Grazing and Browsing - Removal of Ground Cover

Background: The plants mechanically protect ground against aggressive effects of wind, rainfall, runoff, also against direct exposure to the sun, heating, drying up, all harmfull to soil biological activity. By grazing and browsing, herbivores remove a part of the biomass, modifying the vegetal cover and the soil protection. This cover is assessed by the rate of vegetal cover (vs. bare soil). | Background Impacts Positive Impacts Negative Impacts Technology Options

According to the type of plant, reactions to grazing diversely affect the cover :

- When severely grazed, many perennial grasses develop tillers close to the ground, increasing the soil cover; the best example beeing the production of a lawn maintained by grazing.

- Annual grasses, when heavily grazed during growing season, hardly develop a complete plant and achieve their reproductive cycle ; in this case the cover is affected. The plant cover can completely desappear on the long term.

- Tall perennial grasses in tufts or tussock, when severely grazed, are not directly damaged by the teeth of animals, but soil between the tufts become exposed to light and sun, helping weeds and particularly young ligneous plant to germinate and growth. Finally, affecting the competition of grasses to broad leave plants, grazing causes an evolution of the pasture composition, generally perceived for farmers as a degradation.

- In sub-arid climate with steppe vegetation, shrubs and low ligneous plants are just defoliated by grazing pressure and their density can be affected by overgrazing. Between each plant, soil is generally bare if annual plants have not the possibility to growth, beeing exposed to erosion.

- In vegetation with shrubs and trees, browsing clears more or less leaves and branches until the maximum high of browsing (often between 1.50 and 2 meters for cattle and goats). Eating young sprouts and seedlings, animals can threaten the natural regeneration of these plants. Ruminants are sometimes used to clear the woody vegetation and maintain and open landscape.

Impacts

Impacts of grazing and browsing on ground cover can be positive or negative according to :

- the type and structure of the vegetation,
- intensity of grazing,
- the frequency (see continuous grazing and rotational grazing) and season of grazing.

Positive effects:

> Heavy grazing in wet temperate or tropical conditions can lower and spread the grass cover, producing a carpet or a continuous protective layer.

> Grazing removes a part of the biomass and prevents accumulation of litter, which could impede regrowing and future germinations of grasses.

> Cutting the young culms before flowering, the grazing delays the reproductive cycle of certain grasses and maintains the quality of the vegetative plants in the pasture, much more nutritious than the ripe plants.

Negative effects:

> Grazing of annual plants in growing season limits the capacity to produce seeds. Heavy selective grazing decreases the competitivity of the most palatable species and favors the less useful species. Excessive grazing and browsing can cause finally weakness and death of palatable plants. Deterioration of ground cover is often linked with trampling and soil compaction.

> A deficient ground cover exposes soil to erosion. Strong winds on very dry soils takes out fine particles and dust, charging atmosphere with them. These particles affect the purity of air and the light transmission in atmosphere.

Technology Options

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