Brief description
In 2013 the scope of the Island-wide Survey was expanded to gather data at each survey site about scale insect assemblages. This involves a vegetation survey of twelve key tree species that play a role in YCA-scale insect mutualism. These tree species are an effective proxy for the scale species present in an area. The dataset contains vegetation transect survey data on the target twelve key tree species that play a role in YCA-scale insect mutualism, collected during the Island-wide Survey.Lineage
Data Creation
Survey design:
The IWS was designed around the existing Christmas Island Geographical Information System (CIGIS) database produced by Geoscience Australia. This database contains a variety of spatial information (e.g., topography, digital elevation, vegetation, soil types, and roads), much of which is applicable to conducting and interpreting a field survey for invasive ants. For the survey, a grid of ~1000 sites was superimposed across the island with intervals of 365m between sampling sites. To maximize access to the sites, the grid was rotated to superimpose it on a network of drill lines (tracks made for mine soil sampling) distributed across the island and then offset by 25m (so as not to survey on drill lines). After the first IWS, many sites were excluded as they were not located within YCA prone areas (e.g., minefields). With the subsequent development of the IWS and the inclusion of a number of additional species many of these excluded sites have been reinstated. Surveys take place in the dry season (beginning around the end of May) when YCA are most active and Red Crabs are burrowing. In 2013 a vegetation survey component was added to gather detailed data at each survey site about scale insect assemblages. This involves a vegetation survey of twelve key tree species that play a role in YCA-Scale insect mutualism. These tree species are an effective proxy for the scale species present in an area. The diversity of tree species and the YCA activity index will show whether a site is suitable for future release of scale insect biological control agent.
Transect establishment:
At each survey site (marked with a red or orange tag nailed to the north side of a tree), a 50m transect is established with a compass and a Yamayo 3× Million 50m tape measure. Each transect is established along the random bearing direction that was determined in 2001 (although some bearings are altered each survey due to access difficulties, tree falls, lost tree markers etc), being careful to minimise disturbance to YCA and Red Crabs. In general, the transect is not deviated for vegetation that can be negotiated using a machete.
Sampling design:
Repeated Measures
Systematic Sampling
Measurements:
Raw Observations
Raw Observations - Count Data
Measurement Attributes:
Abundance; Location and Presence
Vegetation transect survey:
From the marked site tree, walking along the transect tape, the target tree species within 5m of each side of the tape is recorded. The survey area (5m either side of the 50m transect tape) is 500m2. The targeted tree species are tallied, in two categories, those between 15-50cm diameter and those 50+cm diameter at breast height (1.5m above ground), noting: 1. Trunks that fall within 5m are recorded even if they extend beyond the 5m distance. 2. Diameter is gauged on the wide side of a tree to ensure it fits into the category recorded. 3. Circumference of trees is not measured. 4. Gauging diameter 1.5m above ground is optimal for consistency; however, in the case of buttresses or multiple trunks the next best height is used to gauge tree diameter. 5. On sloping ground, measurement is taken parallel to the ground at the standard 1.5m height. 6. Ficus: a. Best attempts are made to ascertain and record the number of individual Ficus trees. b. The total diameter of multiple trunks are estimated for categorization. c. When a Ficus is strangling a host tree, either: the presence of an aerial tree is noted in comments i.e., Syzygium strangled by Ficus in canopy; or in the case of a Ficus touching the ground wrapped around a host tree and of size, both are categorized and recorded as individuals. If a target tree species is under-represented through the survey, because of small size, it is recorded in a third category: Lots < 20cm. Non-target species that have YCA traffic are tallied for interest. At the conclusion of the species count, the amount of tree traffic across the entire survey area is gauged for each species, and recorded as either NA, Nil, Low, Mod, High.
Flora sampling technique:
Transect Sampling.
Notes
CreditWe at TERN acknowledge the Traditional Owners and Custodians throughout Australia, New Zealand and all nations. We honour their profound connections to land, water, biodiversity and culture and pay our respects to their Elders past, present and emerging.
The Australian territory of Christmas Island lies in the Indian Ocean, 2,600 km northwest of Perth and 500 km south of the Indonesian capital, Jakarta. Christmas Island National Park (CINP) is 85 km2 in size and makes up almost two thirds of Christmas Island. Introduced sap sucking scale insects, such as Tachardina aurantiaca and Pulvinaria urbicola, produce carbohydrate rich honey dew as a waste product which is consumed by Yellow Crazy Ant (YCA) colonies. YCAs will farm these scale insects and provide them with protection in order to access this honey dew. Large amounts of carbohydrates in the system allow YCA to form into supercolonies. The objectives of the vegetation survey are to: gather data at each survey site about scale insect assemblages; gather data on diversity of tree species and YCA activity/tree traffic across each tree species; provide an understanding of YCA-scale-tree dynamics at each site; provide information about potential sites where scale insects might colonise in the future, and therefore where new YCA infestations may occur; and inform selection of sites for future release of scale biological control agents. The introduced Yellow Crazy Ant (YCA) (Anoplolepis gracilipes) is considered the most significant threat to Christmas Islands biodiversity. The YCA was accidentally introduced to Christmas Island sometime between 1915 and 1934 and numbers remained low and had no obvious impact on the islands biota until 1989, when the first high density supercolony was discovered. YCA supercolonies can rapidly change forest structure and composition, alter ecosystem processes, and pose a threat to many endemic species, including listed threatened and endangered species. In 2001, as a part of the Action Plan for research and management of YCAs, a survey design was developed by La Trobe and Monash University for an Island-Wide Survey (IWS) to determine the extent of supercolony formation and impact of YCAs on Christmas Island, to guide control and management programs while assessing the impact of YCA on Red Crabs. The survey is now undertaken biennially and has been refined since its inception to assess the distribution of a number of native and introduced flora and fauna species including crabs, reptiles, land birds, sea birds and mammals.
Created: 2014-08-27
Issued: 2022-03-14
Modified: 2024-05-12
Data time period: 2013-05-27 to 2013-09-25
text: IBRA region: Indian Tropical Islands; The Island-wide Survey covers the 135km<sup>2</sup> extent of Christmas Island.
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Point-of-truth metadata URL- URI : geonetwork.tern.org.au/geonetwork/srv/eng/catalog.search#/metadata/bf1343d3-8fc4-4ad4-86ea-8ba6c0639348
- global : bf1343d3-8fc4-4ad4-86ea-8ba6c0639348
