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Climate warming leads to more frequent tree reproduction at expense of growth, long-term study suggests

A new long-term study reveals alarming insights into the impact of climate change on the European beech (Fagus sylvatica), one of Europe's most widespread and ecologically important tree species.

Conducted by an international team led from the University of Liverpool, the study uses four decades of monitoring data to identify a sharp 28% decline in tree growth since 2005, attributed to temperature-driven changes in seed production.

Published in the journal the Proceedings of the National Academy of Sciences, highlights the complex interplay between rising temperatures, seed production and tree growth.

Lead author Dr. Andrew Hacket-Pain, from the University of Liverpool's Department of Geography & Planning, said, "Many studies have focused on how climate change will reduce tree growth in Europe by increasing the frequency and severity of summer droughts.

"Our research demonstrates that climate warming—independent of changes in drought—results in growth decline because it causes the trees to shift resource allocation from growth to reproduction. Under warmer temperatures, the trees in our long-term study reproduced more, and grew less as a consequence.

"This result is important because it suggests that beech growing in less drought-prone regions of Europe are not protected from the effects of climate change, as suggested in previous studies."

Increased allocation to reproduction would be expected to benefit beech, albeit at the expense of reduced growth. However, previous research from the group has shown that this is not the case. The more regular and desynchronized reproduction caused by climate warming, dubbed "masting breakdown," counterintuitively leads to a reduction in how many viable seeds they produce and disperse.

Dr. Hacket-Pain added, "Normally, beech minimizes the proportion of seeds lost to animals that eat their seeds through cycles of starvation and satiation, but more regular reproduction breaks these cycles. Beech trees are allocating more effort into reproduction but it is the seed predators that benefit, not the trees themselves."

The findings paint a concerning picture for beech, a cornerstone species in temperate forests in Europe. Declining reproduction threatens their ability to regenerate and populate the next generation of European forests, while reduced growth compromises the trees' ability to sequester carbon.

Co-author Dr. Maciej Barczyk, from the Adam Mickiewicz University in Poland, said, "Our research uncovers a critical yet under-recognized mechanism through which climate change can impact forests. These effects may cascade across Europe's beech-dominated forests."

The study involved collaboration among researchers from the UK, Poland, and New Zealand.