November 20, 2025 • 9 mins
A recent study reveals how the soil-borne pathogen *Phytophthora plurivora* is impacting the health of common lime trees in European cities, significantly reducing their ability to provide vital ecosystem services like cooling and carbon sequestration. Using innovative IoT sensors, researchers found that infected trees experience substantial declines in water usage, cooling power, and growth, highlighting the need for proactive strategies to enhance the resilience of urban forests in the face of climate change and pathogen threats.
Read the full article at https://www.paperleap.com/blog/articles/the-hidden-pathogen-threatening-our-urban-forests-0cccuj
Read the full article at https://www.paperleap.com/blog/articles/the-hidden-pathogen-threatening-our-urban-forests-0cccuj
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Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Speaker 1 (00:00):
Welcome to the paper Leap podcast, where a science takes
the mic. Each episode, we discuss cutting edge research, groundbreaking discoveries,
and the incredible people behind them, across disciplines and across
the world. Whether you're a curious mind, a researcher, or
just love learning, you're in the right place before we start.
(00:21):
Don't forget to subscribe so you never miss an insight.
All the content is also available on paper leap dot com. Okay, ready,
let's start. Walk down almost any tree lined street in
a European city and you'll likely see the common lime
tree Tillia x europea. With its broad green canopy, sweet
(00:45):
scented flowers, and generous shade. It's one of the unsung
heroes of urban life. These trees cool our neighborhoods during
summer heat waves, filter out pollution, and offer a sense
of calm amidst the bustle of city life. But like
many quiet heroes, lime trees have a hidden vulnerability. A
(01:05):
soil dwelling pathogen called phytal Thora plurivora is slowly undermining
their health, with consequences that ripple far beyond the trees themselves.
That's the story behind a study published in Plant Environment
Interactions by a research team at the University of Sheffield.
The work of researchers Eleanor Absalom, Anthony Turner, Matthew Clements,
(01:32):
Holly Croft and Jill Edmondson explores what happens when these
beloved street trees fall ill and why the results matter
for the future of our cities. City trees are important
natural infrastructure serving multiple functions. Trees act like living air
conditioners through a process called transpiration. Essentially, sweating water through
(01:56):
their leaves, they cool the surrounding air heat waves. This
effect can mean the difference between life and death for
vulnerable city residents. Also, studies consistently show that access to
trees lower stress, boost mood, and even improves recovery rates
in hospitals. Finally, trees absorb carbon, filter pollutants, and reduce
(02:22):
storm water flooding by soaking up excess rainfall. But these
benefits depend on healthy, mature trees. Big trees with leafy
crowns and strong root systems do far more for cities
than young saplings, so when a disease cuts into their strength,
the whole urban ecosystem feels it. Phytal Thora literally plant
(02:46):
destroyer is a notorious genus of pathogens. These microscopic organisms
aren't fungi, though they behave like them. They're water molds
thriving in damp soils. The Potato famine of the eighteen
forties that was caused by a Fidophora species fidal Thora
(03:06):
plurivora is especially dangerous because it's a generalist. It doesn't
stick to just one kind of tree. It's been linked
to the decline of beech, oak, and alder in European forests,
and it's spreading through urban areas too. Infected lime trees
often show bleeding, bark, root rot, leaf yellowing, and canopy
(03:28):
die back. The pathogen has been present in Sheffield for years,
with local lime trees first showing symptoms in the late
two thousands, but until now no one had looked closely
at how infection affects not just the tree survival, but
also the ecosystem services they provide. The research team took
(03:49):
a novel approach. They wired up ten mature lime trees,
five healthy looking, five infected with Internet of Themes IoT
SAP flow set in tiny devices called dendrometers. SAP flow
sensors measured how much water was moving through the trees
minute by minute. Since water movement is tied to cooling
(04:12):
and carbon uptake, this gave a direct measure of how
well each tree was functioning. Additionally, dendrometers tracked subtle changes
in trunk diameter, allowing the team to see whether trees
were growing, shrinking, or stagnating. They also collected data on
leaf density, chlorophyll levels, and local weather conditions to paint
(04:34):
a full picture. This high tech monitoring ran through the
blistering summer of twenty twenty two, when Sheffield saw record
breaking heat waves and drought. If there was ever a
stress test for urban trees, this was it. The results
showed a quiet but steep decline. Infected trees used eighty
(04:56):
seven percent less water than their healthy neighbors. On average,
a healthy tree cycled through about two hundred and ninety
eight liters of water per day, while an infected one
managed only twenty five liters. Because less water flowed, infected
trees lost much of their natural air conditioning capacity. Their
(05:16):
urban cooling effect was cut by a similar margin, dropping
from nearly four hundred and eighty six kilowatts of energy
loss per day in healthy trees to just sixty one
kilowatts in the sick ones. Healthy trees grew thicker over
the summer, adding abou zero point three five percent to
their trunk diameter. Infected trees, by contrast, actually shrank slightly
(05:39):
minus zero point two two percent. However, not all infected
trees were equally impaired. Some still managed water flow and
growth similar to healthy ones, possibly because their disease was
less advanced. Put simply, when these trees got sick, they
look worse and stopped perform their ecological role. The study
(06:03):
highlights how diseased trees can no longer protect cities in
the ways we depend on them too. This is especially
worrying for several reasons. First, climate change is making it worse.
Warmer wetter winters help pathogens spread, while hotter, drier summers
make stressed trees more vulnerable. Second, urban forests are genetically uniform,
(06:29):
as many city streets are lined with cloned cultivars of
just a few species. The lack of diversity creates a
buffet for pathogens. Finally, management decisions are tough. A tree
that looks outwardly healthy but is harboring infection might still
be cooling the street and cleaning the air. Should it
be cut down to stop the spread or kept to
(06:51):
preserve its benefits. The research team that conducted the study
emphasizes this trade off. Some infected trees were still well
functioning nearly as well as healthy ones. Removing them too
soon could rob communities of cooling shade during critical heat waves.
But waiting too long, however, risks sudden branch failures and
(07:12):
wider spread of disease. So what can we take away
from this research? Early detection matters. To this end, Smart
sensors could give city managers a way to spot infected
trees before they collapse. That's safer for the public and
helps in making nuanced decisions about removal. Also, diversity is key.
(07:35):
Relying on cloned cultivars or a narrow palette of species
sets up urban forests for disaster. A more diverse planting
strategy spreads the risk Moreover, trees need allies. Protecting urban
trees from disease also means tackling climate change and reducing
stressors like soil compaction and pollution. Healthy trees resist infection better. Finally,
(08:01):
policy must balance trade offs. A one size fits all
removal policy might backfire sometimes letting a partially infected but
still functional tree stand could provide vital ecosystem services in
the short term. Street trees often fade into the background
of daily life, but they're silent partners in making cities livable.
(08:24):
This study reminds us that those partners are vulnerable. A
microscopic invader in the soil can ripple up to affect
city temperatures, public health, and even climate resilience. Because in
the end, protecting urban trees isn't just about trees, It's
about protecting ourselves. That's it for this episode of the
(08:47):
paper Leaf podcast. If you found it thought provoking, fascinating,
or just informative, share it with the fellow science nerd.
For more research highlights and full articles, visit paperleaf dot com.
Also make sure to subscribe to the podcast. We've got
plenty more discoveries to unpack. Until next time, keep questioning,
(09:08):
keep learning,
Welcome to the paper Leap podcast, where a science takes
the mic. Each episode, we discuss cutting edge research, groundbreaking discoveries,
and the incredible people behind them, across disciplines and across
the world. Whether you're a curious mind, a researcher, or
just love learning, you're in the right place before we start.
(00:21):
Don't forget to subscribe so you never miss an insight.
All the content is also available on paper leap dot com. Okay, ready,
let's start. Walk down almost any tree lined street in
a European city and you'll likely see the common lime
tree Tillia x europea. With its broad green canopy, sweet
(00:45):
scented flowers, and generous shade. It's one of the unsung
heroes of urban life. These trees cool our neighborhoods during
summer heat waves, filter out pollution, and offer a sense
of calm amidst the bustle of city life. But like
many quiet heroes, lime trees have a hidden vulnerability. A
(01:05):
soil dwelling pathogen called phytal Thora plurivora is slowly undermining
their health, with consequences that ripple far beyond the trees themselves.
That's the story behind a study published in Plant Environment
Interactions by a research team at the University of Sheffield.
The work of researchers Eleanor Absalom, Anthony Turner, Matthew Clements,
(01:32):
Holly Croft and Jill Edmondson explores what happens when these
beloved street trees fall ill and why the results matter
for the future of our cities. City trees are important
natural infrastructure serving multiple functions. Trees act like living air
conditioners through a process called transpiration. Essentially, sweating water through
(01:56):
their leaves, they cool the surrounding air heat waves. This
effect can mean the difference between life and death for
vulnerable city residents. Also, studies consistently show that access to
trees lower stress, boost mood, and even improves recovery rates
in hospitals. Finally, trees absorb carbon, filter pollutants, and reduce
(02:22):
storm water flooding by soaking up excess rainfall. But these
benefits depend on healthy, mature trees. Big trees with leafy
crowns and strong root systems do far more for cities
than young saplings, so when a disease cuts into their strength,
the whole urban ecosystem feels it. Phytal Thora literally plant
(02:46):
destroyer is a notorious genus of pathogens. These microscopic organisms
aren't fungi, though they behave like them. They're water molds
thriving in damp soils. The Potato famine of the eighteen
forties that was caused by a Fidophora species fidal Thora
(03:06):
plurivora is especially dangerous because it's a generalist. It doesn't
stick to just one kind of tree. It's been linked
to the decline of beech, oak, and alder in European forests,
and it's spreading through urban areas too. Infected lime trees
often show bleeding, bark, root rot, leaf yellowing, and canopy
(03:28):
die back. The pathogen has been present in Sheffield for years,
with local lime trees first showing symptoms in the late
two thousands, but until now no one had looked closely
at how infection affects not just the tree survival, but
also the ecosystem services they provide. The research team took
(03:49):
a novel approach. They wired up ten mature lime trees,
five healthy looking, five infected with Internet of Themes IoT
SAP flow set in tiny devices called dendrometers. SAP flow
sensors measured how much water was moving through the trees
minute by minute. Since water movement is tied to cooling
(04:12):
and carbon uptake, this gave a direct measure of how
well each tree was functioning. Additionally, dendrometers tracked subtle changes
in trunk diameter, allowing the team to see whether trees
were growing, shrinking, or stagnating. They also collected data on
leaf density, chlorophyll levels, and local weather conditions to paint
(04:34):
a full picture. This high tech monitoring ran through the
blistering summer of twenty twenty two, when Sheffield saw record
breaking heat waves and drought. If there was ever a
stress test for urban trees, this was it. The results
showed a quiet but steep decline. Infected trees used eighty
(04:56):
seven percent less water than their healthy neighbors. On average,
a healthy tree cycled through about two hundred and ninety
eight liters of water per day, while an infected one
managed only twenty five liters. Because less water flowed, infected
trees lost much of their natural air conditioning capacity. Their
(05:16):
urban cooling effect was cut by a similar margin, dropping
from nearly four hundred and eighty six kilowatts of energy
loss per day in healthy trees to just sixty one
kilowatts in the sick ones. Healthy trees grew thicker over
the summer, adding abou zero point three five percent to
their trunk diameter. Infected trees, by contrast, actually shrank slightly
(05:39):
minus zero point two two percent. However, not all infected
trees were equally impaired. Some still managed water flow and
growth similar to healthy ones, possibly because their disease was
less advanced. Put simply, when these trees got sick, they
look worse and stopped perform their ecological role. The study
(06:03):
highlights how diseased trees can no longer protect cities in
the ways we depend on them too. This is especially
worrying for several reasons. First, climate change is making it worse.
Warmer wetter winters help pathogens spread, while hotter, drier summers
make stressed trees more vulnerable. Second, urban forests are genetically uniform,
(06:29):
as many city streets are lined with cloned cultivars of
just a few species. The lack of diversity creates a
buffet for pathogens. Finally, management decisions are tough. A tree
that looks outwardly healthy but is harboring infection might still
be cooling the street and cleaning the air. Should it
be cut down to stop the spread or kept to
(06:51):
preserve its benefits. The research team that conducted the study
emphasizes this trade off. Some infected trees were still well
functioning nearly as well as healthy ones. Removing them too
soon could rob communities of cooling shade during critical heat waves.
But waiting too long, however, risks sudden branch failures and
(07:12):
wider spread of disease. So what can we take away
from this research? Early detection matters. To this end, Smart
sensors could give city managers a way to spot infected
trees before they collapse. That's safer for the public and
helps in making nuanced decisions about removal. Also, diversity is key.
(07:35):
Relying on cloned cultivars or a narrow palette of species
sets up urban forests for disaster. A more diverse planting
strategy spreads the risk Moreover, trees need allies. Protecting urban
trees from disease also means tackling climate change and reducing
stressors like soil compaction and pollution. Healthy trees resist infection better. Finally,
(08:01):
policy must balance trade offs. A one size fits all
removal policy might backfire sometimes letting a partially infected but
still functional tree stand could provide vital ecosystem services in
the short term. Street trees often fade into the background
of daily life, but they're silent partners in making cities livable.
(08:24):
This study reminds us that those partners are vulnerable. A
microscopic invader in the soil can ripple up to affect
city temperatures, public health, and even climate resilience. Because in
the end, protecting urban trees isn't just about trees, It's
about protecting ourselves. That's it for this episode of the
(08:47):
paper Leaf podcast. If you found it thought provoking, fascinating,
or just informative, share it with the fellow science nerd.
For more research highlights and full articles, visit paperleaf dot com.
Also make sure to subscribe to the podcast. We've got
plenty more discoveries to unpack. Until next time, keep questioning,
(09:08):
keep learning,
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