Central Nepal Himalaya Research Articles

Impacts of 3DVAR data assimilation on the near surface weather variables and predictability of rainfall over the mid-hills of central Nepal Himalaya during Pre-Monsoon Season

Impacts of 3DVAR data assimilation on the near surface weather variables and predictability of rainfall over the mid-hills of central Nepal Himalaya during Pre-Monsoon Season

Assessing the geometry of the Main Himalayan thrust in central Nepal: A thermokinematic approach

Abstract Since the 2015 Gorkha earthquake in Nepal, the relationship between the geometry of megathrusts and the control it exerts over the nucleation and propagation of major earthquakes has become an important topic of debate. In this study, we integrate new geologic mapping, a newly interpreted cross section from the Daraundi valley of central Nepal, two published cross sections from the neighboring Marsyangdi and Budhi Gandaki valleys, and a suite of 270 thermochronometric ages to create an integrated and validated three-dimensional kinematic model for the central Nepal Himalaya. We use this model to investigate the assertion that the westward propagation of the Gorkha rupture was restricted by deep-seated structures in the Main Himalayan thrust. The integrated kinematic model based on these cross sections indicates that the ~30 km southward step in the Main Central thrust system mapped in the Daraundi valley, along with the corresponding step in the distribution of reset muscovite (Ar-Ar) ages, is not the result of a lateral structure in the modern Main Himalayan thrust. Instead, the step in the surface geology is the result of a considerably shorter Trishuli thrust sheet in the Daraundi transect (~30 km compared to between 105 and 120 km in the other transects). The corresponding southward step in the distribution of reset muscovite Ar-Ar ages is the result of the Lesser Himalayan duplex being completely translated over the Main Himalayan thrust ramp, elevating and exposing rocks heated to >400 °C farther south in the Daraundi transect. Our integrated model also highlights the 10–15 km of out-of-sequence thrusting that occurs on the Main Central thrust system across central Nepal. Importantly, these out-of-sequence thrusts sole directly into the modern Main Himalayan thrust ramp, and, together with the distribution of reset zircon (U-Th)/He and apatite fission track ages, show that the modern ramp is distinctly linear from east to west, with no support for a lateral structure at the ramp or to the south.

Habitat overlap and interspecific competition between snow leopards and leopards in the Central Himalayas of Nepal

Traditionally, leopards (Panthera pardus) and snow leopards (P. uncia) occupy distinct habitats. This study explored the coexistence of snow leopards and leopards within the Gaurishankar Conservation Area in Lapchi Valley, Nepal. Both leopard species are crucial for ecosystem stability as apex predators. Camera trapping data from 2018 to 2023 confirmed twenty species of wild mammals and two species of domesticated livestock in Lapchi Valley, where snow leopards have strong spatio-temporal overlap (Δ=0.74) with leopards. Snow leopards exhibited distinct temporal patterns before and after the leopards’ arrival in the study area. Generalized Linear Mixed Effect Models (GLMM) revealed seasonal and prey-type associations with leopard presence, highlighting the snow leopards' preference for cold season and wild prey. Leopards, however, did not show a significant seasonal preference. The findings highlight Lapchi Valley's ecological richness as well as the need for comprehensive conservation strategies. The record of spatial and temporal overlap between the leopards and snow leopards provides important insights into the behavioral dynamics of apex predators and the need for targeted biodiversity conservation in the face of changing ecosystems. The study emphasizes the valley's transboundary significance, calling for collaborative efforts between Nepal and China to help promote effective conservation management. Lapchi Valley's isolation, traditional and religious importance, and recent infrastructure developments further impact the conservation challenges.

Alteration in the mantle transition zone structure beneath Sikkim and adjoining Himalaya in response to the Indian plate subduction

We map the depth variations of 410 km and 660 km discontinuities (d410 and d660) beneath the Sikkim Himalaya and adjoining regions using 18816 P receiver functions. The average variation of d410 and d660 for the entire study region is found to be 395±4 km and 652±5 km, respectively, with the mantle transition zone (MTZ) thickness being ∼255 km. A major upliftment in the upper mantle discontinuities is seen in the southeastern portion of the study region close to Shillong plateau, where the average depth of d410 and d660 is 373±4 km and 648±6 km, respectively. Overall, 90% of the grids have an uplifted transition zone. An upliftment of ∼20 km in d410 is observed beneath the central Nepal Himalaya and east of the Bhutan Himalaya. For the remaining grids, the d410 is elevated by ∼10 km. For d660, ∼15 km of elevated topography is observed in Central Nepal Himalaya and the northern part of Arunachal Himalaya, while the remaining areas have a relatively flat d660. The upliftment in the upper mantle discontinuities reflects presence of a thick Indian lithosphere beneath the study region. Furthermore, clear positive and negative conversions are observed between 450 km and 550 km depths, reflecting a highly heterogeneous nature of the MTZ. In addition, strong negative amplitude conversions corresponding to ∼350 km depth suggest presence of low velocity zones in the northernmost parts of Himalaya and southern Tibet. The low velocity zones may reflect compositional changes in response to the relict slab dynamics.

Failure mechanism of large-scale landslide in the central Nepal Himalaya

The geomorphological and geological characteristics of central Nepal reflect the dynamic nature of tectonic and mass movement processes that lead to the occurrence of large-scale landslides (LSLs). The mechanism of the LSL failure process is not well understood due to the different deformation stages controlled by geological structures and causative/ triggering factors. Regional tectonic structures and local rock mass characteristics play a vital role in the formation of LSLs. Engineering geological characterization was performed to evaluate the rock/soil properties, and the associated state of danger (cracks, seepage, etc.). The rock mass rating (RMR) and geological strength index (GSI) methods were used to estimate rock mass quality and strength parameters. The estimated strength parameters together with laboratory test data were used to set up a two-dimensional (2D) landslide surface to simulate the failure scenarios. The simulation of landslide models was iterated under different loading conditions by incorporating geological heterogeneities. The results have demonstrated that the movement of the slope was affected by different stress conditions over time, which were verified using spatiotemporal landslide data. The landslide exhibited a three-stage failure mechanism with the development of tension-induced cracking at the rear and shearing failure of the critical locking section in the middle section. The tension shear and joint-step-path rupture along joint surfaces occurred during different stages of the landslide failure processes. The simulated results showed that the genetic development of LSL is mainly attributed to the geological structures and sudden changes in stress conditions. Thus, the research outcomes can be illustrative to evaluate the role of geological discontinuities, geotechnical parameters and triggering effects by the numerical simulation techniques for the failure mechanism of LSLs.

Spatial variability of slope movements in central and western Nepal Himalaya: Evaluating large-scale landslides to cut-slopes

Spatial variability of slope movements is common in the Himalayan terrain of central and western Nepal Himalaya due to the intricate topography, differential geo-environment, and frequent rainstorms. The process of mass movements in the Himalaya has been described in the past by many researchers. The spatial variability of slope movement phenomena is scale dependent and is affected by causative and triggering processes. The limited researchers delivered output to understand the scale-dependent spatial variability resulting from the causative and triggering mechanism of slope movement phenomena. This study has presented a rigorous scientific examination of the spatial variability of slope movements, focusing on large-scale landslides to cut slopes across the central and western regions of the Nepal Himalaya. To achieve this, a multidisciplinary approach was employed, encompassing geospatial analysis, remote sensing, and field investigations. High-resolution satellite imagery was utilized to identify and map slope movement features, while digital terrain analysis techniques aided in quantifying their characteristics. This approach quantitatively analyzed slope movement distribution, frequency, and characteristics in terms of various geo-environmental settings. The findings reveal diverse patterns of slope movements influenced by complex interactions between geological factors, geomorphology, triggering factors, and anthropogenic activities. Geological and geomorphological heterogeneity play roles differently in the spatial distribution of slope movements. Moreover, rainfall distribution and peak ground acceleration act similarly for the scale dependency phenomena of slope movement. The spatial variation concerning the causative and triggering variables signify the scale-dependency nature of slope movement processes. This study has provided insights into the scale dependency and spatially variable nature of slope movement events due to variations in causative and triggering mechanisms in the Nepal Himalaya.

Decoupling of physical and chemical erosion in the Himalayas revealed by radiogenic Ca isotopes

Determining the rate of CO2 consumption associated with the Himalayan uplift is an essential prerequisite to understanding climate evolution throughout the Cenozoic. The riverine fluxes of dissolved calcium can be used to quantify uptakes of atmospheric CO2 by chemical weathering, but this approach requires deciphering the silicate-derived Ca flux from the generally dominant carbonate-derived Ca flux. Here we present high-precision radiogenic calcium (40Ca) analyses of bank sediments and dissolved loads from a network of rivers in central Nepal Himalaya and Bangladesh, to constrain the sources and relative contributions of carbonate and silicate-derived calcium to the dissolved loads of Himalayan rivers. Calcium isotope analyses were performed in multidynamic mode by thermal ionization mass spectrometry, yielding an external precision of ±0.4 ε-units (2 S.D.). Our results show that silicate catchments exposed in the Himalayan range have variably radiogenic ε40Ca compositions relative to seawater, ranging from +0.7 in the TSS to +14 in the LH. In contrast, sedimentary carbonates, including metamorphosed dolomites with variably radiogenic 87Sr/86Sr, exhibit uniform ε40Ca identical to modern seawater. The homogeneous ε40Ca composition of sedimentary carbonates confirms the relative resistance of radiogenic Ca signatures to post-depositional alteration and provides a robust baseline against which the contribution of silicate weathering to the riverine Ca flux can be evaluated. Dissolved load compositions of rivers draining LH catchments exhibit ε40Ca values ranging from 0 to +11, reflecting the relative contribution of unradiogenic carbonates and highly radiogenic metapelitic units of the LH sequence. HHC rivers show a more moderate range, from 0.5 to +2, reflecting the less radiogenic composition of HHC paragneisses. Himalayan front rivers draining all three lithotectonic units of the Himalayan range exhibit moderately radiogenic ε40Ca, ranging from +0.5 to +1.4 and overall similar to the average composition of the Ganga mainstream in Bangladesh. Using an approach combining conventional alkalinity budgets with isotopic mass balance calculations, we show that the dissolved silicate Ca flux of major Himalayan front rivers is primarily derived from the weathering of metapelitic rocks of the lesser Himalaya. In contrast, regions of the high range that generate the bulk of the detrital flux to the Gangetic floodplain represent a subordinate source of silicate-derived Ca. This result demonstrates that the chemical weathering of Ca-silicates in the Himalayan system is decoupled from physical erosion. The extensive erosional activity observed in the high range may thus play a limited role in promoting CO2 consumption and global cooling by silicate weathering.

Characterization of large-scale landslides and their susceptibility evaluation in central Nepal Himalaya

Large-scale landslides (LSL) are characterized by complex nature of failure mechanism, which depend on geological setting and associated factors of the area. The aim of this research is to identify the distribution pattern of LSL and all landslides in the central Nepal Himalaya and evaluation of their controlling factors. 7239 landslides were extracted from the study area by the interpretation of satellite imageries and field surveyed information. 28 landslides were classified as LSL and descriptive statistics were calculated. A comparative susceptibility assessment between all landslides and LSL was performed by frequency ratio model (FRM). Landslide susceptibility assessed from FRM was classified into five categories using the natural breaks method and adjustment from field evidences: very low, low, medium, high, and very high. The very high, high and medium susceptibility classes comprised of 38.91%, 33.29%, 18.76% for all landslides, and 39.51%, 29.65%, 20.98% for LSL. The result clearly indicated that the role of controlling factors varies differently depending upon the size of distributed landslides. To understand the significance of controlling factors for LSL, different potential cases were validated by success rates with area under the curve (AUC). The computed AUC in success rates for LSL is 65% and for overall landslides with similar controlling factors is 75%. The AUC values in different potential cases showed that the prime factors to control the LSL are geomorphology, rainfall, and geological structures.

Near‐Surface Geomechanical Properties and Weathering Characteristics Across a Tectonic and Climatic Gradient in the Central Nepal Himalaya

AbstractShallow bedrock strength controls both landslide hazard and the rate and form of erosion, yet regional patterns in near‐surface mechanical properties are rarely known quantitatively due to the challenge in collecting in situ measurements. Here we present seismic and geomechanical characterizations of the shallow subsurface across the central Himalayan Range in Nepal. By pairing widely distributed 1D shear wave velocity surveys and engineering outcrop descriptions per the Geological Strength Index classification system, we evaluate landscape‐scale patterns in near‐surface mechanical characteristics and their relation to environmental factors known to affect rock strength. We find that shallow bedrock strength is more dependent on the degree of chemical and physical weathering, rather than the mineral and textural differences between the metamorphic lithologies found in the central Himalaya. Furthermore, weathering varies systematically with topography. Bedrock ridge top sites are highly weathered and have S‐wave seismic velocities and shear strength characteristics that are more typical of soils, whereas sites near valley bottoms tend to be less weathered and characterized by high S‐wave velocities and shear strength estimates typical of rock. Weathering on hillslopes is significantly more variable, resulting in S‐wave velocities that range between the ridge and channel endmembers. We speculate that variability in the hillslope environment may be partly explained by the episodic nature of mass wasting, which clears away weathered material where landslide scars are recent. These results underscore the mechanical heterogeneity in the shallow subsurface and highlight the need to account for variable bedrock weathering when estimating strength parameters for regional landslide hazard analysis.

Geometry, kinematics, and magnitude of extension across the Thakkhola Graben, Central Nepal Himalaya

The Thakkhola Graben has been a region of geologic inquiry for many decades. Although it is widely viewed to be in a class of structures that are important in accommodating the three-dimensional strain within the Himalayan thrust wedge, we still lack a detailed understanding of the total finite strain accommodated by graben-bounding faults, as well as their shape and cross-cutting relationships with structures deeper in the thrust wedge. Using geologic mapping and structural analysis, we show that a suite of pre-extensional shortening structures is offset by normal-oblique faults bounding the Thakkhola Graben that we use to define a piercing line. We calculate these faults to have accommodated 8.7 kilometers of vertical thinning, 7.2 kilometers of arc-perpendicular shear, and only 2.2 kilometers of arc-parallel extension. The magnitude of arc-parallel extension is quite low compared to extensional structures to the west in the Gurla Mandhata-Humla region. The cross-cutting relationships established in this study and timing constraints determined by previous works are consistent with a structural history of crustal thickening leading to foreland propagation of the locus of arc-perpendicular shortening contemporaneous with hinterland extension.

On the impact of earthquake-induced landslides on Red Panda Ailurus fulgens (Mammalia: Carnivora: Ailuridae) habitat in Langtang National Park, Nepal

In addition to the threats of human encroachment, infrastructure development, tourism activities, habitat fragmentation, and human-wildlife interactions, natural disasters also pose a threat to the habitat of endangered species such as the Red Panda. This study aims to assess the impact of the 2015 Gorkha earthquake-induced landslides on the Red Panda’s habitat in Langtang National Park (LNP), central Nepal Himalaya. Remote sensing and geographical information system were applied to estimate the potential and core habitats of the Red Panda, and collect information on earthquake-induced landslides. Field sampling and verification of remotely collected data were done within a year of the earthquake. Considering preferred vegetation types, elevation range, aspects, distance from water sources, and Red Panda presence points, an area of 214.34 km2 was estimated as the potential habitat of Red Panda in the Park. Thirty-nine landslides were identified in LNP triggered by the Gorkha earthquake, 14 of which occurred in the core Red Panda habitat. As a result of the earthquake-induced landslides, a significant decrease in tree density was observed in the areas affected by the landslides. Similarly, the bamboo cover was observed to be significantly lower in the areas affected by landslides compared to the unaffected adjacent areas. The average size of the landslide, causing damage to the Red Panda habitat was 0.8 ha. The potential habitat damaged by the earthquake-induced landslide was estimated to be 11.20 ha which is equivalent to the habitat required by one Red Panda. The findings could be useful in initiating restoration of the damaged Red Panda habitat in LNP.

Acute cold stress: a potential threat to Royle's pika (Ochotona roylii) survival at Central Himalayas of Nepal

Climate change and its threat to human life and biodiversity are under discussion as the major issue of this century. In this study, pika (Ochotona roylii) was taken as a model animal to study the effect of changing climatic parameters in the Central Himalayas of Nepal. The study was carried out for three consecutive years (2011−2013) in the Kyanjing Valley situated at 3900 m asl, Langtang National Park, Nepal. The study focused on the population density of pika, its lowest elevation distribution, and temperature patterns of the pika-burrows and their immediate surroundings. An iButtons Temperature Recorder was installed inside a pika-burrow for acquiring burrow temperature while the ambient temperature data were obtained from the nearby metrological station. The population density of pika decreased compared to those based on the previous studies. Over the last 25 years, there was a significant increase in the minimum temperature (R2 =0.77) that decreased the snow cover which might have reduced the insulation effect and colder winter to animals living inside the burrow. The temperature inside the burrow was recorded below −5°C for nearly 50% time during January alone and 25% time during total winter days. The environment with a temperature below −5°C could be a threat to the survival of pikas suffering from acute cold stress. Neither there was any record of heat stress (above 25°C) recorded nor there was an increasing trend of the ambient maximum temperature within the LNP during the study period. The lowest elevation of the pika's habitat was found to have shifted 200 m upwards over the last 46 years, indicating that the animals had either migrated upwards or facing extinction locally at lower elevations. However, this short-term study is not sufficient to reflect the effects of climate change on the population of pika in the Central Himalayas. Therefore, a long-term study is required to explore the relation between pikas and their vulnerability to the changing climate

Diversity of birds recorded at different altitudes in central Nepal Himalayas

Factors determining the spatial distribution of bird species along altitudinal gradients have been important in their ecological and biogeographical research. Here, have used the data on bird species recorded in Manang, central Nepal Himalayas and attempt to determine the drivers of bird species diversity. We also carried out indicator species analysis to observe if any bird species are associated with different altitudinal ranges and land use gradients. We recorded 1331 individuals belonging to 82 species of both resident and itinerant birds. In our study, altitude was the major factor determining species richness and abundance. Position of study localities is main factor determining bird community composition. Diversity of bird species were mainly found in habitats that were far human settlements, having high annual mean temperature and more roughness. Species diversity was high during July-August compared to September-October and in north-facing slopes, and also in shrub and tree covered areas than grassland and places with mostly snow and grassland. Indicator species analysis showed only 21 species were significantly associated with altitudinal gradients, mostly below 3000 m a.s.l. and only eight bird species were associated with two land use gradients (grassland and snow-glacier). In conclusion, position of sampled localities, altitude, aspect, land use types and different climatic factors were important determinants of bird diversity along altitudinal gradients in Manang. To protect bird diversity in Manang, we need to protect habitats that are located mainly in low altitudes for most of the bird species. However, high altitude habitats with snow and glaciers are also important for few bird species. Thus, a large area with heterogenous habitats is important for bird species management and conservation.

Asymmetric development of the Himalaya: quantitative evidence from strain analysis in Kimin-Ziro-Tamen area, Arunachal Lesser Himalaya, India

The eastern segment of the Himalaya makes a quarter of the mountain belt. While its plate tectonic setting is well understood, the intensity of deformation along the thrusts is not well constrained. This knowledge gap has restricted a quantitative comparison of deformation and crustal shortening in the Eastern Lesser Himalaya with the Central and Western Lesser Himalaya. In this study field evidence, together with microstructural investigations, and two-dimensional (2D) finite strain analysis are used to decipher the deformation pattern in the Kimin-Ziro-Tamen area of the Eastern Lesser Himalaya. Present investigations reveal that micro-to-outcrop-scale structures such as plastically deformed quartz grains, crenulation cleavages, S-C fabric, pull-apart grains, pinch-n-swell structures, boudins and faults confirm that the rocks have been subjected to ductile and brittle-ductile phases of deformation with a regional top-to-south shear sense. The 2D finite strain estimated here is comparable to that in other parts of Eastern Lesser Himalaya, such as the Sikkim and Bhutan Himalaya. However, the strain estimated here is higher than in the Central and Western Lesser Himalaya, such as in the Central Nepal Himalaya, Almora Crystalline Zone, the Garhwal Lesser Himalaya and the Hazara-Kashmir Syntaxis in Pakistan. This provides quantitative proofs of greater deformation and crustal shortening in the Eastern Lesser Himalaya than the Central and Western Himalaya, and of the asymmetric development of Himalaya.

Major geomorphic events and natural hazards during monsoonal precipitation 2018 in the Kali Gandaki Valley, Nepal Himalaya

Highest geomorphic activity in the central Nepal Himalayas is mainly driven by monsoonal precipitation. In contrast, the northern flanks of the Nepal Himalaya lay in the relative dry rain shadow of the mountain range.During the monsoon 2018, major floods and geomorphic events occurred in the Kali Gandaki (KG) valley impacting both the monsoon-affected and the dry parts of the catchments. We analyze the events and its triggers based on field observations, multiple satellite image interpretation, climatological analysis using Global Precipitation Measurement and MODIS snow cover data, hydrological analysis and media analysis.The hydro-meteorological triggers are complex. Exceptional precipitation in April and May 2018 occurred in the entire study area, followed by a rather dry period. Precipitation in August was exceptional in the northern part whereas below average in the South. We argue that dynamics of snow accumulation and delayed melting contributed significantly to flooding and increased geomorphic activity in the southern part in August whereas flooding in the northern part was mainly triggered by rainfalls. We thus define 2018 as an abnormal (pre-)monsoon year with less rainfall than average but being more catastrophic.Sediment dynamics in the study area are still controlled by the Dhampu rock avalanche dam and the braided river floodplain north of this knickpoint, where sediment pulses delivered from tributaries are rarely connected from the main river. During the monsoon floods 2018 sediment connectivity was given for most tributaries due to the steepness of the catchments.The study area is subject to major human impact. Mostly in the south, numerous hillslopes have been undercut by road construction, leading to higher geomorphic sensitivity. Severe landslides might thus be triggered in future even by less intense rainfall events.Magnitude and frequency of such abnormal (pre-)monsoon precipitation are highly relevant for sediment flux and natural hazards studies.

Palynological evidence for the Neogene environment analysis of the Thakkhola Graben, Nepal

The Thakkhola Graben, a north-south graben, lies in central Nepal Himalayas consisting of Neogene sediments. The presence of pollens in these sediments provides a unique natural laboratory to understand the paleoenvironment during the formation of the graben. This study provides a detailed description of the pollen collected from the Tetang and Thakkhola formations with the help of the Light Microscope and Scanning Electron Microscope. A variety of pollen assemblages from the Thakkhola Graben explains that the sediments contain dominant alpine trees with some steppe vegetation. Presence of evergreen subtropical and temperate deciduous broad-leaved forest, needle-leaved element, and high altitude taxa show a mixed pollen assemblage in fluvial-lacustrine sediments of the graben. The presence of evergreen subtropical and temperate deciduous broadleaf forest (Quercus, Betula, Juglans, Alnus), needle-leaved element (Pinus, Tsuga) and high altitude taxa (Picea, Abies) with Artemisia, Chenopodiaceae, Poaceae, Rosaceae show mixed pollen assemblages indicating warm and humid paleoclimate. The coniferous pollen indicates the altitude was higher during the deposition time and the presence of Betula, Quercus, and Juglans suggests temperate forest. Domination of Artemisia and Chenopodiaceae shows a strong influence of the Himalayan topographic barrier during the sediment deposition.

The Weather Hazards Associated with the US-Bangla Aircraft Accident at the Tribhuvan International Airport, Nepal

AbstractSafe flights over the Tribhuvan International Airport (TIA), Kathmandu, Nepal, remain a considerable challenge. Since the airport opened, there have been 13 aircraft accidents during landings and takeoffs that have claimed 392 lives. A detailed understanding and dependable forecast of atmospheric conditions that may develop over the complex terrain of the midhills of central Nepal Himalaya are yet to be achieved. The present study discusses the near-surface atmospheric conditions possibly associated with the most recent fatal crash at TIA on 12 March 2018 as revealed by the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) Model routine forecast. At the time of the accident, two prominent gap winds were converging in the valley, thereby, forming a crosswind and a mix of strong up- and downdrafts over the airfield. As a result, the near-surface atmosphere was significantly turbulent. Unexpected encounters with such turbulent winds are a likely contributor to the fatal crash. This indicates that the knowledge of near-surface atmospheric conditions, critically needed by pilots in advance, for safe operations over the airfield may be generated with WRF-ARW forecasts.

Middle Miocene denudation of the Higher Himalayan Crystallines revealed by chemical composition of detrital garnets from the Siwalik foreland basin sediments, western and central Nepal

The Middle Miocene to Early Pleistocene Siwalik Group is composed of sediments deposited in the Himalayan foreland basin. In this study, the heavy mineral assemblage and chemical composition of detrital garnets from the sandstones in the Lower Siwalik sub-group, which are exposed along the Karnali River in western Nepal and the Tinau Khola in central Nepal, are studied and the provenance shift during the Middle Miocene is discussed. The heavy mineral assemblage in the lower section of the Lower Siwalik sub-group is characterized as predominantly zircon-tourmaline-rutile. Chemical analysis of the detrital garnets showed a monomodal almandine-rich composition with low pyrope (Prp<10) and moderate grossular (Grs10-20) content. The composition pattern subsequently changed to a bimodal distribution with an increase in pyrope (Prp10-25) and low grossular (Grs<10) content with the appearance of detrital staurolite. These results indicate that the Middle Miocene erosion of the Higher Himalayan Crystallines (HHC) are the source of the deposits in the Siwalik Group. Changes in the heavy mineral assemblage and garnet composition are recognized in the Karnali River section at 14–12 Ma and in the Tinau Khola section at 11–10 Ma, which suggests that the denudation of the HHC progressed from west to east in the western and central Nepal Himalayas.

Ecological Status and Peoples’ Perception of Mistletoes in Panchase Protected Forest, Central Nepal Himalayas

Realizing the importance of Panchase Protected Forest, an important corridor of the Chitwan-Annapurna Landscape (CHAL) area, the ecological status and peoples’ perception of mistletoe was studied to supplement the information on mistletoes of Nepal Himalayas. Mistletoes were studied along the forest trails and data were collected within 10 m radius plots 20 m inside the trails to record the incidence of mistletoe occurrence and severity of infection during three field visits in 1917 and 1918. Fifty people were interviewed using a semi-structured questionnaire and Biodiversity Conservation Confidence Index was calculated to understand peoples' perceptions about mistletoes. A total of seven mistletoe species, six belonging to four genera in the family Loranthaceae, and a single genus in the family Viscaceae were documented from 27 host species belonging to 24 genera in 18 unrelated angiosperm host families. Loranthaceae mistletoes were more generalists having a wide host range while Viscaceae mistletoe showed a high degree of host specificity. The irregular and patchy distribution of mistletoe is governed by host availability, forest structure, and site mesoclimate. Knowledge regarding the importance and uses of mistletoes and its values in natural plant communities is limited to older generation people. Age groups, profession, and the mechanism of indigenous knowledge inheritance in the rural mountainous communities of the Panchase area are very poor and are eroding rapidly which is against promoting the indigenous knowledge system especially in the younger generation. More conservation initiatives are needed through the stakeholder involvement to protect the rich biodiversity of the area.

Tree-ring climate response of two Larix species from the central Nepal Himalaya

Changes in the global temperature and precipitation regime have been significantly driving species responses, notably in sensitive areas such as the Himalayas. By conducting a study at two high altitude (3200–4100 m) valleys (Langtang and Tsum) situated in the central part of the Nepal Himalayas, we presented tree-ring width site chronologies for two Larix species (Larix griffithii and L. himalaica) for the first time. The longest chronology spans from 1771 to 2015 AD and showed a recent decline in the growth of Larix species in both sites, controlled mainly by drought. Tree growth showed a negative response to temperature and a positive response to precipitation, indicating that moisture stress is limiting the growth of the species. Based on the Larix ring width chronology statistics and climate response results, these species have good potential for past climate reconstruction such as temperature, rainfall or drought indices. Also, the study revealed that the Himalayan endemic Larix species investigated are promising for tree-ring based multi-aspect environmental change studies in the future.