Tree-ring studies of Toona ciliata from subtropical wet hill forests of Kalimpong, eastern Himalaya

We present a 180-years long (1824-2003C.E.) tree-ring width chronology of the fast growing broadleaf tree Toon (Toona ciliata Roem.) from the subtropical wet hill forests of Kalimpong, in the eastern Himalaya of India. The majority of tree ring studies conducted in the Himalaya have been based on conifers. Our analyses demonstrate that winter temperature prior to the season of growth, current year April precipitation and April-May drought (scPDSI) exhibit direct relationship with the ring-width chronology when correlated with monthly or seasonal climate data. The observation of the tree-growth and climate relationship showed that optimum temperature, precipitation and soil moisture together serve to modulate the radial growth of Toon in the region, however the mean minimum temperature of winter season (October-February) is the most significant climatic factor. Based on the expressed population signal (EPS) statistic, our record is reliable only back to 1945C.E., however this study clearly establishes the dendroclimatic potential of this tropical broadleaf species to carry out future tree-ring based long-term climate reconstruction in the sub-tropical Himalaya.