Wenjin Wang, Zhejiang University in China, discusses their article: Seasonal climate variations drive decoupling between the duration and amount of xylem growth along a hydrothermal gradient in the southern Altai Mountains
Climate change is transforming forests across the world. A key question many ecologists and forest managers are asking is: will warmer temperatures lead to more tree growth by extending the growing seasons? Intuitively, one might think so — longer growing seasons should mean more growth. But our research in the southern Altai Mountains of Central Asia tells a more complex story.
Taiga forests in the southern Altai Mountains in Xinjiang, northwest China. Photo credit: Wenjin Wang.
Watching tree wood growth at a cell-by-cell level
Most people think of tree wood growth in terms of tree rings. Each ring represents a year of growth, which tells us about the overall conditions during that year. But what if we want to know what happens within that year — how trees respond to temperature and rainfall in spring, summer, and even week by week?
To answer this, we used a method called micro-sampling. This technique involves collecting tiny samples of wood (microcores) from trees throughout the growing season using a tool called Trephor and counting the number of wood cells formed at different stages of development. It’s a bit like watching the tree “build itself,” layer by layer.
Over two years, we collected weekly samples from Siberian spruce at four study sites along a climatic gradient in the southern Altai Mountains, from warm and dry to cold and wet. This allowed us to closely examine how temperature and precipitation affect the timing (when growth starts and stops) and the amount (how many cells are produced) of tree growth.
A surprising decoupling
One of the key findings from our study is what we call a “decoupling” between the duration and amount of wood growth. Traditionally, it’s been assumed that a longer growing season, thanks to warmer temperatures, should lead to more growth. But our results challenge that assumption.
We found that warmer springs tended to trigger earlier growth, extending the period during which trees were actively producing wood. However, in years or sites with dry summers, this longer season didn’t translate into more wood cells being formed. Instead, growth slowed or even stopped earlier due to limited water availability. In other words, heat alone isn’t enough — trees need water, too.
In these relatively dry forests, it’s not just the length of the growing season that matters, but how efficiently trees can grow during it. Since cell production rates are strongly influenced by water availability, dry conditions can limit growth even when there’s more time to grow. This suggests that longer seasons do not necessarily mean more wood — and that water plays a central role in shaping forest productivity under climate change.
Final thoughts
As the climate warms, forests in regions like the Altai Mountains may not automatically grow faster or store more carbon, especially if precipitation becomes less reliable.
By literally looking inside trees, we uncovered subtle yet crucial ways in which seasonal climate conditions shape their growth. Monitoring wood formation at such fine scales gives us a clearer, more detailed picture of how trees respond to shifting climates. With continued long-term observation, we can better understand how forests adapt and how we can help them thrive in a changing world.
