Vegetational dynamics in some tropical abandoned rice fields in the western part of Orissa, India

Abstract

In many areas of tropics, agroecosystems are developed by clearing the natural forests. Conversion of natural forests to agricultural systems leads to loss of several soil ecological attributes responsible to maintain the soil fertility. Therefore in such converted agroecosystems the soil fertility often declines. In order to meet the deficiency of soil fertility, the farmers adopt the practice of nutrient input to such agricultural systems. However, poor farmers of tropics being unable to adopt such soil management strategy abandon the agricultural systems because of decline in production and leave the fields to remain fallow. The present study examined the vegetational succession and quantitative community characteristics in some abandoned agricultural ecosystems of western part of Orissa, India. The phytosociological attributes in different abandoned rice fields were studied by taking quadrates of suitable sizes (1 × 1, 5 × 5 and 10 × 10 m² for herbaceous grass and nongrass, shrubs and tree species respectively). Quantitative community characteristics like frequency, abundance, density of different plant species, diversity and dominance index were examined. Importance Value Index (IVI) was calculated to understand the importance of individual species in a community. The distribution patterns of different species were analyzed by species sequence curve method. Our finding showed that there is decrease in the number of grass stands and increase in the nongrass stands with the increase in the year of fallow periods. The study also indicated an increasing trend of species richness, abundance and diversity with increasing year of abandonment indicating the growth of secondary succession in this region.

Key words: Vegetational succession, quantitative community characteristics, importance value index, species sequence curve.