Better Understanding Pasture Vegetation

Beef cattle farming Farming Dairy cattle farming

The vegetation that feeds ruminants is by nature heterogeneous and diverse. To better understand and appreciate it, estimating its quantity and nutritional quality during the growth period is not enough. This must be enriched by the accumulation of biomass over time, focusing on what can be harvested by the herds at various times of the year. Attention must also be paid to the survival and reproduction of plants, in order to anticipate the renewal of food availability in the medium and long term.

Heterogeneous and diverse vegetation is often judged negatively based on a limited number of characteristics. Yet, they offer advantages for building feeding systems, based on grazing in each season of the year.
Vegetation is living and it is good to recognize its dynamics. This allows diversifying objectives, better choosing practices, and evaluating results obtained without comparing them to sown vegetation.

The valorization of each plot is unique. It is built through adapted practices that organize the encounter between vegetation and herd. One of the keys to success is therefore to know how to characterize your vegetation well by enriching the list of

characteristics to define them precisely and by observing them to understand the dynamics.

Better knowing your vegetation allows you to:

Make the best use of heterogeneous and diverse vegetation.
Rely on the living nature of vegetation.
Know how to define your own objectives and decide in advance and daily on practices to achieve them.

What does characterizing mean?

Characterization is an evaluation of the current state of vegetation functioning. It can only be turned into a value judgment by comparing it with the pursued objectives. Here we propose a list of interesting characteristics to note on vegetation in order to diversify the types of food availability they can offer.
These characteristics are grouped into three main categories:

Food availability: it enriches the view on the quantity and nature of biomass accumulating over time, beyond plant growth periods.
Food qualities: they vary with plant development.
Survival, mortality, and reproduction of plants: they allow anticipating the renewal or not of the previous characteristics in the medium and long term.

Food availability of a plant cover

Available vegetation is the green growth of plants accumulating over time, which will evolve more or less rapidly (green to yellow color), and finally enter degradation (gray to brown color). A plant grows from the moment new leaves or stems appear and develop each day. Even if vegetation growth has stopped, there is food availability: standing biomass that remains for a longer or shorter time.

Management possibilities through practices

Practices will directly act on factors specific to vegetation: the development cycle of plants throughout the seasons, the accumulation of plant reserves, and the diversity of the plant community. They can also influence environmental and microclimate factors (soil fertility and life, moisture, temperature, and light at soil level). However, they cannot act on the local climate. They must therefore anticipate seasonal uncertainties and variabilities.

Specificity of wetlands: water

Wetlands have the particularity of presenting a different pedoclimatic context due to the presence of water. This therefore modifies

both the seasonality of vegetation growth and accessibility periods (bearing capacity, flooding…). To valorize or manage vegetation, it is necessary to carefully consider the adaptation of practices to different periods.

Food qualities of a plant cover

Focusing on the food qualities of available vegetation means focusing on the ration that animals will choose to ingest at a given time. Qualities are determined by the different nutrients present in plants (soluble sugars or starch, fiber, nitrogen, etc.) and by palatability to animals. These qualities can vary greatly throughout the year.

Management possibilities through practices

The food qualities of a plant cover evolve over time according to the phenological stages of plants and the botanical diversity within the plot (different growth strategies depending on species).

Practices will act on these and thus modify the food qualities of vegetation. Beyond changing nutritional input, they will direct the capacity and motivation of animals to harvest and digest different components of vegetation at a given time. Pedoclimatic factors will also impact food qualities more or less directly. For example, climate influences the speed of plant development, soil moisture conditions select a type of flora.

Nutritional value analysis

Nutritional value analysis informs us of the chemical properties of the analyzed forage (composition in cellulose, nitrogen, soluble sugars…) at a given time. But it does not inform about the performance expected from it, since it is unknown whether it will be ingested by animals. Some plants with good forage values (for example Bulrush: 0.85 UFL, Floating sweet-grass: 0.9 UFL during their spring growth) are often refused, yet sometimes consumed. Conversely, others with lower forage values are often consumed or sometimes refused. It depends…

The explanation for this observation is not found in nutritional value tables but in understanding the animal-vegetation relationship that the farmer largely builds through livestock and grazing practices (food education, appetite stimulation, paddock delimitation, etc.).

Survival, reproduction, and mortality of plants

Vegetation renewal corresponds to the ability of different plants to survive and reproduce spontaneously. Vegetation is composed of populations of species and ages varied. Renewal occurs by seeding or vegetative means. Plant mortality depends greatly on age classes. Young stages are the most fragile; very old individuals always end up disappearing.

Management possibilities through practices

Practices will directly act on plant survival by allowing them more or less time to perform photosynthesis and thus replenish their energy reserves. They will also modify light competition between species. And they will act in the longer term by impacting reproduction by seed or vegetative means. Seedling survival is particularly fragile in the first year. Finally, they will act over time by renewing more or less the soil fertility. Indeed, environmental and climatic factors, whether modified by practices or not, also have an influence that is important to consider.

Case of woody plants

Woody species (shrubby and/or arboreal) offer other vegetation strata than herbaceous covers. It is necessary not to forget them in the characterization of a plot's vegetation. Because their presence directly and indirectly influences food availability and qualities. Most of them even have significant productivity and excellent capacity to remain standing. Despite a controversial name, "woody," their green foliage and young stems during summer periods provide them with interesting nutritional composition (nitrogen content, digestible fibers…). Nothing to do with indigestible lignin. Moreover, characterizing their dynamics (expansion, stabilization, or regression) is essential to guide animal harvesting according to the pursued objective.

Autres fiches Pâtur’Ajuste

Sources

SCOPELA, with the contribution of farmers. Technical sheet of the Pâtur’Ajuste network: Better know your vegetation. April 2021. Available at: https://www.paturajuste.fr/parlons-technique/ressource/ressources-generiques/mieux-connaitre-ses-vegetations