Polyphenols

LEACHATE FROM LEAVES

When it rains, the concrete ground under Eucalyptus trees has a stain, which are amino acids and organic acids leached from tree leaves. In addition, sugars such as sucrose and glucose are leached and feeds microflora and fauna, and add to soil carbohydrate and organic matter. The sugars also feed symbiotic mycorrhizal fungi (which in turn feeds the tree with water and nutrients) and saprophytic fungi.

POLYPHENOLS

Polyphenols are also leached from leaves, and they are also the Wall 4 or chemical barrier of the compartmentalisation of decay in trees (CODIT) model promoted by Alex Shigo (1986). Polyphenols are made up of multiples of a phenol molecule, which is a hydroxyl (OH) group attached to a carbon aromatic ring, or C6H5OH (or C6H6O). There are four major groups of polyphenols - lignans, stilbenes, phenolic acids and flavonoids. 

LIGNANS

Lignans are found in many plant tissues and seeds and act as antifeedants, in order to deter animals from eating plants. They are understood to have an impact on human diets.

STILBENES

Stilbenes act as phytoalexins (plant defending chemicals) that shields plants from attack, especially by fungi. They are the Wall 4 or chemical barrier of CODIT. They may be allelopathic and such leachates are present in tree species such as Acacia, Eucalyptus and Pinus. Allelopathic leachates restrict the growth of weeds and other plants, and reduce seed germination until conditions become favourable. Leaf litter are often present for allelopathic effect to take place but not always. 

PHENOLIC ACIDS

Naturally occuring phenolic acids in plants are caffeic, vanillic, coumaric, ferulic, gallic, sinapic and, salicyclic acids, amongst others. They act in several roles in plant biology and metabolism where they are antioxidants, and they are found in teas, beers, wines, grains and other products. Salicyclic acid is known as aspirin. Phenoxy acids and polyphenols has antioxidant and anti-inflammatory roles in human health. They contribute to the defence of plants in the CODIT model. They can also bind nutrients that are important for human health.

FLAVONOIDS

Flavonoids could be anthocyanins that provide colour to flower petals, prevent UV light damage to tissues, help nodule formation, and protect plants against diseases (Stiller et al. 2021). They could also be tannins, which are water soluble, astringent tasting, and bind proteins and amino acids. Tannins add taste to chocolate, in teas and coffee, and add flavour of red wines. Tannins in oak barrels enhance the flavour of wines contained within them. They can be allelopathic and a high concentration discourage grazing by mammals and insects.

ABSCISSION ZONES

Some of the many aspects of plant metabolisms that involves polyphenols are leaf abscission and abscission zones. Polyphenols are found in the leaf abscission layer (Figure 1) and when the leaf is shed, that layer become oxidised and become antibiotic when exposed to air. This is a function of Wall 4 or the chemical barrier in the CODIT model (Morris et al. 2019). The risk of infection is reduced at the shedding site by antibiotics. There could also be a thin layer of dead plant cells at abscission zones after shedding to further protection from pathogens. Pruning should not be done past abscission zones, so as not to reduce the polyphenols present and leave tree wounds susceptible to disease and decay. Polyphenols are present in the tissues on the adaxial (upper) side of a branch and are present under the epidermal cell layers at branch unions and nodal positions. These are the parts that are vulnerable to insect and fungi attack.

Figure 1. Deposition of polyphenols at leaf abscission zone. Not the polyphenols (dark stained regions) in the abscission layer, but also those under the epidermal (bark) layer and on the adaxial (upper) side of the petiole's point of attachment to the twig.

Phytoalexins are antimicrobial chemicals that plants produce de novo (from scratch) in response to pathogen infection. Stilbenes are sometimes activated in order to target a particular species of fungus.

ALLELOPATHY

A concentration of polyphenol restricts the germination of seeds and plant growth under trees that leaches them. Alleopathic effects may be overlooked due to environmental factors such as drier soil above tree roots and shading of light. River red gums (Eucalyptus camaldulensis) reduce vegetation under their canopy by polyphenols in an arid environment, but heavy rainfall or floods would leach out or dilute water-soluble polyphenols from the soil. That would in turn allow germination and growth of seedlings, as well as weed proliferation. 

In parks and gardens, the space under trees may be utilised to grow other plants but polyphenols such as stilbenes in the soil may restrict that. Leaf litter could be removed from under the trees regularly, and leach out polyphenols from the soil using irrigation, since they are water soluble.

COLOURS OF POLYPHENOLS

Timbers that contain polyphenols that contribute to their durability and colour, which vary from almost black through brown to orange or cream. Tannins in the timber could be leach after exposure to weather and decay. 

Spotted gums (Corymbia maculata) and other tree species may leach tannins from leaves, and fallen leaves may leave imprints on concrete paths and timber decking. Surfaces could also be stained by bits of timber with high tannin content. Tannins could be washed by vehicle exteriors and other non-porous surfaces quite easily but for porous surfaces, high-pressure spray may be required. A heavy-duty chlorine solution may be an effective cleanser.

Original article

1. G.M. Moore. 2025. You Eat Them, You Drink Them, They Can Stain Concrete, but They are Great for Trees!, Arborist News Aug 2025

References

2. Morris H, Hietala AM, Jansen S, Ribera J, Rosner S, Salmeia KA, Schwarze FWMR. 2019. Using the CODIT model to explain secondary metabolites of xylems in defence systems of temperate trees against decay fungi. Annals of Botany. 125(5):701-720. https://doi.org/10.1093/aob/mcz138

3. Shigo A. 1986. A new tree biology. Durham (NC, USA): Shigo and Trees, Associates. 595 p.

4. Stiller A, Garrison K, Gurdyumov K, Kenner J, Yasmin F, Yates P, Song BH. 2021. From fighting critters to saving lives: Polyphenols in plant defense and human health. International Journal of Molecular Science. 22(16):8995. https://doi.org/10.3390/ijms22168995

5. Teka T, Zhang L, Ge X, Li Y, Han L, Yan X. 2022. Stilbenes: Source plants, chemistry, biosynthesis, pharmacology, application and problems related to their clinical Application - A comprehensive review. Phytochemistry. 197:113128. https://doi.org/10.1016/j.phytochem.2022.113128

Climate Change and Trees

Trees provide shade and shield against heat in the urban environment, and healthy trees are a necessary part of the infrastructure. While some arborists does not partake in the planning and planting of trees, there should be awareness on climate-ready trees that are adapted for a warmer and stormier world. In this article, "climate analogs" are defined as areas elsewhere that currently have climate conditions, which a specific location is projected to have in the future. The article's author mentioned that this article was a supplement to a earlier article (Planning for Climate-Ready Tree Species: What Next?, Daniel C. Staley, Arborist News June 2023).

Not all woody plants currently present in an area can tolerate future climate conditions (Fitzpatrick and Dunn 2019; Tian et al. 2023; Sjöman et al. 2024).

There are a few scenarios that the climate is predicted to become. Climate analog tools such as FitzLab and Copernicus were mentioned, and FitzLab was explored for the article. 

Climate analog tools uses global climate models, which in turn uses climate change scenarios, in order to give model outputs that are widely used as a standard tool for decision-making (Schmolke et al. 2010). There are a few climate change scenario temperature projections from now till year 2100, depending on how humans could change their practices. Tree species composition and health would change, if temperatures were to reach the top three scenario trajectories.

A pessimistic scenario sees more industrial activities, fossil-fuel use and deforestation, and a less pessimistic scenario sees a shift to renewable energy, less deforestation and reforestation to be less warming to the world. An official narrative from the Intergovernmental Panel on Climate Change (IPCC) describes different societal actions leading to a few scenarios, from which to choose and use climate analog tools to find areas with climate-ready trees. 

- SSP5_8.5: Increased energy use, deforestation and emissions, which results in about 4.4 degrees C projected temperature rise by 2100

- SSP3_7.0: 'Business As Usual', results in about 3.6 degrees C projected temperature rise by 2100

- SSP2_4.5: Some reduction in fossil-fuel use, slowing of deforestation and reduction in emissions, results in about 2.7 degrees C projected temperature rise by 2100

- SSP1_2.6: Significant reduction of fossil-fuel use, and sustainable development, results in about 1.8 degrees C projected temperature rise by 2100

The article suggested to choose a scenario or scenarios that nearby governments/institutions are using but if there are no such planning done by nearby governments/institutions, then choose a scenario and alternative scenario (for comparison), and provide clear justification on why they were chosen. Explanation of scenario narratives and pathways are in Hausfather 2018.

Samples of climate analog tool inquiry using FitzLab tool (FitzLab 2025):

San Jose, California -> (in year 2080) Redlands, California

Würzburg, Germany -> (in year 2080) Villa Fontana, Emilia-Romagna, Italy

However, climate analog tools does not take into consideration site factors such as shade, aspect, exposure to coastal winds, heavy snow. 

Native woody plants in a project area today may not be suitable 60 years or 80 years later. Plants that are adapted to future conditions should be considered, which are not currently native. These plant species could be introduced to meet the requirement of future urban environments.

References

1. Dan Staley. 2025. How to Find Climate-Ready Trees for your Project, Arborist News Apr 2025

2. FitzLab 2025. Climate analog tool [online tool]. https://fitzlab.shinyapps.io/cityapp

3. Fitzpatrick MC, Dunn RR, 2019/ Contemporary climatic analogs for 540 North American urban areas in the late 21st century. Nature Communications. 10:614, https://doi.org/10.1038/s41467-019-08540-3

4. Hausfather Z, 2018 April 19. Explainer: How 'shared socioeconomic pathways' explore future climate change/ London (United Kingdom): Carbon Brief. https://www.carbonbrief.org/explainer-how-shared-socioeconomic-pathways-explore-future-climate-change

5. Schmolke A, Thorbek P, DeAngelis DL, Grimm V. 2010. Ecological models supporting environmental decision making: A strategy for the future. Trends in Ecology & Evolution. 25(8):479-486. https://doi.org/10.1016/j.tree/2010/05/001

6. Sjöman H, Watkins H, Kelly LJ, Hirons A, Kainulainen K, Martin KWE, Antonelli A. 2024. Resilient trees for urban environments: The importance of intraspecific variation. Plants, People, Planet. 6(6):1180-1189. https:/doi.org/10.1002/ppp3.10518

7. Tian P, Liu Y, Ou J. 2023. Meta-analysis of the impact of future climate change on the area of woody plant habitats in China. Frontier in Plant Science. 14:1139739. https://doi.org/10.3389/fpls.2023.1139739 

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In Arborist News June 2024, page 71, 72, of an interview article with an arborist in Australia, Rebecca Barnes made mention of Dr. Dave Kendal, who works with tree species analysis for projected climates. Furthermore she expressed concern that climate change is a challenge in her country for the future. "Many of the native tree species in Australia have specific and niche environments. Unusual changes in temperature and rainfall are affecting these environments, which leads to tree decline, which, in turn, leads to pests and diseases and also leads to areas that are more prone to bushfire."

Dr. Kendal is one of the members who carried out an assessment of the risk from climate change for living collections and landscape at Melbourne Gardens, which is commissioned by the Royal Botanic Gardens Victoria. By year 2070 and assuming 'business as usual emissions', under an extreme climate future, temperatures are forecast to increase by 3 degrees C. The assessment identified areas that required "management intervention such as procuring new species, succession replanting or improving site conditions". The project also resulted in the development of a decision support tool to enable managers to run their own assessments of climate risk for new plant introductions.

Reference: Assessment of Climate Change Risk to Living Plant Collections, https://www.rbg.vic.gov.au/initiatives/landscape-succession-strategy/assessment/

Foliage with Angular Spots

Dendro and and his assistant Codit were asked to visited a wedding venue to examine defoliating Viburnum suspensum. They met its grounds manager, Amelia. Several of those shrubs are near a gazebo, and she expected that the background should be green and suitable for wedding photos. Since last year, there was defoliation and leaf spotting on one shrub, and that spread to others. Their landscape contractors assumed it was a leaf spot disease and sprayed a fungicide three times for one year, but there was no improvement. In the middle of their conversation, the pop-up sprinklers activated and sprayed water onto their pants and shoes. Amelia apologised, as the irrigation should have been turned off during the meeting, but Dendro and Codit commented that cultural conditions are important. Upon further questioning, Amelia shared that the shrub bed is irrigated every other day, and long enough to soak the grass and mulch. Dendro replied that foliar pathogens are spread and supported by excessive moisture.

Codit examined the leaves on the ground and noticed that the spots on them are angular. "Fungal leaf spots are often medium to dark brown and more rounded, while bacterial spots are generally dark brown with a yellow halo", he explained further, "angular leaf spots are less common". Foliar nematodes and plant pathogenic bacteria can cause angular leaf spots. Dedro recommended sending samples to plant diagnostic laboratories to know for sure the pest and disease issues, or health problems, in order to be sure. 

Upon inspection on a leaf with a magnifier, Codit spotted grayish fuzz growing on spotted tissue and deduced that the disease is viburnum downy mildew, Peronospora viburni. Downy mildew diseases are caused by oomycetes, which are fungus-like organisms, not true fungi. Diseases caused by oomycete are usually worse when conditions are wet, as they produce spores that swim in water. Phytophthora species is an oomycete that can infect foliage as well, but its often seem on roots, and stem/trunk cankers on woody plants. Downy mildews are often host-specific, so one plant genera is being infected by one species of downy mildew - Viburnum suspensum shrubs in this case.

Amelia connected the dots and realised that the reason why the landscape contractor's fungicide applications were not working was because the disease is not a fungus. Dendro reminded Amelia to send leaf samples to a diagnostic lab, and inform the landscape crew to rake up and dispose of gallen infected leaves regularly. In addition, to turn the sprinklers away from the viburnum foliage so that they are not wetted. Finally, to do scouting so as to catch disease and insect problems early.

Reference: Arborist News, Apr 2025, pages 22, 23, 56, 57