New Zealand Journal of Ecology (2010) 34(3): 324- 331

Decomposition dynamics of invasive alligator weed compared with native sedges in a Northland lake

Research Article
Imogen E. Bassett 1*
Jacqueline R. Beggs 1
Quentin Paynter 2
  1. School of Biological Sciences, Tamaki Campus, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
  2. Landcare Research, Private Bag 92170, Auckland 1142, New Zealand
*  Corresponding author

Invasive weeds have been shown to alter ecosystem processes such as decomposition and nutrient cycling. However, little is known about the effects of introduced biocontrol agents on these processes. This study examined the effects of alligator weed (Alternanthera philoxeroides) and its biocontrol agent, the alligator weed flea beetle (Agasicles hygrophila), on nutrient cycling in a northern New Zealand lake. Alligator weed litter decomposed significantly faster than either of two native sedge species (Schoenoplectus tabernaemontani, Isolepis prolifer) in a litterbag experiment. In addition, the presence of the alligator weed flea beetle resulted in large amounts of decaying alligator weed litter entering the lake in early summer. Both the timing and magnitude of this litter input were uncharacteristic of seasonal biomass dynamics of the native sedges. Combined with alligator weed’s rapid decomposition, this indicates altered patterns of nutrient cycling at the lake, with potential flow-on effects including facilitation of further weed invasion.