Using a marsh organ to predict future plant communities in a Chinese estuary invaded by an exotic grass and mangrove

Abstract

Exotic species vary in how harmful they are. The earlier we can predict the outcome of an invasion, the more time is available for management. We conducted a “marsh organ” experiment with six elevation treatments to evaluate how the exotic grass Spartina alterniflora, which has invaded almost the entire coastline of China, affects a native (Kandelia obovata) and an exotic (Sonneratia apetala) mangrove in Zhangjiang Estuary, southern China. Survival of transplants in monoculture over two growing seasons in the marsh organ was high except at extreme high and low elevations. All three plants displayed hump‐shaped patterns of biomass across elevation in monoculture, but K. obovata performed best at slightly higher and S. alterniflora at slightly lower elevations, whereas S. apetala performed well across all four intermediate elevations and grew larger than the other two plants. In mixtures, S. alterniflora suppressed growth of mangrove seedlings of both species by up to 90%. The competitive effect of S. alterniflora was greatest at intermediate elevations where its biomass was greatest. When transplanted into adjacent stands of S. alterniflora, K. obovata remained stunted, but S. apetala grew quickly and began to emerge from the canopy of S. alterniflora by the end of the second growing season. At this site, past and ongoing disturbances to mature stands of K. obovata are likely to allow both exotics to increase in abundance. Aggressive management intervention will be needed to prevent estuaries in southern China from transitioning to near complete dominance by the exotic mangrove S. apetala.

Self‐thinning and size‐dependent flowering of the grass Spartina alterniflora across space and time

“…Spartina alterniflora stems also varied in height among sites, due in part to variation among sites in plot elevation and soil salinity. Plant height decreased with plot elevation and soil salinity in both the mid‐marsh and creekbank habitats (Figure S4a,b), which is consistent with many previous results showing that S. alterniflora height decreases with elevation and salinity (Linthurst & Seneca, ; Pearcy & Ustin, ; Peng, Chen, Pennings, & Zhang, ). Across sites, however, these same variables did not predict the proportion of stems flowering, suggesting that the relationship between plant height and flowering differed among sites.…”

Contrasting plant adaptation strategies to latitude in the native and invasive range of Spartina alterniflora

“…In the native range, S. alterniflora varies greatly in height, shoot density and flowering across elevation as a function of abiotic stress (Richards et al, 2005;. S. alterniflora in China also retains similar plastic responses to elevation (Peng et al, 2018;Zhu et al, 2019). In the USA, sampling S. alterniflora in the 'midmarsh' produced similar latitudinal patterns as we have described here for samples collected from the low marsh (Kirwan et al, 2009;, so we hypothesised that, if we had included midmarsh sampling in this paper, contrasts between the native and exotic ranges would have been similar to those that we documented in the low marsh.…”

Tidal and Meteorological Influences on the Growth of Invasive Spartina alterniflora: Evidence from UAV Remote Sensing

“…Following the fundamental ecophysiological principle "law of tolerance" [55], intertidal plants tend to show a hump-shaped growth pattern along the inundation/elevation gradients [7,56]. This hump-shaped growth pattern had been confirmed for S. alterniflora in this wetland via a "marsh-organ" experiment with elevation treatments spanning from −0.5 m to 2.0 m (corresponding to 14.4~0 h/day for inundation duration) [21], showing S. alterniflora reaches optimal growing condition at an inundation duration of~7 h/day (equivalently at an elevation of 0.5 m). In this study, isolated patches over this wetland had the highest elevation only up to 0.6 m; therefore, we did not have an enough elevation range to further confirm this hump-shaped growth pattern at the landscape scale.…”

“…Spartina alterniflora, one of coastal salt marshes native to the Atlantic coast, has received much attention in the past decades due to its role as an invasive species in many parts of the world [15][16][17][18]. In terms of spatial variation over the intertidal zone, S. alterniflora is distributed across a wide elevation gradient between mean high water (MHW) and mean low water (MLW) [19,20], and the growth of S. alterniflora shows a hump-shaped cross-shore pattern over the elevation gradient [7,14,21]. Tidal inundation or relative surface elevation is a widely documented environmental control of the spatial variation of S. alterniflora growth [21,22].…”

“…In terms of spatial variation over the intertidal zone, S. alterniflora is distributed across a wide elevation gradient between mean high water (MHW) and mean low water (MLW) [19,20], and the growth of S. alterniflora shows a hump-shaped cross-shore pattern over the elevation gradient [7,14,21]. Tidal inundation or relative surface elevation is a widely documented environmental control of the spatial variation of S. alterniflora growth [21,22]. In terms of temporal variation, S. alterniflora growth follows a distinct seasonal pattern correlated with temperature [23] and precipitation [13].…”