Bryophyte species richness
Over the eight years post wet-up, our seven annual vegetation surveys yielded a total of 33 bryophyte species, 21 of these considered species that inhabit natural peat-forming plant communities of fens and bogs of the region. Twelve species are either species characteristic of early succession or upland species (non-peatland species) (Table 1). In 2014, 21 species were found on the wetland, increasing to 24 in 2015, 23 in 2016, and 25 in 2017. In 2018 and 2019, species richness decreased to 16 species, and continued to decrease to 13 in 2021. In 2014, bryophytes occurred 248 times on the wetland, varying from six species found only once to Ptychostomum pseudotriquetrum that was found 58 times. In 2015-2016, bryophyte occurrences varied from 315 in 2015 to 262 in 2016; however, in 2017 the number of occurrences decreased to 182, and continued to decline in 2018 to 122, 112 in 2019, and 74 in 2021 (some data reported in House et al. 2022). Ptychostomum pseudotriquetrum continued to be the most frequent species until 2021 when Drepanocladus polygamus was most frequent (House et al. 2022).
Between 2014 and 2015, non-peatland species occurrences dominated over peatland species, with between 76 and 66% of the occurrences non-peatland species; however, non-peatland species declined in 2016 and 2017 while peatland species either declined less or remained steady, so that between 2016 and 2019 peatland species occurrences made up between 58-51% of the total; in 2021 peatland species made up 68% of the bryophyte occurrences (Figure 1).
Of the 20 peatland species, Aulacomnium palustre was the most frequent peatland species on the wetland, occurring in 81% of the plots in which peatland species occurred. Campylium stellatum and Tomentypnum nitens also occurred on the wetland in lower frequencies. Peatland species almost always occurred in plots that also contain A. palustre. In 2014, only eight plots contained peatland species without the occurrence of A. palustre (similarly the same is true for 2015 - 8 plots, 2017 - 2 plots, 2019 - 5 plots, and 2021 - 3 plots).
Peatland bryophyte occurrences in four vegetation types
In 2014, one year after wet-up, only 72% of the plots were in those dominated by forbs and graminoids and only 28% in plots dominated the three vascular plant species that would dominate in 2015 and onwards (Figure 2a). In 2014, of the 27 plots (out of 85 possible plots) in which peatland bryophytes were found, only 11 plots were in those dominated by Typha latifolia, Carex aquatilis, or Calamagrostis canadensis, while 16 plots were in the forb-graminoid vegetation plots. In 2015, the number of plots in the forb-graminoid vegetation type decreased to 37% and to 14% in 2021. In comparison, the number of peatland bryophytes occurring in the forb-graminoid vegetation type increased to 19 in 2015, and then decreased to 5-9 in 2017-2021. Overall, the number of plots with peatland bryophyte species decreased from 51 in 2015 to 29 in 2017 19 in 2019, and 12 in 2021 (Table 2).
Typha latifolia-dominated areas: Plots dominated by Typha increased from 2 in 2014 to 9 in 2015, 11 in 2017, 16 in 2019, and 29 in 2021. No bryophytes were found in any of these plots (Table 2, Figure 2a-e).
Carex aquatilis-dominated areas: Seven plots were dominated by C. aquatilis in 2014, increasing to 17 in 2015; and varying from 23-24 plots in 2017-2021. In 2014, only 2 of the 7 plots dominated by C. aquatilis had peatland bryophytes. In 2015, peatland bryophyte occurrence increased, occurring in seven (41%) plots, decreasing to between 2-3 plots in 2017-2021 (Table 2, Figure 2a-e). In all years, 17% of the plots dominated by C. aquatilis contained peatland bryophytes.
Calamagrostis canadensis-dominated areas: In 2014, 15 plots were dominated by C. canadensis, comparatively in 2015 Calamagrostis dominated in 29 plots, decreasing to 14-20 plots in 2017-2021. In 2014, peatland bryophytes occurred in nine (60%) of C. canadensis-dominated plots, and increased dramatically in 2015, with 23 (79%) plots having peatland bryophytes. Similarly, in 2017, 90% of the plots had peatland bryophytes, but this decreased to 30% in 2019 and 25% in 2021 (Table 2, Figure 2a-e). In all years, 63% of the plots in C. canadensis-dominated plots contained peatland bryophytes.
Forb-graminoid-dominated plots: In 2014, 61 plots had abundant forb-graminoid species, 16 of these had peatland bryophytes. In 2015, forb-graminoid plots decreased to 32, but 21 (65%) of these had peatland bryophytes. In 2017-2019 forb-graminoid plots varied from 23-32, decreasing to 12 in 2021, with peatland bryophytes occurring in 30-42% of the plots (Figure 2a-e). In all years, 38% of the plots in forb-graminoid plots contained peatland bryophytes.
Sodium concentrations in the surface water of SHW have increased over the eight years since wet-up (Biagi 2019, 2021b; House et al. 2022); however, the increases have been most pronounced along the southern boundary of the wetland, with 17 plots having concentration greater than 400 mg L-1 (Figure 2f).
Vascular plant species richness and cover
Over all years, mean vascular plant species richness [alpha] in plots with mosses was 10.0 (±0.8 S.E.) compared to 7.5 (± 0.9 S.E.) in plots without mosses (Typha-dominated plots excluded). When analyzed by vegetation type, vascular plant richness was greater in plots with mosses compared to those without only in the forb-graminoid vegetation type (f = 29.35, p = .001, Online Resource 1), and there differing only in 2014 (p = =0.002) and 2017 (p = .001). In all three vegetation types with mosses, vascular plant richness decreased over the eight years (f = 7.97, 12.58, 15.58 all p = 0.001).
Similarly, vascular plant cover (here equated to a surrogate for shade) differed between plots with and without mosses in the graminoid-forb group (p = .001) with plots with mosses having 92.8% ± 6.8 (S.E.), and plots without mosses had 74.3% ± 9.2. The other groups (dominated by Typha, Carex, and Calamagrostis) did not differ between plots with and without mosses (all p > .07 – 106.0% [±8.7 S.E] in plots with mosses compared to 89.4% [±5.9 S.E.] in plots without mosses). Vascular plant cover increased over the eight years of sampling in each of the three vegetation types with mosses (f = 5.01 p = .001, f = 38.92 p < .001, 11.56, p = < .001).