Pine trees are very sensitive to moisture, and are therefore extensively used as hydro-climate proxies at different spatio-temporal scales across the Himalayan region. Blue pine (Pinus wallichiana) has been suggested to be suitable for reconstruction of hydro-climate and regional glacier dynamics. However, climate reconstructions based only on P. wallichiana tree-rings have not yet been attempted from the Nepal Himalaya region. No dendroclimatic study has been carried out focusing mainly on the inner- and trans-Himalaya.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) developed a 405-year long (1611–2015C.E.) tree-ring chronology of blue pine from the Dolpo area of the trans–Himalayan region in Nepal to reconstruct drought variability in that remote region.
The researchers reconstructed drought for the past 319 years (1697 to 2015C.E.) based on the well-replicated part of a P. wallichiana ring-width chronology. They also compared their drought reconstruction with tree-ring based drought or precipitation reconstructions from the Himalayas, adjacent regions in China, and broader Asia to test for coherency in long-term drought occurrence in the region.
They found that radial growth of blue pine is limited mainly by moisture stress during the spring–summer season. The trans-Himalayan region experienced prolonged drought during 19th and 20th century. The reconstructed drought had variabilities at frequencies similar to those of broader scale climate-modes such as ENSO (El-Nino Southern Oscillation) and AMO (Atlantic Multidecadal Oscillation).
Further, drought in Dolpo region was also significantly correlated with sea surface temperatures in the Indian Ocean and the Atlantic Ocean, which suggests that climate in that part of the trans-Himalaya might have remote connections with broad-scale atmospheric circulations.
“Blue pines can withstand different drought events and continue growing. It indicates that the species is resilience to climate change, especially in dry environments”, said Dr.Narayan Prasad Gaire, a Nepalese postdoc at XTBG.