Oak trees show that allergy season is becoming longer and more intense 

A team of researchers led by the University of Cordoba (UCO) has recently undertaken a comprehensive study to analyze the blooming patterns in oak trees of the Quercus genus in Andalusia and their implications for allergy season, particularly in light of climate change. 

This research, conducted by the Systemic and Applied Botany group, focused on the impact of global warming on the flowering times and pollen production of various oak species, using data on pollen concentrations collected across Andalusian capitals.

“We chose Quercus because it is the most representative tree in Andalusia in the natural environment, and it is an anemophilic tree (pollinated by the wind) found where there are very high concentrations of pollen in the atmosphere, so it is a good bioindicator to study the impact of climate change on blooming,” said co-author Pura Alcázar, a botanist at UCO. 

Oak trees and more intense allergy seasons

The findings indicate a shift towards longer and more intense pollen seasons for Quercus species, including holm, cork, common, Portuguese, and kermes oaks. 

“Fundamentally, there has been an increase in the blooming of these species, and in their intensity, because there is a higher concentration of pollen in Andalusia,” Alcázar explained. Notably, the season starts earlier for species like the holm oak, which are more temperature-sensitive, leading to an extended pollen season overall. However, variations were noted, such as in Granada, where the expected earlier onset did not occur, likely due to pre-spring rainfall during the study period.

Climate factors and allergy season 

The researchers attribute these changes directly to climate factors such as rising temperatures and increased CO2 levels, which not only prompt earlier blooming but also enhance the intensity of the pollen seasons. “Plants need CO2 to photosynthesize; if more is available, they are more active,” Alcázar said, highlighting the dual impact of temperature and CO2 on plant behavior.

While Quercus pollen is not traditionally considered a major allergen, its increasing presence and the prolongation of its season could heighten its impact on those with sensitivities. 

“If we are increasingly exposed and our immune system is more sensitive, the same thing can happen with other species, such as the cypress, which years ago featured harmless pollen, and now represents the main problem in terms of winter allergy,” added senior author Carmen Galán, a professor of botany at UCO.

Gauging the duration of pollen season

The data for this study were collected using volumetric devices that capture air samples to measure daily pollen concentrations. This methodology is critical for accurately gauging the onset and intensity of pollen seasons and for ensuring that the findings are comparable with other studies.

Ultimately, this research, part of the CLIMAQUER project, highlights the necessity of a standardized approach to defining and calculating pollen seasons to ensure consistency across different studies and to better understand the evolving challenges posed by climate change on public health related to pollen allergies.

More about oak trees

Oak trees are a diverse group of trees and shrubs known for their strength, longevity, and distinctive hardwood. They are primarily found in the northern hemisphere, thriving in a range of habitats from cool temperate to tropical regions in the Americas, Asia, Europe, and North Africa. Oak trees are ecologically significant, providing essential habitats and food sources for various wildlife species through their acorns and leaves.

Types of oak trees

Oaks can be either deciduous or evergreen, depending on the species and the climate of their environment. Deciduous oaks shed their leaves annually, while evergreen oaks retain their foliage year-round, which can be a survival advantage in less fertile soils or drier climates. The leaves of oak trees are typically lobed and vary in size and shape among species, contributing to their widespread identification.

Wood of oak trees 

The wood of oak trees is highly valued for its density and durability, making it a popular choice for furniture, flooring, and barrel-making, particularly in the wine and whiskey industries where oak barrels are prized for imparting flavor. Oak wood is also used in construction due to its resistance to fungal and insect attacks.

Ecological role 

Ecologically, oaks play a crucial role in their ecosystems. Their acorns are a vital food source for many animals, including birds, mice, and larger mammals like deer and bears. Oaks also form a complex root system that helps stabilize soil, preventing erosion and promoting water quality in watersheds by filtering rainwater and reducing runoff.

The study is published in the journal Regional Environmental Change.

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