Analysis of kettle pond plant communities of Cape Cod National Seashore (1995–2020)

Smith, Stephen

doi:10.36967/2300645

Along transects and within boxplots, several ponds have experienced significant changes in macrophyte species composition since 1995, while others have remained relatively unchanged. In 2020 new occurrences of Phragmites australis (common reed) were documented in Duck (a single plant, which was immediately removed), Gull, and Higgins ponds. Three state-listed rare species that occur in CACO kettle ponds were not found in 2020. These included Sabatia kennedyanna (Plymouth rose gentian) (found in 2016 at Great-T), Drosera filiformis (threadleaf sundew) (found in 2016 at Great-W) and Sagittaria teres (quill-leaved arrowhead), which was once abundant but has now been absent for decades. Reductions in the cover of N. odorata (white waterlily) along transects was observed in Great-T, Ryder, Higgins, and Snow ponds, although this trend was apparent in boxplots only in Herring Pond. E. acicularis (dwarf harigrass) also diminished in cover in several ponds, including along Duck, Dyer, Gull, Long, Round-E, and Slough ponds. J. militaris (bayonette rush) appears to have undergone a variety of short-term changes including reductions along transects in Great-T, Higgins, Long, and Snow ponds. Boxplots only exhibited a reduction in Higgins Pond, however. L. dortmanna (Cardinal flower) is another taxon common to most CACO ponds. Its abundance along the Gull Pond transects decreased, contrasted by an increase in Long Pond transects, and in Great-W and Round-E boxplots. The proliferation of Utricularia spp. in Great-T Pond is one of the most conspicuous changes that has occurred over the last decade. The plant community shifts reported here are likely the result of both short-term (e.g., trampling, geese grazing, extreme drought or high water, etc.) and long-term (e.g., climate warming, diminishing acidity, increasing alkalinity). That said, many of the statistically significant increases or decreases in cover were restricted to just one or two transects, and sometimes the changes in individual taxa contrasted each other among the different transects. One-dimensional line-intercept transects are likely detecting changes that are not real on any meaningful spatial scale. On the other hand, the number of boxplot sites should be increased to obtain much better spatial resolution. Accordingly, we propose increasing the number of box plot sites in each pond from five to ten for all future monitoring.

Analysis of kettle pond plant communities of Cape Cod National Seashore (1995–2020)

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