Invasive trees as a nitrogen source?

Greetings from a newbie,

I am slowly learning about permaculture and have been working my garden in the right direction. I have noticed that we have Chinese silk trees all over the place. I now know that they are classified as an invasive exotic. However, since they are already all over the place, and they fix nitrogen, I would like to use them as companions with my fruit trees. I am thinking I could prune them into a large shrub form and plant them in relative proximity to my semi-dwarf fruit trees. I could probably control the number of pods they produce with fall pruning.

Anyone have a better suggestion? I like the idea of using what is already here.

Invasive/exotic is somewhat of a misnomer, but I'll avoid that discussion for now. Suffice to say that most of our crops and animals can also be considered invasives/exotics, so that's something to think about.

Unless they're horribly overgrown or running amok, I'd use them. As far as I know, the silk tree is not toxic or suppressive to most other plants, the flowers are very popular with pollinators, and prunings and pods can be used as animal fodder or enrichment for your compost pile/mulch. They are also considered frost/winter hardy, even naturally occurring as far north as Korea. All in all, quite valuable, IMHO.

The mimosa or Persian silk tree (Albizia julibrissin ) is a good or excellent nitrogen fixer (estimates vary).  It also provides a good source of nectar for honey bees, hummingbirds, and butterflies over the summer. And the bark is used by some herbalists against anxiety, depression and other conditions. The foliage does not cast heavy shade, especially if occasionally pruned for chop-n-drop mulching ... very good for polyculture.

It has been declared 'invasive' in some areas, but unless it totally takes over a landscape and crowds out endangered native plants, I don't see it generally as a problem.

http://en.wikipedia.org/wiki/Albizia_julibrissin

i have a similar situation with eleagenus here, I like them and they grow all over, so I try to just take advantage of the opportunity. We also have a ton of alder, so I try to chip up the dead ones to use as mulch (they are NOT long lived)

I'm not familiar with your plant, however, with the alder they tend to die as the other trees grow, which means they are basically a nurse plant, as are the aspens here..

First a word about N fixation: with cover crops, accessing the fixed N does not happen unless the plant is killed in a timely fashion.  N fixers are fixing N for their own use, and you have to destroy the plant before blossom, and especially before seed set, to access/release it best.  If your N fixer has set seed, it has prettymuch used up the N in its nodules. 

If there is plenty available N in the soil, N fixers will be lazy, and not fix N from the air and will not form the nodules.  So if they do use the available N from the soil, and complete their life cycle, you may actually be looking at a net loss of N in your soil.  It is now in the seed.

The idea of utilizing N fixing trees doesn't make sense to me, unless those trees are remarkably different from green manures.  But from what I can tell, they're not.  Except that their natural life cycle is considerably longer.  N fixing trees can pave the way for other N needing species to grow in a given location, but the process is slow, transitional, and dependent upon the N fixers dying and creating new soil composition over a long time as they break down. 

Since Permaculture is supposed to be a controlled mimic of natural biological systems, the use of invasives seems contrary to me.  The only role invasives play in native ecosystems is a destructive one.  Planting invasive trees expecting to reap & take advantage of their N fixation, without understanding the manner in which N fixers work, (how death & time plays a key role in making that fixed N available) sounds counterproductive.  Over the life of that invasive tree, (unless you grow & kill them over & over) it's going to send out billions of seeds... and it's not guaranteed that any appreciable amounts of N will be gained from its being planted when it eventually dies a natural death.  But plenty more invasive trees will be gained, spread far & wide from that mother tree... 

What if you coppice the nitrogen-fixing tree just as it begins to set seed?

H Ludi Tyler wrote:
What if you coppice the nitrogen-fixing tree just as it begins to set seed?

It'll stop seed production, but won't have any effect on releasing the N sequestered in the root nodules. 

Coppising is great if you want to encourage sucker production for raw materials.  Making baskets, stakes, etc.  But from a woodlot maintenance point of view, unless you keep up with it, (forever) you'll end up with multi trunk trees which are hazardous (water collects in the crotch & rots the bases) and difficult to cut down safely when you do want the lumber....

http://en.wikipedia.org/wiki/Nitrogen_fixation
http://en.wikipedia.org/wiki/Actinorhizal_plant

If you want to read about N fixation presented in understandable layman's terms, I can't recommend this book too much: http://www.johnnyseeds.com/p-7976-northeast-cover-crop-handbook.aspx  (You don't have to get it from Johnny's it's available elsewhere.)

So if one wanted to obtain the nitrogen it would be better to wait until the seeds are almost mature to coppice and then use the material for mulch.

nedwina wrote:

Since Permaculture is supposed to be a controlled mimic of natural biological systems, the use of invasives seems contrary to me. 

The term 'invasive' is one that is invented and applied by humans. The use of this term is sometimes accurate and valuable, but can also be biased and arbitrary.

When a cleared field is abandoned, it is pioneered by species which grow rapidly and release lots of small seeds that travel long distances. Are these not 'invasive' in many ways? But if they are the invasive species that people are used to, they are not labeled negatively.

Sure, introducing a species into a new niche can be disruptive - kudzu, fire ants, and many other species demonstrate that when a species is moved to a place without the natural pests and controls, it can be very successful (at the expense of other species). 

In the original post, da_wanderer noted that there are already mimosa trees all over the place... in that case, one is merely using plants that are already present. If one lived in a place where there were no mimosa trees and there was reason to believe that they might thrive and get 'out of control' then one should think hard about the wisdom of introducing it. But if they are already there and running rampant, the impact of growing them is not so great, IMO.

nedwina wrote:
First a word about N fixation: with cover crops, accessing the fixed N does not happen unless the plant is killed in a timely fashion.  N fixers are fixing N for their own use, and you have to destroy the plant before blossom, and especially before seed set, to access/release it best.  If your N fixer has set seed, it has prettymuch used up the N in its nodules. 

I'm not sure if that is as true as it used to be assumed it is.  The hair roots on most plants are very short-lived and are constantly being renewed.  Some only live for a matter of hours.  There is nitrogen in all living things.  The N in the hair roots is available, via microbes, for other plants.  This isn't the flush you get from disking in clover, but it is a slow and steady release.

When the leaves drop, either in the fall or fron pruning, the N in them is made available.  Again, this isn't as concentrated as disking clover, but it should come close.

Invasive is in the eye of the beholder.

nedwina wrote:
First a word about N fixation: with cover crops, accessing the fixed N does not happen unless the plant is killed in a timely fashion.  N fixers are fixing N for their own use, and you have to destroy the plant before blossom, and especially before seed set, to access/release it best.  If your N fixer has set seed, it has prettymuch used up the N in its nodules. 

If there is plenty available N in the soil, N fixers will be lazy, and not fix N from the air and will not form the nodules.  So if they do use the available N from the soil, and complete their life cycle, you may actually be looking at a net loss of N in your soil.  It is now in the seed.

The idea of utilizing N fixing trees doesn't make sense to me, unless those trees are remarkably different from green manures.  But from what I can tell, they're not.  Except that their natural life cycle is considerably longer.  N fixing trees can pave the way for other N needing species to grow in a given location, but the process is slow, transitional, and dependent upon the N fixers dying and creating new soil composition over a long time as they break down. 

Since Permaculture is supposed to be a controlled mimic of natural biological systems, the use of invasives seems contrary to me.  The only role invasives play in native ecosystems is a destructive one.  Planting invasive trees expecting to reap & take advantage of their N fixation, without understanding the manner in which N fixers work, (how death & time plays a key role in making that fixed N available) sounds counterproductive.  Over the life of that invasive tree, (unless you grow & kill them over & over) it's going to send out billions of seeds... and it's not guaranteed that any appreciable amounts of N will be gained from its being planted when it eventually dies a natural death.  But plenty more invasive trees will be gained, spread far & wide from that mother tree... 

What you're discussing does mainly apply to green manures and a huge N boost that heavy nitrogen feeders or grain crops require. This is a different situation. When using N-fixers or N-fixing trees, N is lost in appreciable amounts and absorbed by the surrounding area due to litter fall, biomass removal (leaves, branches, stems, tops, etc.) for composting or mulching, root die off and turnover, browsing by animals and their waste deposition, humus building, etc. N added in this way is mostly and gradually cumulative within the system, whereas killing green manures or coppicing produce large pulses of ready N and C into the system, which become available to the following (annual) crops. Perennial crops/forest don't generally require such large pulses of N, since they usually have lower N requirements and a bank of nitrogen already built up in humus, litter fall, etc. in the soil. Too much N and basically all you end up with is leaves, not fruits or roots. That's fine if you want to grow leafy greens and annual grains, since they live fast and die young. Not fine for orchard trees.

Edit: I wanted to note also that killing green manures and plowing them under is not really mimicking natural systems, either. And second edit: others posted while I was writing my original post, so apologies for the redundant info.

Dad planted a Leucaena leucocephala given him by a family member.
I am trying my best to stay ahead of the seeds sprouting everywhere
all over the property now.
I'll be cutting some down a bit (pollard or coppice) next winter as we need
a mountain of Woodchips and mulch -
But there is NO way I'll use them as N fixers near my indigenous Fruiting trees.
Going to try Pigeon Peas and some annuals rather.

Jonathan_Byron wrote:
The term 'invasive' is one that is invented and applied by humans. The use of this term is sometimes accurate and valuable, but can also be biased and arbitrary.

When a cleared field is abandoned, it is pioneered by species which grow rapidly and release lots of small seeds that travel long distances. Are these not 'invasive' in many ways? But if they are the invasive species that people are used to, they are not labeled negatively.

Sure, introducing a species into a new niche can be disruptive - kudzu, fire ants, and many other species demonstrate that when a species is moved to a place without the natural pests and controls, it can be very successful (at the expense of other species). 

In the original post, da_wanderer noted that there are already mimosa trees all over the place... in that case, one is merely using plants that are already present. If one lived in a place where there were no mimosa trees and there was reason to believe that they might thrive and get 'out of control' then one should think hard about the wisdom of introducing it. But if they are already there and running rampant, the impact of growing them is not so great, IMO.

The term "invasive" is often misused.  But there is an official definition.  All it takes is a quick search to see that Mimosas are considered an Invasive species by the USDA and by various state authorities. Granted, in some locations they are more prevalent (and destructive) than others, but I fail to see your reasoning in this statement:

But if they are already there and running rampant, the impact of growing them is not so great, IMO.

I don't subscribe to such a philosophy.  But perhaps it is because I am constantly battling Invasive species on my property, and have witnessed their destructiveness first hand. 

Permaculture by definition is supposed to be "sustainable" and based on "ecological relationships"...there is nothing "sustainable" about Invasive species, and since they destroy native "ecological relationships", why would they be included/condoned in Permaculture?  I simply don't get that.   

Are mimosas destructive?  And in what way?    They are quite beautiful trees and I've not seen anything like solid stands of them - they seem to be scattered through the forest.

maikeru wrote:
What you're discussing does mainly apply to green manures and a huge N boost that heavy nitrogen feeders or grain crops require. This is a different situation. When using N-fixers or N-fixing trees, N is lost in appreciable amounts and absorbed by the surrounding area due to litter fall, biomass removal (leaves, branches, stems, tops, etc.) for composting or mulching, root die off and turnover, browsing by animals and their waste deposition, humus building, etc. N added in this way is mostly and gradually cumulative within the system, whereas killing green manures or coppicing produce large pulses of ready N and C into the system, which become available to the following (annual) crops. Perennial crops/forest don't generally require such large pulses of N, since they usually have lower N requirements and a bank of nitrogen already built up in humus, litter fall, etc. in the soil. Too much N and basically all you end up with is leaves, not fruits or roots. That's fine if you want to grow leafy greens and annual grains, since they live fast and die young. Not fine for orchard trees.

Edit: I wanted to note also that killing green manures and plowing them under is not really mimicking natural systems, either. And second edit: others posted while I was writing my original post, so apologies for the redundant info.

Understood.  (Well, sort of, LOL.)  Seems to me that the killing & plowing under of green manures is a deliberate manipulation & acceleration of the natural N releasing systems you have described there, no?  But certainly the point is to have it happen on its own, at a slower pace, and in measured amounts suitable to perennial crops.  

H Ludi Tyler wrote:
Are mimosas destructive?  And in what way?    They are quite beautiful trees and I've not seen anything like solid stands of them - they seem to be scattered through the forest.

It depends on where you are.  Mimosas/Silk trees (Albizia julibrissin) is "regulated" in TN, and a "troublesome weed" in FL.

http://www.invasive.org/browse/subinfo.cfm?sub=3004

If you do a search on "Albizia julibrissin invasive" all kinds of links pop up.  Invasive status is largely decided on a state level.  And can be very political.

i used to use the mimosa tree as a compost material plant when i live in a warmer climate. i would chop it to the base and in 3 weeks it would be a 7ft tall thick bush ready for me to chop again, and again every 3-4 weeks. it never needed water, no pests.

nedwina wrote:
It depends on where you are.  Mimosas/Silk trees (Albizia julibrissin) is "regulated" in TN, and a "troublesome weed" in FL.

When something is labeled a "troublesome weed" that almost always reflects a world view rather different from my own. Many people in my community consider the dandelion to be a troublesome weed, and they spray lots of herbicide in an attempt to eradicate it. I have no problem with dandelions growing in my yard.  Mimosa is similar to dandelion in that it thrives in disturbed areas - it prefers edges of forests and in vacant lots. 

I don't see mimosa as being problematic in my area, and I suggest that a bigger problem is forest fragmentation and habitat disruption - such human activity guarantees that the ecological status of forests will change, whether from native edge species or introduced edge species.  I have never seen nor heard of mimosa growing like kudzu and choking out large areas. 

nedwina wrote:Permaculture by definition is supposed to be "sustainable" and based on "ecological relationships"...there is nothing "sustainable" about Invasive species, and since they destroy native "ecological relationships", why would they be included/condoned in Permaculture?  I simply don't get that.   

Even ecology is subject to bias and distortion. Our ideas of ecological succession were shaped by the Book of Genesis with it's linear progression,  when a more accurate set of concepts might be found in the Trimurthi and the balance between creation, destruction, and preservation. Certainly recent developments like fire ecology and historical re-creation of ecosystems of the past using fossil pollen should move us away from the view of ecosystems as static or having any pre-defined optima. Yet this type of new ecology has not permeated most people's thinking - we want to keep things the way they are, even when that changes everything. 

And more than a few ecologists have pointed out the similar rhetoric among those who oppose introducing new plants and those who oppose immigration - from key vocabulary like 'natives' and 'invaders' to a conviction that things can and should be controlled.  Below is a link to one such essay - I don't agree with everything that is said in that article, but that is a position in the discussion that has some good points. Do we want to eliminate honey bees in North America since they are an introduced species? Or do recognize that honeybees play a positive role, even though they may compete with native bees, even though they must be considered invasive from the perspective that also considers mimosa a foreign invader?

http://www.nytimes.com/2011/04/03/opinion/03Raffles.html?_r=2&ref=todayspaper

hubert cumberdale wrote:
i used to use the mimosa tree as a compost material plant when i live in a warmer climate. i would chop it to the base and in 3 weeks it would be a 7ft tall thick bush ready for me to chop again, and again every 3-4 weeks. it never needed water, no pests.

great idea. had forgotten how quick they rejuvenated. mulberries seem to do well too (different nutrients).

N-fixing deciduous trees like legumes and alder help build the soil even if they aren't cut down to the ground or otherwise "managed", since the leaf drop will return the fixed nitrogen back to the soil.  There is also natural root die-back which adds nitrogen to the soil.  Perhaps the idea that nitrogen fixers only add nitrogen when killed comes from herbaceous N-fixers like clover and alfalfa.

N-fixing trees are definitely working to build up soil in many parts of the world such as in sub-Saharan Africa.  There are some good articles on nitrogen-fixing legumes for agroforestry, for example on agroforestry.net.

I suspect in most areas there is a small number of truly noxious weeds, which are often officially listed by local governments. That still leaves a lot of options.  I would say that it's wrong to label a tree invasive just because it spreads in the wild.  If it's not taking over and becoming a monoculture, then it's adding to biodiversity, not detracting from it.  Some areas will benefit from the "invasive".  Nature is always changing, and attempting to turn back the clock to a pristine earlier time is not necessarily the best option.  Some ecologists are starting to realize this and accept that it's time to start looking at the ecosystem as a whole (more the way a permaculturist would look at it) rather than just looking at the ecosystem as a battle between exotics and natives.

Recommended reading: Invasion Biology: Critique of a Pseudoscience by David Theodoropoulos. For an alternative view of the "invasive species" debate.

Jonathan_Byron wrote:
When something is labeled a "troublesome weed" that almost always reflects a world view rather different from my own...
http://www.nytimes.com/2011/04/03/opinion/03Raffles.html?_r=2&ref=todayspaper

Species die off and are replaced all the time.  Life on the planet is not unchanging.  I don't refute that.  Not at all.  But the manner & speed in which our native species are endangered or dying off, due to habitat destruction from various reasons, (perpetrated largely by humans) is not happening at a pace where Nature can correct.  Predator/prey relationships build over centuries, not over a few generations.  Even when there is a substantial event that wipes out an ecosystem, the survivors and newcomers (and their corresponding predators) are from the general area- not from another continent.   

Certainly there are introduced species (exotic or otherwise) which have little or no impact on native ecosystems.  Or even observable beneficial ones.  Those were Happy Accidents.  And are handy to point out when this discussion occurs.  But the comparison between them and Invasives is apples & hand grenades.

And today's benign non native can become tomorrow's destructive Invasive should conditions change.  Which they do, all the time.   

There is this attitude (whose foundaton can be found in Genesis too, BTW) that we humans can do whatever we want, whenever we want, and Nature's systems will adapt and continue to provide for us.  And there weren't many indications to assume otherwise, for centuries.  But here in the Modern Age, with the global exchange of flora, fauna, bacteria, fungus, etc., it is becoming clear that we can't reshuffle & redesign Nature (by accident or whatever) on a global scale without consideration and expect her to accomodate our hubris.  There are consequences.  Some pretty serious ones. 

Maybe you don't see Invasives altering your ecosystems in your backyard, but I do.   I spend tremendous time, energy & money trying to keep them at bay.  If I don't, my native food chains will suffer, and I, the resident human, will suffer also.  If you ever find yourself in the Northeast, drop me a line and I'll give you a personal tour and show you what I've learned first hand.

I'm also a landowner and have had my "battles" with certain invasives, in my case Phalaris arudinacea (Reed Canary Grass), and Himalayan blackberry here in Northwest. 

I forget who said this, but I remember someone suggesting that they didn't feel it was appropriate to take a warlike mentality into their gardening and permaculture activities.  There is an aspect of how we approach the natural world that reflects what is inside of us.  If we insist on having a lawn free of weeds, this "battle" mentality leads us to chemical warfare.  Now most of us who are into permaculture have realized the ill effects of lawn herbicides, but this warlike attitude still comes up when we are dealing with "invasive" species.  Perhaps we even resort to chemical methods to battle these "evil invaders".

I say, can we not declare peace instead of declaring war?  I still have some work to do to manage the "overly exuberant" species growing on the areas I manage, but more often than not I try to see the virtues inherent in these plants rather than the evils.  And among these virtues may well be nitrogen fixation. 

Instead of a sweeping judgment about invasives vs. natives, I suggest we look at each species and manage appropriately for the characteristics of that species and the desired effects on our land and the ecosystem as a whole.

One area I manage is an official wetland, and there is a management agreement in place to control the reed canary grass by shading it out with trees, and control the blackberry by digging it out.  So, I am dutifully performing my function there.  However, at least when pulling out these plants, I try to remember to thank them for what they have done and perhaps bless them as they recycle back into the earth.  And I appreciate the blackberry for the berries it provides to me as well as to many birds, andother wildlife, and for the shelter it provides, and so on.  Most people around here tolerate some degree of the invasive blackberry for its benefits.

I don't see a problem with using a tree such as the Mimosa if it is already very prevalent in an area and can be turned to a positive purpose.  Eradication in that case is not going to serve much of a positive benefit since the plant is already established in the ecosystem.
Instead, I say we should look at how to work with the plants that are already there, if possible.

There is a longer arc of history that we aren't seeing when we see just the immediate effects of invasives.  Often other species adjust and adapt, over time, and the new species becomes integrated in a healthy way into the local ecosystem.  It often helps that fungi and insects adapt or arrive to take advantage of the new arrival.

oh, but where will the war stories be if you do not have wars and misery, trials and tribulation.

nedwina wrote:
.Maybe you don't see Invasives altering your ecosystems in your backyard, but I do.   I spend tremendous time, energy & money trying to keep them at bay.  If I don't, my native food chains will suffer, and I, the resident human, will suffer also.  If you ever find yourself in the Northeast, drop me a line and I'll give you a personal tour and show you what I've learned first hand.

maybe those invaders can be turned to allies... when we lived in NC, japanese honeysuckle and bamboo were classic invasive plants that we initially saw as a problem.  I soon discovered that our meat rabbits loved them for food.  problem = resource

even if they aren't edible (to something) most plants can be used as compost, mulch, nutrient accumulators easily.  we had mimosa trees pop up in our orchard from time to time and they would bcome a contribution to the compost regularly.

Regarding the book ("Invasion Biology:...") recommended a few posts back, the author, David Theodoropoulos is the owner/operator of J.L.Hudson, Seedsman.  He is an excellent source for many permaculture plant seeds.

The mimosa trees I see around here are found along edges. They grow to 40 feet at most. I don't really see them as being destructive given their height and preferred location.

I just view them as a potential resource that I have readily at hand. I will try coppicing some of the young ones and see how they respond.

Thank you for all the replies.

da_wanderer wrote:
The mimosa trees I see around here are found along edges. They grow to 40 feet at most. I don't really see them as being destructive given their height and preferred location.

I just view them as a potential resource that I have readily at hand. I will try coppicing some of the young ones and see how they respond.

Thank you for all the replies.

Please post the results. had to cut a few trees before having a 90+/- foot pine dropped. Was interesting to see how different species reacted and how sassafras seemed to be okay with a cut back, as long as you cut it high. (the one cut a foot above the ground had not come back last I checked).

nedwina wrote:
Understood.  (Well, sort of, LOL.)  Seems to me that the killing & plowing under of green manures is a deliberate manipulation & acceleration of the natural N releasing systems you have described there, no?  But certainly the point is to have it happen on its own, at a slower pace, and in measured amounts suitable to perennial crops.  

You can call it that. Tree N-fixers are good to help remineralize and recharge topsoil.

I use the self sown Albizia julibrissin plants that pop in my vegetable garden as a valuable nitrogen source for my vegetables by cutting them back when they get a few feet high and sheet composting them in the paths between the beds.  In some cases I will let them grown a little taller before cutting them back, such as if they are providing shade for some lettuce plants or if they are providing a living trellis for a self sown pole bean plant.

I definitely agree with those who said Albizia are not something to fear about planting.

Do they spread on non-native lands? Yes.

However, as others have stated, they tend to be on forest edges and are rather small spread out plants with little footprint on native habitats.

Things like Kudzu, Morning Glories, or Water Hyacinths all choke out native vegetation, which is why they are demonized.

I have never seen anything similar in the case of Albizia.

Albizia julibrissin isn't tall enough to persist in our native forests and would be overgrown and shaded out by shade tolerant native trees that seeded in under its shade.  It is a short lived pioneer species in the succession sequence and has value because it increases soil fertility by fixing nitrogen during its short occupancy.  Its closest southeast native equivalents would be black locust and honey locust (both of which are non-native to my region although the honey locust has been introduced and is feral along with albizia).  In my region its closest native pioneer competition is slippery eld and persimmon, neither of which fix nitrogen.

I have 100's of them popping up where a tree was cut down and need to know when to pick them for mulching.  Too close together to let them grow to tree size.  New to this.  Please help, 

FarmerGal wrote:
I have 100's of them popping up where a tree was cut down and need to know when to pick them for mulching.  Too close together to let them grow to tree size.  New to this.  Please help, 

The general rule of thumb is to chop and drop when precipitation is over evaporation.

So depending on your location answers will vary.

nedwina wrote:
First a word about N fixation: with cover crops, accessing the fixed N does not happen unless the plant is killed in a timely fashion.  N fixers are fixing N for their own use, and you have to destroy the plant before blossom, and especially before seed set, to access/release it best.  If your N fixer has set seed, it has prettymuch used up the N in its nodules. 

This is a wide-spread opinion with a parenthetic crypto-assumption that plants are self-centered that I would want to take issue with (and so do researchers of sustainable agriculture IN HORDES)
https://permies.com/permaculture-forums/10681_0/permaculture/paul-was-right-rhizodeposition

The complexity of N-fixation and N-redistribution is far beyond simple modeling as this.
(1) legumes and other plants living in symbiosis with nitrogen fixing bacteria DO provide N to adjacent plants throught leaf-drop, root-dyeback and rhizodeposition— AND the contribution from the latter is substantial.
(2) stressing N-fixing plants by cutting-back above-ground parts—Fukuoka's "stressing plants"-method—(mowing, trimming, coppicing) will produce root-dyeback with decay in proportion to plant material removed and leads to consequent nutrient (including but not exclusive to N) and mineral enrichment of the soil AND you have some mulch for added soil-amendments
(3) interplanting non-N-fixers with legumes INCREASES N-fixation rates precisely because there is (scientifically proven) nutrient-flow signaling connections in plant communities. AND SO this is another argument for polycultures—even N-fixing is diminished in the shared richness of N-fixing plants present in predominant monocultures. (a point that you have made in the next paragraph.)

Long live heterogenous abundance in life! Long live the Locust!

"The general rule of thumb is to chop and drop when precipitation is over evaporation."

Brad, could you please explain that a bit more?

    Sometimes an invasive has spread to the point where it's considered endemic. This means that it has already spread into every corner of the environmentat which presents conditions suitable for its growth. This state of affairs has certainly occurred with dandelions for instance. Because they have small windborne seeds and they are already everywhere you're unlikely to harm the natural environment by finding some use for this plant.

    With most plants which are very small or those which have very small seeds the invasion must be controlled in the early stages for control measures to be successful. Generally very large creatures or large seeded plants don't tend to get away and go feral quite as easily. It's unlikely that we'll we will ever be plagued with feral elephants or with coconut infestation. The size and reproductive speed of these organisms makes them unlikely candidates for invasiveness since they could be easily controlled through hunting and seed gathering.

   On Vancouver Island we have two invasive species of plants which have spread to just about every patch of soil which can support them. These are Scotch broom and Himalaya blackberry. Both plants produce many seeds which are spread by seed drop, water flow, birds, soil movement etc.. The time to try and prevent this infestation is long passed in both cases as their complete eradication would require the entire environment to be turned upside down at huge environmental and economic expense.

    I have had serious scotch broom infestation on my land. One broom plant can produce 35,000 seeds per year which can travel 20 feet from the parent plant when the pods burst in late summer. They can travel much further if there is wind or slope. These seeds can also be transported by the flow of runoff water and in the plumage of birds. Ants transport the seeds for their own uses. And broom seeds can persist in the environment for 30 years or more before sprouting when conditions are right. Scotch broom seeds are everywhere in this environment always waiting for their chance to sprout yet the entire island is not covered in this plant. It thrives in areas of disturbed soil where there is hot sun and it quickly dies out if it is shaded. So the only way to control the plant without resorting to poisons is to allow other plants to grow up and shade it out.

     Because this is an absolute infestation I see no reason why the plant can not be used for something. I use it as a high nitrogen mulch. I've done this in areas where I'm trying to control broom and I would not hesitate to bring broom from a neighboring property for this purpose since this would not change the fact that we have 100% saturation so far as broom seeds are concerned. The mulch is used to help young trees cope with the hot dry conditions on steep slopes. It has worked. These young trees are now tall enough that only a few spindly and struggling broom plants remain and soon the forest will win.

   I would certainly never bring unknown invasive to my property since I'd be worried about an infestation. But once a plant becomes endemic in the entire region you might as well learn to live with it and put it to some useful purpose.

   Much of this line of thought could be applied to areas infested with tumbleweed, tilapia and other invasives which we are  unlikely to ever eradicate.

pebble wrote:
"The general rule of thumb is to chop and drop when precipitation is over evaporation."

Brad, could you please explain that a bit more?

I'll give it a shot. From my understanding this means that whenever you are experiencing more precipitation than evaporation you should chop and drop. So during the rainy season is when you are cutting your mulch and dropping it to the ground. During the hot dry season you would not cut as you would prefer to keep the soil shaded and cool. In the temperate zone it's a little more complicated as we don't have a rainy and dry season. Where I am we have a wet March – May, so that is the time when I would be chopping up large herbaceous plants. June – Aug is fairly hot and dry so I would not cut mulch during that time.  Sept – Nov rain picks back up and the heat dies down so I can start mulching with my annuals that are finishing up as well as cut back woody plant materials, tree trimming, coppice, pollard. This gives nature the wet winter to break down that large woody parts. As with everything results may vary and timing is very important. You don’t want to cut things to late in the rainy season where they won’t have time to grow back before the dry season. I hope this helps.

Brad Davies wrote:
The general rule of thumb is to chop and drop when precipitation is over evaporation.

So depending on your location answers will vary.

So shading protects the soil from drying out BETTER than mulching it? I dunno'...
—....well... I guess... it depends... (*)

In other words, there is no general rule of thumb.
In the world of Sepp Holzer one observes the land, does what one deems to be beneficial and THEN observes the outcome—and the cycle moves forward. You surely will find out what is best for your circumstance if you watch closely.

* it depends on the amount and persistence of precipitation, your soil's water holding capacity, the orientation of your land in regard to sun exposure, wind direction, climate & microclimate, AND the kind of mulch-plant you chop'n'drop—quite a system to have algorithmic set of rules to come up with.

cini wrote:
So shading protects the soil from drying out BETTER than mulching it? I dunno'...
—....well... I guess... it depends... (*)

In other words, there is no general rule of thumb.
In the world of Sepp Holzer one observes the land, does what one deems to be beneficial and THEN observes the outcome—and the cycle moves forward. You surely will find out what is best for your circumstance if you watch closely.

* it depends on the amount and persistence of precipitation, your soil's water holding capacity, the orientation of your land in regard to sun exposure, wind direction, climate & microclimate, AND the kind of mulch-plant you chop'n'drop—quite a system to have algorithmic set of rules to come up with.

Good point.

I'll go home tonight and check my reference, Permaculture Design Certification DVD collection, by Mollison and Lawton, but I am fairly confident that Lawton said exactly that. While I don't think that Lawton is saying this is an exact rule, he is using it as a generalization to answer the common question of when to chop.

I also don't think he means to say that shade is better than mulch, nor did I mean to imply that. Instead you should strive to time it so that you have both. Lawton gave an example of a permaculture project that they had done in S. America, again I'll check tonight for specifics. After they had left the locals had followed customs and what their neighbors were doing, which was slash and burn. Instead of burning though they mulched their fruit trees with the "slash". Sounds good, except they slashed right before the dry season, as was tradition. So instead of nice mulch piles under their fruit trees they ended up with dry piles of kindling waiting to ignite the whole place.