Characterizing Spatial Patterns of Gypsy Moth Regional Defoliation

Washington D.C.

1989

S. 557-568

11 Abb., 1 Tab., 21 Lit. Ang.

Bandaufführung

7380

16240

Aerial sketch maps of defoliation caused by the gypsy moth, Lymantria dispar (L.), in Massachusetts from 1961 to 1986 were digitized into an array of 1.9 x 1.9 km cells. Defoliation frequency was mapped by summing defoliation incidence for each cell. Spatial autocorrelation analysis indicated that defoliation was not distributed randomly over the state but was instead distributed in clumps of varying size. Directional spatio-temporal autocorrelation analysis showed no evidence for unidirectional spread of defoliation through time. Yearly defoliation, as a proportion of maximum, was used in a clustering algorithm to categorize different portions of the state in terms of defoliation synchrony. Two-state transition models were used to characterize defoliation initiation and termination. Different regions showed different probabilities of both outbreak initiation and termination. Transition probabilities varied substantially relative to the amount of defoliation in adjoining areas, indicating an apparent "spread" of defoliation.