An intro to sustainable soil building
Although we may find it difficult to live without our i-pods, computers, CD’s, central air, and automobiles, clean air, clean water, and clean food are the absolute bare necessities for human survival, and all three are dependent upon healthy soil. Drinkable water does not come from a plastic bottle or a tap, but is produced by the earth’s hydrological cycle, in which plant-life, trees and the soil all play an interactive role. The clean air that we breath doesn’t come from air-conditioners with filters and fans, but from plants and trees that depend on healthy soil. Although many of our children today may think otherwise, the food we eat doesn’t come from cans, boxes or trays wrapped in plastic, sterilized with a blast of radiation, sitting on a super-market shelf or in a refrigerated cooler. Nor is healthy food made in a lab. Healthy food comes from the natural cycle that includes animals and plants which depend on healthy, productive soil.
For sustainable health, we must find ways of promoting sustainable soil productivity. Modern chemical agricultural practices provide the illusion of healthy soil through the use of massive petro-chemical inputs. However, without these inputs, there is no health or growth. Through chemical agricultural practices, soil erosion is promoted instead of being prohibited. “Each day 57 million tons of topsoil are lost to erosion.” (data from The Global Citizen by Donella H. Meadows published in 1991). Often these petro-chemicals wash off into our water supplies and are absorbed into the food that we eat, causing expensive health problems later in time. I could go on and on, but will resist the urge to do so. The point of this article is not to bash current agricultural practices, but rather to show how we can promote the building of sustainable productive soil through permaculture design.
When we talk about the health of soils, it’s important to consider the biodiversity of life within it, and to understand how these lifeforms interact with, or loop into the life cycles above the ground. It’s worth noting that “[T]here are more living organisms in a handful of fertile soil than there are human beings on this earth.” (Peter Lester -Biodynamic Perspectives Farming & Gardening from The New Zealand Biodynamic Association). In fact, there is more life below the surface of the earth, than above it.
We have recently come to understand, that stability and productivity are related to and dependent upon biodiversity. This might lead one to believe that the land with the highest biodiversity will also be the most stable and productive. The key, however, is interactive biodiversity. Renowned permaculture designer and teacher Geoff Lawton often says that, “Interactive diversity gives you real stability, which gives you real fertility which gives you an economy.” Yet, the laws of biodiversity are dependent upon the laws of physics.
Finding the Sweet Spot: Peak Productivity=Peak Interactive Biodiversity
If we recall what we know about chaos theory, network theory, etc. we will remember (or perhaps discover) that there is a tipping point, or an edge where volitile change can happen. In soil, this is the edge of productivity, or what we could call “peak productivity” which is directly co-related to peak interactive biodiversity.We now know that there is a tipping point where this peak biodiversity, after being reached, can fall out of balance. This edge is what we must look for to find good land, or to help us build productive earth out of sterile, infertile, or less than ideal land...or to help us keep soil from declining into infertility. We could call it the sweet spot of soil productivity and it’s located on the spacial, chemical, temporal, physical and biological edges of the earths surface. Our goal and duty as human beings is to design, build and sustain this healthy edge of productivity in the landscape so that we can continue to depend on it to support our lives. This can all be done through a little thoughtful design.
Please note that this article is to be used for attaining productive soil for the sake of human settlements. Therefore, it is not to be taken as a template for the entire surface of the earth. There are lifeforms, and eco-systems that depend on a certain soil type in what we humans may consider conditions that are less than ideal. However, those conditions are necessary to sustain that life and I do not mean to suggest that all the earth be blanketed with the same kind of soil or ecosystem everywhere. My hope is to point permaculture designers into a direction that will better serve human settlements.
There are many things that contribute to the productivity of a soil. Age, place, climate, topography, physical and chemical structure, existing biota and plant-life, pH, etc.
To understand how all the pieces fit together would take a book the size of my Grandmother’s ancient German Bible, and quite frankly, there have been many complicated books written on the subject already, as well as whole university courses taught on the subject. Therefore, I will not go into all the gruesome details here, however, I will go into the basics, so that we, the people involved with permaculture, can design a landscape around us to get the most out of our environment and our soil.
Getting a feel for it all (texture):
First of all, for us to stay alive, it is important that we get balanced nutrition, our nutrition comes from the soil. So, for us to have a nutritious life, there must be a balance of nutritious life in the soil. The basic necessities for life to exist in the soil are air, water, minerals, and an ideal pH. We humans also need a diverse diet full of a variety of nutrients, both vitamins and minerals. For us to get this, the soil must also contain a variety of nutrients, which means that both above and below the soil, there must be a diversity of life to provide that variety. Each plant and animal above ground provides different elements to the substance of the soil below them. Our job as human managers of the earth, is to build and maintain this balance, and insure that a variety of nutrients is continually returned to the soil.
For plants to grow, and soil biota to stay alive, there must be air and water in the soil. For air and water to exist in the soil, it must have the proper texture. If you have too much sand, there will be a lot of air, but water drains right through taking precious nutrients with it. If you have too much clay then water is retained, but there isn’t enough air therefore anaerobic conditions set in, decomposition and microbial activity come to a halt and productivity is severely slowed down. The ideal texture for plants to be as productive as possible, would be somewhere in the middle, in other words, a sandy clay loam. A sandy clay loam has a healthy balance in the ability to retain both moisture and air so that soil biota can exist, and travel freely throughout the soil moving nutrients around with them.
It’s important to have soil biota such as microflora and fauna (bacteria, fungi, actinomycetes, and algae) micro, meso and macro-fauna such as centipedes, worms and termites. These soil biota are the managers, or underground stewards of the earth. Some serve as highway makers, others as transporters, others act like the underground internet. Termites and ants are the earthmovers, as well as digesters and soil makers. Worms, specifically, break down organic material into smaller forms that can be digested by the smaller beings such as bacteria and fungi, in order that the minerals can be more easily taken up by plants. Worm castings (worm poop) are natures best fertilizer, and worms can create 60 tons of worm cast per acre per year. This seems to support what Darwin was known to have said, namely, that “worms create the soils of the earth.”
Earthworms, termites and ants (as well as prairie dogs and gofers) make tunnels that aerate the soil, and allow water to seep into it. 18% of rainforest foliage goes to the leaf-cutter ants nests, where it eventually decomposes in their own form of a compost bin where the nutrients are finally returned to the soil. For all of these creatures to continue doing their jobs, the soil must also have a good supply and variety of organic matter in the form of high quality and palatable plant and leaf litter. Variety of plant life is important, for if the leaf litter being fed to the soil is of but one kind, then the diet of the soil is out of balance.
Men, and women cannot live by bread alone...we must also have steak, veggies, sushi, fruit and (at least in my case) beer. Likewise, a healthy swath of soil (and the biota that lives in it) cannot exist on just the leaf litter of one plant, such as we see in monocultures of grass (the suburban tribute to waste and wealth...the lawn), rice, corn, wheat, soybeans, or any field born from the mind set of modern agriculture today.
Instead, each swath of soil, must also have a variety of plant and animal life above it for it to remain healthy. If a field returns only one plant to the soil, then expensive nutrient inputs will be required later on. The fact that we must remember, is that every life form provides food and nutritious elements for something else. When the balance of this supply and demand is lost, then the soil, and therefore the entire system, will eventually fall out of productivity.
Variations on a theme (soil types):
Now would be a good time to introduce the many different types of soils that make up our landscape.
There are basically variations of two types of soil surface. Mor humus, and Mul humus. The similarity in names can be a bit confusing. The difference is that Mor humus is typical of coniferous forests, usually where over browsing or some other disturbance or action such as fire has resulted in dominance of coniferous species who’s acidic litter is less palatable than trees with deciduous leaves. Needles tend to contribute to an acidic surface O horizon which is dominated by fungi (not bacteria), is noticeably without worms, and instead has a notably high number of mites and Collembola. These soils are “subject to heavy leaching and are characterized by low rates of decomposition and plant nutrient availability, and hence low plant productivity.” (The Biology of Soil: A community and ecosystem approach by Richard Bardgett pg. 3). The result, is a soil lacking in the biodiversity of life necessary to keep a soil productive. In contrast, a more productive and biodiverse soil is the Mul humus which can usually be found under grasslands (not lawns) and deciduous forests. Mul humus soils are formed on calcium-rich parent material, are brown in color, mildly acidic, and are characterized by an “intimate mixing of the surface organic and mineral-rich A horizon as a result of the high abundance and activity of soil biota, especially earthworms, leading to high rates of decomposition, nutrient availability, and plant growth.”(Bardgett pg. 6)
From the above passages, we can be led to believe that for a soil to be productive, it must have a high quality leaf litter containing a variety of nutrients which can then contribute to an abundance of earthworms, or other soil biota (depending on the climate) to make those nutrients available again to the plants. Coniferous forests can at times be seen as a sign of an older forest, or as a forest with a soil past its prime. The area had most likely reached a deciduous forest stage at one time but had possibly been over-browsed, or stripped of high-quality leaf litter(in one way or another), thus slowing decomposition rates in the soil surface and thus nutrition availability to plants.
"Fertile mul soils associated with productive ecosystems...tend to support a high level of plant, animal, and microbial diversity owing to ample provision of resources and a high level of heterogeneity, caused largely by the activities of the organisms themselves. In contrast, the harsh climatic conditions and abundance of recalcitrant organic matter typical of unproductive, mor type soils mean that fewer species are present (Ponge 2003)"(as per Bardgett pg. 55)
The moral of the story can be summed up in a phrase that I came up with just to help us all remember what soil is productive, and what soil is not.
“Mor humus needs more life and biodiversity. mul humus already has multitudes.”
Although coniferous forests are a thing of beauty in their own right, our goal is to build and maintain the optimal interactive biodiversity that exists on the temporal edge of deciduous forests and grasslands.
Soil Parents, or “The apple doesn’t fall far from the tree, and seldom rolls up-hill.”
When looking for ideal and productive soil, we also need to consider the original parent material that created it. The brown, fertile and highly productive mul humus soils are formed from the weathering of basic (not acidic) lava. They “tend to be rich in minerals such as Ca, Mg, and potassium (K) [are] fine textured (clayey), and have a high ability to retain cations of importance to plant nutrition.” (Bardgett pg. 7)
The lesser productive mor humus is formed from acidic lava (for example granites and rhyolites), are sandy by nature, poorly drained, have a low ability to retain cations and are low in Ca and Mg.
Just as we can’t choose our parents, we can’t choose our soil parent material. If the parent material is acidic lava to begin with, it’s highly unlikely that it will turn into a mul humus all on it’s own. But it’s very possible, with a helping hand from permaculture design, that we can nurture the soil back into productivity. But to do so, we first need to look at what makes an ideal productive soil, and then find ways of assisting soil to reach and maintain that state. Permaculture has a big bag of tricks to actually build an ideal soil in less than ideal places. Look for more on how to do this in a later article.
The salt of the earth (acid or alkaline):
“Soil pH is of concern to the soil ecologist because it controls nutrient availability and it directly impacts on soil biota...availability of P in soil is typically low under acidic conditions, owing to the formation of iron and aluminium phosphates...[that] dissolve to release P into soil solution as pH rises, making it available for plant uptake; The availability of P is typically greatest between pH 6 and 7.” (Bardgett pg. 22) The perfect garden will be between pH 5 and 7. The more acidic a soil becomes, the less P is available. In old coniferous forests, the soil becomes acidic, therefore slowing productivity.
Unfortunately for us today, alkalinity is a problem. Modern agriculture has taught farmers to willingly salt their land through the practice of irrigation. When we mine rivers, lakes and aquifers of their water, and spray, or sprinkle it on our land, 80% of it vaporizes thus concentrating minerals like salt onto plants and the soil. The result is first an increase in alkalinity, and eventually (maybe not over the lifetime of one farmer, but indeed eventually) a decrease in productivity and finally, desertification. Furthermore, irrigation via pumped aquifers is unsustainable. Currently, the Ogallala Aquifer is being pumped at a rate causing it to lose over 1m of depth a year, while it is being recharged at a rate of 1cm a year.
Urban expansion, and treeless landscapes formed by large monoculture fields, have increased rainwater runoff, which increases erosion, contributes to flooding, which also contributes to an increase in alkalinity. Large dams which increase evaporation, have the same mineral concentration effect as aquifer depleting irrigation.
Rain, however, has a natural pH of 6.2 which is within the realm of the perfect pH for a garden of 5 to 7. Rain harvesting, via roof-top collection, tree-planted swales, small dams, and ponds, or drip irrigation would be a much more viable, healthy and sustainable option to insure that our soil has the proper pH and plenty of moisture.
I plan to go into quite a bit more detail on various ways to best adjust the pH of your soil, in a future article.
Life at the water’s edge:
In permaculture, we often study how to maximise the edge of water. For example, instead of making circular ponds on a standard garden, park or farm, we see star-like shapes in a permaculture landscape. The ultimate system for creating maximum water edge in a productive farming system is the chinampa of South America. Chinampas maximise productivity of a property by increasing the amount of aquaculture in cooperation with gardens made on fingers of created soil extended out into bodies of water. However, just by looking at land use, we are failing to see how the water’s edge actually enhances the productivity of the soil. Water is not just important for the sake of moving nutrients, and providing oxygen to soil biota and roots, but it’s necessary in the form of water features for the actual health and interactive biodiversity of a soil.
“The riparian zone (the zone between terrestrial and aquatic ecosystems)...possess[es] an unusually high diversity ...maintained by a variety of [natural] disturbances (e.g. periodic flooding, drought, freezing, abrasion, erosion, and occasionally toxic concentrations of nutrients) that create a spatial and temporal mosaic with few parallels in other systems (Ettema et al. 2000)” (Bardgett pg. 45)
Keeping this in mind, it makes good solid sense to increase the amount of riparian edge to our soil systems (through the implementation of water features with lots of edge) not just to improve the productivity of our soil, but to increase the biodiverse yield of our systems. This interactive biodiversity increases the productivity of soil around or along the water’s edge. By including a large number of small aquacultures in our system, we also increase not just the productivity of the area, but the health and stability of the system as a whole. Keep in mind that in the zero gravity environment of water, life uses less energy for production, therefore increasing efficient productivity. There’s also an endless variety of stacking levels available through combinations of plants and aquatic life forms.
From the top to the bottom: Topography and Drainage
Since water always flows downhill at a 90 degree angle on contour, it is common sense to understand that the soil on top of a hill will be more freely drained than at the bottom, and the bottom will be more moist, if not boggy. Below keypoint (the point at which the hill switches from convex to concave) or toward the bottoms near rivers, streams and lakes, you will most likely find soil blueish-grey in color as a result of water-logging which causes anaerobic activity...often resulting in gley. This is also typical of places with a high altitude and precipitation which reduce microbial activity and rates of decomposition. There then tends to be a surface of organic material that is not decomposing, and not allowing drainage of water...thus anaerobic conditions ensue or gleying can occur thus further slowing the nutrient cycle and therefore reducing plant productivity.
Basically, the things to avoid are excessive drainage or waterlogging, and to avoid low temperatures which reduce microbial activity. We should strive to keep our soil warm with cover materials and insulation such as mulch or ground-covers, and strive to encourage decomposition rates. We should do what we can to encourage proper drainage where needed, and to avoid leaching via too freely drained areas. If you have a choice of where to put a garden, avoid the top of a hill, or the bottom. It’s an absolute must to avoid bare soil anywhere. Bare soil will be hammered by any rains that do fall, and will likely become hardpan, thus reducing absorption, and the return of nutrients into the soil.
Immature or Over the Hill (the age of soil):
New soils, such as those recently uncovered by retreating glaciers, have not yet had the chance to accumulate enough life to be truly productive, while old soils usually end with low plant productivity.
Just as children (both male and female) need to be taught to feed and even cook for themselves, so soil can be nurtured to be productive. Just as the elderly start to move slower, and often lose the will to eat, so does soil lose its physical productivity. Yet this need not be the case. Just as a healthy diet and exercise can aid longevity, so can we as designers and managers of our environment, both improve and maintain the productivity of both aged or immature soil.
To find soil that’s in it’s prime, we have to look at successions, or the seral stages that nature goes through to develop a prime and productive soil.
The first stage is bare soil. It’s interesting to note that just like at single bars, the earliest colonizers are almost exclusively predators (such as spiders) and herbivores and decomposers show up later. “In *these systems...inputs of insects potentially provide significant quantities of N and P to the developing ecosystem from the earliest stages of succession. That spiders entrap nutrients in such a way could be of high importance in early ecosystem development in these extreme environments.” (Bardgett pg.55)
(*these systems =Central Alpin glacier foreland of the Rotmoostal (Obergurgl, Tyrol, Austria))
This same phenomenon of spiders as first pioneers was also observed by a French expedition for the search of life on the devastated, ash covered island of Rakata after the eruption of Krakatau back in 1884.
As herbivores and birds appear, they return their feces to the soil, containing nutrients, and perhaps seeds from elsewhere. The soil is not in it’s ideal condition, so pioneering species appear first, usually in the form of grasses. Grasses develop massive root structure below ground, further improving the conditions of the soil. In fact, a full two-thirds of the grasses biomass is often below the soil. This root structure combined with the new biomass above ground regulates soil temperature, and creates the spongy texture necessary for air, water, and soil biota to exist.
Conditions eventually become ideal for other lifeforms, such as the decomposing biota, and bacteria and fungi that will appear. The pioneering species are the first plants able to germinate in otherwise uninhabitable soil. As they improve soil conditions (adding nutrients, improving soil structure, aeration, drainage and moisture content) eventually, the soil is ready for the seeds of other species to germinate. These would be the pioneering trees and shrubs, including nitrogen fixers (usually deciduous), as well as phosphorus and potassium accumulators that further improve the environment of the soil with deeper root structures than grass, which pump both water and nutrients such as phosphorus, potassium and sulfur from deep in the ground. Fungal hyphae spread millions of miles of their nutrient network within the soil, and the web of life expands horizontally and vertically in depth. This improves nutrient supply, variety and flow, biodiversity, texture and allows other more delicate or finicky species to germinate. The variety of microclimates created within a multi-storied, stacked system, further aid in creating conditions that suite a large variety of plant and animal life above and below the ground. This interactive biodiversity allows for a rich variety of nutrients to be returned to the soil.
Coniferous species appear with their often narrow root structure and their acidic (and thus unpalatable) leaf litter and begin to challenge the other species. Due to their lesser foraging popularity, they are less browsed and their leaf litter is left on the ground un-touched by worms and their co-workers. The soil becomes more and more acidic, and decomposers move away. Soon the soil is not ideal for the biodiversity of deciduous species that make a soil productive. As the system becomes less diverse and dominated by coniferous species, organic matter builds up, drainage is reduced, and leaching, or anaerobic conditions start to set in, and productivity slows down. P becomes occluded, and the soil is then over the hill.
As just stated, when soils age, P becomes occluded, thus becoming unavailable to plants and soil biota. "Prolonged weathering of minerals leads to the formation of Fe and Al oxides that have a strong affinity for P. This P limitation to vegetation is further exacerbated in old soils because low soil fertility sets in motion a feedback whereby reductions in biological activity in soil reduce decomposition of plant litter, further intensifying nutrient limitation." (Bardgett pg. 12)
Furthermore, as soils age, they go from Bacterial dominated systems to fungal dominated systems with AM mycorrhizal and Facultative AM or ectomycorrhizal taking up the middle, and Ectomycorrhizal dominating the oldest soils. Nitrogen availability to plants is optimal in the middle stages while (un-decomposed) organic matter slowly comes to a peak toward the end. We also find a peak of organic P being available in the middle as well.
When it comes to bringing a more youthful, productive bounce back into aged soils, we need to look again at what has just been described above. Organic matter is accumulating over time, usually because decomposition is slowing down. It looks as though the same thing is happening as with a deciduous forest turning coniferous. Plant diversity and quality leaf litter is disappearing from the system for some reason or another, probably browsing, human-caused elimination, or perhaps a natural disturbance such as fire. Perhaps there has been a decrease in soil-biota numbers due to use of bio-cides, thus causing a build-up of litter without decomposers to process it...resulting again in a slow-down of nutrient cycling, and therefore soil productivity. Either way, when a diverse quality of leaf litter is lost (a decomposers food base), the decomposers then disappear (or vice-versa), other litter is thus accumulated, and the system is thrown out of balance left to age with only ectomycorrhizal fungi to manage the abundance. Soil is no longer being built, nutrients are no longer made into soluble form for plants, and un-used products (i.e.-waste materials) are accumulating. Nutrient availability for plants is decreasing, and the productivity needed to sustain a biodiversity of plants cannot continue for long under those circumstances.
If left alone, the soil will still be there (until weather erosion takes it’s toll) but it will eventually lose its peak productivity, and will take years and years to cycle back into productivity. We, as good designers, stewards and managers of the earth can step in to nurture this productivity into existence, and maintain it indefinitely with good management. We can improve the leaf litter quality and assist in the re-introduction of appropriate and necessary native species that can aid in decomposition, whether it be AM mycorrhizal fungi, worms, ants, termites, grasses, trees, shrubs, squirrels, rodents or birds or simply compost. Whatever the case may be, through intelligent, eco-systemic design we can help nature create the sustainable habitat needed for productivity.
Sweet spot: The Edge Always Has The Best of Both Worlds:
From what we’ve read above, we see that the sweet spot of soil productivity would seem to be somewhere between grassland, water edge and deciduous forest. These are the edges where interaction between highly productive mul-humus soil and the above ground biodiverse activity is maximised.This is where permaculture has an edge (no pun intended...okay, yes it was) over the person who uses industrial chem-ag to create rather sterile monoculture deserts void of biodiversity.
Permaculture design strives to include a number all of these landscape elements within one property or plot of land. It strives to increase edges and interactions between these elements and to sustain the biological lifeforms within them. It does so through the creation of rain-water harvesting swales planted with trees, in cooperation with small dams, ponds, and chinampas to increase the highly productive riparian edge between soil and water and providing aquaculture yield.
Instead of one field full of straight lines of just one crop, permaculture utilizes both orchards and intercropped or multi-cropped fields, often together with a swale tree/shrub planting system on contour. This increases biodiversity of leaf litter, as well as overall yield and the health of the soil. Permaculture also strives to maintain a constant groundcover to maintain a moderate soil temperature and moisture in the soil, which will also protect it from becoming hardpan, and thus retain the healthy structure of the soil and all the lifeforms below.
Furthermore, permaculture design strives to use the right place for the right plant. Freely drained hilltops, and or ridgelines should be covered with drought resistant trees, if not just for soil stabilization, wind-combing and erosion reduction, but to manage the hydrological cycle, underground water levels and nutrient flow both down-wind and down-hill. Soil located mid-way down-hill, where soil is most productive, can be taken advantage of for highly productive and dense food planting. The bottoms can be planted with moisture loving phosphorus and potassium accumulators to avoid those elements leaching from the system, while also helping to avoid anaerobic conditions and reduce erosion.
A well designed permaculture landscape makes use of rain-water harvesting systems such as swales which drought-proof the land via absorption while recharging ground-water. Harvesting of rainwater with a naturally ideal pH avoids salinization of the landscape from irrigation. A permaculture landscape will incorporate drip irrigation and grey-water filtration gardens, making more efficient use of water with a beneficial pH while also eliminating the harmful practice of salting the land.
When looking at an effectively and properly designed permaculture landscape, you will not see just an orchard, field, garden, lake, or a massive prairie, but a combination of all these elements stacked next to and upon each other in an aesthetically pleasing flow of mosaic patterns and systems...physically, spatially and temporally.
Through proper management of a permaculture landscape, you will also see a biodiversity of plants, and systems working together to constantly provide a variety of high quality leaf litter and nutrients, often returned in the form of mulch or compost to therefore create a constant supply of nutrition for the soil biota, which will further turn those nutrients into a soluble form for plants. An ideal permaculture landscape creates a variety of microclimates to allow a larger number and variety of plant and animal species to co-exist, increasing interactive biodiversity, stability and therefore providing fertility.
With permaculture, when we work with soil (as we humans often do, and wisely should do), we constantly strive to maintain soil productivity. We look for what is missing, and then look for ways that nature would provide it for us. More often than not, there is always something we can do to help nature along these lines. Therein lies our labor of love, and our duty; to help nature stay healthy and in balance, so that our lives will be in healthy balance too.
The healthier our soil, the healthier our lives will be. The more balanced and diverse our diet is, the healthier we will be. The more biodiversity we have on our land, the more diverse diet our soil will have, and therefore, our diet will be richer and healthier for it. The more diverse systems we employ on the land, the more productive, aesthetically pleasing , stable and sustainable it will be. The more sustainable our systems are, the healthier both our environment and our health will be.
Be looking for further articles explaining how to manage forest, grassland, and aquaculture systems and how to harvest rainwater, and balance the pH of your soil.
Sources and further reading:
The Biology of Soil: A community and ecosystem approach by Richard Bardgett
Noah’s Garden: Restoring the Ecology of Our Own Back Yards by Sara Stein
Biodynamic Perspectives: Farming and Gardening by the New Zealand Biodynamic Association
The Diversity of Life by Edward O. Wilson
Restoring the Tallgrass Prairie by Shirley Shirley
Water: The Fate Of Our Most Precious Resource by Marq DeVilliers
The Global Citizen by Donella H. Meadows
Native Roots: How The Indians Enriched America by Jack Weatherford
Indian Givers: How The Indians of the Americas Transformed The World by Jack Weatherford
Nexus: Small Worlds and the Groundbreaking Theory of Networks by Mark Buchanan
Tipping Point by Malcolm Gladwell