Climate and Vegetation Changes at Coringa-Herald National Nature Reserve, Coral Sea Islands, Australia

Abstract

Climatic changes at Coringa-Herald National Nature Reserve (CHNNR) in the last 82 yr include a 0.7 C rise in mean minimum winter temperatures and increases in drought duration and frequency. Between 1991 and 2002, a plague of the scale insects Pulvinaria urbicola (Cockerell), together with attendant ants destroyed Pisonia grandis R.Br. rain forest at South-West Coringa Islet. Scale insect damage of P. grandis has also been recorded at North-East Herald Cay. This study explored the reasons for vegetation dieback during current climate. Woody species such as Argusia argentea (L.) Heine, Cordia subcordata Lam., and the grasses Lepturus repens (G. Forst.) R.Br. and Stenotaphrum micranthum (Desv.) C. E. Hubb. have also declined at CHNNR. Ximenia americana L. and Digitaria ctenantha (F. Muell.) Hughes were found to be locally extinct. Dieback of forests results in reduction of canopy-breeding seabirds and burrowing shearwaters (Puffinus pacificus [Gmelin)]. Dieback species were replaced by the shrub Abutilon albescens Miq. and/or fleshy herbaceous plants such as Achyranthes aspera L., Boerhavia albiflora Fosberg, Ipomoea micrantha Roem. & Schult, Portulaca oleracea L., and Tribulus cistoides L. Increasing duration of droughts and increased temperatures, together with damage caused by exotic insect pests, appear to be the key drivers of the current vegetation changes.

Proximity to encroaching coconut palm limits native forest water use and persistence on a Pacific atoll

“…Mortality of trees might actually be related to a number of simultaneous factors, e.g., defoliation with water deficit, insect colonization, and salinization of groundwater lenses, without an a priori causal agent (Batianoff et al ., ). One potential confounding factor was the presence of the green scale insect P. urbicola seen on the leaves of many P .…”

“…This mutualism between introduced scale and ant communities was implicated in fostering higher population levels of both, causing defoliation of P . grandis trees on Palmyra Atoll (Handler et al ., ) and in other Pisonia forests worldwide (Batianoff et al ., ). On the other hand, the mechanisms driving these outbreaks spatially as well as other types of stress within Pisonia forests are cryptic though not mutually exclusive.…”

Lichen Monitoring Delineates Biodiversity on a Great Barrier Reef Coral Cay

“…These events resulted in much more open forest environments in the 1970s and 1980s compared to the present. Drought can also stress Pisonia trees, making them more susceptible to mortality through infestation by scale insects (Pulvinaria urbicola Cockerell) and attendant ants, which collectively reduce Pisonia cover [1]. There is evidence that climate variability may influence scale insects and ant population dynamics, with trees being more susceptible to infestation through stressed trees mobilizing nutrients in the soil during drought events and indirectly through a reduction in Nitrogen soil inputs due to rising sea temperatures reducing prey availability to resident seabirds [2].…”

“…Changing climates are projected to impact low-lying islands as sea levels rise, cyclonic disturbances intensify, and droughts and exotic invasions multiply [1][2][3][4]. Plant communities which occupy such locales will likely register the first effects of rapid climate shifts.…”

Characteristics of Coral Cay Soils at Coringa-Herald Coral Sea Islands, Australia

“…CHNNR has a tropical and maritime climate characterized by seasonally variable rainfall, consistently high annual temperatures (21.9 C mean monthly minimum in July to 30.7 C mean monthly maximum in January), and high evaporation rates (Farrow 1984, Bureau of Meteorology 2008, Batianoff et al 2010). Rainfall at nearby Willis Island (1,115 mm) occurs predominantly during the four ''wet'' months of January-April.…”