Germination effects on pasture composition in a dry monsoonal climate.
Germination and establishment in annual self-sown swards of (a) Stylosanthes humilis and (b) the associated grass weed Digitaria ciliaris were studied in 4 seasons in a dry monsoonal climate at Katherine, Northern Territory. (b) germinated in a series of 'false starts' followed by a single major wave of germination; (a) germinated in a single major wave. Changes in the species ratio during germination-establishment are defined in terms of a series of filters. At least 3 filters appear to operate. The 1st filter (ad,s) describes the change from hard to soft seed and the change in the soft seed population caused by 'false start' germination waves; the 2nd filter (as,g) describes the germination of seeds in the main germination event; the 3rd filter (ag,e) quantifies establishment of seedlings. Germination in this dry monsoonal climate usually occurs in one major wave, and therefore the change in species ratio from seed production to establishment can be described by a serial and consecutive arrangement of the 3 component filters. The 1st and 3rd component filters favoured (a). As a result, the combined filter (ad,e) also favoured (a). Values of (ad,e) varied from year to year, but were consistently higher on run-off than on run-on areas.