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Abstract. Treeline shifting in tandem with climate change has widely been reported from various parts of the world. In Nepal, several impacts of climate change on the physical environment have been observed, but study on the biological impacts is lacking. This dendrochronological study was carried out at the treeline in the high mountain slope of Kalchuman Lake (3750–4003 m a.s.l.) area of Manaslu Conservation Area in the central Nepal Himalaya to explore the impact of climate change on the treeline dynamic. Two belt transect plots (size: 20 m wide, > 250 m long) were laid which included treeline as well as tree species limit. Ecological mapping of all individuals of dominant trees Abies spectabilis and Betula utilis was done and their tree cores were collected. Stand character and age distribution revealed an occurrence of more matured B. utilis (max. age 198 years) compared to A. spectabilis (max. age 160 years). A. spectabilis contained an overwhelmingly high population (89%) of younger plants (< 50 years) indicating its high recruitment rate. Population age structure along the elevation gradient revealed an upward shifting of A. spectabilis at the rate of 2.61 m year-1 since AD 1850. The upper distribution limit of B. utilis was found to be stagnant in the past few decades. An increment in plant density as well as upward shifting in the studied treeline ecotones was observed. The temporal growth of A. spectabilis was correlated negatively with the monthly mean and minimum temperature of June to September of the current and previous year. The regeneration of A. spectabilis, on the other hand, was positively correlated with August precipitation and monthly maximum temperature of the month of the current year. The growth and regeneration of A. spectabilis was more sensitive to maximum and minimum temperature rather than average temperature. The growth of the B. utilis was mainly limited by moisture stress during the pre-monsoon season. As these two species presented species-specific responses to climate change with differential pattern in regeneration condition, much wider differences are anticipated in their population status as climate continues to change throughout the century.

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Global climate change has multidimensional impacts with several biological fingerprints, and treeline shifting in tandem with climate change is a widely observed phenomenon in various parts of the world. In Nepal several impacts of climate change on physical environments have been observed. However, studies on the biological impacts are lacking. This dendrochronological study was carried out at the treeline ecotone (3750–4003 m a.s.l.) in the Kalchuman Lake (Kal Tal) area of the Manaslu Conservation Area in central Nepal Himalaya with the aim to study the dynamic impact of climate change at the treeline. The study provides an insight into regeneration and treeline dynamics over the past 200 yr. Two belt transect plots (size: 20 m wide, >250 m long) were laid covering forest line, treeline as well as tree species Abies spectabilis and Betula utilis was done and their tree-cores were collected. Stand character and age distribution revealed an occurrence of more matured B. utilis (max. age 198 yr old) compared to A. spectabilis (max. age 160 yr). A. spectabilis contained an overwhelmingly high population (89%) of younger plants (<50 yr) indicating its high recruitment rate. Population age structure along an elevation gradient revealed an upward shifting of A. spectabilis at the rate of 2.61 m yr⁻¹ since 1850 AD. The upper distribution limit of B. utilis was found stagnant in the past few decades. An increment in plant density as well as upward shifting in the studied treeline ecotones was observed. Thus, two species presented species-specific responses to climate change and much wider differences anticipated in their population status as climate continues to cha spectabilis correlated negatively with the mean monthly temperature of May–August of the current year and with September of the previous year. The regeneration of A. spectabilis, on the other hand, was positively related with May–August precipitation and January–April temperature of the current year. The reconstructed average summer temperature (May–August) using tree ring data revealed alternate period of cool and warm period with warming in the 2nd half of the 20th century. Further palynological and geochronological studies of sediments of the Kalchuman Lake would advance our understanding of past climatic trends and dynamics of the associated treeline and vegetation in the area

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