Paynter Q.,Private Bag 92170 |
Main A.,University of Queensland |
Hugh Gourlay A.,Landcare Research |
Peterson P.G.,Private Bag 11052 |
And 3 more authors.
Journal of Applied Ecology | Year: 2010
A seed-feeding biocontrol agent Bruchidius villosus was released in New Zealand (NZ) to control the invasive European shrub, broom Cytisus scoparius, in 1988 but it was subsequently considered unable to destroy sufficient seed to suppress broom populations. We hypothesized that an invasive mite Varroa destructor, which has caused honeybee decline in NZ, may cause pollinator limitation, so that the additional impact of B. villosus might now reach thresholds for population suppression. We performed manipulative pollination treatments and broad-scale surveys of pollination, seed rain and seed destruction by B. villosus to investigate how pollinator limitation and biocontrol interact throughout the NZ range of broom. The effect of reduced pollination in combination with seed-destruction was explored using a population model parameterized for NZ populations. Broom seed rain ranged from 59 to 21 416 seeds m-2 from 2004 to 2008, and was closely correlated with visitation frequency of honeybees and bumblebees. Infestation of broom seeds by B. villosus is expected to eventually reach 73% (the average rate observed at the localities adjacent to early release sites). The model demonstrated that 73% seed destruction, combined with an absence of honeybee pollination, could cause broom extinction at many sites and, where broom persists, reduce the intensity of treatment required to control broom by conventional means. Nevertheless, seed rain was predicted to be sufficient to maintain broom invasions over many sites in NZ, even in the presence of the varroa mite and B. villosus, largely due to the continued presence of commercial beehives that are treated for varroa mite infestation. Synthesis and applications. Reduced pollination through absence of honeybees can reduce broom seed set to levels at which biocontrol can be more effective. To capitalize on the impact of the varroa mite on feral honeybees, improved management of commercial beehives (for example, withdrawal of licences for beekeepers to locate hives on Department of Conservation land) could be used as part of a successful integrated broom management programme at many sites in NZ. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.
Dymond J.R.,Private Bag 11052 |
Shepherd J.D.,Private Bag 11052 |
Newsome P.F.,Private Bag 11052 |
Gapare N.,Ministry for the Environment |
And 2 more authors.
Environmental Science and Policy | Year: 2012
It is necessary to estimate the area of afforestation and deforestation in New Zealand, since 1990, to meet reporting obligations under the Kyoto Protocol. We describe a method for national mapping of forest change that achieves high accuracy, but only requires moderate effort. A national coverage of satellite imagery is standardised, classified (automatically) for land cover, and then compared with an existing 1990 land-use map to identify polygons (>1. ha) of possible forest change. Each one of these possible change polygons is checked by operators for actual or spurious change. The resulting forest change map showed the area of afforestation between 1990 and 2008 was 579,000 (±10,000). ha, and the area of deforestation was 75,000 (± 5000). ha. This means that reported emission credits can never be reported to better than plus or minus 2%. Likewise, reported liabilities for emissions can never be reported to better than plus or minus 6%. © 2011 Elsevier Ltd.
Burns B.R.,Private Bag 3127 |
Floyd C.G.,Private Bag 3127 |
Smale M.C.,Private Bag 3127 |
Arnold G.C.,Private Bag 11052
Austral Ecology | Year: 2011
Residual forest fragments in areas dominated by pastoral agriculture can have high value for biodiversity conservation but are still subject to ongoing degradation as (i) processes initiated by fragmentation continue to operate, for example, changes in canopy replacement probabilities; and (ii) deleterious processes impinge upon them from the surrounding matrix, for example, browsing and trampling by vagrant livestock. Responses by management to slow or reverse these processes require evaluation. Stock (mainly cattle and sheep) exclusion by fencing and mammal pest (mainly Trichosurus vulpecula (brushtail possum)) control are currently used as management tools to maintain or improve the vegetation condition of fragments in New Zealand. We examined the effectiveness of these tools by sampling vegetation composition, forest structure and regeneration of woody species in 41 old-growth fragments dominated by Beilschmiedia tawa, selected to populate a factorial design that included four different fencing classes (unfenced, fenced 2-10, 10-20 and >20years ago), with and without sustained mammal pest control. Fencing for more than 10years led to higher abundances of native ground ferns and shrubs, and lower abundances and numbers of mostly adventive herbaceous ground cover species. In contrast, lianes were less abundant with mammal pest control, whereas herbs were more abundant. Fencing led to a high-density pulse of seedlings and saplings of woody species within 10years that then thinned. Mammal pest control allowed increases in abundance of some species palatable to T. vulpecula, and increased the ratio of canopy to subcanopy seedlings in the regeneration pulse caused by fencing. Neither treatment, however, led to the restoration of indigenous species richness to reference forest levels, nor allowed densities of juveniles of shade-tolerant canopy species to establish to levels commensurate with replacement of existing canopy trees. Most woody seedlings that established following fencing were of short-lived subcanopy species. These management actions will therefore slow but not reverse the long-term degradation of these forest fragments, which will eventually differ substantially from continuous forest under current management regimes. Additional measures such as replanting may be necessary not only to ensure replacement of some current species but also to restore lost species. © 2010 The Authors. Journal compilation © 2010 Ecological Society of Australia.