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Mechanisms responsible for the high species richness of disturbance-prone floras remain speculative. After fire, speciose shrublands in Australia possess mosaics of microsites that vary widely in seedling density and species richness and provide an ideal context in which to test a) the self-regulation hypothesis that species survive and grow better as they become rarer in the mix, and b) the synergistic hypothesis that species perform relatively better at increasing levels of competition under poorer growing conditions. Both processes should serve to promote species co-occurrence at the local scale. We planted germinants of 10 native shrub species in nutrient-poor sands in 30 cm (high density) and 40 cm (low density) square, buried but open-bottomed, boxes. Each box simulated a field-type microsite, containing one individual (solitary), or 49 individuals with each species contributing three (5% of the total, rare), five (10%, equal), 25 (51%, dominant) or 49 (100%, monoculture) seedlings. Best performance per plant (gauged as % survival × shoot mass per survivor) occurred among all ten species when solitary in the box. When grown in the presence of other plants, mixtures of species performed better on a 1) per plant, and 2) whole microsite, basis than monocultures at both densities, and 3) when rare rather than dominant in the mix, conforming with the self-regulation hypothesis, all independent of species identity. Expected niche differentiation of soil-based resources among species mixes would explain increased fitness per plant with decreasing abundance per species. Overall performance (performance per plant × absolute number of survivors per microsite) was maximized when all species were moderately rare (10% of initial numbers among 10 species) in the mix. Under good (low density) and poor (high density) growing conditions, increasing competition (indexed as total shoot mass) from the dominant species in the mix, led to a gradual fall and merging of shoot mass of

To investigate the mechanical behaviors of steel fibre reinforced concrete (SFRC) segments which are firstly used in the test section of the Shanghai Rail Transit Project Line 6, and to propose some useful suggestions for design and construction, a numerical analysis and field test are conducted. The contents of this study involve: (1) the behaviors of the segments against the jacking force, (2) the occurrence and development of cracks, the distribution of stress and strain of segment body, and (3) the distribution of stress and strain in circumferential joints of lining. The results show that safety against the jacking force of shield and the distribution of tensile strain in segment body and joint meet the requirement of design and construction. No cracks have been found in segments under the construction load. This indicates that the steel fibre provides the concrete of the segment with an improved crack resistance. It should be noticed that, although there is no cracks, the maximum tensile strain of rabbets of circumferential joints is much larger than the critical strain of the concrete. It is suggested that the rabbets should be reinforced in design., To investigate the mechanical behaviors of steel fibre reinforced concrete (SFRC) segments which are firstly used in the test section of the Shanghai Rail Transit Project Line 6, and to propose some useful suggestions for design and construction, a numerical analysis and field test are conducted. The contents of this study involve: (1) the behaviors of the segments against the jacking force, (2) the occurrence and development of cracks, the distribution of stress and strain of segment body, and (3) the distribution of stress and strain in circumferential joints of lining. The results show that safety against the jacking force of shield and the distribution of tensile strain in segment body and joint meet the requirement of design and construction. No cracks have been found in segments under the construction load. This indicates that the steel fibre provides the concrete of the segment with an improved crack resistance. It should be noticed that, although there is no cracks, the maximum tensile strain of rabbets of circumferential joints is much larger than the critical strain of the concrete. It is suggested that the rabbets should be reinforced in design.