Can trees protect their genetic diversity for millions of years?

In the face of relentless environmental shifts, seven of the most prevalent forest trees in Europe have proven their tenacity. They’ve managed to keep their genetic diversity intact, even as their ranges shrunk and tree numbers plummeted during the ice age cycles.

This resilience was highlighted in a recent study conducted by a multidisciplinary European consortium. Pascal Milesi is an associate professor of plant ecology and evolution at Uppsala University and the study’s lead author.

““From a biodiversity perspective, this is very positive because these trees are keystone species on which many other species depend,” said Professor Milesi.

Genetic diversity of trees

The research team set out to explore the impact of fierce ice age cycles on the genetic diversity of tree species. Throughout the ages, trees have endured alternating warm and cold periods.

During the last ice age, around 10,000 years ago, the tree populations were significantly constrained, leading scientists to predict a loss of genetic diversity.

Yet, surprising as it may be, these species demonstrated immense genetic diversity, indicating a resilient response to their rapidly evolving habitats.

What’s their secret?

“We believe the reason for this high genetic diversity is related to the way these tree species survived through the ice ages and to fact that tree pollen can travel thousands of kilometres, bringing together trees that grow far apart,” said Professor Milesi.

“This is a welcome sign. The evolutionary processes that were at play in the past may also be useful to cope with today’s rapid climate change.”

Joining forces with researchers from 22 other European institutions, Professor Milesi examined seven species of forest trees ubiquitous in Europe.

The team gathered needles and leaves from approximately 3,500 trees from 164 different populations scattered across Europe and proceeded to extract and analyze the DNA.

Ice age cycles and tree diversity

“Contrary to what was long thought, the ice age cycles had little impact on the genetic diversity of these seven key species. This is mainly explained by a combination of unique characteristics, namely long generation time and the ability of their pollen to spread thousands of kilometers,” said Milesi.

This trait enables trees separated by vast distances to exchange genetic material, ensuring a broader and more diverse gene pool. As a result, these species can better adapt to changing environmental conditions, maintaining their resilience over centuries.

Spotlight on Sweden

Turning the spotlight on Sweden, the researchers zeroed in on the Norway spruce, Scots pine, and silver birch. Together, these species make up the majority of the Swedish forest, serving as a lifeline for other species.

They are also a significant contributor to the Swedish economy and society, accounting for the vast majority of timber used in Swedish forestry.

Celebrating the diversity of trees

“Due to the sixth mass extinction event and the ongoing biodiversity crisis, people can easily get the feeling that it is too late and be ready to give up,” said Professor Milesi.

“This study sends a positive signal about our forest and provides important information to help manage forest biodiversity in the face of climate change.”

Predicting future trends

The future of European forests amid the climate crisis shows promise due to the resilience of key tree species.

Research highlights that strong genetic diversity can help these trees cope with environmental challenges, but rapid adaptation to changing climates is vital.

Ongoing monitoring and conservation efforts to preserve genetic diversity are essential for maintaining forest health and supporting both ecosystems and human communities that rely on them.

Mighty seven tree species

The species under study were the European beech (Fagus sylvatica), Maritime pine (Pinus pinaster), Sessile oak (Quercus petraea), Silver birch (Betula pendula), Scots pine (Pinus sylvestris), Norway spruce (Picea abies), and Black poplar (Populus nigra).

As we reflect on these findings, we are reminded of the remarkable resilience of nature and the urgent need to respect and protect it. The future of our forests hinges on how well we respond to the ongoing challenges.

The study is published in the journal Nature Communications.

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