Rooting depth and below ground biomass in a freshwater coastal marsh invaded by European Reed (Phragmites australis) compared with remnant uninvaded sites at Long Point, Ontario

Abstract

Invasive European Reed (Phragmites australis subsp. australis) outcompetes native vegetation, reducing floristic diversity and habitat value for wildlife. Research in coastal salt marshes has indicated that P. australis invasion may be facilitated by its relatively deep rooting depth, but in freshwater marshes the growth pattern of below ground tissues in relation to water depth is uncertain. To determine if P. australis is rooting more deeply than resident wetland plant species in a freshwater coastal marsh on Lake Erie, Ontario, we measured the vertical distribution of below ground biomass in P. australis invaded marsh sites and compared it to the below ground biomass distribution in nearby sites not yet invaded by P. australis. These invaded and uninvaded sites were paired by water depth, which is known to influence resource allocation and rooting depth. Below ground biomass in invaded sites was greater than in uninvaded sites (t28 = 3.528, P = 0.001), but rooting depth (i.e., the depth at which 90% of total below ground biomass is accounted for) was comparable (t28 = 0.992, P = 0.330). Using water depth and site type, general linear models could predict below ground biomass (F2,55 = 9.115, P < 0.001) but not rooting depth (F2,55 = 1.175, P = 0.316). Rooting depth is likely affected by other factors such as substrate type and the depth of the organic soil horizon.