Plant community compositional stability over 40 years in a Fraser River Estuary tidal freshwater marsh

Long-term data sets documenting temporal changes in vegetation communities are uncommon, yet imperative for understanding trends and triggering potential conservation management interventions. For example, decreasing species diversity and increasing non-native species abundance may be indicative of decreasing community stability. We explored long-term plant community change over a 40-year period through the contribution of data collected in 2019 to two historical datasets collected in 1979 and 1999 to evaluate decadal changes in plant community biodiversity in a tidal freshwater marsh in the Fraser River Estuary in British Columbia, Canada. We found that plant assemblages were characterized by similar indicator species, but most other indicator species changed, and that overall α-diversity decreased while β-diversity increased. Further, we found evidence for plant assemblage homogenization through the increased abundance of invasive species such as yellow flag iris (Iris pseudacorus), a..., Sampling design & harmonization between observations
Our main goal was to sample the vegetation in a representative way to allow comparison with the datasets collected in 1979 (Bradfield & Porter, 1982) and 1999 (Denoth & Myers, 2007). This publication will reference dates the data were collected, rather than publication dates of the corresponding studies.
In the original 1979 study, eight transects (Q-X) were laid out in a subjective fashion to cross through the main features of vegetation diversity at Ladner Marsh (Fig. 1 in Bradfield & Porter, 1982). All transects spanned a similar elevation range across the marsh platform, with the three main plant assemblages (Sedge, Fescue, Bogbean) separated by apparent changes in hydrological conditions along transects.
In the 1999 study, Bradfield & Porter’s (1982) Fig.1 was used to visually approximate the locations of transects to repeat the vegetation survey (Denoth & Myers, 2007). In this study (2019 survey), transe..., All analyses were performed in R Studio v. 4.2.1. Please see ReadMe, then metadata files for each data file. R code is annotated with notes about the analysis process and often links to resources used to produce analyses., # Plant community compositional stability over 40 years in a Fraser River Estuary tidal freshwater marsh

| Name | Description |
| ---- | ----------- |
| d1979\_formatted.csv | Plant community data collected in 1979 |
| d1979\_formatted- METADATA.pdf | Metadata for plant community data collected in 1979 |
| d1999\_formatted.csv | Plant community data collected in 1999 |
| d1999\_formatted- METADATA.pdf | Metadata for plant community data collected in 1999 |
| d2019\_formatted.csv | Plant community data collected in 2019 |
| d2019\_formatted- METADATA.pdf | Metadata for plant community data collected in 2019 |
| d2019\_position.xlsx | Location data for plant sampling conducted in 2019 |
| d2019\_position-METADATA.pdf | Metadata for location data for plant sampling conducted in 2019 |
| CommunityStability.Rmd | All code used to conduct analyses found in manuscript and publication |