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Population structure, intraspecific competition and phasic development of Urochondra setulosa (Trin.) CE Hubb., a coastal halophytic grass of Pakistan

Khan, D. and  S.S. Shaukat

Abstract: The population structure, intraspecific competition and phasic development of growth in a population of Urochondra setulosa (Trin.) C.E. Hubb., in a dry salt marsh of Hawkes Bay, Karachi, Pakistan, are described. Density and cover values averaged 26000 plants/ha and 1951 sq. m /ha, respectively. Size class distribution was asymmetrical (X-2 = 37.62, p < 0.001) as 84.8% of the population concentrated in initial classes of plants smaller than 50 cm crown diameter. The crown size data fined best (P < 0.001) to the negative power/ logarithmic equation indicating decreasing rate of mortality with age. Drawn to scale, crown outline diagrams indicated that when a hummock reaches to a critical size of around 60 cm in diameter begins to undergo degeneration and consequent hollowing in crown develops which increases with age. Among various developmental phases, mature hummocks dominated (40%) the frequency distribution, followed by building ones (23%). The frequency of seedlings + seedlings intergrading to pioneer was more or less equal to the frequency of degenerate and eroded phases. The phenomenon of phasic development is cyclic in time though quite incoherent in space. The spatial pattern of the population was contagious as determined through rest of fitness of Poisson series and the magnitude of variance mean quotient (2.58). Bivariate Simple Linear Correlation analysis for multiple nearest neighbours measurements indicated significant competitive influence of reference plants extending upto the third neighbour only. Multivariate Canonical Correlation Analysis (CANCOR), however,indicated intense competition only between the reference plant and the second and third nearest neighbours. The first nearest neighbour appeared to exhibit substantially lower competitive interaction with reference plant. The results are discussed in view of population structure, pattern and the biological characteristics.

Univ Karachi, Dept Bot, Karachi 75270, Pakistan