Geostatistical Analysis of Spatial Distribution of Endoclita signifer Larvae on Eucalyptus

Abstract

Endoclita signifer is a native wood borer species adapted to infest Eucalyptus in Guangxi of China. To better understand its spatial distribution in Eucalyptus forests, geostatistical approach was employed to analyze survey data of small scale (plantation level) and large scale (provincial level). The small scale results showed that the spatial distribution pattern was clumped regardless of infestation level. But the distance of spatial dependence was different with different infestation levels. These distances were 20.0 m, 40.3 m and 69.4 m for light, moderate and severe infestation levels, respectively. This indicated that as infestation level increased, the spatial distribution was less clumped. At the large scale level, the spatial distribution pattern was random when infestation was light. At the moderate and severe infestation level, the distribution pattern was clumped. The distance of spatial dependence was 43.6 km, 15.5 km and 12.47 km for light, moderate and severe infestation, respectively. This trend was opposite to that of the small scale. The large scale survey results reflected the occurrence of E. signifer in Guangxi province. Eucalyptus trees are cultivated in every county of Guangxi. Plantations with light infestation were scattered in a random pattern across the province. Moderate and severe infested plantations were mainly distributed in the central and southern areas of the province where Eucalyptus cultivation has longer history compared to other areas. Furthermore, the distance of spatial dependence was 17.4 km and 21.3 km for the 2nd generation forests (ratoon) and the 1st generation forests (established via seedlings), respectively. The observed spatial distribution patterns of E. signifer larvae seemed closely related to its biology and its successful adaptation to attack exotic Eucalyptus. These results provide fundamental knowledge for forecasting and evaluating E. signifer infestation and damage of Eucalyptus forests.