Wednesday, September 29, 2010

Stone Mulching in the Desert

Some years ago in rural Michigan a forested area was cleared and all the trees except three young hemlocks were cut down. These small trees were left to manage for themselves. In the forest where they had been protected from wind and excessive heat, they also had to compete with other trees for basic nutrients. Yet they had managed to do alright.

Left on their own, however, in a bulldozed area, two of the three trees died within a year. The third tree ended up flourishing and became a beautifully shaped and canopied tree - quite different from typical forested hemlocks.

The only difference between the trees was that the surviving tree, quite by chance, happened to have a load of loose rocks dumped right next to it soon after the land was cleared. In the months following, the rocks kept vital moisture from evaporating near the tree and many worms and insects were able to enjoy the clement conditions they provided. These small creatures worked the ground into a nourishing environment for the roots. This couldn’t have happened where the ground was dry.

This is just one example (and there re many) of the value of mulching with stones. Unfortunately these discarded resources are usually considered only in the context of how to get rid of them. This is too bad. Stone mulches offer a lot of benefits. But they are particularly helpful in dry areas.

You have probably learned by experience that the soil under rocks can be moist when everything else is dry. Some people use this fact to calculate watering times for their garden. When it’s dry underneath, it’s time to water. And, in fact, the most important benefit of having stones around plants is that it keeps water from evaporating too quickly.

This can make a very big difference to a plant. In many dry areas, water usually evaporates quicker than roots can grow. Since soil dries out from the top first, plants have an incentive to grow roots as deep and as fast as possible, keeping their feet wet, so to speak. Once the soil is dry around the roots, a plant has very little time left to produce seeds before it dries out. Its entire life cycle is dependent on a few weeks of moisture every year. (This is why many desert plants have thick leaves and roots. It allows them to store more water when the rains do come, and it buys them more time to develop seed and fruits when it becomes dry again.)

But what happens if a non-succulent plant happens to be growing next to a stone in the desert? Initially the amount of rainwater may be the same as before. But because the stone slows down evaporation, it allows the plant’s roots to grow for a longer period – essentially keeping up with the rate of evaporation. Plants with deeper and better developed roots are bigger, healthier, and set more fruit. It’s no surprise that plants growing next to rocks often look so good.

Of course there are other benefits to stone mulches than just water retention. Roots often grow next to stones because it’s a place to leverage growth. It’s also a place where rainwater (or sprinkler water) seeps into the soil first. The small space left from this seepage also allows worms and insects to move easier, creating a vital microclimate for roots.

Of course the use of stone mulches is not the only way to build soil. Other mulches do too. But stone mulches have a bit more value in dry areas than other mulches do. Take, for example the experience of Dorothy Anderson.

Dorothy lived in Wisconsin a couple of generations ago. Now Wisconsin is not the driest place in the world but the summer heat can often dry things out. Dorothy was also an avid gardener and paid attention to how her neighbors did things. When she learned that mulching (with hay, weeds, etc.) was bringing bountiful harvests to others, she was determined to do the same thing herself. But then she ran in to some difficulty.

She didn’t have a lot of leftover plant material to use as mulch and when she put what little she could find in her garden, it just dried up and covered the dry ground. She didn’t get much benefit from it. It took several years and a lot of foraging to get enough weeds and other organic matter to really help her garden.

For those of us living in the dry Southwest, we certainly understand this kind of problem. In fact the problem is a lot worse for us. Not only is it hotter and drier but there’s less plant waste to go around. If we really want to mulch, we often go to the hardware store and just buy it. And if we don’t put out enough, it doesn’t do us any more good than the little Dorothy started with.

The situation changes, though, if we use stones. Place a handful or two of grass (or straw) mulch on the ground here in Fresno and it will quickly dry up and get blown away. But if you put the same handful on the ground and place a stone on top of it, things change. The most obvious thing is that the mulch stays there. It’s also shaded and small insects will crawl under the stone to get out of the sun. If moisture is added it will stay near the soil surface much longer than in surrounding areas.

A study conducted in the 70’s in the desert Southwest showed that moisture evaporates from bare soil at a fairly even rate of about an inch every three days. Under the same conditions, moisture evaporated from a stony area at a rate of about an inch every two weeks. This added moisture is as good as gold to plants in dry areas. It also creates an environment for soil-building organisms such as earthworms, arthropods and even fungi. A flat stone in the desert is a way to build soil if we know how to use it.

One of the interesting histories of the Southwest is the agricultural use of stone mulches by the Anasazi. Dale Lightfoot at Oklahoma State University has evaluated these mulches extensively in dozens of abandoned farming areas near Santa Fe, New Mexico where these mulched areas can still be identified - over 700 years after they were made. The areas show up clearly using aerial infra-red photography because they are greener than surrounding areas. These erstwhile garden sites are noted for their regular arrangements of cobbled stones with borrow pits from which the stones were taken.

Lightfoot concludes that these stone mulches not only increased (and still increase) soil moisture but that they also reduce erosion, extend the growing season and increase crop yields. This is quite a list for a dry country not known for its lush gardens.

The biggest drawback of these stone gardens is that they are not sustainable. Whatever nutrients can be found in the soil are used up by successive crops so that new areas have to be prepared every several years. In China, where stone mulching has been used (as recently as a century ago) this problem was understood to affect the children and grandchildren of farmers who would have to extend significant resources removing stones in order to work nutrients back into the soil.

This problem has not been overcome. It is one of the main reasons that stone mulching is not practiced commercially on large farms. It just isn’t practical to remove several tons of rocks from a field and then to turn around and replace them after working the soil.

But that said, stone mulches still have their place. In fact they should be more widely used in dry areas. We know a few more things about nutrient cycling today than did the Anasazi or Chinese of former times. We know, for example, that stone mulches can be sustainable if organic material (such as cut grasses, straw, fallen leaves, etc.) is placed under stones each year.

Modern gardeners who do this use larger stones than the Anasazi did - since it’s easier to move them. Flat stones are also preferred to round cobbles. Various kinds of composts are placed in a garden spot with rows of flat stones (roughly the size of salad plates) covering the compost. Plants are then allowed to grow between the rows of stones.

For trees, a thick layer of compost with stones placed around the trunk does the same thing. It only takes a little effort to remove the stones once or twice a year and add more compost, and then replace the stones. The total effort is less than that required for weeding - which, of course, is no longer required. And the results have been impressive. Difficult soils are improved with the arrival of worms and insects, moisture is retained; and, most importantly, plants are much happier (if we can use that word) and more productive.

Stone mulching may not be a realistic possibility for farmers whose livelihood depends on their harvest (although creative orchardists could likely make it work). But on a smaller scale, and for those of us who care about sustainability, it makes a lot of sense - especially out here in the desert.


Lightfoot, D.R. 1994. The Agricultural Utility of Lithic-Mulch Gardens: Past and Present. GeoJournal 34(4): 425-437.

Lightfoot, D.R. and F.W. Eddy. 1995. The Construction and Configuration of Anasazi Pebble-Mulch Gardens in the Northern Rio Grande. American Antiquity 60(3): 459-470.

Rodale, J.I. 1949. Stone Mulching in the Garden. Rodale Press, Emmaus, PA.

Rodale, R. et al. 1972. The Organic Way to Mulching. Rodale Press, Emmaus, PA.

Friday, September 3, 2010

Library Insurance

It is a sad time for libraries. Once the pride of our communities (from small towns to large universities) they now struggle to keep patrons. And in order to keep up with the times, they are becoming a lot of things in order to justify their very existence - a lot of things, that is, except libraries in the real sense of that word. Books are being replaced by services and with the loss of these books, we run the risk of losing much of what we have worked so hard to learn.

A library is (and has always been) a place to keep literary and artistic materials. Traditionally, libraries have been comprised of current literature and stacks of older literature. (Many libraries also keep special collections of historic value.) Both were important. They also provided an atmosphere of learning. Libraries that were associated with colleges and universities provided an atmosphere where students could study quietly amid the volumes that they needed as reference materials. They also had access to the latest findings from their chosen fields with resources available to find information on practically any subject.

Today our libraries are mostly empty and students are finding all they think they need via computer. I have no intention of being critical of computers. To the extent that they improve our lives I welcome them. I must insist, however, that the move from the world of the library to the world of the computer is a risky thing. It is a move that threatens to destroy a great deal.

In the world of scholarship, for example, fewer and fewer volumes are being printed of many (perhaps most) important periodicals. Scholars are preferring to access articles on line from their office rather than walk over to the library. This is a convenience (I admit - and indulge in it myself). I certainly see no harm in this especially as it reduces the amount of environmental inputs and required shelf space needed to store books.

Many institutions have been wise enough to keep hard copies of these volumes on hand in case digital resources become temporarily unavailable. Of course it is impossible for any single institution to keep hard copies of everything that gets printed. So as a way around this, academic communities began a number of years ago sharing their holdings through a process of inter-library loan. This has been a real boon to scholars who have gained easier access to more materials. With an ever increasing amount of information getting printed, this service has become indispensible to serious research.

It's worth considering for a moment what shelf space in libraries meant many years ago and how it was managed. I have many fond memories of walking through the stacks of books as a graduate student at BYU in the 1980's and being amazed at the number of books. When I later transferred to The Ohio State University and discovered that its library was several times larger than BYU's I was even more amazed. The stacks of books made up several floors in the main library and space was being made to add more shelves in the mezzanine. Many subject libraries were already being moved to satellite locations to make room for the ever increasing number of volumes.

Some time later when I began studies at Colorado State University, I noticed that space was being handled in a different way. Many of the volumes had been moved to a storage facility - basically an over-sized warehouse. Requests had to be made for these volumes and there was a lapse of a day or two before a runner could find them and make them available. It was fortunate that many of these volumes had been moved because the Cache le Poudre River flooded in the mid-1990's and many of the volumes on the first floor of the library were destroyed.

Meanwhile, many volumes of older literature are now being digitally copied and made available on-line. Cornell University, for example, has made available hundreds of volumes of older agricultural literature that is hard to find elsewhere. This again is a great resource. Every year, more and more volumes become available in all branches of learning. And as a bonus we now have hand-held digital devices that make reading this material much easier and more enjoyable than older technology allowed. It is a great time to be doing research now that many older texts are becoming more readily available at our fingertips.

So doesn't all of this contradict my point? Not in the least. With all the technology (great as it is) our literature is increasingly at risk. Notice the trend. Fewer and fewer hard copies are being printed as more and more people are staying away from libraries (because more and more resources are available on-line). Libraries compensate by reducing shelf space in order to draw in more patrons with services (even coffee shops). It doesn't take much to imagine a scenario of computer collapses where vast amounts of information are irretrievably lost. This sort of collapse doesn't have to be a global melt-down. It could be local, or a series of local disasters.

Let me offer an example. I have in my library several volumes of taxonomic revisions that are very difficult to find. I require them for my research on insect diversity. I have worked at building this collection over 30 years. Much of this work was published when insect taxonomy was of greater interest to the academy than it is today and many more volumes were printed. Now when I say that many volumes were printed, I don't mean to compare this literature to the number of volumes that works of popular fiction generate. But many of these earlier taxonomic works had printing runs of several thousand copies. Even so, they are hard to find today.

If that is true of older literature, what is the situation like today? Important taxonomic research is still being conducted but it is often printed in journals with fewer and fewer hard copies produced. Authors buy fewer and fewer reprints because their work can be accessed on-line. It is very likely that hard copies are missing of these works from entire regions of the US. As a result, hard copies of current taxonomic research will be many times harder to come by in future than the older literature is today. Digital versions of this work are usually located on one server (hopefully backed up). If it gets lost... I think you get the point.

What then can be done? Clearly we should not be limiting computer resources. They are truly valuable - even if, indirectly, they justify the demise of traditional libraries and the loss of books. One thing, however, should be done: you should continue to keep hard copies in your own library.

I’m not suggesting that you accumulate a wall of books of best-selling authors. They will survive the short term disaster without difficulty. And their long-term survival will depend on their usefulness to later generations. I am suggesting that you save less popular works - titles and authors that because of their limited popularity are usually missing from libraries.

My collection of Gerald Durrell books, for example, or my volumes about science and religion. It is rare that I find any of these titles in local libraries. I don’t generally flatter myself about my collection. Mostly it takes up a lot of space – space that my wife would love to have. But it is a bit of security. I’ve been buying books for a few decades and only rarely pick a title because of its monetary value. I buy books that interest me. Even so, many of these volumes are now hard to find. What will they be worth in 50 years or more?

So again I urge you to buy real books. Think of it as insurance for the authors you love – for the books that you love. It may be that you end up saving one for future generations. Stranger things have happened.