Reversing biodiversity decline in forest remnants: A restoration experiment using biocontrol beetles and manual clearance

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Beverley Clarkson

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The ecological health and functioning of lowland forest ecosystems on agriculturally-modified floodplains in northern New Zealand are under serious threat from weed invasion. The most widespread alien plant species is the monocotyledonous herb, Tradescantia fluminensis. Tradescantia forms dense carpets covering the ground, which prevent the regeneration of native forest species, especially in farm remnants fenced from stock. A restoration experiment was established in 2016 to compare two different approaches to management of Tradescantia, namely three biocontrol beetle species from Brazil (released as a trio), which target different parts of the plant, and hand clearing. We set up the experiment at four sites (two with lower nutrient soils, two with higher nutrient soils) to assess the impact of biocontrol beetles and manual clearing on Tradescantia biomass and native plant regeneration. Monitoring of browse damage indicates establishment of all beetle species occurred within one year, and widespread dispersal (several hundred metres) of at least one biocontrol beetle species within three years. Although decreases in Tradescantia biomass occurred in all biocontrol plots by year three, the biomass at the two nutrient-enriched sites remained relatively high. At the end of three years, woody seedling establishment was highest in the hand-cleared plots, second highest in the biocontrol treatments, and lowest in the control treatments. Although the experiment needs to continue for several years before noticeable ecological benefits are achieved, it provides early promise of the use of biocontrol beetles in slowing or reversing biodiversity decline in floodplain forest remnants.

Resource Type:
Audio/Video, Conference Presentation, SER2019

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Society for Ecological Restoration