Spatial pattern analysis of weeds in selected rice fields of Samarahan, Sarawak

B. B. Baki

Abstract

Exploratory surveys were conducted in Samarahan Division, Sarawak in 1990 – 1991 to ascertain common weeds prevailing in rice fields. Spatial pattern of weed species in five 1 m²  quarats in each 87 farms were analysed. Three indices of dispersion (variance-to-mean ratio, Lloyd’s mean crowding and Lloyd’s patchiness) and the Moran’s I statistics of spatial autocorrelation were calculated. Weed species were almost exclusively composed of annuals, dominated by Fimbristylis miliacea and 30 other principal species. These species exhibited aggregated distributions with Lloyd’s mean crowding values ranging from 0.738 for Fuirena umbellatato 21.933 for Fimbristylis miliacea. Spatial autocorrelation values based on Moran’s I statistics were found to be positive and significantly greater than E (I) at p  = 0.05 for 17 species, thus suggesting aggregation or patchiness. The degree of clustering for those species were highly irregular indicating that plants distribution is probably due to biological or agroclimatic factors.

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