Dynamics of plant populations in Heteropogon contortus - Tropical ...

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84 D.M. Orr Seed production (seeds/m 2 ) (a) 8000 6000 4000 2000 0 b a a b ab a Narrow-leaved ironbark Silver-leaved ironbark Burning 1993 1994 1995 1996 Seed bank (seeds/m 2 ) (b) 1200 1000 800 600 400 200 0 Narrow-leaved ironbark Silver-leaved ironbark Burning 1992 1993 1994 1995 Figure 5. Changes in (a) seed production measured in autumn and (b) soil seed bank measured in spring of H. contortus in unburnt narrow-leaved ironbark and silver-leaved ironbark pastures and mixed pasture burned in spring in H. contortus pasture in southern Queensland. Within years, columns with different letters are significantly (P
Fire on Heteropogon contortus and Aristida spp. populations 85 (a) 4 Narrow-leaved ironbark Silver-leaved ironbark Burning (B) (NLI) (SLI) Basal area (%) 3 2 1 B, SLI >NLI 0 1992 1993 1994 1995 1996 (b) 1.2 1 Basal area (%) 0.8 0.6 0.4 B, SLI >NLI B, SLI >NLI 0.2 0 1992 1993 1994 1995 1996 Figure 6. Changes in the basal area of (a) H. contortus and (b) Aristida spp. measured in autumn in unburnt narrowleaved ironbark and silver-leaved ironbark pastures and mixed pasture burned in spring in H. contortus pasture in southern Queensland. severe drought precluded the increased level of seedling recruitment that could be expected. This finding that low rainfall was the major limitation to seedling recruitment contrasted, for example, with seedling recruitment studies of Themeda triandra (kangaroo grass) in southern Africa (O’Connor 1996), which indicated that seed supply was the major limitation to recruitment. Implications for grazing management Results presented here indicate that burning H. contortus pastures in spring in combination with reduced grazing pressure does not always increase the proportion of H. contortus. Some of this failure was probably due to the lower than average rainfall received throughout most of the study. Another factor may be that different taxa
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Dynamics of plant populations in Heteropogon contortus - Tropical ...

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