Categories: Conservation agriculture

Grazing and burning to maintain biodiversity

In this second part of our series on managing grasslands for biodiversity, grassland ecologist Dr Richard Lechmere-Oertel discusses guidelines and…

Grassland changes because of grazing and burning pressure. Environmental and management regimes can cause a shift in plant and animal species composition, thus altering the grassland. The biological architecture and function, soil structure and
fertility, water provision, nutrient cycling and fodder flow are all affected.

In terms of human livelihood or biodiversity, such changes are often seen as ‘degradation’, or a negative shift relative to the original state of the system or a management objective. Change can be seen by measureable indicators (see Table 1). Grassland ecologists see change progressing in a series of step-like stages, with observable movement in species composition, structure and function.

There is no single biodiversity-friendly best-practice that applies equally to burning and grazing all grasslands. Ecosystems, with varying biodiversity components, respond differently to different grazing and burning treatments. Thus, the focus is on
principles of burning and grazing that can be adapted to the condition of a specific grassland to meet specific objectives.

Burning for biodiversity
As farmers know, fire is complex. Differences in fuel load and moisture content, season, type of burn (head burn or back
burn), and prevailing weather (time-since-rain, wind, temperature, and relative humidity) will give different (intentional or unintentional) results. These variables influence the heat of the fire, the height of the flames and the duration of exposure.
Incorrectly applying or excluding fire can have undesirable results such as bush encroachment, soil loss, shifts in species
composition and so on.

The decision on when and how to burn grassland should be based on:

  • Clear management objectives (know what you want to achieve).
  • Knowledge of the ecology of the specific grassland and its probable response to burning.
  • An assessment of the veld condition and fuel load at the time, rather than recipe-based management. Only burn when there is sufficient biomass to do so. It is important to be a ‘student of the veld’, recording observations of veld and biodiversity condition and adapting management according to the objectives and prevailing conditions.

Grazing for biodiversity
Grazing is the most important management factor influencing grasslands. Many grassland species can sustain grazing pressure, and grazing seems to maintain the ecological character of grassland ecosystems, particularly the more arid ones.
However, most grasslands are not adapted to the sustained high grazing pressure typical of many livestock operations
with little management variety (fire frequency and type, grazing intensity, resting and others).

The species composition in grassland often changes when some species gain a competitive advantage as a result of selective grazing. Palatable species and individual tufts gradually lose vigour, at the expense of unpalatable species and
tufts, and eventually die.Over time, the grassland becomes dominated by the undesirable (or Increaser) species while the desirable species (or Decreasers) disappear.

Mesic grasslands recover slowly from disturbances that kill the grass tufts, while arid grasslands recover more easily by seeding. The effects of grazing and fire are difficult to separate as they have a close and subtle interaction. Mesic grasslands are generally adapted to, and indeed require, a combination of fire and grazing. The proportion of each will vary across the range of ecosystems from mesic to dry, but to exclude either will be detrimental. In general, the lower the grazing
pressure, the more fire is needed, especially in mesic and coastal grasslands.

Most grassland ecosystems lose some plant species under the sustained pressure typical of many commercial grazing regimes. But an appropriate grazing regime has several positive effects on biodiversity:

  • It stimulates biomass production and removes dead and moribund plant material that limits new growth.
  • Hoof pressure breaks up the soil surface, improving infiltration of rainfall and seed germination. This is particularly important where the soil surface has become hardened.
  • It redistributes nutrients through dung and urine and increases the nutrient cycling rate.
  • It creates spatial and temporal habitat diversity, increasing plant and animal diversity.

Grazing for biodiversity and sustainable productivity is possible using the following principles adapted to local ecosystems and management contexts:

  • Use an adaptive management approach that responds to veld condition, climate variation and species composition changes. It must include an intentional grazing plan based on camps of known carrying capacity and sensitivity (this will be more fully described in Part 3).
  • Rest each camp for a full growing season every three to five years. Despite the many options of rotational grazing (high intensity, low duration or continuous systems) and the many opinions as to which is best, all grasslands respond well to rest. Rest is very different to recovery in rotational grazing, which describes the few weeks the grass has to re-grow after being grazed. Neither recovery nor delaying grazing until later in the season provides adequate rest. To achieve rest, move the livestock through a series of camps, utilising 60% to 75% of the farm’s total area every year in the growing season and resting the balance.
  • Avoid overgrazing and selective grazing. Both cause significant changes in species composition, especially when combined with inappropriate burning.
  • Be conservative in areas with higher plant diversity, especially during spring when grasses and forbs are more vulnerable. Avoid high-intensity and selective grazing in areas that are important for plant biodiversity.
  • Avoid prolonged sheep grazing in areas of high plant biodiversity. Don’t leave sheep to graze high-lying rocky areas
    for long periods as they are often the last refuge areas for plant diversity.
  • Prevent cattle from forming deep paths by repeatedly walking the same route or grazing steep slopes during wet periods, accelerating soil erosion.

Consider four key factors when developing a grazing plan:

  • Carrying capacity at the camp scale;
  • Livestock species and breed;
  • Stocking rate;
  • Rest and rotation.

The following part of this series will model a farm-scale rotation plan that can be adapted to a specific management and
environmental context.

This article was written on behalf of the SA National Biodiversity Institute (Sanbi) Grasslands Programme. Email Dr Richard Lechmere-Oertel at richard.bpm@gmail.com. The electronic booklet Grazing and Burning for Grassland Biodiversity can be downloaded at www.grasslands.org.za.

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