Managing productivity in brittle grasslands

High rainfall tropical savanna in the middle of the growing season. This is 35" (890 mm) precipitation high veld near the Zietsman farm outside Karoi, Zimbabwe. High-production brittle grasslands like this are dependent on high levels of grazing and animal impact (once supplied by wild game) to recycle vast amounts of standing vegetation before the next growing season. If that doesn't happen, the huge mass of dead growth shades and kills the grasses trying to resprout underneath.

Herd of neighbor's cattle being contract grazed in September 1996 on the Zietsman farm. The foreground was strip grazed the previous day; the background strip will be grazed the next day. Notice dense forage in the background, visible over the cattle's backs, and excellent ground cover on the grazed area.

Fire could remove standing dead growth in time for the rains, but it leaves the ground bare and vulnerable to erosion, pollutes the air with valuable nutrients, and tends to reduce biodiversity. Nor will fire break soil crusts to allow water to soak in and seeds to sprout, or produce beef to generate farm income.

Same herd waiting for herder to move onto new patch as herder takes up wire. Grazing density is 3000/ha (1200/acre) moved every 1/2 to 1 hour.

Typical high rainfall tropical savanna at the beginning of the rainy season. Bulk of previous year's grass is removed and on the ground, with vigorous greenup after just 1.5" (40 mm) of rain. Here Johann Zietsman walks his paddock

Left: grazed at extreme density for very short time through the dormant season. High animal impact from cattle mimics the pounding of wild herds that once renewed the veld. Right: grazed year round at low density (conventional management). Chivhu, Zimbabwe — fenceline contrast on the O'Neill ranch (high-rainfall tropical savanna).

Growing season, mid-rainfall subtropical savanna in Entre Rios, Argentina. These mid-rainfall areas have somewhat lower productivity than the really high-rainfall areas. Consequently, plants typically need longer recovery periods between grazings.

Lower biological productivity also means grass plants accumulate less lignin, are therefore higher in nutritive quality, and are less physically difficult to break down and lay on the soil surface. Ultra-high stock densities and extreme levels of animal impact therefore become less critical than in higher producing brittle savannas.

Same place in Entre Rios, Argentina during dormant season. Annual rainfall here is 20-25 inches (500-640 mm).

African mid-rainfall tropical savanna during dormant season. Precipitation is 16-20 inches (400-500 mm). Sandy Speedy farm near Vryburg, South Africa.

High plant diversity in a mid-rainfall subtropical savanna during dormant season. Sandy Speedy farm near Vryburg, South Africa.

Growing season, mid-rainfall tropical savanna. This herd of 1000 cattle grazes 25-acre paddocks for 1-day periods. Farm managed by Keith Harvey near Vryburg, South Africa.

Growing season, mid-rainfall tropical savanna. 450 head/acre (180/ha) moved 5 times per day. Marius Nel farm near Vryburg, South Africa.

Dormant period on low-production mild temperate steppe getting 12" (300 mm) precipitation annually. On mild steppes, extremely erratic rainfall limits production. This increases space between plants, so we rely more on litter to protect the soil surface. The High Lonesome, Lordsburg, southwestern New Mexico, U.S.A.

Soil surface condition on upland range on the High Lonesome. Good ground cover and good greenup of warm-season perennials for a low-production, highly brittle area following 1.5" (40 mm) rain in July.

The litter accumulation you see at the soil surface is extremely important, because seeds have such a hard time germinating and establishing on bare soil in arid environments. Without the litter, precipitation is largely ineffective due to high evaporation rates off of bare, exposed soil.

Mild steppe in the dormant season, following several years of above-average forage production. Steppes tend to get their precipitation spread out over the whole year. Months or years may pass before rains come in close enough succession to create good growing conditions. High Lonesome, southwestern New Mexico, U.S.A.

Cool season annuals growing in a big tobosa grass (native warm season perennial) draw in March after unusually abundant winter rain. Highly brittle mild steppe on the High Lonesome ranch, southwestern New Mexico, U.S.A.

Mild winter temperatures make cool season growth possible, but it is very erratic and unpredictable. As of early 2003, this amount of cool season growth hadn't recurred since the picture was taken in 1995. Warm season growth on the tobosa grass is more reliable, but still happens in only 40-50% of summer growing seasons -- very different from the predictably abundant growth in high-production, highly brittle environments.

Low-production mild steppe southeast Arizona after 1.5 years recovery from heavy grazing pressure from cattle. Cool-season annual grasses, warm-season perennial grasses, winter fat, shrubby buckwheat, and four-wing saltbush all have had the chance to grow through 1 cool season and 2 warm seasons, resulting in high forage volume (pasture mass) to feed the returning herbivores and add to the litter bank.

14" (360 mm) semi- to highly brittle cold steppe in western Colorado, U.S.A. This area was grazed heavily in mid-June during peak growth . I took the photo in October, after decent summer rain but only 5-6" (130-150 mm) new growth. These plants are not recovered. Grazing them a second time in the same growing season would result in widespread overgrazing as well as the removal of lots of valuable litter-making material.

Same as previous, but a paddock cattle didn't move onto until September. This is what fully recovered plants look like here in a pretty good year. On our place east of Montrose, Colorado, U.S.A.