Carlos Nabinger

Grassland ecophysiology and grazing ecology.

Environmental constraints and plant responses to defoliation morphogensis of pasture species and adaptation to defoliation animal interactions sustainable grazing management of natural pastures.

Worldwide evidence of a unimodal relationship between productivity and plant species richness

Grassland diversity and ecosystem productivity The relationship between plant species diversity and ecosystem productivity is controversial. The debate concerns whether diversity peaks at intermediate levels of productivity—the so-called humped-back model—or whether there is no clear predictable relationship. Fraser et al. used a large, standardized, and geographically diverse sample of grasslands from six continents to confirm the validity and generality of the humped-back model. Their findings pave the way for a more mechanistic understanding of the factors controlling species diversity. Science, this issue p. 302 The humped-back model of plant species diversity is confirmed by a global grassland survey. The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.

Produção animal e de forragem em pastagem nativa submetida a distintas ofertas de forragem

This trial was conducted in natural pasture area of the Agronomic Experimental Station of Universidade Federal do Rio Grande do Sul (Porto Alegre-RS), from 10/25/2000 to 09/13/2001, with the objective of evaluating the treatments: 8%, 12%, 16% of dry matter allowance (DMA) over the year, 8% of DMA at spring and 12% at summer, autumn and winter (8-12%); 12% of DMA at spring and 8% at summer, autumn and winter (12-8%) e 16% of DMA at spring and 12% at summer, autumn and winter (16-12%), using steers on continuous grazing with variable stocking rate. The experimental design used was blocks randomised with two replications. The biggest average daily weight gain over the year (0.466 kg/an/day) was obtained in the increased DMA treatment. This treatment, also, was the only management the animals increased weight at winter. The animal production/ha was smaller in the 16% and 16-12% treatments. The DMA changing over the seasons, as a procedure to manipulate the vegetation structure and composition to increase forage production and average daily weight gain was efficient, and its effect upon the forage and animal production go on all the seasons.

Fluxo de biomassa em pastagem de azevém anual (Lolium multiflorum Lam.) manejada em diferentes alturas

In an italian ryegrass pasture under continuous stocking with sheep, biomass flows were estimated from 2 to 20 October 1999. Treatments corresponded to four different sward heights (5, 10, 15 and 20 cm) maintained by variable stocking. The experimental design was the randomized complete block design with three replicates. The fluxes were defined by morphogenetic and structural variables obtained from measurements performed on marked tillers. During the period in which the intended sward heights were established, significant effects in sward structure resulted in alterations on the biomass fluxes. The growth and intake fluxes showed a quadratic response with maximum values between 10 and 15 cm grazing heights, while the senescence flux increased linearly with sward height. Maximum daily live weight gain and animal yield per hectare were obtained within this interval, indicating this interval being the most appropriate to pasture management. The evaluation period was coincident with the floral induction phase, so the leaf lamina mass was progressively smaller and biomass fluxes showed a negative balance for all treatments.

Campos in southern Brazil.

The Brazilian subtropical region is located between the extreme southern border ofthe country (approximately 33°S) and the Tropic of Capricorn. This chapter dis-cusses the main grazing ecosystems found in this region (states of Rio Grande doSul, Santa Catarina and Parana), based on a tradition of beef cattle livestock pro-duction, which started at the beginning of Brazilian colonization at Rio Grande doSul and, little by little, spread north to the grasslands of Santa Catarina and Parana.Few places in the world present such diversity in native forage species, withalmost 800 grasses and 200 legumes.

Effects of grazing on the roots and rhizosphere of grasses.

Fertilizer inputs are currently being reduced in many areas (Commission, European Communities, 1992) and the resultant drop in pasture fertility will reduce the stock carrying capacity. As a consequence, individual plants will be defoliated less frequently (Curll and Wilkins, 1982) and less nitrogen will be deposited as urine (Thomas et al., 1988), thus influencing plant competition and composition. Research to date has concentrated on the effects of grazing on above-ground aspects, and it has recently been stated that ‘the effects of herbivory on the timing, mass and quality of below-ground inputs remains one of the greatest unresolved issues of the dynamics of nutrient cycling’ (Ruess and Seagle, 1994). The soil microbiota in grasslands consists of populations of microorganisms, including bacteria, fungi, protozoa, nematodes, and microand macroarthropod groups (Ingham and Detling, 1986). These all rely for their growth, at least in part, on carbon or nitrogen substrates via litter, root production, sloughage and exudation. Figure 4.1 illustrates the main links in the detrital trophic food web and shows the primary role of plant roots, the connectivity and some of the many trophic interactions. Although nearly all soil organisms belong to the detrital food web, significant numbers of root herbivores exist in grassland soil (Curry, 1994), also relying on plant roots for their survival. Any alteration in plant-derived carbon, such as through defoliation, will have consequences at many levels in the food web (Fig. 4.1). Since microbial activity, supported in part by root-derived carbon, drives soil nutrient cycling, the production and use of carbon from root systems is also a key issue in the functioning of soil ecosystems (van Veen et al., 1989). 4

Variáveis morfogênicas e estruturais de azevém anual (Lolium multiflorum Lam.) manejado em diferentes alturas

Morphogenetic and structural variables were obtained from measurements performed on marked tillers and were quantified during August to October 1999 in a ryegrass pasture grazed by sheep under continuous stocking and variable stocking rate in order to maintain the sward at four different heights (5, 10, 15 and 20 cm). The experimental design was a randomized complete block with three replicates. Fifty marked tillers per experimental unit were assessed and distributed along transects lines. Sward measurements were performed in two periods: the first one, from the start of grazing until the point where the intended grazing heights were established, with no differences among treatments. In the second (after achieving the intended grazing heights), leaf elongation rate, total green leaf lamina length per tiller and leaf size showed a positive response to increasing sward heights, while the time to leaf lamina elongation decreased. The variables leaf appearance rate and leaf life span, tiller population density and number of live leaves per tiller were not affected by treatments.

From the bite to precision grazing: understanding the plant-animal interface to exploit the multi-functionality of grasslands.

Precision livestock involves innovative technologies to monitor the animal within its pastoral environment. Understanding ingestive behaviour is fundamental to management decisions based upon animal and vegetation monitoring. The way such information can be used is not yet clear. In precision agriculture, the governing principle has been to correct or manage variability so as to homogenise yield at maximized levels. If the same reasoning is applied in livestock production, it can foster classical mistakes in grazing management. However, if precision livestock production can help integrate heterogeneity in managing animals on pasture, then we have a powerful new tool for responding to the new paradigms involving the multi-functionality of grasslands. This paper discusses this concept, and presents the bite as the basic unit of the process to be monitored. A few types of equipment and their application in monitoring site use and the spatial-temporal dynamics of animal biting are presented. The discussion concludes with how to build pastoral environments with precision bite management, and how to create sward structures to influence the temporal and spatial dynamics of animal biting.

Forage Allowance as a Target of Grazing Management: Implications on Grazing Time and Forage Searching

Abstract This work aimed to evaluate the following hypotheses: 1) the daily grazing time (GT) and 2) forage searching are more associated with the sward structure than with the levels of daily forage allowance (FA). To this end we proposed a model that was tested through an analysis of the sward structure, grazing time, and displacement in grazing by heifers on the natural grassland of the Pampa Biome (southern Brazil), which has been managed by FA levels since 1986. For three seasons, between January 2009 and February 2010, we evaluated the effect of FA on the main descriptors of the sward structure (herbage mass, sward height, and tussocks frequency) and the effect of these on the GT, displacement rate (DR), and daily displacement (D) in grazing. The data were analyzed with the use of regression and descriptive analyses from three-dimensional contour graphs with the data of the sward structure and GT. The DR was not associated with the FA levels or sward structure; however, the DR presented a positive linear relationship with the D and GT. The incremental change in the GT was accompanied by an increase in the D. Lastly, independently of the level of the FA and season evaluated, the lower values of GT were always associated with the following structural configuration: forage mass between 1 400 and 2 200 kg DM · ha−1, sward height between 9 and 13 cm, and tussock levels not exceeding 35%. Outside these limits, a penalty occurred in the GT and displacement patterns of the heifers. We found evidence that a better understanding of the cause–effect relationships between the sward structure and the ingestive behavior of the animals demonstrates the possibility of increasing the performance of domestic herbivores with important economic and ecological consequences. Resumen El objetivo del estudio fue evaluar las siguientes hipótesis: (i) si el tiempo de pastoreo diario (TP) y (ii) la búsqueda de forraje están más estrechamente relacionados a la estructura del pasto que a los niveles diarios de oferta de forraje (OF). Con este fin, propusimos un modelo que se puso a prueba en base al análisis de la estructura del pasto, el tiempo de pastoreo y el desplazamiento en pastoreo en terneras sobre un pastizal natural del Bioma Pampa (sur de Brasil) que, desde 1986, se ha manejado con distintos niveles de OF. En tres épocas, entre Ene/2009 y Feb/2010, se evaluó el efecto de la OF sobre los principales descriptores de la estructura del pasto (biomasa de forraje, altura y frecuencia de matas) y el efecto de éstos sobre el tiempo de pastoreo (TP), la tasa de desplazamiento (TD) y el desplazamiento diario (D). Los datos fueron analizados mediante regresión y por análisis descriptivos a partir de gráficos de contorno tridimensionales en base a los datos de estructura del pasto y TP. La TD no tuvo relación con OF ni con la estructura del pasto, pero mostró una relación lineal positiva con D. Incrementos en TP estuvieron asociados a incrementos en D. El estudio demostró la importancia de la estructura del pasto al constatar que, independientemente del nivel de OF y de la época del año evaluada, los valores más bajos de TP siempre estuvieron asociados a estructuras del pasto caracterizadas por una masa de forraje de 1 400 a 2 200 kg MS · ha−1, alturas de 9 a 13 cm y frecuencia de matas en el pastizal menores al 35%. Fuera de estos límites hubo una penalización en el TP y en el patrón de desplazamiento en pastoreo de las vaquillas. Encontramos evidencias de que el mejor entendimiento de las relaciones causa-efecto entre la estructura del pasto y el comportamiento en pastoreo harían posible incrementar el rendimiento de los herbívoros domésticos, con importantes consecuencias económicas y probablemente ecológicas.

Reserve formation and recycling of carbon and nitrogen during regrowth of defoliated plants.

Most herbaceous plants store carbon and nitrogen. There are several possible ecological advantages that the ability to store resources confers upon a species, which can be particularly important when considering plant competition and vegetation dynamics. These advantages include: (i) allowing growth to occur when either the availability of the external nitrogen is low (e.g. in the spring for growth of Molinia caerulea (Thornton and Millard, 1993)) or a short growing season means that uptake of soil nitrogen alone is not sufficient for growth (Jaeger and Monson, 1992); (ii) supporting reproduction by recycling resources from vegetative to reproductive growth – for example, in species exhibiting monocarpic senescence (Millard, 1988) and particularly in biennials (Heilmeier et al., 1986); and (iii) enabling more rapid recovery from catastrophic events, such as defoliation (e.g. Thornton et al., 1993a). It is this last role for storage that is considered in this review. Before we consider the quantitative significance of storage of both carbon and nitrogen in grasses in relation to defoliation, we shall first examine briefly the physiological strategies for storage used by herbaceous species. Experiments to quantify the storage and remobilization of both carbon and nitrogen will then be discussed and their limitations in determining the ecological significance of these processes in relation to vegetation dynamics highlighted. In order to understand competitive interactions between defoliated plants there is a need for field experiments that quantify storage and remobilization. Recent research is discussed which has developed a range of techniques that might allow such field experimentation in the future. 5