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Case Study “Ailanthus altissima  Reduce The Diversity Of Flora Under Their Canopies Due To Allelopathy”




Allelopathy has a huge impact on modern day Horticulture; however it is not widely recognised or understood even though the consequences of planting a tree with allopathic tendencies could be fatal for all ground flora and plant species located around it. After information is given on how allelopathy works and how it is truly classified, A study has been conducted to find differences in ground flora species growing under allopathic and none allopathic trees. Differences were statistically found creating new opportunities to carry out research within this discipline.




“Ailanthus altissima  Reduce The Diversity Of Flora Under Their Canopies Due To Allelopathy”




Allelopathy is an important issue regarding trees and mixed species integration. Community composition and the co-existence of plant species may be strongly influenced by interactions between species (Inderjit and Callaway, 2003).


Within the horticultural industry the phrase allelopathy started to become understood since the 1970s, after years of refinement and different theories, allelopathy is now defined as a substance (biological phenomenon) that is produced by one plant that inhibits another plant known as allelochemicals.


These are chemical compounds that have no apparent role in life processes or plant structure; these compounds are called secondary metabolites. (Heisey, R. M. 1990)  


It has become apparent that plants manufacture a great diversity of secondary metabolites, including terpenoids, alkaloids, glycosides, flavonoids, coumarins, quinones, saponins, and phenolic compounds.


Evidence through research now suggests that these allelochemicals (as they are classed) play a defensive and attacking role. Attacking meaning they inhibit other plants growth rates, and the defensive role meaning that they can protect themselves against pathogens invading. 


Research and Literature Review:


Currently allelopathy is being researched widely. More books and journals are highlighting the significance of knowing what allelopathy is. Though many different avenues are being explored, modern day research usually leans towards the farming world, research in extracting these chemicals given by allelopathic plants, and creating natural herbicides is popular as from a business mind more money could be made using this research.

Through my research and literature review I have found journals specifically identifying allelopatic trees and the way they create this allelopathic effect. It is evident that there are many ways these allelochemicals reach ground level, although there is some confusion on the process in which a tree becomes truly ‘allelopathic’. Some researchers believe that a tree can only be truly allelopathic through the displacement of these chemicals through their roots, when some believe that trees become allelopatic via ‘any’ form of transferring  these allelochemicals into the soil.Research has shown it is essential to identify allelochemicals involved and find their natural concentrations and fluxes throughout the environment in order to build a picture of their function (Rachel M 2005).


Allelochemicals have been known to change soil composition and regulation of nutrient cycling, availability, and organic matter dynamics by changing the level of microbial (Inderjit, and J. Weiner. 2001). Allelopathic root exudates may serve as prospective organic carbon sources for microbes in the rhizosphere, or may suppress the growth of some species (Bias et al. 2001).


Not only does the concentration of allelochemical effect the soil composition but also the chemical and biological characteristics of the soil can affect the amount and concentration of allelochemical released. For example (Aerts and Chapin 2000) research shows level of soil resource availability can determine the quantity of secondary metabolites (allelochemical) in plant tissues, for example plants growing in resource-limited environments or under stress often have higher tissue concentrations of secondary compounds than those in less stressful locations. Ultimately highlighting that soil composition can change natural processes, even the process of allelopathy.


Root allelopathy has been shown to be dependent on plant densities, root distribution, soil and microbial composition (Hierro and Callaway 2003).

Modern day research clearly has this biggest impact providing factual up to date evidence helping experts of the day to make informative decisions within the horticultural and agricultural industry. 



Project Idea And Research:


The subject of allelopathy has created much interest throughout the last 10 years. During my literature review I found that the most popular form of research is to find different plant species that are allelopathic, however researching the species affected by the allelochemicals has not really been explored.

I have decided then to explore different species that are affected by these allelochemicals.


This research will directly influence the horticultural industry, helping experts with planting schemes. The future choosing of ground cover plants under allelopathic trees could be greatly influenced by this research.


I aim to specifically focus on one tree species which is widely recognized as to having strong true allopathic tendencies. Although this allelopathy has never been proven, much research has suggested Atlanthus altissima as being allopathic.


The usage of journals books and websites to create good reasoning points and to help back up conclusions and theorized ideas will be evident. This will create good research and will be an interesting ecological study. Although this is not ground breaking research little has been researched specifically on species that can and cannot grow in allopathic conditions.


Atlanthus altissima (species to be used)-


Atlanthus altissima is a deciduous tree in the Simaroubaceae family. It is native to both northeast and central China and also Taiwan. The tree has fast growth rates reaching heights of 15m in 25 years; although this is the case these trees have a life rate of approx. 50 years. The tree was first brought from China to Europe in the 1740s and was used as a popular garden tree. However it wasn’t long before faults where found in the tree. Firstly a bad odour is emitted by the male flowers and as time went by other problems became evident, suckers from the tree would not only appear on the base of the tree but also sprouting from its vast root system. These suckers grew fast and chocked light from ground species planting. Because of these draw backs Atlanthus altissima was seen less and less in a domestic situation but, in the 19th century was used for lining streets and pavements.



Atlanthus altissima often called tree of heaven has been extremely successful in invading and dominating certain habitats in various parts of the world. Altissima forms pure stands that are resistant to invasion by other tree species (Rod, M H. 1997). There are a few factors that make this plant so residual. Firstly, its reproduction methods are versatile creating most situations an easy space to reproduce. Altissima can reproduce from their roots, their roots can create small shoots and this can be an advantage as they have large root systems. When new shoots appear their growth rate is rapid beating any ground opposition to light, this also is a contributing factor. They also disperse there seeds using the wind covering vast distances, this is the main way of reproduction.


The secret

Another contributor to the invasiveness and success of Ailanthus altissima may be a secondary metabolite that provides competitive superiority through a process known as allelopathy. (Coder, K D. 1999) gives evidence of this using many different references, although nothing is fact strong support is shown that this tree gives of allelochemicals effecting plant species in its proximity.


Allelochemicals given off by Ailanthus altissima


Members of the Simaroubaceae, including Ailanthus, produce a class of bitter-tasting secondary metabolites called quassinoids (Heisey, R. M. 1990). Some of the first research on Ailanthus altissima was completed by Voigt and Mergen (Mergen, F. 1959) reported that water extracts of foliage and stems were injurious to tree seedlings of other species, and that the major phytotoxic compound produced by Ailanthus altissima is a quassinoid compound called ailanthone an (allelochemical).


Ailanthone (Edward, F 2008) (C20H24O7) is the active compound of Ailanthus altissima, much research has taken place to find where the highest concentration of this allelochemical is found, in order to do this an assaying of water extract from different tissue of the tree took place. Research has found that the strongest concentration of ailanthone if found in the lowest of the thin outer bark (Peigler, R. 1993), it has also been found in the roots leaves and branches.


Isolation research of ailanthone has been conducted many times; the latest research on this compound is by a Korean scientist (Yin (2007) who has used ailanthone and isolated it by using polar solvents. once isolation is complete the usage of chromotophy and MNR spectra is used to produce measured extracts of ailanthone.


(NCBI 2008) gives the latest results of the Chemical structure of Ailanthone


Molecular weight          376.40036 (g/mol)

Molecular formula        C20H24O7

Molecular weight          776.40g

Melting Point                 235-237oc

Boiling Point                   642oc

pKa                                   11.85

Vapour Pressure            3.9 E-19 torr

XLogP                               -0.5

H Bond Donor                 3

H Bond Acceptor            3

Tautomer Count             13

MonoIsotopic Mass       376.152203














NCBI (2008) 2d Chemical structure of

Ailanthone, the Phytotoxic Compound

Of Ailanthus altissima


Experiment Plan:


The ecological study will consist of locating a mature Ailanthus altissima species in a location where the shrub layers and ground layers have not been disturbed or maintained. Ensuring the tree is mature will ensure all plenty of ailanthone (Allelochemical) has been placed into the soils surrounding the tree consistently for many years. Also finding a natural location where plant layers have not been maintained produce good data as only naturally growing species will be plotted. It is important to do this as the scenario gives data where no human intervention has taken place.


I will use a square meter perimeter stick to transect each meter in a straight line going out towards the drip line of the tree. Each Cardinal points of the tree will be used in the study.


I will use the perimeter square meter stick starting at the trunk/base of the tree. Carefully I shall move towards the drip line of the tree, transecting each meter up to a 5m radius ensuring that cardinal directions are followed


I will plot data using a tally chart system; the tally of individual species found on each square meter will be more accurate than other forms of data plotting and will give me precise detailed data for this ecological study.


I will repeat this process in the same location within 20m with a tree species that shows no allopathic tendencies throughout my research. The plotting of this data will be performed in the same intricate way to ensure results are more accurate/ true.


The only variable that will be the changed will be the species of tree I take data from.


I will choose only one replicate to keep the study simple and easy to distinguish changes in data. This will help to predict probabilities found using the data collected. This gives readers numerical facts.


The plotting of data will be conducted during the early spring months when new flora is appearing for the annual year. Also doing it this time of year will ensure late snow and frost does not kill of any flora.


Experiment Location


I will conduct my experiment at Kew Gardens as they have a large mature Ailanthus altissima on their grounds. After discussion via email they have gladly allowed me to conduct my research and ecological study on the Ailanthus altissima on their grounds.


Data analysis


Once I have collected the data using my tally system, using statistical analysis I will create numerical data, plotting them onto graphs, creating standard deviations and standard errors. This will give my research mathematical depth helping readers clearly define numerical differences in my data collected.


After statistical analysis has been completed I will use the data to create a discussion based on my findings. Theorised principles may be discovered and a summary of my findings will hopefully present informative information to leading experts that can be used within the industry.


Items needed for experiment

The following list is items needed to complete this experiment successfully.

- 1m perimeter square quadrant & compass

- String line and two pointers

- Tally system easily editable on A4 paper

- Identification book

- Clip board

- Tape measure

- All weather clothing


Step by Step of experiment/data plotting:

The step by step process of plotting the data will be completed the same way, for both the allopathic tree and the non-allopathic tree.


Step one

I locate the tree Ailanthus altissima making sure it is good weather easy for plotting data (another person could help out)

Step Two

Carefully evaluating the area under the crown of the tree (not stepping on small flora), locate north on the compass at the base of the trunk.

Step Three

Create a straight line from the base of the tree following the cardinal point to a distance of 5m using your string and two pointers. Ensuring the string line follows the direction of the cardinal point (North, South, East, West)

Step Four

Starting at the base of the tree, place your 1m square quadrant on the floor starting at the string pointer nearest the base of the tree.

Step Five

Transect all flora and grass inside the 1m square quadrant, itemising the flora in species on the tally chart system.

Step Six

Repeat this process at each cardinal point, following the string line at each meter using the square meter quadrant, to a distance of 5m.




























Researching species of flora I may find when I transect each 1m square quadrant is vital, having knowledge of species will help me identify them. A list was compiled of species that are commonly found during the early spring months. Being able to identify species will help me to identify flora species accurately.

The research suggests that very few plants can grow under allopathic trees. (Horace G 1999) explains that the few plants that do grow in allopathic soil conditions usually look sickly and chlorotic. A carful inspection of flora when completing my field research, under the Ailanthus altissima will help me to identify these symptoms.


I feel that there is not enough research on plants that grow under allopathic trees; this makes it hard to predict results. Knowing the toxicity of the allelochemical ailanthone I feel that no plants only grass will grow under the Ailanthus altissima, there might be some surprises as research on plants growing under Juglans nigra has taken place. This is also an allopathic tree giving of an allelochemical called hydrojuglone. (S. Ercisli 2004) research and many other articles show that certain plants can grow in these toxic soil conditions, calendulas, grape hyacinth, daylilies, bluebells, black-eyed Susan’s, asters, marigolds, pansies, morning glories, phlox and Jack-In the pulpits.


(Lou Paun 2005) gives a list of spring flowers that could be found during early spring. I have also found personally some of these species during the early spring months and many references also point to these species being ‘spring plants’.



Spring plants

Daffodils                           Daisies Dandelions

Ragwort Clover                 Grass

Primroses                          Ground ivy

Bluebells                           Snowdrops

Wood anemone                 Cow slip








I have found that my data produced results showing that there are flora species that do not seem to be effected (growth) by ailanthone the allelochemical produced by Ailanthus altissima. When plotting data this became immediately evident to me, as visually you could see differences in plant species diversity on the graphs.


This made the whole process of plotting the data interesting and encouraged me to find other differences in the ‘field’ ecological study.

Patterns were also found showing a higher concentration of ground flora dotted further away from the base of the tree, ‘if relating this to allelopathy’ This shows that there is a stronger concentrate of allelochemical being deposited into the soil nearer the trunk, making it harder for competition planting to sprout within the trees canopy. However the further out towards the drip line, I found that there was a more diverse growing pattern of plants. At 3m plus we see species diversity pick up especially with Clover, Dandelion’s and Daisies.


The statistical analysis of my data helped to show numerical differences, although there are many ways to show/plot this data. Charts where produced, this helped to highlight differences in data, producing anomalies. The charts created helped readers to define differences by using ‘picture and colour’.

Pearson correlation tests were used to find similarities and association between a certain species at different lengths away from the base of the tree.


We can see that the p values for allot of the correlation tests are less than (0.5), this means there are meaningful similarities found in the data being tested. We can see that in the daisies and dandelion correlation test that the p value is very low (0.05). Showing the further away from the base there is a strong possibility that the number of daisies and dandelions will go up following suit. However the same species on the non-allopathic tree shows a less similar set pattern.


Most of the result’s produced correlation coefficient data less than 1. However daisy’s dandelions and daffodils where producing r2 value around the 0.970 area. These species produced stronger correlations than others making them more predictable around ailanthus altissima. Comparing these results to the same species found in the proximity of fungus sylvatic the correlation coefficient test produced less stronger results varying from an r2 of 0.500 - 0.900 area.







I feel that even though some plants in my research may seem to be more suited to allopathic conditions. More research is needed to back up the theories produced from my research.


 I was given a time scale of approximately 6 months which only enabled me to collect data from one annual growing season. Multiple data would need to be collected over a certain number of years as this would produce more accurate results.

Another way to test results found from the ecological study would be experimental planting of ground flora in ailanthone toxic soils, this could take place to ensure anomalies in data are fully tested. 


However this ecological study did produce results creating new ideas that could be researched in the future, the gradual refinement of our knowledge on allelopathy gives us insight into these plants and their interaction with neighbouring species.


“Rather than just removing these plants from our environment, the information provided through research of allelopathy equips us with the knowledge, showing us how to integrate them within our horticultural lifestyles.”




Aerts and Chapin III, (2000) The mineral nutrition of wild plants revisited: a re-evaluation of processes and patterns. Adv. Ecol. Res, 30: 1-67


Rachel M (2005)  Testing the Allelopathic Effect of Festuca paniculata. Universitry of Joseph Fourier 1-16


Coder, K D. (1999) Potential Allelopathy in Different Tree Species. University of Georgia


Coder, K D. (1999) Tree Allelochemicals: Ways and Means. University of Georgia Daniel


Coder, K D. (1999) Allelopathy in Trees and Forests: A Selected Bibliography. University

of Georgia


Callaway and Aschehoug (2000) Invasive Plants versus Their New and Old Neighbours: A Mechanism for Exotic

Invasion. Science, Vol 290: 521-523


Rod, M H. (1997) Allelopathy and the Secret Life of Ailanthus altissima. Arnoldia fall 0004-2633. 3.


Inderjit, and J. Weiner. (2001) Plant allelochemical interference or soil chemical ecology? Perspectives in Plant Ecology, Evolution and Systematics, 4: 3-12.


Bais, H.P. (2002) Enantiomeric-Dependent Phytotoxic and Antimicrobial Activity of (+/-)-Catechin. A Rhizosecreted Racemic Mixture from Spotted Knapweed. Plant Physiology, 128: 1173-1179



Hierro and Callaway, (2003) Allelopathy and Exotic Plant Invasion. Plant and Soil, 256: 29-39


Heisey, R. M. (1990) Allelopathic and herbicidal effects of extracts from tree-of-heaven (Ailanthus altissima) American Journal of Botany 77:662-670


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Mergen, F. (1959) A toxic principle in the leaves of Ailanthus Botamcal Gazette 121: 32-36.


Edward, F (2008) Tree of heaven, America, PCA plant conservation alliance alian plant working group,


Yin (2007) composition for prevention treatment of obesity especially for inhibiting expression glut-4 ap-2 genes comprising extract of ailanthic and ailanthone, Korea,  2007:801164


NCBI (2008) Ailanthone substance summary, Pubcem


Horace G (1999) Biologically active products, agrochemicals, America, CRC press


Lou Paun (2005) A List Of spring Flowers, Verified by Master Gardener Kathleen Roberts,


S. Ercisli (2004) The allelopathic effects of juglone and walnut leaf extracts on yield and growth, Turkey, Agricultur


al Faculty Ataturk University in Erzurum 283–287


Written By Simeon Balsam


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