Stable Regimes in an Unstable System: Floral Community and Diversity in the Grand Sable Dunes
thesisposted on 10.06.2019, 20:40 by Jonathan C Danielson
Grand Sable Dunes, as a perched dune field on the shore of Lake Superior, is a sensitive
ecosystem subject to continual disturbance. Repeated natural disturbances necessitate specialized
plant communities to develop. There were two objectives of my research in this system that are
treated in separate chapters. They include: 1) the quantification of successional changes in the
plant community over time, and the identification of population demography changes for rare
species within the dunes and 2) the evaluation of evaluate in pollinator species for two plants
Hieracium caespitosum (Yellow Hawkweed) and Lithospermum caroliniense (Carolina
For the first objective, target plant community composition and structures (i.e. richness,
diversity) were quantified in 2011 and 2018 across Grand Sable Dunes in 1 m² quadrats.
Additionally, two relatively rare plant species (Cirsium pitcheri and Tanacetum bipinnatum)
were selected to quantify demographic (i.e. flowering, non-flowering) patterns and changes over
time. Samples for C. pitcheri and T. bipinnatum were acquired via circle-plots 2.5 m in diameter.
Population comparisons between 2011 and 2018 illustrate minimal change in community
structure (richness and diversity). Composition increased slightly with eight species occurring in
2018, but not 2011. Additionally, community similarity was high (~78%) between the two years.
C. pitcheri occurrence was inversely related to presence of other species. Plant community
composition in eastern and western survey zones within the dunes appear to be diverging. Minor
changes in the plant community composition and structures indicate successional changes have
occurred, but without major disturbance. This divergence in community composition may be
related to weather related incidents associated with Lake Superior disturbance potential.
The secondary objective concerns pollinator species on two similar plant species found in
the Grand Sable Dunes. Individuals of H. caespitosum and L. caroliniense were observed and all
floral visitors were identified to family. The majority of arthropod families were observed
visiting both H. caespitosum and L. caroliniense, with an absence of typically important families
(e.g. Apidae, Bombiliidae). Halictidae, Muscidae and Syrphidae were the most common visitors,
with L. caroliniense attracting far more Muscidae than their H. caespitosum competitors.
Overlap in visitors for both species was observed, which may lead to decreased reproduction in