Grazing Management in Tropical Savannas: Utilization and Rest Strategies to Manipulate Rangeland Condition

Abstract

Grazing management is important for sustaining the productivity and health of rangelands. However, the effects of grazing management on herbage growth and species composition in the tropical savannas of northern Australia are not well known. In this eight-year study the influences of utilization rate and resting pastures from grazing on vegetation dynamics were measured at three sites in northeast Queensland, Australia. The sites had high, medium, and low soil fertility, and there were two land condition classes (States I and II) at each site. Severe drought occurred during the first four years, but above-average rainfall was received in the second half of the study. High utilization rates reduced biomass, perennial grass basal area, and ground cover. The reduction in biomass was due to both higher consumption and decreased primary production. State I condition plots at the high and medium soil fertility sites were initially dominated by decreaser perennial grasses, but these declined at all utilization levels, particularly the high rate. They were largely replaced by exotic perennial grasses. At the low fertility site there were no exotic grasses, and the decreaser grasses increased in all treatments, with the increases greatest in plots with low utilization or medium utilization plus resting. In the State II condition plots at the high and medium fertility sites, low or moderate utilization, led to an increase in both decreaser and exotic perennial grasses; with high utilization the decreaser perennial grasses declined and were replaced largely by exotic perennial grasses. This study clearly demonstrated that either conservative stocking with year-round grazing or a grazing system that includes some wet-season resting will help maintain land in a desirable state or help facilitate the transition from a less desirable ecological state to one more desirable for pastoral production and rangeland condition. Resumen El manejo del pastoreo es importante para mantener una productividad sostenida y la salud de los pastizales. Sin embargo, el efecto del manejo del pastoreo en el crecimiento del forraje y la composición de las especies en las sabanas tropicales del norte de Australia se desconocen. En este estudio de 8 añ os se consideró la influencia de la tasa de utilización y el descanso del pastoreo en potreros en la dinámica de la vegetación. El estudio se llevó a cabo en tres sitios en el noroeste de Queensland Australia. Los sitios tenían niveles de fertilidad en el suelo altos, mediano y bajo, y se tenían dos clases de condición (Estado I y II) en cada sitio. Se presentó una sequía muy severa durante los primeros 4 añ os pero durante la otra mitad del estudio la precipitación fue por arriba del promedio. Las altas tasas de utilización redujeron la biomasa y el área basal y cobertura ae´rea de las gramíneas perenes. La reducción en la biomasa se debió tanto al alto consumo y la reducción de la producción primaria. Las parcelas en el estado de condición I en los suelos con fertilidad mediana y alta estuvieron domin...

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

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“…However, all involved relatively small, uniform paddocks of between 3 and 30 ha, with small groups of animals (e.g. Burrows et al, 2010;Ash et al, 2011). This lack of scale and spatial complexity limits their relevance to larger, more heterogeneous commercial paddocks where production and rangeland responses may be significantly different (Ash and Stafford Smith, 1996).…”

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.…”

Unassisted invasions: understanding and responding to Australia’s high-impact environmental grass weeds

“…In a central Australian National Park, buffel grass became dominant in the 1990s when drought in the mid-1980s reduced native grass cover (Clarke et al 2005). Buffel grass also expanded after a return to above average rainfall following a drought period in semiarid Queensland in the period 2005-2011 (Fensham et al 2013) and, in the semiarid tropics, it increased rapidly after a severe drought followed by above average rainfall in the period 1992-2001 (Ash et al 2011).…”

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