along estuarine elevation gradients are
seldom experimentally field-tested under tidal regimes of the Pacific
Northwest of North America. Addressing this knowledge gap is important to
better understand estuary restoration and plant community response to sea
level rise. Methods: Germination was tested in marsh organ mesocosms
across an elevation gradient (0.5–1.7 m above mean sea level). Seeds were
sown on sterile peat moss, and the tops of pipes were secured with
horticultural “frost cloth” to ensure no experimental seeds were washed
out and no new seeds were introduced. The trials tested artificial and
overwinter chilling regimes, as well as the presence and/or absence of a
near-neighbor transplant. Results: Carex lyngbyei had significant
elevation-driven germination after overwinter and artificial chilling.
Schoenoplectus tabernaemontani had near-significant germination across
elevation after overwinter chilling, and germination in the absence of
competition was significantly greater than with a near-neighbor
transplant. Discussion: Carex lyngbyei had the highest germination rate at
higher elevations, which suggests restricted seed recruitment potential,
and required clonal expansion to extend into lower marsh elevations.
Identifying species-specific recruitment niches provides insight for
restoration opportunities or invasive species monitoring, as well as for
estuary migration under sea level rise.