|Drawing by Kyle Chamberlain|
Talus Garlands aka Stone Mulch could be a boon for gardeners in dry areas or a drought situation. I know Texas lost many trees last year, and although the first part (in red) of the information below was taken from a permaculture article (Rethinking Water: A Permaculture Tour of the Inland Northwest), the principles of how it works should apply in many other areas.
“Scabland” is a term used to describe the parts of Washington State which are too rocky to grow wheat on. These scablands are comprised of coulees, cliffs, and mesas, eroded into basalt bedrock. The walls of such formations often have piles of broken rock about their base. Being a berry enthusiast, I noticed that the best place in the steppe to find serviceberries was on the north side of such rock piles. In fact, the north sides of a rock piles are about the only places that stay green in the summer.
Research revealed that botanists had already named this phenomenon, calling it a “talus garland community”.
Talus garlands can support pome and stone fruits (Amelanchier and Prunus), currants, elderberries, several hawthorns, roses, edible greens like nettle and goldenrod, as well as naturalized species like cherries, plums, apricots, grapes and apples.
It seemed obvious that mimicking a talus garland would be a great way to grow woody plants on dry land. But before trying to build such a mimic, we needed to understand how they work in nature.
Why are talus garlands so green? There are several theories:
- Shade from the southern sun minimizes evaporation and causes winter snow to melt later in the year
- Drifting snow collects in the loose rock
- Piled stones condense moisture from night air (thanks to the Designers Manual for the hint)
- Stones protect soil moisture from sunlight and arid air
- Stones minimize competition from grasses
- Stones protect plants and debris from fire
- Freshly eroded basalt provides ample mineral nutrients
- Stone provides an ideal growing surface for lichens, which speed the breakdown of rock and fix nitrogen (lichens are the primary nitrogen fixers in some deserts)
- Loose stone provides some protection from browsers, especially during early growth
- Stone piles provide habitat for animal associates, like packrats, cottontail rabbits, marmots, chipmunks, snakes, lizards, ext. Animal associates distribute seeds, provide manure, control pests, etc. (Rabbits and marmots are very tasty themselves)
Research reveals: "the mulching of agricultural fields and gardens with stones, pebbles, cinder and similar lithic (stone) materials is a variant agricultural strategy that has been used to evade drought and increase crop yield for more than a thousand years in the Old and New Worlds. Lithic mulch agriculture (LMA) is uniquely suited to the constraints of dryland environments, yet its use has remained confined." (Source)
Wiki says: A stone mulch can significantly increase crop yields in arid areas. This is most notably the case in the Canary Islands: on the island of Lanzarote there is about 5.5 inches of rain each year, and there are no permanent rivers. Despite this, substantial crops can be grown by using a mulch of volcanic stones, a trick discovered after volcanic eruptions in 1730. Some credit the stone mulch with promoting dew; although the idea has inspired some thinkers, it seems unlikely that the effect is significant. Rather, plants are able to absorb dew directly from their leaves, and the main benefit of a stone mulch is to reduce water loss from the soil and to eliminate competition from weeds.
Here's a paper on Stone mulching by the Hopi in Arizona and New Mexico.