Analysis of Frequency and Density Effects on Growth in Mixtures of Salvia Splendens and Linum Grandiflorum Using Hexagonal Fan Designs

Abstract

(1) The use of hexagonal fan designs as an efficient method for the analysis of frequency and density effects on growth and survival in two-component mixtures is illustrated in greenhouse experiments with the annual cultivars Salvia splendens and Linum grandiflorum. (2) Density had a large effect on vegetative and reproductive weight of Salvia, but a lower effect on Linum. These effects were consistent with the dwarf, large-broad-leaved habit of Salvia and the tall, small-narrow-leaved habit of Linum. Reproductive effort in Salvia declined with increasing density but increased in Linum. (3) There were complex density and frequency interactions, with the growth of Salvia at low densities being affected by a higher frequency of Salvia, and at high densities being affected by a higher frequency of Linum. At low densities, mixtures tended to give increased yields at low Salvia frequencies, but lower yields at high Salvia frequencies than in monocultures. (4) The density and frequency responses in the mixed hexagonal fan designs were generally consistent with responses in pure fans, or pure stands at fixed density, although there was evidence that the results in the mixed fans could not solely be accounted for by nearest-neighbour effects. (5) Data from such designs could be used to construct replacement series graphs, and density-frequency response surfaces, and to examine population regulation in two-species mixtures using graphs of population growth given different initial numbers of the two components. Complex patterns of population regulation were revealed that did not fit expectations from simple two-species competition models. (6) Hexagonal fan designs provided an approximately four-fold economy in seeds and nearly a ten-fold economy in space, compared with separate hexagonal plots providing the same range of frequencies and densities. However, there are considerable statistical problems associated with the analysis of such designs. Nevertheless, they promise to be an important exploratory tool for examination of yield and population regulation in two-species mixtures.