Permaculture Plants – Tagasaste, the Nitrogen Fixing Tree for Large Sites

tagasaste_3-1-4
Photo credits for all images in this article – Narelle Dandy, https://simplyorganicmag.com.au/

 

Permaculture is all about energy-efficient design, and if you can add a single design element to a site that can perform many functions, then that’s an incredible gain in efficiency!

A tree that could do almost everything would be incredible, but it doesn’t exist. The next best thing would be a tree that does a whole lot of useful things, and everyone who’s ever studied permaculture has probably heard about tagasaste or tree lucerne at some point or other.

How useful is tagasaste? To better understand a design element in permaculture, we perform a functional analysis by making a list of it’s inputs and outputs, its functions and properties.

 

A tagasaste tree can be used as:

  • A nitrogen-fixing tree, which can capture nitrogen from the air to improve soil fertility.
  • A productive source of high quality, palatable and non-toxic fodder and seed for livestock and poultry, with a high 20-24% crude protein content of its leaves.
  • A fast growing windbreak growing up to 7m, which can be hedged.
  • A nurse crop tree to protect young or frost sensitive trees.
  • A bee forage tree which produces prolific blooms of creamy white flowers in spring on previous year’s growth, producing a honey that is white in colour and mild flavoured.
  • A source of timber and firewood, the tree produces a useful dense wood and can be coppiced easily. Tagasaste doesn’t grow in a form suitable for milling, so it can’t be used to make timber planks or beams, but is suitable for making small items.
  • A source of material for pulp and paper making.
  • A feature tree in landscaping. Tagasaste is an attractive evergreen tree with a gracefully weeping habit and masses of white flowers.

 

Adding to its usefulness is that fact that it’s hardy and drought-tolerant, able to grow in areas of low rainfall, as low as 350mm per year, and survive winters as cold as -9°C.

This highly versatile tree often used as a case study in permaculture classes, because it has so many uses on large properties and farm, and brilliantly illustrates the design principle of ‘Each Element Performs Many Functions’.

 

Description

Tagasaste, also know as Tree Lucerne (Chamaecytisus palmensis syn. proliferus) is a drought tolerant evergreen tree from the Fabaceae (legume) family, originating from the Canary Islands. It’s grown extensively as a fodder tree to feed livestock on farms and used for land rehabilitation. Being a legume, tagasaste roots have nodules which house nitrogen-fixing Rhizobium soil bacteria, which live in a symbiotic relationship with the plant. The bacteria can capture nitrogen from the air and convert it into soil nitrogen which plants can utilise, and in exchange the plant provides sugars for them which they produces by photosynthesis.

In terms of size, Tagasaste trees grow quite large and are really only suitable for larger properties and farms. The unreliable internet sources which just cut-and–paste each other’s uncited information claim a height 3-4m high, which is inaccurate. If we look at reliable authoritative sources such as government agriculture extensions, scientific research, primary industry organisations and botany information centres, we find that Tagasaste grows closer to 5-7m (16-23’) high, with a canopy that is equally wide. The confusion probably stems from the fact that Tagasaste can have a variable habit, they don’t all grow to the same shape, some may be erect in habit or while other may have a more prostrate form.

tagasaste_4-1-2
Tagasaste tree growing in the background covering the side of the house

 

The branches of this tree are long, leafy and pendulous, hanging down towards the ground.

Leaves are trifoliate, they’re a compound leaf divided into three leaflets. Each leaf is up to 7 cm in length and the undersides of the leaves are pubescent (softly hairy), just like the younger branches and flower sepals (the green petals at the base of the flower collectively known as the calyx which envelop the flower bud). The leaves are described as being dull green, bluish-green or grey-green in colour,

tagasaste_2-1-2
Tagasaste leaves are trifoliate, consisting of three leaflets

 

Tagasaste produce scented, creamy white pea-like flowers in spring, but sometimes as early as winter, providing a source of forage for bees when other sources are scarce. The pollinated flowers produce flattened, black-coloured seed pods which are around 5 cm long. The pods contain 10 small, flat, oval shaped, glossy black seeds, 5mm long x 3mm wide x 1mm thick.

tagasaste_5-1-2
Tagasaste seeds pods, showing glossy black seeds

 

tagasaste_1-1-2Close-up of Tagasaste seeds pods, which can disperse the seeds short distances by explosively releasing when mature.

 

Tagasaste Growing Requirements

Tagasaste is adaptable to a wide range of climates, growing in the tropical highlands and subtropics as well as in temperate regions with wet winters and dry summers.  It thrives in semi-arid areas with 350-1600 mm of annual rainfall, but can survive with as little as 200 mm of rain a year. With cold, It’s moderately frost tolerant when established, surviving frosts down to -6°C (with reports as low as -9°C). Young seedlings are frost tender and should only be planted out when all risk of frosts has passed.

This tree can be grown on a wide range of soils types (gravels, loams, acid laterites and limestones), but prefers sandy, gravelly deep and well drained soils. Good drainage is essential where rainfall is heavy, as tagasaste is very sensitive to waterlogging and wet heavy soils, even short periods of waterlogging can lead to infection by the fungal root disease Fusarium oxycarpum. Plant the tree in raised beds or on slopes and hillsides in areas where waterlogging may occur. Tagasaste are also not tolerant of saline soils.

Even though tagasaste prefer acidic soils (with a pH ranging from 4.8 to 6.5), they can cope with moderately acid to neutral soils (with a pH of 5.0 to 7.0), and survive in alkaline soils with pH 8.5, but alkaline and saline soils reduce their growth.

 

Environmental Impact of Tagasaste

What happens to the surrounding environment when Tagasaste is planted? Is it beneficial or harmful?

Let’s look at the matter objectively using information from reliable scientific sources and draw our conclusions from there!

When conducting research of published literature on the topic, it’s common to find different government department and organisations providing conflicting information, sometimes quite biased and unscientific. Certain government departments with a ‘weed-ist’ agenda claim Tagasaste to be a ‘weed’, an undesirable plant, but from my findings which I’ll detail below, the rationale doesn’t hold up when compared to the research-backed information from other government and research organisations with an agricultural focus, or against a basic foundational knowledge of ecology…

 

Improvement of soil fertility

Tagasaste is a nitrogen-fixing legume which will improves the nitrogen levels in the soil, acting as a pioneer species, creating more favourable conditions for the growth of other plant and tree species. It’s important to note that nitrogen-fixing (capturing atmospheric nitrogen from the air and converting it to a form usable by plants) can only happen if nitrogen-fixing bacteria are already present in the soil, as they reside in the tree’s root nodules.

The tree’s extensive root system which runs up to 10m deep is capable of tapping into water and nutrients very deep in the soil and bringing nutrients to the soil surface, making them available to shallower rooting plants as a mulch below the canopy.

According to one Australian government website – “Its nitrogen-fixing ability also increases soil fertility, helping other weeds to colonise invaded sites and out-compete the native species.”

Increasing soil fertility is a problem? Australian native wattles (Acacia species) also perform exactly the same ecological role as nitrogen-fixing pioneer trees, they’re from the same Fabaceae family as Tagasaste, and they play a pivotal role in the process of ecological forest succession, the creation and regeneration of forests. In fact, many Australian native plants, from tall trees to low groundcover plants are nitrogen-fixing leguminous plants! Also all plants require nitrogen to produce vegetative growth. This claim that nitrogen-fixing plants are problematic in Australian soils lacks scientific credibility in my opinion.

 

Soil conservation and reclamation

Tagasaste is used for revegetation of eroded areas, it’s planted as an easy to establish and fast-growing windbreak, to reduce wind erosion of the topsoil. The deep, extensive root system also helps bind the soil on steep slopes, reducing the impact of water runoff.

It’s been used to reclaim severely damaged ground, successfully growing in mining dumps and slag heaps. In New Zealand, tagasaste has been grown on gold dredge tailings.

Even though the tree is sensitive to saline soils, tagasaste has been assessed for salinity control In Western Australia, it’s been used to reduce water runoff and seepage, helping offset the rising water table effect which bring salts up to the soil surface.

Once again, according to another Australian government website, “In south-western Western Australia it grows in disturbed natural vegetation on lateritic soils in higher rainfall areas it is a serious invader of disturbed bushland. In all regions where it is found, it readily invades roadsides, creek banks and other disturbed sites and spreads from these areas into native bushland and grasslands.”

The claim is that tagasaste is a weed because it invades disturbed ground. The key word here is disturbed, and this is where the problem lies. Anybody who has studied ecology is familiar with the natural process of ecological forest progression. It’s a well-known fact that if any stable ecosystem is disturbed, either by natural or man-made factors, a small cycle of ecological progression, similar to the one which created the whole ecosystem, will occur. When this cycle happens, tough, short-lived annual plants (labelled weeds) will be carried in by the wind to stabilise the disturbance and prevent soil erosion and soil loss. Eventually short-live pioneer trees, often nitrogen-fixers, such as wattles, tagasastes and others will move in to shade the annual pioneer plants out and create a microclimate suitable for the climax canopy trees which will take their place. This is either wilful ignorance or intellectual dishonesty. The problem is not Nature’s reaction to disturbed ground, but the cause of the disturbance to a stable ecosystem which can resist ‘weeds’ naturally. What caused the disturbance??? Logging, overgrazing, irresponsible farming practices, overzealous bushland regeneration groups pulling up ‘weeds’ and removing trees but not replacing them with something else?

 

Self seeding pioneer plants, or human disturbance, which is the problem?

To directly quote another website claiming an alleged problem “Tree lucerne (Chamaecytisus palmensis) accumulates large quantities of long-lived seeds in the soil seed bank and readily germinates after fire or other disturbance, forming dense infestations that can smother native vegetation and prevent regeneration. Its nitrogen-fixing ability also increases soil fertility, helping other weeds to colonise invaded sites and out-compete the native species.”

If tagasaste was able to self-seed into stable ecosystems, the Australian government agricultural extension agencies wouldn’t need to advise farmers of seed treatment methods to improve tagasaste seed germination! To directly quote an agricultural fact sheet:

“The hard coat of tagasaste seed results in a very low germination of untreated seed. This can be overcome in two ways.Scarifying. Seed can be scarified by contact with an abrasive surface. … Hot water treatment.This involves dropping the seed into boiling water then immediately removing the container from the heat source and allowing the seed to soak in the water as it cools. Successfully treated seed swells and can be sieved off, and the unswollen seed treated again. New Zealand experience indicates that the swollen seed can be re-dried for mechanical planting, retaining its improved germinability”.

Once again, the keyword is disturbed soil! Anything and everything will pop up in disturbed soil as a natural restorative action to protect the soil.The fact that pioneer plants will arise after forest fires is expected, otherwise the soil will all erode away, and no forest would regrow. There’s more to Australian forests than monocultures of eucalypts regrowing from lignotubers after fires. Many plant and tree species exhibit this function. Nature’s wisdom seem to be interpreted as humanity’s problem, because human know how things ‘should be’, what would Nature know about sustaining and perpetuating life anyway…

The claim that tagasaste can form “dense infestations that can smother native vegetation” is bogus. Weed control is a concern for farmers trying to grow tagasaste. Research has shown that young tagasaste seedlings are impaired by competition from other plants. To quote an Australian government website for farmers, “Although tagasaste transplants grow rapidly, weed competition can be a problem, particularly with annuals such as Wimmera ryegrass and capeweed.Again there is little research information regarding weed control in tagasaste. Good seedbed preparation before planting or sowing can often be a help in weed control.”

A more honest assessment can be read on the website – Weeds of the Blue Mountains, under the title of ‘Impact on bushland’: “Tree Lucerne tends to stay at the edges of bush, but because it produces so many seeds, it has the potential to invade and modify native bushland.”

The survival of young tagasaste trees is reduced by grazing animals which find them quite palatable, and mature trees also face challenges to their longevity. It has been reported that where the bark from tagasaste has been stripped off by browsing sheep, it’s been observed that many of the trees died of Phytophthora fungus. Tagasaste have very few pest problems,  but they are susceptible to the tree lucerne moth  (Uresiphita ornithopteralis) and emerging seedlings are eaten by cutworms, grasshoppers and slugs.

On discussing the ability of tagasaste to spread, the Tropical Forages website, a collaborative effort between CSIRO Sustainable Ecosystems, Department of Primary Industries & Fisheries (Qld), Centro Internacional de Agricultura Tropical (CIAT) and the International Livestock Research Institute (ILRI) states that it “Spreads by seeds from the dehiscent pods.  However, hard seeds may not germinate in the soil for several years, and susceptibility of young seedlings to grazing limits its survival to protected or fenced areas.” When discussing weed potential, they state, “A fast growing species used for fodder and is invasive in a wide rage of landscapes.  It has naturalised in almost all areas where it has been planted, along roadsides or in adjacent bushland.  On lateritic soils in higher rainfall areas it is a serious invader of disturbed bushland.”

It’s an ecological fact that pioneer plants are designed to spread through disturbed ecosystems as part of a natural process to restore stability and protect the soil, which takes hundreds of years to form naturally. Unfortunately humans have a habit of disturbing stable ecosystems, throwing them out of balance, and then blaming the pioneer plants which are the symptom of the disturbance, not the cause, which is usually anthropogenic.

Common sense should dictate that when living near natural environments, responsible plant selection should be exercised, and all efforts should be made to minimise disturbance to the native flora and fauna which are in a delicate balance in any stable ecosystem.

 

Use as firebreaks

The dubious claims that tagasaste trees are a ‘weed’ because their seeds might germinate in large numbers after fires doesn’t stand up to scrutiny, its contradicted by the fact that tagasaste are used in Western Australia as a firebreak to protect pine plantations. The tagasaste trees, if planted densely enough to act as an effective firebreak, can not only prevents the spread of forest fires, and the loss of forests, but they also prevent the germination of their own dormant seeds in the soil!

 

Saving our bees!

Tagasaste provide high quality pollen and nectar, and although spring flowering, can start flowering during winter, increasing the source of nectar for bees. According to Australian Geographic, Australia has more than 5,000 native bee species, and studies suggest that the main impacts of the controversial neonicotinoid insecticides are on wild bees rather than domestic honey bees in hives. They state that “the combination of wide scale use of multiple agrochemicals, loss of plant and habitat diversity, and climate change is a significant threat to both wild and domesticated bees.”

More bee forage on rural properties to support both wild and domesticated bee populations is a necessity, and bees don’t care where the plants originated from. With more bees, there’s increased pollination of edible crops, a huge benefit for farmers and food growers.

 

Using Tagasaste in Permaculture Designs

Tagasaste trees have quite an impressive list of uses, but that doesn’t mean they should automatically be included in any and every permaculture site plan. With good permaculture design, once we have performed a functional analysis of a design element, we need to critically assess whether the element is suitable for the site being designed, and what relationships we can establish with existing and new design elements on the site, and not just include it on the whim because other people are using it on their permaculture properties! There needs to be good design rationale for including any element in a design.

Tagasaste are excellent trees for large properties, especially on rural sites where grazing livestock are kept, but they’re less than ideal for small properties, especially urban sites.

There are better nitrogen-fixing trees for small-scale gardens, and if you want to use an Australian native alternative, then you may be interested in Austral Indigo!

 

 

References:

  1. Heuzé V., Thiollet H., Tran G., Hassoun P., Bastianelli D., Lebas F., 2017. Tagasaste (Cytisus proliferus). Feedipedia, a programme by INRA, CIRAD, AFZ and FAO. https://www.feedipedia.org/node/310, Last updated on February 28, 2017, 19:04
  2. New South Wales Department of Agriculture – Tagasaste (tree lucerne) Agfact P2.1.7, first edition 1986 Paul Dann, Research Agronomist Division of Plant Industries, Canberra Barry Trimmer, Livestock Officer (Sheep and Wool) Division of Animal Production, Orange (Reviewed May 2003, Brendan George) – http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0005/147272/tagasaste.pdf
  3. Eastham, J.; Scott, P. R.; Steckis,R. A., 1993. Evaluation of Eucalyptus Camaldulensis (river gum) and Chamaecytisus Proliferu (Tagasaste) for salinity control by agroforestry. Land Degrad. Dev., 4 (3): 113-122, http://dx.doi.org/10.1002/ldr.3400040302
  4. O’Donoghue, B., 2011. Tastee Tagasaste. Victoria Park Alpaca Stud, Alternative fodder, http://victoriaparkalpacastud.com.au/en/Tagasaste_Articles
  5. Nectar and Pollen Sources of New Zealand by R.S. Walsh, first published in 1967 and second edition in 1978 edited by Trevor Walton with assistance from David Williams, Rotorua.
  6. PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. http://plantnet.rbgsyd.nsw.gov.au
  7. VicFlora, Flora of Victoria website, sponsored by Royal Botanic Gardens Foundation Victoria, source: Jeanes, J.A. (1996). Fabaceae. In: Walsh, N.G.; Entwisle, T.J. (eds), Flora of Victoria Vol. 3, Dicotyledons Winteraceae to Myrtaceae. Inkata Press, Melbourne.
  8. Food and Agriculture Organization of the United Nations (FAO) – http://www.fao.org/ag/AGA/AGAP/FRG/Visit/Ida/Chamaecytisus%20palmensis.htm
  9. F. López, A. Alfaro, M.M. García, M.J. Díaz, A.M. Calero, J. Ariza, Pulp and Paper from Tagasaste (Chamaecytisus Proliferus L.F. SSP. Palmensis),
    Chemical Engineering Research and Design, Volume 82, Issue 8, 2004, Pages 1029-1036, ISSN 0263-8762, https://doi.org/10.1205/0263876041580730.

 

 

 

 

About Angelo (admin)

Angelo Eliades is a presenter, trainer, writer, permaculture consultant, urban permaculture pioneer and food forest specialist.
This entry was posted in Gardening Information, Permaculture and tagged , , , , , , , , , , , , , , , , , , , , . Bookmark the permalink.

4 Responses to Permaculture Plants – Tagasaste, the Nitrogen Fixing Tree for Large Sites

  1. Elisabeth Ellicott says:

    Hi. I’m a huge fan of Tagasaste and trying to learn more about them. I have successfully cultivated 30 young plants from underneath mature trees. They are approximately 30-50cm tall in their pots now. I’m getting ready to plant them very soon and am concerned that these plants haven’t had any manual inoculation nor the has the soil they are going to be planted in. Should I be inoculating them at this stage in their life before planting or because they grew in the soil of mature trees, have they been naturally done?

    Thank you,
    Elisabeth

    Like

  2. Steve says:

    Was an interesting read until I got to the weed section. Opposition of government bias with your own bias does not disarm the argument. That it has weedy tendencies when it is in optimal conditions is not necessarily negative. It is merely a caveat that should be considered, not that it is without merits. But brushing off scientific consensus because a useful plant has downsides is foolishness.

    That same tendency can easily be utilized by systems not commonly touched in permaculture – animal fodder. But that is not the same as harmless.

    Like

    • Angelo (admin) says:

      Thanks for your comment Steve, I try to provide useful information to readers!

      In respect to bias, I’d like to clarify that even though I have my own subjective preferences as all people do, I aim to be as objective as possible in my articles by steering away from the emotive demonisation of any species and providing objective, factual data presented in a balanced fashion to provide context, or caveats as you describe them. Unfortunately, having a science qualification doesn’t confer people with the ability to construct logically coherent arguments, I know as I have two and have also studies the philosophy of logic!

      Framing the ability of nitrogen-fixing species to improve soil fertility as a negative argument is preposterous, considering that this is a feature common to many pioneer plants and trees, especially a large number of Australian natives. Nitrogen-fixing pioneer species play a critical ecological role in the process which gives rise to new ecosystems known as forest succession or ecological succession. If this were a valid logical argument, then we would have to rip up all Australian natives from the Fabaceae family which also fix nitrogen and improve soil fertility, such as acacia, casuarina, glycine, hardenbergia, Indigofera, kennedia and senna to name a few, and declare them all weeds!

      The failure to state that a certain plant or tree species only becomes a problem when there is human disturbance to the environment is the informal logical ‘fallacy of omission’, as it falsely suggests that there is only one causal factor, the presence of a particular species, when the elephant in the room is the glaringly widespread problem of human disruption and destruction of natural ecosystems.

      Please notice that I did provide a link to a whole article I wrote about an Australian native alternative, which I in fact do grow. Balance is important! 🙂

      Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s