Seed rain of Microlaena stipoides

Microlaena stipoides (Microlaena) is a native grass that is recognised as being of increasing importance in natural grazing systems in south-eastern Australia. Critical to its wider use is understanding how it spreads, particularly through seed production as the precursor to seedling recruitment. Pitfall funnel seed traps were used to measure reproductive potential of a vegetation community via seed rain. The abundance and weight of Microlaena seed in the seed rain of a grazed native grass pasture was measured over nine months (November 2010 to July 2011) at Chiltern, north-east Victoria. During the period of the experiment 544 mm of rainfall was received, above average summer rainfall. The primary dispersal method for Microlaena seed is by gravity. Within six dense swards of Microlaena nine seed rain traps were established. The traps were set out in a 3 x 3 pattern with a spacing of 0.4 m between trap centres. Phenological growth stage of the Microlaena was recorded. Over the measurement period a total of 265 seeds were collected; equivalent to 23 kg seed/ha. The peak period of seed production, in terms of both weight and number, was from late December to early January. The average seed germination of 60% was recorded 17 weeks after collection. These low seed yields, combined with climate and competitive risks suggest that few seedlings are likely to establish and persist as plants in any one year. Used in conjunction with other monitoring methods, these results offer a valuable insight about the dynamics of an individual species, and can contribute to the development of appropriate management strategies to maintain populations of Microlaena within grazed pastures.