Why some Himalayan trees can't grow any higher up the mountain
Yang Y, Wu ZC, Yue Q, Gao SY, Sun H
Climate Adaptation
If you've ever wondered why the alpine tree line on a mountain hike forms such a sharp edge, this explains it: it's not one universal cold cutoff, it's a species-by-species race between when leaves emerge and how much frost they can survive.
High on Himalayan mountainsides, different kinds of trees stop growing at slightly different elevations, and researchers wanted to know why. They discovered that larch and fir trees leaf out early but can tolerate hard freezes and even regrow from tiny buds if damaged, so they're limited mainly by a general lack of warmth rather than frost injury. Oak and rhododendron trees, on the other hand, keep their leaves year-round, flush much later, and live right at the edge of what their frost tolerance can handle, so a single hard freeze can determine exactly where they stop growing up the mountain.
Key Findings
Deciduous larch flushes earliest and shows the greatest freezing tolerance and largest safety margin against cold damage.
Evergreen oak and rhododendron species flush about two months later than larch and operate near their freezing damage threshold, with freezing tolerance likely setting their upper elevation limit.
Treeline conifers (larch and fir at 4350-4400 m) can resprout from small auxiliary buds after freezing damage, an option unavailable to oak and rhododendron with their larger buds; conifer range limits instead reflect the general low-temperature growth limit of trees rather than freeze injury.
chevron_right Technical Summary
Scientists studying the world's highest treeline in the Himalayas found that different tree species hit their altitude limits for different reasons: some run out of warmth to grow, while others freeze because they leaf out too early with too little cold tolerance.
Abstract Preview
Original paper
Low-temperature range limits of trees explained by freezing tolerance, current microclimate and historical extremes.
Explaining the low-temperature limit of trees requires in situ information on the actual temperature conditions, the trees' phenology and freezing tolerance. Here, we report the seasonal course of ...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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