Permaculture Designers Manual
CHAPTER 11 –
Section 11.1 –
Introduction to Dryland Strategies in Permaculture
The dunes, like harmonic chords, multiply and peat the notes of the rustling, shifting sands… you now hear what sounds like the sonorous music of distant drums- roll after roll…
(Quillci, 1969, on the Tobol, or music of the dunes)
The development of conservative strategies for the preservation of dry-land species, and for the responsible human use and management of arid lands is probably the world’s most pressing problem in landscape management.
Only sporadic world attention is given to famine or drought in arid areas, with such “sudden” emergencies consuming great quantities of resources and finance, much of which is wasted in mismanagement.
Problems of aridity, salted soils, and long-term drought can always be expected where we venture into desert borders with pastoral-ism and cropping, for added to the natural background fluctuations of rainfall due to earth and moon orbits, and solar radiation variance, we as exploiters add deforestation, soil erosion, and the consequent salting of waters and soils.
All desert areas are extending; many dryland areas are being created, and antecedent plant and animal species are thereby brought to extinction.
A great many arid-area species are not so much dry-adapted as drought-evading.
Plants dry off, cease growth, or exist only as seeds and tubers in drought.
Animals aestivate, migrate to humid areas, or take refuge near oases and wetter areas.
Many animals get sufficient water by eating succulent vegetation, by browsing at night to take advantage of condensation, or by predation on insects and other species of animals.
Almost all small animals burrow by day to escape soil temperature fluctuations, often to 1 or 2 m deep.
Some termite colonies develop deep galleries (to 40 m) to mine water, and also arrange air conditioning by adapted permeable surface nest structures.
Increasing desertification of agricultural lands has focused world attention on salt and drought-tolerant plant species of potential use.
Gary Nabham (In Annals of earth IV(1), 1986) has totalled 450 edible plant species for the Sonoran and Great Basin deserts of the North American interior (20% of the total species).
The semi-arid or transitional areas are particularly species-rich, thus desertification is taking a rapid toll on potential useful plant diversity.
Of the 936 woody plants in the West Australian wheat-belt, 45% are at risk.
Large reserves are urgently needed; the present reserves in arid lands are “entirely inadequate to conserve even a usual proportion of the genetic variation…” (Nabham, ibid.)
Cold high mountain deserts like the Cobi have some 60 flowering plants, and 360 species of birds (Geo 7(4) 1986), while large areas of the arid Sahara have 6-8 plant species in total, and recent deserts such as the Thar some 15-18 species.
Most of the world arid species lie in the Kalahari, Sonoran, and Australian deserts.
Arid lands are areas where direct evaporation exceeds rainfall, and where annual precipitation averages fall below 80 cm, and as low as 1 cm (sometimes only as dew).
Although the greater parts of these, areas are hot desert, there are substantial montane hot-cold deserts, and very cold desert areas near the north and south Polar Regions.
Typically, an extensive hot desert area consists of a savannah edge towards more humid monsoon areas, a Mediterranean climate edge, and extensive scattered shrub-forb associations (forbs are any non-grass or herbaceous plants), dunes on harder pavement areas, and almost bare pavements of harder rocks with facated pebbles (gibber plain or reg).
Where over-grazing has not been the dominant feature of land use, a desert may present an eye-level appearance of a low-crowned forest with shrub undeer-storey, and some areas may be as rich or richer in plant species than a more humid forest environment.
In detail, however there will usually be larger or smaller areas of bare soil between all major plant clumps or species.
Closer inspection may reveal a fungal-algal-lichen (cryptogam) crust on the bare areas, more or less intact depending on the frequency of hoofed animals.
This cryptoganic crust is a critical and delicate feature preventing wind erosion; its preservation is essential for soil stability.
Some features of the deserts are:
- Plants produce copious seed with long viability; seed is often wind-dispersed;
- Termites and ants are more effective than worms as aerators and decomposers;
- Rain may fall in mooaic patterns, so that vegetation is also varied mosaic of fire and rain, and ephemeral plants at different response stages from growth to decay are evident. New generations of shrubs may experience favorable seedling conditions as rarely as every 7 – 20 years. This then becomes the period of recruitment of new forests or shrublands.
- Much of the water run-off system may end not in rivers but in inland salt-pans or basins (endorthic drainage), from which all water eventually evaporates;
- Normal erosion is by wind, but rare cloudbursts shape the main erosion features and move vast quantities of loose material from the hills in turbulent stream flow. Wind transports materials locally in dust storms.
- Animals burrow, seek shade, or are nocturnal in order to conserve water; many are highly adapted for water conservation.
- Plant associations may be very varied in response to changes in long-term aspects such as slope, soil depth, salinity, browsing intensity, pH, and rock type.
SEMI-ARlD areas have steppe, scrub, and low forest vegetation, ARID is steppe and scattered low shrubs, and true DESERT has little but oases and ephemeral vegetation appearing after the rare rains.
Deserts have a rainfall classification of:
- Hyperarid: 0-2 cm annual average (e.g Atacama, Namib desert, central Sahara).
- Extremely dry: 2-5 cm annual average
- Arid: 5-15 cm annual average (e.g Mohave, Sonora, Sahara margins).
- Semi-arid: 15-20 cm, maximum 40 m (much of the Australian deserts, Asian deserts, Kalahari).
Above 40 cm, and to 75 or 100 cm rainfall we have (potentially) dry savannah forests; and it’s up to this latter level that we will be dealing with tn this Module.
Rainfall as not dependable in arid areas, with a normal 30%
variation and a potential 90%, variation any one year.
Potential evaporation can range from values of 700 cm/year in hyper-arid areas to 100 cm in steppe.
We can also regard the polar ice caps as hyper-arid (for precipitation) but evaporation levels are very low; wind removal of snow replaces evaporation.
Both the very cold and hyper-arid hot deserts have one thing in common-they mummify and preserve a great range of organic and fabricated substances, which presents a management problem when dealing with pollution, as breakdown of most organic substances can be very slow in the absence of water.
A paradox in almost all large desert or and areas is the existence of two types of more humid environments:
EXOTIC RIVERS which flow in from better-watered or forested regions, and OASES.
There is a third, invisible water resource, that of AQUIFERS
All must be used with great caution, as water in all of these resources can be locally exhausted, and aquifers can be depleted over vast areas by immodest use.
This misuse can cause widespread subsidence, collapse of the aquifer, and a permanent disappearance of those oases which were in depressions fed by the aquifer.
Instead of concentrating on exotic water in deserts, we should attempt to increase the input of water into the aquifers, soils, and streams; and to re-humidify the desert air by planting trees and protecting existing
It is the presence of trees and shrubs, transpiring rather than evaporating water, that keep the desert salts from evaporating at soil level.
Once evaporation alone operates, capillary action quickly brings subsurface salts to the surface as magnesium, sodium, calcium, and potassium compound; (chlorides, sulphates, corbonates) and we can no longer establish vegetation.
When we talk of arid lands, we should also remember equatorial low islands, unstabilized sand dunes in midsummer even in cool climates, and whole periods of relative drought even in more humid areas (including the dry winters in many subtropical areas).
That is why it is important to specify pioneering and drought-hardy plants for many situations, and why any strategy to get water into soil, and keep it there, is worthwhile.
There are large areas or Mediterranean climate on desert borders which are “arid” if they have deep sands and poor water retention.
A profound question to ask about desert concerns our basic usage.
Livestock herding has been traditional – and devastating.
Australians, Peruvians and Africans, Arabs, and Tibetans have all used arid areas for herding.
Aboriginal Australians managed better, by harvesting the natural abundance of deserts so that the artificial stress of herds was not superimposed on the natural stresses of dry seasons.
We should re-think our strategies of desert use, and the way we occupy arid lands.
It is possible to establish a carefully-developed core settlement, to set out hardy plants for many kilometers along favorable areas or CORRIDORS and to take advantage of the rare rains to establish a wide biological resource for dry years.
It is not possible to count on permanent cropping or herding in regions that experience one good year in every 4-9 years.
As for desert re-vegetation, by far the most effective and cheapest strategy is to exclude browsing animals from headwaters areas, when after a few years thousands of young plants may establish.
Desert borders are now used for a seasonally and uncertain production of wheat, barley, millets, and sorghum’s.
About one year in four produces a reasonable crop, but severe wind erosion and dust storms make this a precarious use of such delicate soils.
Herding and extensive livestock systems also occupy great areas of the deserts, with seasonal or nomadic herding in north Africa and southwest Asia.
If we look at actual income versus land use, the Central Desert of Australia allots some 73% of the area to pastoral-ism, and only 27 to Aboriginal reserves and conservation areas.
However, income is 15% from pastoral-ism, 76% from tourism, and 7-8% from mining in small areas.
Even the mining is a “tourist industry” where it concentrates on precious stones, and Aboriginal art is a large part of the tourist interest.
Pastoral-ism and mining are publicly subsidized, and has a grossly unwarranted system of direct and indirect supports, producing a largely surplus product for the world market.
No wonder pastoralists must maintain a powerful lobby in the halls of government!
People rarely want to live an the desert it is an expensive place to maintain a high standard of comfort in modern terms.
But they love to visit, and to see wildlife, genuine tribal art, and the landscape itself. To Aboriginal people, the land is life itself; they are a part of the whole, and their art respects this.
Deserts are inspirational for designers not only do the hills reveal patterns, rock types, and processes of erosion, but as the light changes from early dawn to late evening, new insights arise from the shadowed and light areas.
What is often unclear on the ground becomes part of a whole pattern if seen from hills or the air.
When we understand these many patterns, the distribution of materials and organisms makes sense, and we are able to creatively inhabit the landscape.
It is little wonder that desert peoples, in the great silences, beauty, and vastness of nature, arrive at profound mystical pattern concepts.
Only the confined oasis- or town-dweller concentrates on the commerce of finance, and conduct.
In the open, survival demands sensitive reaction to environmental imperatives.