Papers by Olivier J F Bonnet
Pastoralism and agriculture have affected range- land ecosystems over the past millennia, includi... more Pastoralism and agriculture have affected range- land ecosystems over the past millennia, including many ecosystems that are currently protected as reserves. However, the legacy of these land-use practices on current ecosystem functioning remains unclear. We studied legacy effects of former human land use on soil physical and chemical properties in a South African savanna. We did this by comparing soil properties in grazing lawns (patches of short grass maintained by the positive feedback between grazing intensity and forage quality) with the sur- rounding less grazed bunch grasslands within three different human land-use history contexts: (i) Abandoned bomas: permanent stone enclosures where livestock were kept overnight, and dung and urine accumulated for several years or decades. (ii) Old fields: areas where vegetation was cleared, soiltilled, and cultivated, but received little or no fer- tilization. (iii) Natural grasslands: not cultivated but grazed by livestock before the establishment of the reserve and wildlife thereafter. Former human land use rather than soil texture was the main deter- minant of grazing lawn location. Moreover, lawn soil properties also varied among land-use histories. In all grazing lawns, soil nutrient concentrations were higher than in adjacent grasslands but aban- doned bomas contained three times more phos- phorus, and twice as much nitrogen and carbon than old fields and natural grassland lawns. In ad- dition to past land use, soil texture influenced lawn soil nutrients: Concentrations of phosphorus, potassium, calcium, magnesium, total nitrogen, and carbon in lawns were higher on clayey soils than sandy soils, whereas phosphorus, C:N ratio, and pH did not change with soil texture. Our study confirms previous findings on the effect of human land use on savanna heterogeneity, but also high- lights how legacy effects may vary among different historic land-use practices.
Despite all the biotic and abiotic factors affecting foraging by ruminants, there is a common and... more Despite all the biotic and abiotic factors affecting foraging by ruminants, there is a common and fundamental process, which is bite gathering. We hypothesised that because the mechanics of bite formation dominate the foraging process, changes in short-term bite mass are reflected in longer-term animal performance across a wide range of sward conditions. We focus at the meal level of foraging, using experiments in which the effect of abiotic factors and digestive constrains are minimised, making intake rate the main currency. We estimated bite mass across a wide range of structural challenges to large-herbivore foraging in a long-term experiment with heterogeneous native grasslands. A conceptual model was developed for average daily gain, where energy gain and energy costs were proximate causal variables. Energy gain was a function of diet quality and components of daily intake rate, where bite mass was the main component estimated. In turn, components of intake rate were determined by sward structure and bodyweight. Energy costs were a function of bodyweight and abiotic conditions. Finally, sward structure, bodyweight and abiotic conditions were determined by experimental treatments, seasons and years. Then, the conceptual model was translated into statistical models that included variables measured or estimated, and coefficients representing all links in the conceptual model. Weight gain was a function of bite mass, forage characteristics, and animal and abiotic conditions. Models were set up to test whether forage and stocking conditions affected monthly gain beyond the effects through bite mass, after correcting for abiotic factors. Forage mass, height and disappearance did help predict monthly gain after bite mass was included in the model, which supported our hypothesis. However, stocking treatments and season had significant effects not incorporated in bite mass. Although the model explained 77.9% of liveweight gain variation, only 35.2% was due to fixed effects, with 10.8% accounted by bite mass and its interactions. Concomitant experiments showed that sward structure (first with sward height and the second with tussock cover) does determine bite mass and short-term intake rate in the complex native grasslands we studied. Yet, other temporal varying components of monthly gain not correlated with bite mass, temperature or wind, added most of the observed variation in monthly animal performance. Part of the model failure to account for variation in performance may be related to a significant and temporally variable grazing of tussocks. We used a bite mass model that assumed no tussock grazing. In light of these results and a parallel experiment, we conclude that tussock grazing must be incorporated in future versions of the model.
Accurate estimates of bite mass and variations in the short-term intake rate of grazing herbivore... more Accurate estimates of bite mass and variations in the short-term intake rate of grazing herbivores has been historically considered as a fundamental methodological difficulty, a difficulty that increases with the complexity of the feeding environment. Improving these methodologies will help understand foraging behaviours in natural grazing conditions, where habitat structure and interactions among different forages influence feeding decisions and patterns. During the past 30 years, we have been developing the 'continuous bite-monitoring' method, an observational method that allows continuous assessment of foraging behaviours, including bite mass, instantaneous intake rate and food selection, in simple to complex feeding environments. The centrepiece of the method is a 'bite-coding grid' where bites are categorised by structural attributes of the forage to reflect differences in bite masses. Over the years, we have been using this method with goats, sheep, llamas and cattle across a range of different habitats. After reviewing the development of the method, we detail its planning and execution in the field. We illustrate the method with a study from southern Brazilian native Pampa grassland, showing how changes in the forages consumed by heifers strongly affect short-term intake rate during meals. Finally, we emphasise the importance of studying animals grazing in their natural environments to first identify the relevant processes that can later be tested in controlled experiments.
Journal of Agronomy
We evaluated the re-establishment of an Italian ryegrass pasture by self-seeding on a no-till int... more We evaluated the re-establishment of an Italian ryegrass pasture by self-seeding on a no-till integrated crop-livestock systems (ICLS) in the southern region of Brazil. This work is part of a long-term experimen- tal protocol initiated in 2003. We tested the effects of various management practices, such as summer crop systems (soybean vs. maize–soybean rotation), stocking methods (continuous vs. rotational) and grazing intensities (low vs. moderate), on Italian ryegrass pasture establishment. In addition, we tested resilience of the system by testing pasture’s ability to re-establish following a year without seed head production. The experiment consisted in the rotation, on the same area, of Italian ryegrass pasture grazed by sheep during the winter and up to the end of the grass production cycle, and soybean or soybean- maize grain crops rotation cultivated during the summer. The pasture established itself by self-seeding since 2005. Data were collected in 2011 and 2012 stocking season. The soybean summer crop, contin- uous stocking and low grazing intensity, all positively affected the production of reproductive tillers in 2011. Grazing intensity in 2011 strongly influenced early vegetative tiller densities (before crop harvest) in 2012. However, none of the grazing intensity or the stocking method treatments affected herbage mass at the end of pasture establishment in 2011 or 2012. On the other hand, the soybean summer crop positively affected pasture establishment, both in term of tiller densities and herbage mass at the end of pasture establishment. The removal of all seed heads in 2011 (preventing seed production) resulted in the total failure of pasture establishment in 2012. Overall, Italian ryegrass establishment by self-seeding relies on the annual replacement of the soil seed bank. This experiment demonstrated that under vari- ous stocking methods, moderate grazing intensity and maize or soybean summer crop, Italian ryegrass pasture establishment by self-seeding remains successful even when the stocking periods extended up to the end of the grass production cycle. Self-seeding with moderate grazing intensity ensures successful pasture establishment, reduces labour and costs and allows to increase the stocking period and so animal live weight gain over the grazing season.
Rangeland Ecology & Management
Instantaneous intake is central to the understanding of large herbivore foraging strategies and r... more Instantaneous intake is central to the understanding of large herbivore foraging strategies and rangeland ecology. Unfortunately, its measurement under field conditions remains challenging because of the difficulty of estimating bite mass. The hand plucking method provides a simple, noninvasive method of estimating bite masses and thus instantaneous intake of grazing herbivores. However, many authors questioned its accuracy and interobserver repeatability. In this study, we tested the accuracy and the repeatability of the hand plucking method using four observers and two herbivore species (i.e., cattle and goats). We compared hand plucked bite mass estimates to actual bite mass of bites taken by the herbivores on natural patches of grass. Training of the observers was fundamental to obtaining accurate bite mass measurements. The mean daily accuracy of the observers’ bite mass estimates increased from 60–80% to 80–94% within 5 d. After training, the relationship between bite mass estimates and actual bite mass was linear and not significantly different from a Y = X relationship. This means that individual bite mass estimates were centered on the real values and thus positive and negative errors canceled each other when combined. As a result, estimates of cumulative intake over about 10 feeding stations had accuracies of over 95%. Furthermore, neither the observer identity nor the herbivore species affected the accuracy of the measurements. The categorization of bites into different size categories proved to be essential in achieving accurate measurements. When observers are trained, hand plucking is a reliable and accurate method of estimating bites mass and instantaneous intake of grazing herbivores. This has important implications for rangeland research and management, as hand plucking is often the only practicable method available for estimating instantaneous intake of free- ranging herbivores.
Journal of Ecology
"1. Grazing lawns are short grassland areas where intense grazing maintains grass in an early gro... more "1. Grazing lawns are short grassland areas where intense grazing maintains grass in an early growth stage. These areas represent a source of high-quality forage for herbivores. However, as herbivores continually remove nearly all the newly accumulated biomass, instantaneous resource availability depends on the dynamics of grass growth.
2. In this study, we investigate how production and consumption inside grazing lawns are synchronized. We then explore how that synchronization affects the ability of large herbivores to use these lawns. We also provide a critical comparison between grazing lawns and intensively managed grasslands in livestock farms.
3. We investigated vegetation production and herbivore grazing activity during a wet and a dry season using clipping experiments and direct observation in two grazing lawns in a South African savanna.
4. Weekly total grazing activity by unit area was strongly and positively related to short-term primary production. This indicates a close synchronization between these two processes. In contrast, grazing activity was poorly related to standing biomass. Primary production had a threshold response to the weekly pattern of rainfall, implying a stochastic dynamics of grass growth.
5. The dynamics of grass production and consumption of grazing lawns is similar to the one of continuously stocked grazing systems from intensively managed grasslands. But the mechanisms regulating the two systems lead to different equilibrium points between production and consumption. The two systems also have opposed nutritional functions within the animal diet.
6. Synthesis.The close synchronization between resource production and consumption inside grazing lawns indicates that instantaneous resource availability is a direct function of the short-term rate of grass growth. In tropical savannas, the main source of variability of lawn grass primary productivity is the stochastic nature of short-term rainfall. As a result, herbivores’ ability to use grazing lawns is poorly predictable in time. This has important consequences on the degree of information herbivores can use in the elaboration of their foraging strategies, and on the potential interest of grazing lawns."
Conference proceedings by Olivier J F Bonnet
Proceedings of the 5th Greenhouse Gases and Animal Agriculture Conference, 24-26 June, Dublin, Irland., Jun 2013
Proceedings of the 22nd International Grassland Congress, 15-19 September, Sydney, Australia,, Sep 2013
Proceedings of the 22nd International Grassland Congress, 15-19 September, Sydney, Australia, 972-973., Sep 2013
Proceedings of the 22nd International Grassland Congress, 15-19 September, Sydney, Australia, 1188-1189., Sep 2013
Proceedings of the 6th Symposium on Strategic Management of Pasture and of the 4th International Symposium on Animal Production under Grazing, 15-17 November, Viçosa, Brazil., Nov 2012
Proceedings of the 3rd Nordic Feed Science Conference, 28-29 June, Uppsala, Sweden., Jun 2012
Conference Presentations by Olivier J F Bonnet
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Papers by Olivier J F Bonnet
2. In this study, we investigate how production and consumption inside grazing lawns are synchronized. We then explore how that synchronization affects the ability of large herbivores to use these lawns. We also provide a critical comparison between grazing lawns and intensively managed grasslands in livestock farms.
3. We investigated vegetation production and herbivore grazing activity during a wet and a dry season using clipping experiments and direct observation in two grazing lawns in a South African savanna.
4. Weekly total grazing activity by unit area was strongly and positively related to short-term primary production. This indicates a close synchronization between these two processes. In contrast, grazing activity was poorly related to standing biomass. Primary production had a threshold response to the weekly pattern of rainfall, implying a stochastic dynamics of grass growth.
5. The dynamics of grass production and consumption of grazing lawns is similar to the one of continuously stocked grazing systems from intensively managed grasslands. But the mechanisms regulating the two systems lead to different equilibrium points between production and consumption. The two systems also have opposed nutritional functions within the animal diet.
6. Synthesis.The close synchronization between resource production and consumption inside grazing lawns indicates that instantaneous resource availability is a direct function of the short-term rate of grass growth. In tropical savannas, the main source of variability of lawn grass primary productivity is the stochastic nature of short-term rainfall. As a result, herbivores’ ability to use grazing lawns is poorly predictable in time. This has important consequences on the degree of information herbivores can use in the elaboration of their foraging strategies, and on the potential interest of grazing lawns."
Conference proceedings by Olivier J F Bonnet
Conference Presentations by Olivier J F Bonnet
2. In this study, we investigate how production and consumption inside grazing lawns are synchronized. We then explore how that synchronization affects the ability of large herbivores to use these lawns. We also provide a critical comparison between grazing lawns and intensively managed grasslands in livestock farms.
3. We investigated vegetation production and herbivore grazing activity during a wet and a dry season using clipping experiments and direct observation in two grazing lawns in a South African savanna.
4. Weekly total grazing activity by unit area was strongly and positively related to short-term primary production. This indicates a close synchronization between these two processes. In contrast, grazing activity was poorly related to standing biomass. Primary production had a threshold response to the weekly pattern of rainfall, implying a stochastic dynamics of grass growth.
5. The dynamics of grass production and consumption of grazing lawns is similar to the one of continuously stocked grazing systems from intensively managed grasslands. But the mechanisms regulating the two systems lead to different equilibrium points between production and consumption. The two systems also have opposed nutritional functions within the animal diet.
6. Synthesis.The close synchronization between resource production and consumption inside grazing lawns indicates that instantaneous resource availability is a direct function of the short-term rate of grass growth. In tropical savannas, the main source of variability of lawn grass primary productivity is the stochastic nature of short-term rainfall. As a result, herbivores’ ability to use grazing lawns is poorly predictable in time. This has important consequences on the degree of information herbivores can use in the elaboration of their foraging strategies, and on the potential interest of grazing lawns."