Tree growth across the Nepal Himalaya during the last four centuries

Abstract

The climate of Nepal has changed rapidly over the recent decades, but most instrumental records of weather and hydrology only extend back to the 1980s. Tree rings can provide a longer perspective on recent environmental changes, and since the early 2000s, a new round of field initiatives by international researchers and Nepali scientists have more than doubled the size of the country’s tree-ring network. In this paper, we present a comprehensive analysis of the current tree-ring width network for Nepal, and use this network to estimate changes in forest growth nation-wide during the last four centuries. Ring-width chronologies in Nepal have been developed from 11 tree species, and half of the records span at least 290 years. The Nepal tree-ring width network provides a robust estimate of annual forest growth over roughly the last four centuries, but prior to this point, our mean ring-width composite fluctuates wildly due to low sample replication. Over the last four centuries, two major events are prominent in the all-Nepal composite: (i) a prolonged and widespread growth suppression during the early 1800s; and (ii) heightened growth during the most recent decade. The early 19th century decline in tree growth coincides with two major Indonesian eruptions, and suggests that short-term disturbances related to climate extremes can exert a lasting influence on the vigor of Nepal’s forests. Growth increases since AD 2000 are mainly apparent in high-elevation fir, which may be a consequence of the observed trend towards warmer temperatures, particularly during winter. This synthesis effort should be useful to establish baselines for tree-ring data in Nepal and provide a broader context to evaluate the sensitivity or behavior of this proxy in the central Himalayas.

Strong link between large tropical volcanic eruptions and severe droughts prior to monsoon in the central Himalayas revealed by tree-ring records

“…Our results indicate that large volcanic events may reduce moisture availability in the central Himalayas. These findings support early work using a tree-ring width network developed from 11 tree species in Nepal where widespread growth suppressions were evident in the early 1800s [28]. These growth suppressions corresponded with the most severe drought in our reconstruction that occurred from 1809À1823.…”

Spring Season in Western Nepal Himalaya is not yet Warming: A 400-Year Temperature Reconstruction Based on Tree-Ring Widths of Himalayan Hemlock (Tsuga dumosa)

“…The inter-series correlation and SNR for this study were higher compared to previous studies of the same species [21,[33][34][35], indicating the robustness of our chronology. Similar to most of the tree-ring-width chronologies in Nepal [19,53,54], we also observed a significant growth depression during the 1810s, followed by a distinct increase in growth since 2003 CE. Thapa et al [54] developed a composite chronology combining 55 tree chronologies from Nepal and mentioned these growth fluctuations as a major milestone for Nepalese tree-ring chronologies regardless of the tree species.…”

Fire history and climate-growth response of Abies spectabilis : A case from Langtang National Park, Nepal Himalaya

“…Similarly, Dawadi et al (2013) also observed fluctuation in the growth of B. utilis over the past 400 years in the Langtang region. Similarly, Thapa et al (2017) also reported increasing or decreasing growth trend in different chronologies from Nepal Himalaya. The differences between the growth trends in the present study and the previous studies could be due to the differences in the species, site conditions as well as methods used to detrend the raw tree-ring series, and the type of chronologies.…”

“…So, inspecting fire-scarred trees dated with dendrochronological techniques will be reliable method for providing quantitative information on fire-regime evidence at multiple scales to study fire events, their frequency, severity and patterns even on remote geographical area. Though several tree-ring related studies have been carried out in Nepal (Cook et al, 2003;Chhetri and Thapa, 2010;Gaire et al, 2011Gaire et al, , 2014Gaire et al, , 2016 but study regarding the fire disturbances in the perspective of dendroecology is still lacking in the whole country (Gaire et al, 2013;Thapa et al, 2017). So this study will help to inform management, and provide insight into the effects of fire on study area.…”