Managing for rainfall variability: impacts of grazing strategies on perennial grass dynamics in a dry tropical savanna

Abstract

Rainfall variability remains a major challenge to sustainable grazing management in northern Australia with perennial grasses the key to the stability of the resources that maintain a sustainable grazing industry. This paper describes the dynamics of five perennial grasses – Bothriochloa ewartiana (Domin) C.E. Hubb., Chrysopogon fallax S.T. Blake, Aristida spp., Panicum effusum R. Br. and Heteropogon contortus (L.) P. Beauv. ex Roem. & Schult. in relation to three grazing strategies – moderate stocking at long-term carrying capacity, heavy stocking and rotational wet season spelling. The research was conducted in permanent quadrats on the predominant land type in an extensive grazing study in an Aristida-Bothriochloa pasture in north Australia between 1998 and 2010. Summer rainfall was above average for two periods – 1998 – 2001 and 2008 – 2010 with drought and below-average rainfall from 2002 to 2007. Low rainfall affected the dynamics of all grasses by reducing survival and basal area through its effect on plant size; this impact was most noticeable for the shorter-lived Aristida spp., P. effusum and H. contortus. The impact of grazing was greatest on the long-lived B. ewartiana and C. fallax; this effect was accentuated by the 2002–07 drought. Heavy grazing during this period further reduced the survival and size of B. ewartiana in comparison with the moderate stocking and rotational spell treatments. In contrast, the survival of C. fallax was reduced in the moderate stocking and rotational spelling treatment during drought, relative to that under heavy grazing. The density of B. ewartiana declined even under moderate grazing and despite two sequences of above-average rainfall because seedling recruitment failed to offset mature plant death. Results from this study emphasised the importance of maintaining the existing populations of key long-lived species such as B. ewartiana through good management. These results also supported the overall findings from the grazing study indicating that stocking at the long-term carrying capacity is sustainable in managing for climate variability.

The importance of grasslands for animal production and other functions: a review on management and methodological progress in the tropics

“…Clearly, management objectives for specific tropical pastures systems vary widely; aspects of management of tropical pastures to improve performance of grazing animals have been reviewed by Minson (1990), Humphreys (1991), Poppi et al (1997) and Lemaire et al (2009). In recent years, the management objectives have often focused on improving the vegetation, sustainability, biodiversity and nutrient cycling of the ecosystems (Ash et al, 2011;Orr and O'Reagain, 2011) as essential aspects of sustainable grazing systems. However, historically there has been limited focus on various objectives which relate to the multiple functions of grassland.…”

Sustainable management for rangelands in a variable climate: evidence and insights from northern Australia

“…The HSR strategy stocked at about twice LTCC gave good economic and animal performance in the initial wet years but suffered major economic loss in subsequent dry years through high costs, poor individual animal production and reduced product value at the meatworks. The strategy was also unsustainable with stocking rates having to be reduced in dry years and perennial grass density and basal area declining (Orr and O'Reagain, 2011). Profitability recovered in later good rainfall years, but after 13 years the overall profitability of the HSR was by far the lowest of all strategies (Figure 1).…”

Virtual herding for flexible livestock management – a review

“…Since then, some research has suggested plants, as well as livestock, benefit when paddocks are rested from herbivory (Sampson 1951;Voisin 1959;Davies 1976;Undersander et al 2002;Oates et al 2011;O'Reagain et al 2011;Teague et al 2013). However, other research does not support this (Herbel 1974;Gammon 1978;Van Poollen and Lacey 1979;Fales et al 1995;Hodgson and Illius 1996;Pulido and Leaver 2003;Briske et al 2008;Orr and O'Reagain 2011). The reasons for this disparity are many, some clear cut while others are more controversial (Briske et al 2014;Teague 2014).…”