Stable Regimes in an Unstable System: Floral Community and Diversity in the Grand Sable Dunes

Abstract

Grand Sable Dunes, as a perched dune field on the shore of Lake Superior, is a sensitiveecosystem subject to continual disturbance. Repeated natural disturbances necessitate specializedplant communities to develop. There were two objectives of my research in this system that aretreated in separate chapters. They include: 1) the quantification of successional changes in theplant community over time, and the identification of population demography changes for rarespecies within the dunes and 2) the evaluation of evaluate in pollinator species for two plantsHieracium caespitosum (Yellow Hawkweed) and Lithospermum caroliniense (CarolinaPuccoon).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 overtime. 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 communitystructure (richness and diversity). Composition increased slightly with eight species occurring in2018, 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 communitycomposition in eastern and western survey zones within the dunes appear to be diverging. Minorchanges in the plant community composition and structures indicate successional changes haveoccurred, but without major disturbance. This divergence in community composition may berelated to weather related incidents associated with Lake Superior disturbance potential.The secondary objective concerns pollinator species on two similar plant species found inthe Grand Sable Dunes. Individuals of H. caespitosum and L. caroliniense were observed and allfloral visitors were identified to family. The majority of arthropod families were observed10visiting 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 inL. caroliniense.