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),
and reed canary grass (Phalaris arundinacea). These observations may
inform concepts of habitat stability in the absence of direct
anthropogenic disturbance and corroborate globally observed trends of
native species loss and non-native species encroachment. Our results
indicate that within the Fraser River Estuary, active threat management
may be necessary in areas of conservation concern in order to prevent
further native species biodiversity loss.