Simulation of defoliation effects on primary production of a warm-season, semiarid perennial-species grassland

doi:10.1016/0304-3800(92)90012-4

Ecological Modelling

Volume 60, Issue 1, January 1992, Pages 45-61

https://doi.org/10.1016/0304-3800(92)90012-4 Get rights and content

Abstract

A simulation study was conducted on the production potential under grazing of a perennial C₄-species grassland. A model of plant growth governed by soil moisture availability and prevailing weather conditions was adapted to account for perenniality, C₄ photosynthesis, intra-seasonal regrowth, and defoliation effects. Model behaviour was validated against a set of field data obtained from the Ñacuñan experimental site, Mendoza Province, Argentina. Primary production, defoliation effects and potential forage utilization as a consequence of different stocking rates and grazing systems were simulated for two consecutive years.

The model indicated that where animals were grazed continuously, primary production was only a slightly reduced by relatively heavy grazing. This occurred because of the particular growth pattern of the vegetation which is characterized by pulses with relatively high growth rates over short periods. These growth rates are considerably higher than potential defoliation rates, even at relatively high animal densities. The effect of an intensive, short duration rotational grazing system compared to continuous grazing had only a small effect on the simulated primary production and on the total amount of utilized green herbage, even though these variables varied widely between subdivisions within a grazing rotation. It is concluded that the growth pattern of the grassland vegetation, determined mainly by the characteristics of the prevailing weather in the region, limits the utilization of the green leaf to about 11–14% of the annual herbage production when animals have to be maintained throughout the year on the grassland. The rest of the available forage must be consumed as dry feed. As a result, the primary productivity of such grasslands appears to have low sensitivity to fairly large variations in stocking rate and grazing management. These results explain some of the inconclusive and conflicting results of grazing trials, and so have significant implications for research policy and grazing management in semiarid environments similar to those studied in the region.

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Accurate predictions of water vapor at large temporal and spatial scales are particularly important in global studies. In recent years, Central Asian grasslands have been subject to both intensive grazing and variability in climatic conditions. However, uncertainties about grazing on water cycling under climate change still exist. Therefore, the Biome-BGC grazing model was applied to assess the effects of grazing on evapotranspiration (ET) and water use efficiency (WUE). Three grassland types were studied during the period 1979–2011: forest meadow (FM), temperate grassland (TG) and desert grassland (DG). ET shows a gradual decreasing trend from FM (365.65 ± 36.86 mm m⁻² yr⁻¹) to DG (183.32 ± 21.15 mm m⁻² yr⁻¹), and WUE ranging from 0.62 ± 0.03 g C kg^-1 H₂O in FM to 1.12 ± 0.10 g C kg⁻¹ H₂O in TG, with an average of 0.83 ± 0.05 g C kg⁻¹ H₂O. Although there was a significant decrease in ET of 1.47–2.72 mm m⁻² yr⁻¹, WUE increased at a rate of 0.004 g C kg⁻¹ H₂O yr⁻¹ in Central Asia. From 1979 to 2011, grazing lowered ET by 7.47% in Central Asia; the reduction rates for FM, TG and DG were 3.10%, 12.70% and 7.42%, respectively. In general, grazing decreased WUE by 3.60%. From non-grazed to grazed scenario, WUE increased by 6.86% for FM, but WUE decreased by 7.27% and 5.61% for TG and DG. An over-compensation of GPP under grazing might account for the higher WUE under certain grazing intensities. In order to achieve maximum utilization of water efficiency, proper grazing intensity for TG, DG and FM should be limited to 0.17, 0.39 and 0.38 head/ha, respectively.
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However, the grazing process was not effectively considered, leading to biased results (Haberl et al., 2007; Krausmann et al., 2013, 2012). Luo et al. (2012) developed the Biome-BGC grazing model by integrating a defoliation formulation (Seligman et al., 1992) into the Biome-BGC model, producing a grazing model for describing the effects of grazing on the carbon cycle of grassland ecosystems. The Biome-BGC grazing model is a process-based model that effectively estimates NPPpot, NPPact, and the carbon consumed by animals (Han et al., 2016; Luo et al., 2012).
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Biome-BGC does not include the grazing process in its original version in the application for grassland ecosystems. However, a defoliation formulation developed by Seligman et al. (1992) could calculate the biomass consumed by animals and analyze the production potential under grazing conditions in grasslands. This defoliation formulation was embedded in the Biome-BGC model, which was then referred to as the “Biome-BGC grazing model.”
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For example, in CENTURY model, grazing effects are simply classified into four categories without taking different grazing intensity into account; Sim-CYCLE grazing model refer the herbivore as customer, but rather to estimate the feedback effect to grassland. On the contrary, Biome-BGC grazing model developed by Luo et al. (2012) integrate a defoliation formulation (Seligman et al., 1992) into Biome-BGC model, producing a grazing model for describing the effects of grazing on the carbon cycle of grassland ecosystems. Luo et al. (2012) applied Biome-BGC grazing model to investigate the effects of grazing on the aboveground NPP (ANPP) in Tianshan Mountains-Junggar Basin (TMJB) with four grasslands along a climatic gradient from mountain to plain.
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Biome-BGC did not include grazing process in its original version in the application for grassland ecosystems. However, a defoliation formulation developed by Seligman et al. (1992) was shown to be able to calculate the biomass consumed by animals and to analyze the production potential under grazing condition in grassland. The objectives of this paper were therefore (1) to integrate grazing process into Biome-BGC model for addressing the effects of grazing on ANPP along the climatic gradients and their variations during the period 1959–2009 in different grasslands from the mountain to basin over the TMJB, (2) to investigate the response of ANPP to grazing intensity and to speculate the possible underlying mechanisms, and (3) to discuss under what ecosystem-environmental conditions grazing can promote ANPP of grasslands in the Central Eurasia continent.
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^☆: This research was conducted under the sponsorship of the Special Project for Improvement and Development of Ecological Research (SPIDER) in Argentina, as part of the activities of the Consejo Nacional de Investigaciones Cientificas Tecnicas (CQNICET), Argentina.

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Simulation of defoliation effects on primary production of a warm-season, semiarid perennial-species grassland☆

Abstract

Ecol. Modelling

Ecol. Modelling

Agric. Syst.

Ecol. Modelling

Ecol. Modelling

Ecol. Modelling

Utilización invernal de gramineas estivales en un establecimiento ganadero de los llanos de La Rioja

IDIA Supl.

The influence of clipping frequency on reserve carbohydrates and regrowth of Eragrostis curvula

Does herbivory benefit plants? A review of the evidence

Am. Nat.

Root growth of grasses and cereals

Regiones Fitogeográficas Argentinas.

Distribution of C3 and C4 grasses at different altitudes in a temperature arid region of Argentina

Oecologia (Berlin)

Distribution vertical de materia seca en gramineas perennes de la llanura oriental de Mendoza

Deserta

Simulation of grazing systems

Simulation of grazing systems

Curva de produccion forrajera de Pappophorum caespitosum

Deserata

Dynamics of root growth and decay in two grasses native to semiarid Argentine

Aust. J. Ecol.

Vegetation and soil responses to short duration grazing on Fescue grasslands

J. Range Manage.

Calculation of daily totals of gross CO2 assimilation of leaf canopies

Neth. J. Agric. Sci.

Range resources inventory of Mendoza (Argentina)

Utilización de gramineas forrajeras estivales por bovinos en el campo ‘ El Divisadero’, Mendoza

Grazing management of herbaceous Mediterranean foothill range in the upper Jordan valley

J. Range Manage.

SMART: a simple model to asses range technology

J. Range Manage.

Cattle, vegetation and economic response to grazing systems and grazing pressure

J. Range Manage.

Calculation of daily totals of gross CO₂ assimilation of leaf canopies