Forests play an important role in providing ecosystem services and regulating carbon balance. Modelers rely on the implicit assumption that, under the common climate drivers, trees have similar growth patterns over large spatial scale. Using ring-width sequences of 1046 juniper trees from Tibetan Plateau and 538 pine trees in the eastern China, we show that, although tree growth is influenced by climatic factors, individual trees often do not respond in a synchronous manner. After highly synchronous growth events, the number of trees exhibiting common growth change declined progressively and, notably, the patterns of decline exhibited the form of exponential function with parameter of base b ranging from 0.57-0.83 for juniper forests in Tibetan Plateau and from 0.56-0.72 for pine forests in eastern China. Our findings suggest that individual trees in forests tend to grow independently with respect to climate rather than synchronously, and that a relatively uniform pattern of growth de-synchronization is an inherent property of forest tree growth. We propose that this property is essential for trees collectively to have resilience and maintain forest stability, analogous to maintaining a diverse investment portfolio as a strategy to cope with unexpected risks. This new perspective on widespread non-synchronous radial tree growth sheds insight into fundamental ecological processes in forest resilience and can improve assessment and management of forest health risks under future climate change.
Trees greater than 150 years old growing in the current treelines were most likely isolated tree outposts above previous treelines of the Little Ice Age (LIA). An intuitive question is, how did these isolated trees grow at such a high elevation in the cold environment? Here, we tackle this question using tree-ring width data of the Northern Hemisphere’s highest treelines at 4900 m a.s.l. (Basu) and 4680 m a.s.l. (Langkazi) on the Tibetan Plateau. The results showed that an age-related exponential growth trend did not exist in most of the ring-width sequences of the sampled trees. The values of ring widths in the isolated trees had a similar pattern of probability distribution during and after the LIA. The coefficients of variation in ring widths of the isolated trees were significantly greater than those of the non-isolated trees in their common growth period. Synchronicity of annual change in radial growth among trees varied in time. These results indicated that the isolated trees in the LIA developed an adaptive ability to slow down radial growth rate and modulate growth synchronicity among individuals in cold stressful environments. Our study highlights growth plasticity in isolated trees above treelines for coping with harsh conditions in the LIA.
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