Tuesday, March 10, 2009

Land Management: Regenerative Grazing.

The same regions, thus with the same rainfall, same soils, and the same plant species can be either lush or barren, depending only on how they are managed. In particular, the degree of carbon in the soil is critical, as can be noted empirically just by looking. Hundreds of millions of hectares of grazing land worldwide in arid and seasonally dry areas have been reduced to near desert, but it need not be so. By a simple sum we may note that:

one hectare is equal to 10,000 square metres;

soil is typically 33.5 cm (about one foot) deep;

it has a bulk density of 1.4 tonnes per cubic metre;

thus the soil mass per hectare is 0.335 x 1.4 x 10,000 weighs 4,670 tonnes;

an increase in soil organic matter by just 1% means another 47 tonnes;

if we assume that about 50% of this is carbon, we have captured around another 23 tonnes of carbon per hectare;

this is equal to capturing 85 tonnes of atmospheric CO2.

If grazing animals are kept in one area, they repeatedly chew fodder plants and keep them small. Because there is a virtual symmetry between the amount of carbon in the exposed (above ground) plant and that in its root system, if the visible plant is small, so are its roots. Small leaves can only nourish small roots and so overgrazed plants will wither and die while shrubs, weeds and thorns can still reach water and thrive. It is thought that only soil is massive enough and manageable enough to capture significant amounts of CO2 over the next 30 years. All other - technological - carbon-capture schemes will probably take 30 years and more to be implemented and it is debatable how effective they will be.

Removing CO2 from power stations, at source, does not reduce the existing atmospheric carbon burden; neither does burying it in underground aquifers, deep cap rock formations and in exhausted oil wells etc. and it might take 100 years to know whether the strategy is effective or not. Simply establishing tree plantations is not certain either, since they can actually be net emitters in their early stages, and take many years to achieve their full carbon capture potential. Switching over to wind turbines and solar power doesn’t influence existing levels of carbon either, and it is debatable in what volume or how quickly such renewable energy sources can be established. The alternative means for getting-rid of carbon is to liquefy it and dump it on the ocean floor at depth, but this is likely to make the waters more acidic and impede shell formation in creatures that live there, thus impacting on the whole ecosystem.

So, how much carbon are we talking about? According to the UnitedNations Food & Agriculture Organisation "Soil organic carbon is the largest reservoir in interaction with the atmosphere." This sounds promising especially when we note that 650 gigatons (Gt) of carbon are present in vegetation; 750 Gt in the atmosphere and 1,500 Gt in soil. The U.S. Department of Energy concludes:"Enhancing the natural processes that remove CO2 from the atmosphere is thought to be the most cost-effective means of reducing atmospheric levels of CO2." The total area of grazing land on Earth accounts for two thirds of the total land surface, which amounts to 2/3 x 150 million km2 or 100 million km2 (10 billion hectares). We can thus make a simple sum and conclude that an extra 1% of carbon at 23 tonnes/hectare x 10 billion hectares = 230 billion tonnes of carbon stored.

Now we are clearly not going to cover 2/3 of the Earth’s surface with grazing animals, even if we move them around to allow grazing-crops to grow, and we are looking toward appreciable efforts in permaculture on the 15 million km2 of arable land there is available, but the point is clear that a large amount of carbon could potentially be pulled down from the atmosphere by the simple act of moving grazing animals around. Land management by moving grazers around has other environmental benefits too. For example in Zimbabwe, where a river used to run freely, the effect of overgrazing has resulted in a barren land which flash-floods when heavy rains fall. There is a severe loss in biodiversity, livestock are starving and most wildlife has gone. In contrast, a neighbouring river flows almost continually, drought is rare and wildlife has reappeared in large numbers. Again, the only difference is livestock management. The result is that the ability of the land to absorb and retain water is increased; new soil is being created; new plants are bedding-in; there are greater yields of fodder plants; greater biodiversity and a healthier landscape overall. When the livestock are not managed, the pictures speak for themselves, in that there is drought, desertification and economic hardship:

Food plants are killed by overgrazing;

new plants cannot become established successfully;

less forage grows;

the majority of sunlight and rain are wasted on bare soil;

soil loses its ability to absorb and hold water;

streams and wells go dry; livestock production falls;

wildlife disappears.

The actual amount of rain falling is not the critical parameter but what happens to the water once it has reached the ground. Again, using a simple illustrative sum: Just 1 mm more rain captured in the soil each year means an extra litre per square meter. That’s 10,000 litres more per hectare and an additional 1 million litres per square kilometre. The drought is reduced because the soil is able to discharge some of the water into rivers, springs and wells, and there is more forage for animals because the plants can access some of the water too which helps their growth. Some experimental studies done in the U.S. have indicated that by changing livestock management the soil can be made 600% more effective in absorbing water. If the useable rainfall is increased in this way, even formerly arid and barren lands can be made fertile once more.

In a 450 hectare pile of tailings from an old copper mine in the Sonoran desert, to the east of Phoenix in Arizona, life is being restored by grazing cattle on it. As they graze, the cattle push hay and manure into the mine tailings, and have created a layer of soil up to 30 cm (one foot) thick where there was none formed in over 60 years, by just leaving the area exposed to mother Nature. The soil captures water and retains it in the root zone, so rendering it accessible to plants, which flourish, all the while capturing CO2 from the atmosphere through photosynthesis. Presumably the levels of copper are insufficient to cause problems of toxicity either to plants or cattle. The strategy has proved successful even where “hydroseeding” efforts have been literally washed-away by heavy rain.

In northern Australia, unmanaged (free-roaming) cattle and donkeys destroyed a former wetland to the extent that by 1992, there was not enough food growing per hectare to feed a cow for a single day. The usual consequences occurred, or wildlife disappearing for lack of anything for them to eat, most of the rain evaporated and plants could not establish themselves, as a consequence of dry soil and overgrazing. However, by 2001, this same area was producing 800-1,100 cow-days worth of fodder as harvested in three grazings by managed livestock.

In summary, without grazing animals to plant seeds and recycle nutrients, dryland ecosystems desertify because: standing dead growth chokes plants, instead of mulching the soil; seeds sprout on the soil surface, then die; as old plants die, bare ground increases; bare soil loses its ability to absorb and store water; rivers, springs, and wells go dry; droughts become the norm. In arid areas, seeds must be planted deeply or seedlings will die before their roots reach reliable water. Only the hooves of grazing animals can do this economically over millions of hectares. Returning to herding-style management with long recovery periods between grazings heals the land.

AS an example I note that unmanaged grazing stressed forage plants in a pasture land regions in New Mexico, U.S.A. to the extent that by 1986, 11% of it was snakeweed. The standard practice of killing weeds using chemical weed-killers in fact would cement the underlying problem of low biodiversity and 46% bare ground. However, by 1990, a strategy of regenerative grazing had reduced the bare ground to 30% and the snakeweed to 1%. Nine previously dormant perennial grass species also reappeared. A well that had been dry since the 1950’s was found to have 3 meters (10 feet) of water in it too. The size of the herd and beef production doubled per hectare, while the cost to produce a kilo of beef decreased by 50%.

Regenerative grazing can also be the most effective means to restore biodiversity to a region. For example, David Ogilvie’s management of the U Bar Ranch in New Mexico has created a habitat that supports more endangered southwestern willow flycatchers than any preserve. The U Bar also hosts the most prolific population of flycatchers known to exist, and most interestingly they seem to thrive particularly well areas that they share with cattle. In 2001, 132 pairs of southwestern willow flycatchers were counted on the U Bar Ranch in comparison with a mere 7 in two nearby wildlife preserves with a similar combined area, but which are not grazed by livestock. The U Bar also has more common blackhawks and spikedice (as respective examples of a threatened bird and fish species) than anywhere else and large numbers of various other rare species. There is also the greatest density of nesting songbirds known in North America and an unusually high ratio 99:1 of native to exotic fish. Many habitats are now too badly damaged to support the wildlife that once maintained them, and simply protecting them or deliberately reintroducing wild species is usually unsuccessful. However, even in these circumstances, managed livestock practices can successfully restore then maintain these areas until their wildlife populations recover.



Anonymous said...

The English, and probably all European peasants of 1000 years ago where too thick to be able to understand "Land Mangement" much less to comprehend it.
So what they did was invent "Rotation of Crops" which did the same thing.

Professor Chris Rhodes said...

Nice comment.... it might be a case of "back to the future" to get around the oil problem re. agriculture.

Anonymous said...

Not really related, but I know you are interested in this topic.

I think they finally are, "about there": http://www.sciencedaily.com/releases/2009/03/090311103646.htm


Anonymous said...


Yorkshireminer said...

Basically Buffaloes know best.

Professor Chris Rhodes said...

Interesting blog, Dave. I hadn't seen it before!

Thanks Clarence - it does look like a useful technology, if it can be scaled-up. Shame it didn't start 30 years ago. Meanwhile I think we are going to need more conventional photosynthesis.