The rapid and long-lasting growth of grasses following small falls of rain on stony downs in the arid interior of Australia [areas of origin of locust plagues, Queensland]
1994
Hunter, D.M. (Australian Plague Locust Commission, Canberra. Dept. of Primary Industries and Energy) | Melville, M.D. (New South Wales Univ., Kensington (Australia). School of Geography)
Rainfall of about 40 mm is required for significant growth of curly Mitchell grass (Astrebla lappacea) on the clay plains of western Queensland, but only 20-25 mm is sufficient for growth of barley Mitchell grass (Astrebla pectinata) on stony downs. The reason for these differences in rainfall requirements were studied, by examining the effects of various amounts of natural and artificially applied rain on both soil moisture and grass growth. Stony downs consist of grassy areas that alternate with areas that have a substantial stone cover. The stone-covered areas are impermeable, and most rain falling on them runs off, substantially increasing the effective rainfall in adjacent grassy areas. As a result, 20-25 mm of rain on stony downs wetted the soil around the grass to a depth of 140-170 mm and allowed sustained grass response. This is much less than the 35-40 mm of rain required for the same response on red clay or grey clay plains. Grasses respond very rapidly after rain. Some have green shoots the day after rain, and all have responded by the second day. Ephemerals dry off in 4-6 weeks, but most tussock grasses still have some green foliage 8-10 weeks after rain.
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