Climate change is well documented because human activities are having a significant impact in areas such as global temperatures and weather patterns, for example. These changes are not isolated to one country or continent and every living thing is affected. Ice caps are melting, sea levels are rising, wildlife numbers are decreasing1 and flowers are appearing earlier in spring2…The list goes on.

But ‘mother nature’ is very clever. Smarter than any computer or human being (The way we are fighting against her makes that obvious!!!). The natural world gave us plants and trees to support every living creature physiologically and environmentally. The economic support from trees alone is vast also, “1.3bn people depend on forests for employment, forest products, and contributions to livelihoods and incomes”.3 While nearly one-fifth the world is immersed in the world of trees, what are the rest doing?

Protecting trees and increasing the number of trees is one part of the solution in redressing the balance of humans’ impact on the world. Ultimately, if we look after trees, trees will continue to look after us, as they have for centuries. But if we adopt the status-quo tree diseases will continue to wreak havoc.

Climate Change and Phytophthora in Europe

bleeding cankers in birch trees caused by Phytophthora

Source: Dr Duncan Slater

As a manufacturer and supplier of an in-field Phytophthora test we wanted to discuss how climate change has impacted the prevalence of Phytophthora spp. as well as the on-going impact the pathogen has on trees.

For this article, we spoke with Dr. Duncan Slater MIC, senior lecturer in arboriculture at Myerscough College (UK) and a leading force at Arbor Day UK (See end of this article for more information).

“I have managed and taught about trees and the care of trees for over twenty years in the UK, as well as advising many tree owners on how to care for their own trees. Bleeding cankers caused by Phytophthora spp. (a genus of ‘water moulds’) are something I get to see quite frequently on a wide range of tree and shrub species, as well as the effects of this pathogen in root killing. Unfortunately, this pathogen is becoming more frequent here, most probably due to climate change.

“Previously, freezing weather and snow would have substantially supressed this pathogen, but such cold spells are no longer a reliable feature of UK winters, with a succession of mild winters. This can result in a great deal of bleeding cankers forming in late winter and early spring – and although this disease does tend to pick out stressed trees, it can also affect seemingly healthy ones too.

“Unfortunately, the effect that I have observed is not limited to the UK. My academic and industry connections in Scandinavia report many trees now bleeding as climate change affects local minimum temperatures in Denmark, Norway, and Sweden, with many birch trees starting to get bleeding cankers. And I have seen this for myself, when visiting to give talks in these countries.

arboriculturist using in-field phytophthora rapid test“As a teacher about trees, it is important to cover the topic of Phytophthora with my students, as it is such a damaging disease of plants/trees – and it is also important to keep up-to-date with diagnostic techniques (including lateral flow tests for this pathogen, which I regularly include in my teaching sessions) and potential treatments for this problem. Common scenarios for me are where tree owners want to know what is wrong with their tree, or where there is consideration about the health and condition of a protected tree.”


Dr Slater’s climate and Phytophthora observations are clearly not isolated. A 2022 publication on Forest Research’s website noted: “Milder and wetter winters, followed by increased spring rainfall, are likely to enhance the survival and infection potential of many tree pathogens. Hotter, drier summers leading to drought stress in trees will also increase their susceptibility to disease and expand the distribution range of some pathogens.”4

Phytophthora spp. has been a problem for many years. If the increasing instances continue, the negative impact on trees in public parks, country estates and commercial organisation will continue to grow. Diseased trees pose health and safety risks as well as economic implications for businesses who rely on the beauty of their trees to attract paying visitors. Also, how can sustainable forestry be achieved if Phytophthora continues on its destructive path?

It would appear, in the case of trees, everyone has left it up to arboriculturists and forestry workers to shoulder the responsibility of trying to turn the tide when it comes to looking after trees. Tree professionals will always use testing and disease management techniques to try reducing the impact of plant pathogens. But if there is a constant battle with tree diseases, the economic and environmental impact will take its toll far and wide. Therefore, we encourage people to support initiatives like UK Arbor Day to do your bit for trees.

About Arbor Day UK

Arbor Day UK is a tree planting & tree care advocacy organisation. The organisation promotes trees all year, but in February, the 12-month love of trees culminates in an awareness day (called an ‘Arbor Day’) with a mission to plant trees, celebrate trees and celebrate the people that work with trees.

Trees alongside plants are the lungs of the planet, and the knock-on effect of Arbor Day UK’s activities and promotion of protecting trees has many societal and environmental benefits. It is for this reason, the movement has attracted significant support from organisations such as the Woodland Trust and celebrities, such as Arbor Day UK patron, Dan Snow MBE.

Approximately, 45 countries celebrate Arbor Day in one way or another with some countries allocating the day as public holiday.

Protect trees – and they will, in turn, protect us all.



Title Image Source: Dr Duncan Slater.