LA Course #GCE-1-1406
Pruning Basics, Tree Truths & Mulch Myths
Edited by Richard W Gibney RLA/ISA
Sections Go directly to the section by clicking on the title below
Pruning Basics, Tree Truths & Mulch Myths
Edited by Richard W Gibney RLA/ISA
Sections Go directly to the section by clicking on the title below
Note: Click on green text in each section for more information and photos.
Guide to Pruning
By Cass Turnbull
Pruning should be done to enhance a tree's natural beauty, to make it seem less oppressive, and to reduce the size somewhat.
Making Cuts
There are two types of heading cuts, non-selective and selective. A non-selective cut is basically cutting off the tip or end of a branch at no place in particular. Wherever a cut is made, hidden dormant buds located directly below the cut are stimulated into growing into several new branches right at the end of the cut. This new growth is most often skinny, unsightly, and straight water sprouts. Furthermore, the tree speeds up its growth rate, creating weak branches.
Selective Heading
Selective heading cuts, also called reduction cuts, are the right way to reduce the length of a branch by cutting off one or two forks of a branch. The arborist selects the longest fork, follows it back to where it joins a shorter side branch and cuts it off there. The side branch should be big enough to take over as the branch’s terminal leader. The remaining fork will not respond by producing water sprouts. As an average, the remaining side branch should be at least half the diameter of the parent stem. Selective heading is also called drop crotching, crown reduction, or de-horning. It is not as bad as topping, but it poses severe risks and is not the magic solution to the tree that has become too big. Selective heading reduces the amount of regrowth, looks more natural, and is easier on the health of the tree.
Very large cuts on very old trees may succeed in constraining the size, but at an unacceptable cost to the health, safety, and longevity of the tree. Rot invades the main limbs, the tree expends valuable energy to deal with the wounds, and it may decline and die as a result. Even if the tree recovers, it will be more dangerous as a result. The lateral branches that take over as the main branches of the tree will likely be weaker and more prone to breakage even thirty years later. When done correctly, selective heading should be limited to a relatively few branches of a mature tree.
Thinning
The thinning cut removes a branch back to another branch completely. In other words you cut a smaller or side branch off its larger parent stem. Most good pruning cuts consist of thinning cuts. Thinning cuts do not make trees smaller overall; they just reduce the bulk and clutter of the tree, making it sort of “see-through”. Thinning of the lower, most interfering branches of a tree is more permanent and less harmful than crown reduction. Thinning cuts are better for the health and good looks of the trees than heading cuts. Thinning cuts should be limited so that no more than 1/8 total leaf surface of the tree is removed in a single year.
Compartmentalization
Trees are the largest, longest-lived organisms on the planet. The reason is an incredible defense mechanism called compartmentalization. When a tree is injured, it walls-off or compartmentalizes the injured area internally by chemically altering the wood in predictable patterns. Trees do not heal; they set up barriers to rot and then try to out-grow it. Sometimes a tree compartmentalizes well and only a small pocket of rot remains sealed off inside the trunk as the tree grows larger. Sometimes the decay spreads up and down in a long column. The only wood that does not decay is wood that develops after an injury has occurred.
The knowledge of this process means that arborists no longer have to dig out the rotten cavity in a tree and fill it like a dentist. It also means that there is no need to cut back to sound wood or drill a hole to drain water out of the cavity. Both of these activities make a brand new wound that allows the decay to enter into previously protected areas of the tree.
The Branch Collar
Branch wood is different from trunk wood. In the spring, a tree will add a layer of wood to a branch. Then the trunk puts out its own new layer of wood. Where the trunk wood meets the base of the limb, it laminates over the limb creating sort of a bulge called the branch collar. The branch is separate tissue from the trunk and is just held in place, buried inside the trunk by each year's new layer of wood. This lamination process is repeated every year.
When you prune off a limb, you should be careful to cut off only the branch wood and avoid cutting or wounding the trunk wood. This means you cut to the collar but not into it, since that would open up the trunk to decay. If you cut the branch off too far out, away from the trunk, the branch will die back to the collar, leaving a stub of dead wood. In general the right place to cut is almost like a dotted line where the branch starts to get fatter near the trunk. The angle of the cut varies because the collars vary.
Therefore, when pruning heavier branches and ones that have narrow crotches, it is wise to use a multi-cut system of removal. First remove the weight of the branch by cutting it off farther out from the trunk. Start by making an undercut, then saw down from the top of the branch. This prevents the saw from getting stuck and the bark from tearing off and leaving a long wound. Once the weight is gone a more proper pruning cut at the collar can be made.
Pruning Young Trees
A young tree is less than fifteen years old. The main goal of young tree pruning is to remove the suckers, remove the temporary limbs, and to minimize the included bark.
The above excerpts are from my recent book “Cass Turnbull's Guide to Pruning. The intention of this book is to provide a useful pruning guide that clearly and simply describes how to prune trees according to the latest standards. For more information on the book, it is available from Sasquatch Books.
Guide to Pruning
By Cass Turnbull
Pruning should be done to enhance a tree's natural beauty, to make it seem less oppressive, and to reduce the size somewhat.
Making Cuts
There are two types of heading cuts, non-selective and selective. A non-selective cut is basically cutting off the tip or end of a branch at no place in particular. Wherever a cut is made, hidden dormant buds located directly below the cut are stimulated into growing into several new branches right at the end of the cut. This new growth is most often skinny, unsightly, and straight water sprouts. Furthermore, the tree speeds up its growth rate, creating weak branches.
Selective Heading
Selective heading cuts, also called reduction cuts, are the right way to reduce the length of a branch by cutting off one or two forks of a branch. The arborist selects the longest fork, follows it back to where it joins a shorter side branch and cuts it off there. The side branch should be big enough to take over as the branch’s terminal leader. The remaining fork will not respond by producing water sprouts. As an average, the remaining side branch should be at least half the diameter of the parent stem. Selective heading is also called drop crotching, crown reduction, or de-horning. It is not as bad as topping, but it poses severe risks and is not the magic solution to the tree that has become too big. Selective heading reduces the amount of regrowth, looks more natural, and is easier on the health of the tree.
Very large cuts on very old trees may succeed in constraining the size, but at an unacceptable cost to the health, safety, and longevity of the tree. Rot invades the main limbs, the tree expends valuable energy to deal with the wounds, and it may decline and die as a result. Even if the tree recovers, it will be more dangerous as a result. The lateral branches that take over as the main branches of the tree will likely be weaker and more prone to breakage even thirty years later. When done correctly, selective heading should be limited to a relatively few branches of a mature tree.
Thinning
The thinning cut removes a branch back to another branch completely. In other words you cut a smaller or side branch off its larger parent stem. Most good pruning cuts consist of thinning cuts. Thinning cuts do not make trees smaller overall; they just reduce the bulk and clutter of the tree, making it sort of “see-through”. Thinning of the lower, most interfering branches of a tree is more permanent and less harmful than crown reduction. Thinning cuts are better for the health and good looks of the trees than heading cuts. Thinning cuts should be limited so that no more than 1/8 total leaf surface of the tree is removed in a single year.
Compartmentalization
Trees are the largest, longest-lived organisms on the planet. The reason is an incredible defense mechanism called compartmentalization. When a tree is injured, it walls-off or compartmentalizes the injured area internally by chemically altering the wood in predictable patterns. Trees do not heal; they set up barriers to rot and then try to out-grow it. Sometimes a tree compartmentalizes well and only a small pocket of rot remains sealed off inside the trunk as the tree grows larger. Sometimes the decay spreads up and down in a long column. The only wood that does not decay is wood that develops after an injury has occurred.
The knowledge of this process means that arborists no longer have to dig out the rotten cavity in a tree and fill it like a dentist. It also means that there is no need to cut back to sound wood or drill a hole to drain water out of the cavity. Both of these activities make a brand new wound that allows the decay to enter into previously protected areas of the tree.
The Branch Collar
Branch wood is different from trunk wood. In the spring, a tree will add a layer of wood to a branch. Then the trunk puts out its own new layer of wood. Where the trunk wood meets the base of the limb, it laminates over the limb creating sort of a bulge called the branch collar. The branch is separate tissue from the trunk and is just held in place, buried inside the trunk by each year's new layer of wood. This lamination process is repeated every year.
When you prune off a limb, you should be careful to cut off only the branch wood and avoid cutting or wounding the trunk wood. This means you cut to the collar but not into it, since that would open up the trunk to decay. If you cut the branch off too far out, away from the trunk, the branch will die back to the collar, leaving a stub of dead wood. In general the right place to cut is almost like a dotted line where the branch starts to get fatter near the trunk. The angle of the cut varies because the collars vary.
Therefore, when pruning heavier branches and ones that have narrow crotches, it is wise to use a multi-cut system of removal. First remove the weight of the branch by cutting it off farther out from the trunk. Start by making an undercut, then saw down from the top of the branch. This prevents the saw from getting stuck and the bark from tearing off and leaving a long wound. Once the weight is gone a more proper pruning cut at the collar can be made.
Pruning Young Trees
A young tree is less than fifteen years old. The main goal of young tree pruning is to remove the suckers, remove the temporary limbs, and to minimize the included bark.
- Tree suckers are the straight, thin rapidly grown shoots that arise from the trunk, the roots, or below a graft union. The suckers should be cut off just as they meet the trunk. Suckers that arise from below ground are often the result of the tree being planted too deep. If that is the reason, the tree should be dug up and replanted with the trunk flare right at the finished soil level.
- The temporary limbs are the lower limbs that need to be removed to provide clearances for people, cars, etc. These limbs feed the trunk, making it stronger and giving it a good taper. Limbing up a young tree should be done before the limbs become half the diameter of the trunk.
- Included bark occurs when two leaders of equal size are growing at the upper part of the trunk. As the two leaders expand, they push each other apart and the tree can break causing one or both of the co-leaders to break from the tree. The solution is to remove one of the leaders with a proper cut.
The above excerpts are from my recent book “Cass Turnbull's Guide to Pruning. The intention of this book is to provide a useful pruning guide that clearly and simply describes how to prune trees according to the latest standards. For more information on the book, it is available from Sasquatch Books.
How Trees Grow
(Tree Morphogenesis)
By David Lloyd–Jones
Trees grow in annual increments but there are other growth cycles occurring in multiples of years (or even decades), that profoundly influence the development of branch architecture and the characteristic form of mature trees.
Those annual cycles appear to be environmentally influenced but unlike annual cycles, there is a degree of variability that means that they only influence the tree every few years or decades and as a result the way that they subtly and fundamentally influence the shape and form of almost all trees, have been unreported until now.
It is these cycles that differentiate the structure of trees and provide variable geometry and variable strength branch attachments that literally facilitate wind pruning. Those cycles begin and end with a Growth Phase Change and these chronologically organize points of morphological differentiation, also differentiate the growth of trees from a simple fractal shape.
While some of the triggers for morphogenesis in temperate climates have been described in my book, there are undoubtedly more to discover and then there will be others that affect trees in the tropics. In other words, there are plenty of opportunities for arborists to deliver real and valuable insights into the tree species that they are working with by becoming students of tree architecture and environmental ecology.
Primeval origins
In the primeval woodland that prevailed across the globe until just a few thousand years ago, a tree had to develop in the shade of the forest floor, waiting for a large tree to fall so as to create a clearing and a gap in the high canopy into which the young tree could establish itself. To achieve the high canopy a young tree has to make sure that everything that it does, helps it to grow upwards at the maximum rate of growth which that species can achieve, in that location, and with the resources available. Once there, the tree grows on to full maturity, great age, and reproduction. Such trees are consequentially well represented by their offspring and therefore their contribution to the gene pool and the future of that species is significant.
However, once the tree has reached its mature height, it no longer needs to grow so strongly upward and in fact that upward growth trend places ever more structural leverage on the tree which at this stage is still growing as a simple fractal shape. At this point the primeval tree species has to adapt to the different adversities and the opportunities that come from achieving the high canopy.
Apical Dominance
Apical dominance is the phenomenon whereby the main central stem of the tree is dominant over side branches. The apical bud subjugates all other side branches by producing growth hormones that reach and affect all parts of the tree. Those hormone regulated side branches just grow ever outward and as a result they typically have wide angles of attachment to the stem. Because of this, the apical bud is the only one that grows consistently upward or towards the light while the remaining branches are cast in a supportive role by not being allowed to compete for upward growth.
Tree Emergence above the Forest Canopy
As the tree emerges into the area above the general height of the surrounding forest trees it becomes exposed to environmental influences in various ways. First of all, as the tip reaches up above the canopy of the trees it becomes exposed to wind or frosts and a full range of adverse occurrences. The tree has little choice because the growth hormones produced by the apical bud to continue the upward mode of growth. It is hormonally compelled to grow ever upward and as it does, if the growth tip and the apical bud become damaged or knocked off, it triggers the some profound changes in the structure of the tree.
For the first time and in just one brief moment in its life, there is no apical bud and therefore no hormones to impose apical dominance on all of the lateral branches. In that same moment, the side branches are no longer rigorously controlled and prevented from competing with the missing apical bud, and the side branches have a very brief opportunity to grow in forms that are less rigorously controlled than was the case in the young forest tree. So in addition to the tip forking, many of the lateral branches also form in this moment and a more rounded form develops at the top of the tree. To the tree, this would be the point that it comes of age so to speak as it changes from an excurrent morphology to a decurrent morphology.
Growth Phase Change
The first Growth Phase Change is easily understood because just one apical bud controls the development of shape in the tree, but there are subsequent Growth Phase Changes and they require a bit more explanation if only because unlike the first, the second and subsequent Growth Phase Changes need a trigger that affects many or all of the numerous apical buds that replace the single apical bud at the first Growth Phase Change.
If late spring frosts come just as the succulent leaves are emerging, it will have an effect primarily on the most exposed, peripheral buds by causing the cells of the newly exposed leaves and flowers to freeze and rupture. This effectively destroys the bud just at the point in the growing season that the tree is at its most fragile and delicate state.
Mid-summer droughts can also stress the tree and cause it to die back from the tips of the branches so as to make the leaf area smaller which enables the tree to survive the drought and grow on to maturity. Other natural causes include pests, root damage or loss and certain diseases. Any of these can cause the concentrations of major branch junctions all at a point in that structure that represents the same point in time.
This can be seen in the structure of mature trees. Because of these variances to simple fractal growth, the tree oscillates between growth phases and at each it differentiates its structure with a Growth Phase Change creating ever more branches and forked unions supporting them. The variable geometry and structural performance of the branch unions produced at each Growth Phase Change, enable the tree to facilitate wind pruning and by so doing, give the structural elements the ability to reduce loadings in high winds.
In other words, trees are designed by their long evolution to be pruned by wind so that they can come through an energetic storm to reproduce in the future (when less adaptively designed trees might fail). Simply understanding this process enables an arborist to be able to simulate wind pruning. In addition this new way of looking at trees enables an arborist to literally read the life history of the tree and understand that history as a series of events, all of which have changed the tree and left their mark in its mature structures and form.
David Lloyd-Jones is an arborist from Knutsford, Cheshire, UK. You may contact him at this address.
(Tree Morphogenesis)
By David Lloyd–Jones
Trees grow in annual increments but there are other growth cycles occurring in multiples of years (or even decades), that profoundly influence the development of branch architecture and the characteristic form of mature trees.
Those annual cycles appear to be environmentally influenced but unlike annual cycles, there is a degree of variability that means that they only influence the tree every few years or decades and as a result the way that they subtly and fundamentally influence the shape and form of almost all trees, have been unreported until now.
It is these cycles that differentiate the structure of trees and provide variable geometry and variable strength branch attachments that literally facilitate wind pruning. Those cycles begin and end with a Growth Phase Change and these chronologically organize points of morphological differentiation, also differentiate the growth of trees from a simple fractal shape.
While some of the triggers for morphogenesis in temperate climates have been described in my book, there are undoubtedly more to discover and then there will be others that affect trees in the tropics. In other words, there are plenty of opportunities for arborists to deliver real and valuable insights into the tree species that they are working with by becoming students of tree architecture and environmental ecology.
Primeval origins
In the primeval woodland that prevailed across the globe until just a few thousand years ago, a tree had to develop in the shade of the forest floor, waiting for a large tree to fall so as to create a clearing and a gap in the high canopy into which the young tree could establish itself. To achieve the high canopy a young tree has to make sure that everything that it does, helps it to grow upwards at the maximum rate of growth which that species can achieve, in that location, and with the resources available. Once there, the tree grows on to full maturity, great age, and reproduction. Such trees are consequentially well represented by their offspring and therefore their contribution to the gene pool and the future of that species is significant.
However, once the tree has reached its mature height, it no longer needs to grow so strongly upward and in fact that upward growth trend places ever more structural leverage on the tree which at this stage is still growing as a simple fractal shape. At this point the primeval tree species has to adapt to the different adversities and the opportunities that come from achieving the high canopy.
Apical Dominance
Apical dominance is the phenomenon whereby the main central stem of the tree is dominant over side branches. The apical bud subjugates all other side branches by producing growth hormones that reach and affect all parts of the tree. Those hormone regulated side branches just grow ever outward and as a result they typically have wide angles of attachment to the stem. Because of this, the apical bud is the only one that grows consistently upward or towards the light while the remaining branches are cast in a supportive role by not being allowed to compete for upward growth.
Tree Emergence above the Forest Canopy
As the tree emerges into the area above the general height of the surrounding forest trees it becomes exposed to environmental influences in various ways. First of all, as the tip reaches up above the canopy of the trees it becomes exposed to wind or frosts and a full range of adverse occurrences. The tree has little choice because the growth hormones produced by the apical bud to continue the upward mode of growth. It is hormonally compelled to grow ever upward and as it does, if the growth tip and the apical bud become damaged or knocked off, it triggers the some profound changes in the structure of the tree.
For the first time and in just one brief moment in its life, there is no apical bud and therefore no hormones to impose apical dominance on all of the lateral branches. In that same moment, the side branches are no longer rigorously controlled and prevented from competing with the missing apical bud, and the side branches have a very brief opportunity to grow in forms that are less rigorously controlled than was the case in the young forest tree. So in addition to the tip forking, many of the lateral branches also form in this moment and a more rounded form develops at the top of the tree. To the tree, this would be the point that it comes of age so to speak as it changes from an excurrent morphology to a decurrent morphology.
Growth Phase Change
The first Growth Phase Change is easily understood because just one apical bud controls the development of shape in the tree, but there are subsequent Growth Phase Changes and they require a bit more explanation if only because unlike the first, the second and subsequent Growth Phase Changes need a trigger that affects many or all of the numerous apical buds that replace the single apical bud at the first Growth Phase Change.
If late spring frosts come just as the succulent leaves are emerging, it will have an effect primarily on the most exposed, peripheral buds by causing the cells of the newly exposed leaves and flowers to freeze and rupture. This effectively destroys the bud just at the point in the growing season that the tree is at its most fragile and delicate state.
Mid-summer droughts can also stress the tree and cause it to die back from the tips of the branches so as to make the leaf area smaller which enables the tree to survive the drought and grow on to maturity. Other natural causes include pests, root damage or loss and certain diseases. Any of these can cause the concentrations of major branch junctions all at a point in that structure that represents the same point in time.
This can be seen in the structure of mature trees. Because of these variances to simple fractal growth, the tree oscillates between growth phases and at each it differentiates its structure with a Growth Phase Change creating ever more branches and forked unions supporting them. The variable geometry and structural performance of the branch unions produced at each Growth Phase Change, enable the tree to facilitate wind pruning and by so doing, give the structural elements the ability to reduce loadings in high winds.
In other words, trees are designed by their long evolution to be pruned by wind so that they can come through an energetic storm to reproduce in the future (when less adaptively designed trees might fail). Simply understanding this process enables an arborist to be able to simulate wind pruning. In addition this new way of looking at trees enables an arborist to literally read the life history of the tree and understand that history as a series of events, all of which have changed the tree and left their mark in its mature structures and form.
David Lloyd-Jones is an arborist from Knutsford, Cheshire, UK. You may contact him at this address.
Mulch Myths
By Butch Ragland
Lush meadows and healthy forests require soil started from mulch, also known as that fresh layer of organic matter (dead grass and leaves) on the surface. Under that fresh layer of mulch is just-started compost (decaying mulch), followed by finished compost a few inches below the surface. Below all the compost comes the healthy parent soil with compost mixed throughout. This soil is ideal for healthy trees. I call this the Natural Process. In one gram of healthy soil there are as many as 3 billion organisms plus a whole range of interactions between all these organisms.
The Nitrogen-Loss Myth
Have you heard that compost uses so much soil nitrogen that you should add fertilizer to the compost pile to make it work better? The reality is that compost and mulch do not cause nitrogen to be depleted from the soil, as long as they are placed on top of the soil and are not incorporated into the soil by tilling. The idea that mulch causes nitrogen loss is an old wives’ tale. When testing mulch, compost and soil, the carbon to nitrogen ratio (C:N ratio) should be in the 25-30:l range thus providing a good balance of the two elements while making nitrogen available to plants.
A host of organisms, including bacteria, worms, and fungi, break down the organic matter in mulch and compost and begin to change it into a form that will enhance tree growth by the humification process and produce rich soil. Research shows that this process utilizes nitrogen from air above, not the soil below.
Nitrogen is essential for making proteins in the soil. This nitrogen is stored within microorganisms' cellular structures found in the soil and in organic matter. It has been said that 75% of the nutrients in soil are stored in the microorganisms. Because of this, the nitrogen, along with many other trace minerals, cannot be leached from the soil by spring snow melt or summer irrigation. A plant’s roots will feed on this microorganism-stored nitrogen.
The Great Planting Hole Myth
University of California researchers found that putting any organic material into a planting hole caused a first-year reduction in growth of the tree planted in it. After the tree became established it recovered and grew normally. The researchers found that removing the soil from the hole, planting the tree and then putting back the removed soil around the roots gave the best results. No additional organic supplementation into the hole itself is necessary.
Arborists know that soil is a very poor container-growing medium because it is a living organism. Container-growers had to devise a method to grow trees in pots; hence a soil-less mix of sand and bark was developed. This soil-less mix is dead soil, microorganism-wise. It holds the plant upright while the growers deliver the nutrients and water that will allow trees to grow. The techniques used to grow trees in a container do not transfer to the soil, however.
Grit, rock, perlite, vermiculite and all of the things used to create good drainage, moisture-holding properties, etc. and found in the container grown tree, are useless in your tree planting pit and in fact interfere with the natural process. If the soil you are planting in is surrounded by meadows or forest, it will grow trees. Since this is often impossible along city streets, rubble and poor soils such as clay and sandy soil must be changed, but the arborist cannot change them by amending the soil with magic ingredients. The poor soils must be changed by removing 75% of the existing material throughout the entire area available for the mature tree root space and mixing the remaining soil with loam and organic material such as compost to provide permeability and food for microorganisms. Adjusting or altering pH can be accomplished in these small areas.
Mulch makes the Soil Acidic Myth
The importance of regulating pH in the non-urban tree planting pit is another old wives’ tale. Get a soil sample and send it to your testing lab or local extension office for testing. When you receive the results, make your tree selections based on trees that tolerate the existing pH conditions. You cannot change the pH of your soil in any meaningful way. Soil sampling evolved out of farmers needing to control pH as they grow crops in rows. In that situation, the farmer, with the help of a tractor, has destroyed the structure of his field, and must regulate the pH and nutrient levels every year for as long as the soil is used for crops. Manipulation of pH in lawns can be accomplished due to the shallow soil profile in which grass roots grow.
Trees however are a different story. This is because the pH of your particular soil type will not easily move from acidic or basic toward a neutral pH, at least in the root zone, where it counts for your trees. Mulch will move your soil pH slightly toward neutral, but only at the soil/mulch interface.
The Tilling Myth
How did trees grow before the rototiller? Tilling (turning the soil over but leaving it in place) and double digging are not good practices for growing trees. The double digging process requires digging a trench across the tree planting pit, then digging a second, similar-size trench next to the first, this time placing the excavated soil from the second trench mixed with organic matter into the first trench. The problem is that organic matter decomposes too quickly for trees to completely utilize it, thereby creating a feast-or-famine nutrient cycle. Worse, double digging mixes mulch materials into the subsoil, where they are attacked by anaerobic bacteria that excrete metabolic wastes that are actually toxic to trees and aerobic soil organisms.
The Natural Process
Trees can be kept alive in these mythical environments with a lot of attention and work. Meanwhile, the Natural Process needs little help, except in climates where it is especially hot or dry. The dry part is fairly easy to fix with irrigation. Hot depends upon how hot, but irrigation is usually the solution to hot as well.
There is an old adage: After planting, the first year a tree sleeps; the second year it creeps; the third year it leaps. It takes that long for the soil organisms to become intimately involved with the tree’s root system. If you feed the soil organisms, you can rely on nature to do the rest. So just “mulch and get out of the way!”
If lush meadows and forests grow by this method, why would arborists think they can do it better?
Additional Reading
- Rillig, M. and Steinberg, P. D., “Glomalin production by an arbuscular mycorrhizal fungus: a mechanism of habitat modification?”, Soil Biology & Biochemistry, 34:1371-1374. 2002.
- Starbuck, Chris, “Grass Clippings, Compost and Mulch: Frequently Asked Questions”, Department of Horticulture, University of Missouri, 2003.
- Wright, S. F. and Upadhyaya, A., “Extraction of an abundant and unusual protein from soil and comparison with hyphal protein of arbuscular mycorrhizal fungi”, Soil Science, 161:575-586. 1996.
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