The Relative Effects of Willow Invasion, Willow Control and Hydrology on Wetland Zooplankton Assemblages
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WETLANDS RESTORATION
The Relative Effects of Willow Invasion, Willow Control and Hydrology on Wetland Zooplankton Assemblages Yvonne M. Taura 1,2 & Ian C. Duggan 1 Received: 30 March 2020 / Accepted: 12 August 2020 # Society of Wetland Scientists 2020
Abstract Few studies have examined zooplankton assemblages associated with grey willow (Salix cinerea) invasions in wetlands. Our aim was to quantitatively examine zooplankton composition among S. cinerea stands within the South Taupō Wetland, New Zealand, to determine whether these assemblages are affected by willow growth and willow control treatment using the herbicide metsulfuron (C14H15N5O6S). Alternatively, we examined whether wetland hydrology had an over-riding influence. Sampling was performed on three occasions (late-summer, mid-winter, and early-summer). Using Multidimensional Scaling and ANOSIM, we found no significant differences in zooplankton composition or environmental variables among native vegetation, live and dead S. cinerea sites, except for a difference in willow canopy density between late summer and winter. However, zooplankton composition differed on either side of a sand bar, suggesting areas separated by this barrier functioned independently. Overall, we found zooplankton communities to be regulated more by wetland hydrology than by willow presence. A limited willow effect was possibly due to the wetland being at an early stage of invasion, representing stand-alone individuals, with a continuous canopy not yet having formed. Alternatively, willows have lesser effects on invertebrates in wetlands than in streams. Ground control treatment of S. cinerea using metsulfuron had no apparent impact. Keywords Metsulfuron . Microfauna . Wetlands . Salix . Grey willow . Zooplankton
Introduction In the Northern Hemisphere, plant species of the genus Salix provide various ecological benefits; they are seen as ideal for river training and erosion control, and their wide spreading fibrous root systems help bind soil on stream- and hill-sides (Russell 1994). In the Southern Hemisphere, however, Salix species are considered ‘invasive’, having become widespread, with substantial ecological and economic impacts on wetland ecosystems (Adair et al. 2006). The introduction of Salix species to New Zealand was deliberate, with different species planted along waterways to provide erosion protection for riverbanks and for soil conservation purposes (Williams and West 2000). Salix cinerea L. (a.k.a., grey willow) was
* Ian C. Duggan [email protected] 1
Environmental Research Institute, The University of Waikato, Private Bag, Hamilton 3105, New Zealand
2
Present address: Manaaki Whenua/Landcare Research, Private Bag 3127, Hamilton 3240, New Zealand
introduced by the 1870s (Thompson and Reeves 1994), and grows across a wide soil fertility range, from nutrient rich swamps to peat bogs, with only saline or high-altitude sites beyond its limits (Partridge 1994). The dispersal of small seeds adapted to long-distance wind dispersal, vegetative propagation, an
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