Hydrologic and mechanical control for an invasive wetland plant, Juncus ingens, and implications for rehabilitating and managing Murray River floodplain wetlands, Australia

Abstract

Wetlands are prone to increased invasion by plant species following changes in hydrologic regime, leading to shifts in plant community composition and potentially ecosystem function and health. In this paper, the ecology and potential control of Juncus ingens, a native wetland plant in the MurrayDarling Basin of south-eastern Australia, is investigated. J. ingens has benefited from altered Murray River hydrologic conditions by expanding its range and invading seasonally-flooded grassland and riparian habitats along the Murray River. Here results of complementary glasshouse and field research of seedling and mature J. ingens growth and resilience as influenced by hydrologic regime (moist, saturated, partial inundation and when possible, complete inundation) and mechanical control (i.e., clipping) are presented. A moist hydrologic regime (soil held at field capacity) resulted in the most vigorous seedlings (13.9-73.0% more total biomass), while saturated conditions (flooding maintained level with the soil surface) resulted in the most vigorous mature J. ingens (14.1-98.4% more total biomass). Seedling mortality was greatest under complete and prolonged inundation (60% fatal with remaining 40% showing severe stress), conditions suspected to have limited prior invasion but which currently occur infrequently as a result of reduced flooding magnitude. Clipping was fatal for nearly all seedlings regardless of hydrologic regime but was only fatal for mature plants if coupled with prolonged inundation. Coupling ground-level clipping with strategic flooding may be the most effective means for controlling current populations of J. ingens and limiting further invasion, promoting re-colonisation by displaced species and rehabilitating the health of Barmah Forest and similar Murray River floodplain wetlands.

Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ13C‐δ15N, and lignin biomarker

“…Commonly, decreases in plant productivity, species richness, and diversity (Molina et al, 2003;Tuxen et al, 2011;Wang, Li, et al, 2015), as well as differences in belowground biomass allocation (Pierfelice et al, 2017) and species composition (Amores et al, 2013) were observed, with all of vegetation distributions orienting along a salinity gradient (Table S1). Upstream occurred with lower wave energy and tidal inundation, but the high inflow of nutrient-rich freshwater provided optimal conditions for P. australis stand to grow (Magee & Kentula, 2005;Mayence et al, 2010). Because the SOM input rate in soils decreased along the salinity gradient, the contents and storage of SOC and TN in a single P. australis-dominated community were significantly higher than those in mixed P. australis and S. salsa, single S. salsa, and tidal flat (Figure 3a,b; Figure S2a,b).…”

Simulated mechanical control of Nitellopsis obtusa under mesocosm conditions

“…Wakef.)] were reportedly able to survive clipping stress more often than immature individuals due to the amount of belowground biomass available to promote regrowth (Mayence et al 2010; Middleton 1990). Clipping directly targets aboveground biomass, so individuals or species with more belowground biomass may be more tolerant to clipping stresses than those with less belowground biomass.…”