Analysis of small-scale spatial pattern of Endoclita excrescens based on SADIE and SPPA

  Objective  The swift moth, Endoclita excrescens (Lepidoptera: Hepialidae), is a polyphagous forest insect causing great damages to Manchurian ash (Fraxinus mandshurica) in the Northeast China. The spatial patterns of the moth at fine-scale were investigated in this study, which will provide basic information for precision-targeted management.

  Method  Spatial analysis by distance indices (SADIE) was employed to measure spatial aggregation and spatial association of the count of bored holes and the DBH (diameter at breast height) of the host-tree, which were marks of a marked spatial point pattern. The spatial randomness of the distribution of ash tree was tested by the L function. The independence between mark and point was tested by the conditional mean function. Mark variogram and Stoyan mark correlation function were used to measure spatial autocorrelation. Each sample plot was divided into quadrats to calculate SADIE aggregation indices and clustering indices. Two density plans were used to devide the sample plot.

  Result  Results from SADIE indicated that bored holes significantly aggregated in the two sample plots (G1 and G2). In sample plot G1, patches and gaps were separated and located at the two ends of the sample plot, respectively; while in sample plot G2, patches and gaps were mixed. In sample plot G1, trees with small number of bored holes were significantly close to other trees with small number of bored holes at distances of 4.0−4.8 m or 14.5−16.0 m; while in sample plot G2, same spatial patterns were identified at distances of 8.5−9.0 m. The results from mark variogram functions showed that there were no significant spatial autocorrelations at small distances in both sample plots. The spatial patterns of the ash tree and its DBH were strongly associated with the patterns of bored holes, respectively, indicating both of them play roles in the spatial pattern formation of bored holes. Results from either SADIE spatial aggregation index or L function suggested that the host trees were spatially aggregated. And the results from conditional mean of the mark function showed that the mark (count of bored holes) was independent on the point (tree location).

  Conclusion  The spatial pattern of the bored hole of the swift moth is aggregation in the stand of ash. Both the location and size of host trees shape the spatial patterns of bored holes.